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Empirical design of span openings in weak rock Ouchi, Andrea Miyuki 2008

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EMPIRICAL DESIGN OF SPAN OPENINGS IN WEAK ROCK by ANDREA MIYUKI OUCHI B.A.Sc., The University of British Columbia, 2002 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES  (Mining Engineering)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)  September, 2008 © Andrea Miyuki Ouchi, 2008  Abstract This thesis presents ground control best practices in weak rock environments including an augmentation to the existing Span Design curve by adding 463 case histories of RMR76 values ranging from 25 to 60. A Neural Network analysis of this data has been added and compared to the existing Span Design data of 292 case histories. Ground support is almost always used in weak rock environments, though the type of support used can vary widely. The development of the weak rock augmented Span Design Curve has also been calibrated to four different support categories; Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill. Category A is considered “Unsupported” with an average Factor of Safety less than 1.2. Categories B, C and D are considered “Supported” with average Factors of Safety greater than 1.2. All categories are compared the original Critical Span Design Curve presented by Lang (1994). However, only Category A can be accurately compared to the original Critical Span Design Curve as it is “Unsupported” as well. Category A yields good results, however, Categories B, C and D do not, but still demonstrate that spans can remain stable at lower RMR76 values. Design of underground man-entry type excavations in North America relies heavily upon empirical analysis. This design requires a higher Factor of Safety than other non-man entry type excavations. A comparison of the calculated ½ span failure Factor of Safety between all the categories is also presented. The contribution this research provides to the mining industry is the "Unsupported" Weak Rock Updated Span Design Curve and awareness pertaining to the potentially detrimental effects of using resin grounted rebar in weak rock masses and the false sense of security that the use of resin grouted rebar may instill.  It is also shown that spans in the  “Unstable” zone of the new “Unsupported” Weak Rock Updated Span Design Curve can possibly be stabilized if detailed engineering design is applied to obtain “Supported” status.  ii  Table of Contents Abstract…………………………………………………………………………………… ii Table of Contents…………………………………………………………………………iii List of Tables …………………………………………………………………………….vi List of Figures…………………………………………………………………………... vii List of Equations…………………………………………………………………………. x Acknowledgments………………………………………………………………………. xi 1  Introduction…………………………………………………………………………..1  2  Literature Search…………………………………………………………………….. 4 2.1  Rock Mass Classification……………………………………………………….4  2.1.1  Terzaghi’s Rock Mass Classification……………………………………...4  2.1.2  Rock Quality Designation……………...…………………………………. 5  2.1.3  Rock Structure Rating (RSR)……………………………………………...6  2.1.4  Geomechanics Classification (RMR)…………………………………….. 6  2.1.5  Rock Tunneling Quality Index, Q………………………………………..10  2.1.6  Modified Rock Tunneling Quality Index, Q’…………………………… 15  2.1.7  Relating RMR and Q……………………………………………………. 15  2.1.8  Mining Rock Mass Rating (MRMR)……………………………………. 16  2.2  Weak Rock Underground Excavation Failure Mechanisms………………….. 17  2.2.1  Stress…………………………………………………………………….. 18  2.2.2  Structure…………………………………………………………………. 18  2.2.2.1  Stereonet Analysis……………………………………………………. 18  2.2.2.2  Computer Aided Analysis……………………………………………..20  2.2.2.3  “Block Theory”……………………………………………………….. 20  2.2.2.4  Voussoir Arch Failure…………………………………………………21  2.2.3  3  Rock Mass………………………………………………………………..21  2.2.3.1  History of Span Excavation Studies………………………………….. 22  2.2.3.2  Extent of Failure……………………………………………………… 29  Methodology……………………………………………………………………….. 34 3.1  Observational Method…………………………………………………………34  iii  4  3.2  Analytical Methods…………………………………………………………… 34  3.3  Empirical Methods……………………………………………………………. 34  Span Design………………………………………………………………………... 37 4.1  5  6  Span, Stability and Support Definitions……………………………………….37  4.1.1  Definition of Span………………………………………………………..37  4.1.2  Definition of Stability…………………………………………………… 38  4.1.3  Definition of Standard Support…………………………………………..39  4.1.4  Definitions of Weak Rock Support Categories…………………………..39  4.1.4.1  Category A……………………………………………………………. 40  4.1.4.2  Category B……………………………………………………………. 41  4.1.4.3  Category C……………………………………………………………. 42  4.1.4.4  Category D…………………………………………………………… .43  Database……………………………………………………………………………. 45 5.1  Data Collection……………………………………………………………….. 45  5.2  Database Construction………………………………………………………... 49  5.3  Factor of Safety………………………………………………………………..49  5.4  Database Statistics……………………………………………………………. 51  5.4.1  Category A Statistics……………………………………………………..51  5.4.2  Category B Statistics……………………………………………………..56  5.4.3  Category C Statistics……………………………………………………..60  5.4.4  Category D Statistics……………………………………………………..64  Weak Rock Span Design…………………………………………………………... 69 6.1  Category A……………………………………………………………………. 70  6.1.1  Comparison with Barton’s Relationship between Q and De……………..72  6.2  Category B……………………………………………………………………. 73  6.3  Category C……………………………………………………………………. 74  6.4  Category D……………………………………………………………………. 79  6.5  Factor of Safety………………………………………………………………..80  6.5.1  Category A………………………………………………………………. 80  6.5.2  Category B………………………………………………………………. 81  6.5.3  Category C………………………………………………………………. 81  iv  6.5.4  Category D………………………………………………………………. 82  6.5.5  General Comments on FS……………………………………………….. 82  7  Application of the Weak Rock Span Curve………………………………………... 85  8  Lessons Learned…………………………………………………………………….89  9  Conclusions and Recommendations……………………………………………….. 91  References………………………………………………………………………………..94 Appendices……………………………………………………………………………….98 Appendix A: Entire Database………………………………………………………… 98 Appendix B: Grid Prediction Data…………………………………………………...119 Appendix C: Neural Network Results………………………………………………. 129  v  List of Tables Table 1: Qualitative Description of RQD………………………………………………… 5 Table 2: Geomechanics Classification, RMR 1976………………………………………. 8 Table 3: Geomechanics Classification, RMR 1989………………………………………. 9 Table 4: Descriptions and Ratings for the Parameters RQD, Jn and Jr …………………..11 Table 5: Descriptions and Ratings for the Parameters Ja and Jw…………………………12 Table 6: Descriptions and Ratings for the Parameter SRF……………………………… 13 Table 7: Excavation Support Ratios…………………………………………………….. 25 Table 8: Reinforcement Categories……………………………………………………... 25 Table 9: Case history data sources………………………………………………………28 Table 10: The Angle of Cave and the Failure Zone……………………………………..32 Table 11: Support Properties……………………………………………………………. 50 Table 12: Category A Summary of Statistics………………………………………….... 55 Table 13: Category B Summary of Statistics…………………………………………….60 Table 14: Category C Summary of Statistics…………………………………………….64 Table 15: Category D Summary of Statistics…………………………………………… 68 Table 16: Goldstrike Category A weak rock mass span design database……………….. 87  vi  List of Figures Figure 1: Ground Fall Related Injuries in Nevada, 1990-2008 .........................................1 Figure 2: Number of Joint Sets, Jn .................................................................................14 Figure 3: Joint Roughness Number, Jr............................................................................14 Figure 4: Joint Alteration Number, Ja.............................................................................14 Figure 5: Relationship between RMR and Q.................................................................15 Figure 6: Descriptive comparison between RMR and Q................................................16 Figure 7: Gravity Wedge Failure ..................................................................................19 Figure 8: Sliding Wedge Failure ....................................................................................19 Figure 9: Types of Blocks in "Block Theory" ...............................................................20 Figure 10: Extent of Rock Mass Failures ......................................................................22 Figure 11: Relationship between Active Span and Stand-Up Time ................................23 Figure 12: Relationship between Q and the Equivalent Dimension, De ..........................24 Figure 13: Estimate Support Categories based on the Tunneling Index, Q .....................26 Figure 14: Relationship between the stand-up time and span for various RMR classes..26 Figure 15: Critical Span Curve .....................................................................................28 Figure 16: RMR distribution.........................................................................................28 Figure 17: Updated Critical Span Curve .......................................................................29 Figure 18: ½ span zone of rock mass failure influence ..................................................30 Figure 19: 1/3 span zone of rock mass failure ...............................................................30 Figure 20: Asymmetrical jointing of 60º and 30º and Friction angle of 10º ..................31 Figure 21: Local Failure Mode with symmetrical jointing of 30º and Friction angle of 40º ......................................................................................................................................31 Figure 22: Symmetrical jointing of 60º and Friction angle of 40º ..................................31 Figure 23: Deep Seated Failure Mode with symmetrical jointing of 30º and Friction angle of 10º ...................................................................................................................32 Figure 24: Simple Network Structure ...........................................................................35 Figure 25: Span Definition ...........................................................................................37 Figure 26: Typical Bolt Installation for Category A .......................................................40 Figure 27: Typical Bolt Installation for Category B .......................................................41  vii  Figure 28: Typical Bolt Installation for Category C .......................................................42 Figure 29: Typical Bolt Installation with Cablebolts for Category D..............................44 Figure 30: Mine Locations in North America ................................................................46 Figure 31: Database Mine Distribution ..........................................................................46 Figure 32: Weak Rock RMR76 ......................................................................................48 Figure 33: Database Stable/Potentially Unstable/Unstable Distribution .........................51 Figure 34: Category A Data Source Distribution...........................................................52 Figure 35: Category A Stable/Potentially Unstable/Unstable Distribution......................53 Figure 36: Category A RMR76 Distribution ...................................................................54 Figure 37: Category A Span Distribution.......................................................................55 Figure 38: Category B Data Source Distribution...........................................................56 Figure 39: Category B Stable/Potentially Unstable/Unstable Distribution......................57 Figure 40: Category B RMR76 Distribution....................................................................58 Figure 41: Category B Span Distribution .......................................................................59 Figure 42: Category C Data Source Distribution...........................................................60 Figure 43: Category C Stable/Potentially Unstable/Unstable Distribution......................61 Figure 44: Category C RMR76 Distribution....................................................................62 Figure 45: Category C Span Distribution .......................................................................63 Figure 46: Category D Data Source Distribution...........................................................64 Figure 47: Category D Stable/Potentially Unstable/Unstable Distribution......................65 Figure 48: Category D RMR76 Distribution ...................................................................66 Figure 49: Category D Span Distribution.......................................................................67 Figure 50: Category A Updated Weak Rock Curves – “Unsupported” FS<1.2...............71 Figure 51: Comparison of Span Design Curves and Barton's Relationship between Q and De ..................................................................................................................................72 Figure 52: Category B Updated Weak Rock Curves – “Supported” FS>1.2 ...................74 Figure 53: Category C Updated Weak Rock Curves - “Supported” FS>1.2....................76 Figure 54: Comparison of Categories A, B and C Weak Rock Stable-PU Lines .............77 Figure 55: Comparison of Categories A, B and C Weak Rock PU-Unstable Lines.........78 Figure 56: Category D Points on Span Design Curve (no weak rock interpretation) “Supported” FS>1.2 ......................................................................................................80  viii  Figure 57: FS Comparison of Categories .......................................................................83 Figure 58: "Unsupported" Weak Rock Updated Span Design Curve (pattern friction sets, FS < 1.2) .......................................................................................................................85 Figure 59: Goldstrike use of the Weak Rock Updated Span Design Curve.....................86  ix  List of Equations Equation 1………………………………………………………………………………… 5 Equation 2………….……………………………………………………………………. 10 Equation 3……………………………………………………………………………….. 15 Equation 4……………………………………………………………………………….. 15 Equation 5……………………………………………………………………………….. 16 Equation 6……………………………………………………………………………….. 17 Equation 7……………………………………………………………………………….. 22 Equation 8……………………………………………………………………………….. 23 Equation 9……………………………………………………………………………….. 24 Equation 10……………………………………………………………………………… 25  x  Acknowledgments The author would like to thank Dr. Rimas Pakalnis for his guidance and opinions during the progress and development of this thesis. Mr. Tom Brady (NIOSH) has also been of great support throughout this process. Special thanks must be given to all the mines that participated in this study. Appreciation is also extended to NSERC for the invaluable financial aid.  xi  1  Introduction  As “ideal” resources in competent ground conditions are depleted, there is an increase in the number of mines operating in weak ground conditions. This presents potentially difficult and hazardous mining conditions to workers in the industry resulting in a higher frequency of injuries and fatalities. Evidence of this can be shown by the number of fatalities and injuries resulting from uncontrolled rock falls during the time period of 1990 through 2007 (Figure 1) with a low of 2 in 2004 and a high of 28 in 1995 and 1997 (Hoch, 2000 and Brady, 2008).  In mid-1999 NIOSH started conducting visits and  discussions with Nevada mines regarding weak rock and ground falls resulting in a statistical decline of ground fall related injuries over the next two years (Brady et al. 2005). An increase in ground fall related injuries occurred in 2002 and in the middle of that year, NIOSH commenced technical mine visits. There was another spike in injuries in 2005. The last two years have had relatively low numbers of ground fall related injuries. However, 2007 experienced one fatality from a fall of ground. Weak rock conditions are a concern and will continue to be in the years to come. 35 28 27 28  30 Injuries  25 20 10  9  8  19  16  13  15  25  12  14  12 8  10  7  5  5  2  7  2007  2006  2005  2004  2003  2002  2001  2000  1999  1998  1997  1996  1995  1994  1993  1992  1991  1990  0  Year  Figure 1: Ground Fall Related Injuries in Nevada, 1990-2008  The University of British Columbia Geomechanics group and the NIOSH Spokane Research Laboratory have conducted research in the development of safe and cost effective underground design guidelines in weak rock environments with Rock Mass Ratings (Bieniawski 1976) (RMR76) in the range of 20 to 60. The purpose of this study is to update the existing empirical span design for weak rock environments and the development of specific design curves for weak rock environments tailored to the type of  1  support employed (i.e. friction bolts, rebar, cablebolts, shotcrete, cemented rock fill, timber…) The relationship between span and rock quality has been studied for decades. A brief history of studies is presented in this thesis. One relationship of particular interest is that presented by Lang (1994). This study produced the Critical Span Design Curve that has since been widely used throughout the industry. The curve presented by Lang (1994) was later updated by Wang (1999). The Critical Span Curve is a simple and useful tool that aids in the design of underground man-entry openings. There is a need to update the Critical Span Curve for the RMR76 range of 20-50, as there are an increasing number of mines that are operating in these weak ground conditions. This thesis reviews the augmentation of the updated span design curve/critical span graph for weak rock environments and the support systems commonly used in such environments. The augmentation of this design to include a larger database of 463 points in the range of RMR76 of 15-60 will increase its accuracy and reliability in such conditions. Ground support is almost always used in weak rock environments. The type of support used can vary widely. The development of the weak rock augmented Span Design Curve has been divided into four (4) different support categories (with Friction Sets being Split Sets and/or Swellex type bolts); Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill under Cemented Rock Fill. These categories have been separated in order to accurately compare similar support types with similar factors of safety. This thesis presents updated span design curves for each of the support categories. The ½ span failure mechanism calculated Factor of Safety is presented for each of the above categories to show “Unsupported” conditions with a Factor of Safety less than 1.2 and “Supported” conditions with a Factor of Safety greater than 1.2. This thesis presents the results from the numerical analysis of span stability in relationship to the calculated Factor of Safety for each of these categories. A comparison between the categories is also presented to illustrate the magnitude of an increase in support between the different categories based upon the calculated Factor of Safety.  2  Data for this research was gathered by the author, Andrea Ouchi, during site visits conducted in the fall of 2002 and provided from Dr. Rimas Pakalnis and by ground control personnel from each of the participating mines. This thesis consists of eight chapters including a literature search, the methodology employed, a description of the database and the collection of the data, the analysis of each support category and corresponding observations. Chapter 2 presents the literature search of rock mass classification, weak rock underground failure mechanisms, and current rock mass designs. The technique used to calculate the Factor of Safety in this research is also presented in this chapter. Chapter 3 outlines the methodology techniques used in industry, and the techniques used for stability design in this research. The definition of Span and Span Design and the alterations required for this weak rock analysis are presented in Chapter 4. Database description and analysis are presented in Chapters 5 and 6. The study consists of the numerical analysis of each of the databases created for each of the support categories to empirically determine the allowable span opening for a given rock mass. An examination of the Factor of Safety numerical analysis of each of the databases is also presented along a comparison of each category with respect to the Factor of Safety. Chapter 7 presents the use of the “Unsupported” Weak Rock Updated Span Design Curve at Barrick’s Goldstrike mine. “Lessons Learned” area presented in Chapter 8 with specific reference to the use of resin grouted rebar in weak rock mass environments. The conclusions (Chapter 9) summarize these analyses and provide the “Unsupported” Weak Rock Updated Span Design Curve as an easy to use tool for mining professionals in the safe and cost effective drift opening design for weak rock mass environments.  3  2  Literature Search 2.1 Rock Mass Classification  Rock mass classification is used to build a quick initial assessment of the quality of the rock mass according to the characteristics of the rock. Many classification systems have been developed over the years. This chapter describes a selection of these systems.  2.1.1 Terzaghi’s Rock Mass Classification Terzaghi was the first to propose the concept of a rock classifications system (Terzaghi, 1946). This classification system was originally used for the estimation of loads to be supported in the design of steel arches. While this classification system is appropriate for its intended function, it is not used in modern design. However, this classification system has been used in the past and is presented for completeness. The definitions of the classes are as follows: Intact rock contains neither joints nor hair cracks. Hence if it breaks, it breaks across sound rock. On account of the injury to the rock due to blasting, spalls may drop off the roof several hours or days after blasting. This is known as a spalling condition. Hard, intact rock may also be encountered during a popping condition involving the spontaneous and violent detachment of rock slabs from the sides or roof. Stratified rock consists of individual strata with little or no resistance against separation along the boundaries between strata. The strata may or may not be weakened by transverse joints.  In such rock, the spalling condition is quite  common. Moderately jointed rock contains joints and hair cracks, but the blocks between joints are locally grown together or so intimately interlocked that vertical walls do not require lateral support. In rocks of this type, both spalling and popping conditions may be encountered. Blocky and seamy rock consists of chemically intact or almost intact rock fragments which are entirely separated from each other and imperfectly interlocked. In such rock, vertical walls may require lateral support.  4  Crushed but chemically intact rock has the character of a crusher run. If most or all of the fragments are as small as fine sand grains and no recementation has taken place, crushed rock below the water table exhibits the properties of water bearing sand. Squeezing rock slowly advances into the tunnel without perceptible volume increase. A prerequisite for squeeze is a high percentage of microscopic and submicroscopic particles of micaceous minerals or of clay minerals with a low swelling capacity. Swelling rock advances into the tunnel chiefly on account of expansion. The capacity to swell seems to be limited to those rocks which contain clay minerals such as montmorillonite, with a high swelling capacity.  2.1.2 Rock Quality Designation (Deere, 1964) The Rock Quality Designation (RQD) was introduced by Deere in 1964. Based upon core recovery of diamond drilling, it is a quantitative index of rock mass quality. RQD is widely used as a parameter in more complex and modern rock classifications systems. RQD is defined as the percentage of core recovered as intact pieces of 10cm or more in the specified run of core (Equation 1).  RQD(%) =  length of core in pieces ≥ 10cm × 100 length of run  Equation 1  Qualitative descriptions of RQD ranges are as follows: Table 1: Qualitative Description of RQD (after Deere, 1964)  RQD Rock Quality < 25% Very Poor 25-50% Poor 50-75% Fair 75-90% Good 90-100% Very Good  Area of interest  5  2.1.3 Rock Structure Rating (RSR) The Rock Structure Rating system was developed in 1971 by Jacob Associates (Wickham et al. 1971) and was a main focus for Bieniawski’s presentation of RMR in 1976 (Bieniawski, 1976). This system related empirical data of the RSR classification with the Rib Ratio (RR) to identify an optimum support system for the proposed opening. The RSR can be determined for core samples and/or rock walls. A brief description of the system is described in this section. For more information, the reader is encouraged to reference the paper by Jacob Associates. The RSR is calculated from the relationship between the qualitative analysis of the rock type on the large scale, joint spacing with opening direction and joint condition with ground water. The resultant RSR will be between the values of 25 and 100. The Rib Ratio (RR) is based upon the spacings used for steel rib supports. The RR uses Terzaghi’s formula for loose saturated sands (Wickham et al. 1971) compared to actual spacings in case studies. From this comparison, it was found that openings with poor rock conditions (RSR values of less than 27) would require the use of 100% of the theoretical support requirements calculated from Terzaghi’s sand formula. Openings with good rock conditions (RSR values of 77 or more) would not require any support.  Openings with RSR values  between 27 and 77 require different ranges of support system capacities. This study is based primarily on the use of steel rib sets in circular tunnels and therefore is not widely applicable in the mining industry. The study did make some observations on the use of rock bolts and shotcrete and also became the basis for analyzing caving ground at the first block cave operation by Kendorski of Agapito (Brady, 2008).  2.1.4 Geomechanics Classification (RMR) The Geomechanics Classification System (RMR) was originally developed in 1973 with major updates in 1976 (Bieniawski, 1976) and 1989 (Bieniawski, 1989) as more case histories became available. The classification systems presented in 1976 and 1989 will be presented as they are the two systems that are most commonly used in the mining industry today. The RMR system, regardless of update, is based upon the following 6 parameters:  6  1. Uniaxial compressive strength of the rock material 2. Drill core quality, RQD 3. Spacing of joints 4. Condition of joints 5. Groundwater conditions 6. Orientation of joints The first 5 parameters are evaluated for the identified structural region and given values according to the respective (1976 or 1989) system used and summed to give an RMR value. This value is then evaluated with respect to the orientation of joints as found in the respective system. The value weightings for the 1976 classification system can be found in Table 2. The value weightings for the 1989 classification system can be found in Table 3. For the purpose of this research, RMR 1976 is used throughout.  7  Table 2: Geomechanics Classification, RMR 1976 (after Bieniawski, 1976) A. Classification Parameters and their Ratings Parameter Strength of Point-load strength intact rock index 1 material UCS Rating Drill Core Quality, RQD 2 Rating Spacing of Discontinuities 3 Rating  4  5  Condition of Discontinuities (see E)  Rating Inflow per 10m tunnel length (l/m) Ground Joint w ater Water (one pressure/ (major of the principal σ) follow ing) General Conditions  Range of Values >8 MPa  4-8 MPa  2-4 MPa  1-2 MPa  >200 MPa 15 90%-100% 20 >3m 30  100-200 MPa 12 75%-90% 17 1 - 3m 25  50-100 MPa 7 50%-75% 13 0.3 - 1m 20  25-50 MPa 4 25%-50% 8 50 - 300mm 10  Very rough surfaces Not continuous No separation Hard joint w all rock  Slightly rough surfaces Separation <1mm Hard joint w all rock  6  0  None  <25  25-125  >125  0  0 - 0.2  0.2-0.5  >0.5  20  Completely dry 10  Moist only (interstitial w ater) 7  Water under moderate Severe w ater problems pressure 0 4  B. Rating Adjustment for Joint Orientations Strike and dip orientations Very favourable Favourable Fair Unfavourable Tunnels and mines 0 -2 -5 -10 Ratings Foundations 0 -2 -7 -15 Slopes 0 -5 -25 -50 C. Rock Mass Classes Determined from Total Ratings Rating 100-81 80-61 60-41 40-21 Class number I II III IV Description Very good rock Good rock Fair rock Poor rock D. Meaning of Rock Classes Class number I II III IV Average stand-up time 10 yrs for 5m span 6mths for 4m span 1 w eek for 3m span 5hrs for 1.5m span Cohesion of rock mass (kPa) >300 200-300 150-200 100-150 Friction angle of rock mass (deg) >45 40-45 35-40 30-35 E. Effect of Discontinuity Strike and Dip Orientation in Tunneling Strike perpendicular to tunnel axis Strike parallel to tunnel axis Drive w ith dip Drive against dip Dip 45-90º Dip 20-45º Dip 45-90º Dip 20-45º Dip 45-90º Dip 20-45º Very favourable  Favourable  Fair  Soft gouge >5mm thick or Joints open >5mm Continuous  12  25  Rating  Slightly rough surfaces Separation <1mm Soft joint w all rock  Slickensided surfaces or Gouge <5mm thick or Joints open 1-5mm Continuous  For this low range, a UCS test is preferred 10-25 MPa3-10 MPa 1-3 MPa 2 1 0 <25% 3 <50mm 5  Unfavourable  Very Unfavourable  Very unfavourable -12 -25 -60 <20 V Very poor rock V 10min for 0.5m span <100 <30  Dip 0-20º - Irrespective of strike Unfavourable  Fair  8  Table 3: Geomechanics Classification, RMR 1989 (after Bieniawski, 1989) A. Classification Parameters and their Ratings Parameter Strenght of Point-load strength intact rock index material UCS Rating  1  Drill Core Quality, RQD  2 3  4  4-10 MPa  2-4 MPa  1-2 MPa  >250 MPa  100-250 MPa  50-100 MPa  25-50 MPa  15  12  7  4  90%-100%  75%-90%  50%-75%  25%-50%  For this low range, a UCS test is preferred 5-25 MPa 1-5 MPa <1 MPa 2  1 <25%  Rating  20  17  13  8  3  Spacing of Discontinuities  >2m  0.6 - 2m  0.2m - 0.6m  6cm - 0.2m  <6cm  Rating  20  15  10  Condition of Discontinuities (see E)  Very rough surfaces Not continuous No separation Unw eathered w all rock  Rating  30  25  None  <10  10-25  25-125  >125  0  <0.1  0.1-0.2  0.2-0.5  >0.5  Completely dry  Damp  Wet  Dripping  Flow ing  15  10  7  4  0  Inflow per 10m tunnel length (l/m) Joint w ater pressure/ (major principal σ) General Conditions Rating  Ground Water  5  Range of Values >10MPa  Slightly rough surfaces Separation <1mm Slightly w eathered w alls  8 Slickensided surfaces Slightly rough surfaces or Separation <1mm Gouge <5mm thick Highly w eathered w alls or Separation 1-5mm Continuous 20 10  0  5 Soft gouge >5mm thick or Separation >5mm Continuous 0  B. Rating Adjustment for Discontinuity Orientations (see F) Strike and dip orientations Ratings  Very favourable  Favourable  Fair  Unfavourable  Very unfavourable  Tunnels and mines  0  -2  -5  -10  -12  Foundations  0  -2  -7  -15  -25  Slopes  0  -5  -25  -50  C. Rock Mass Classes Determined from Total Ratings Rating  100-81  80-61  60-41  40-21  Class number  I  II  III  IV  <21 V  Description  Very good rock  Good rock  Fair rock  Poor rock  Very poor rock  I  II  D. Meaning of Rock Classes Class number Average stand-up time  20 yrs for 15m span 1 year for 10m span  III  IV  V  1 w eek for 5m span  10hrs for 2.5m span  30min for 1m span  Cohesion of rock mass (kPa)  >400  300-400  200-300  100-200  <100  Friction angle of rock mass (deg)  >45  35-45  25-35  15-25  <15 >20m  E. Guidelines for Classification of Discontinuity Conditions* Discontinuity length (persistance)  <1m  1-3m  3-10m  10-20m  Rating  6  4  2  1  0  Separation (aperature)  None  <0.1mm  0.1 - 1.0mm  1 - 5mm  >5mm  Rating  6  5  4  1  0  Roughness  Very rough  Rough  Slightly rough  Smooth  Slickensided  Rating  6  5  3  1  0  Infilling (gouge)  None  Hard infilling <5mm  Hard infilling >5mm  Soft infilling <5mm  Soft infilling >5mm  Rating  6  4  2  2  0  Weathering  Unw eathered  Slightly w eathered  Moderately w eathered  Highly w eathered  Decomposed  Rating  6  5  3  1  0  F. Effect of Discontinuity Strike and Dip Orientation in Tunneling** Strike perpendicular to tunnel axis  Strike parallel to tunnel axis  Drive w ith dip - Dip 45-90º  Drive w ith dip - Dip 20-45º  Dip 45-90º  Dip 20-45º  Very favourable  Favourable  Very favourable  Fair  Drive against dip - Dip 45-90º  Drive against dip - Dip 20-45º  Dip 0-20º - Irrespective of strike  Fair  Unfavourable  Fair  * Some conditions are mutually exclusive. For example, if infilling is present, the roughness of the surface w ill be overshadow ed my the influence of the gouge. Insuch cases use A.4 directly. ** Modified after Wickham et al. (1972)  9  2.1.5 Rock Tunneling Quality Index, Q The Rock Tunneling Quality Index, Q, was first introduced in 1974 by Barton, Lien and Lunde of the Norwegian Geotechnical Institute, and is sometimes referred to as the NGI system. The Q system is based upon the following 6 parameters and is calculated as follows (Barton et al. 1974): 1. RQD (Table 4) 2. Number of joint sets, Jn (Table 4 and Figure 2) 3. Roughness of the weakest joint set, Jr (Table 4 and Figure 3) 4. Alteration or infilling along the weakest joint set, Ja (Table 5 and Figure 4) 5. Water inflow, Jw (Table 5) 6. Stress Reduction Factor, SRF (Table 6)  RQD   J r  ×  Q =  J n    Ja    Jw   ×     SRF   Equation 2  The weightings given to each of these parameters can be found in Table 4, Table 5 and Table 6 and Figure 2, Figure 3 and Figure 4. The (RQD/Jn) term represents the rock block size, the (Jr/Ja) term represents the interblock shear strength and the (Jw/SRF) term represents the active stress of the rock mass. The resultant values of Q can be in the range of approximately 0.001 and 1000, and are plotted on a logarithmic scale.  10  Table 4: Descriptions and Ratings for the Parameters RQD, Jn and Jr (after Barton et al. 1974) 1 A B C D E  Rock Quality Designation Very poor Poor Fair Good Excellent  2 Joint Set Number A B C D E F G  Massive, no or few joints One joint set One joint set plus random Two joint sets Two joint sets plus random Three joint sets Three joint sets plus random Four or more joint sets, random, H heavily jointed, "sugar cube", etc. J Crushed rock, earthlike  RQD 0-25 25-50 50-75 75-90 90-100 Jn 0.5-1.0 2 3 4 6 9 12  Note: i) For intersections, use (3.0 x Jn) ii) For portals use (2.0 x Jn)  15 20  Jr 3 Joint Roughness Number a) Rock wall contact and b) Rock wall contact before 10cm shear A Discontinuous joints 4 B Rough or irregular, undulating 3 C Smooth, undulating 2 D Slickensided, undulating 1.5 E Rough or irregular, planar 1.5 F Smooth, planar 1 G Slickensided, planar 0.5 c) No rock contact when sheared Zone containing clay minerals thick 1.0 (nominal) H enough to prevent rock wall contact J  Note: i) Where RQD is reported or measured as ≤ (included 10 a nominal value of 10 is used to evaluate Q ii) RQD intervals of 5, i.e. 100, 95, 90, etc. are sufficiently accurate  Note: i) Add 1.0 if the mean spacing of the relevant joint set is greater than 3m ii) Jr=0.5 can be used for planar slickensided joints having lineations, provided the lineations are favourably oriented  Sandy, gravelly or crushed zone thick 1.0 (nominal) enough to prevent wall rock contact  11  Table 5: Descriptions and Ratings for the Parameters Ja and Jw (after Barton et al. 1974) 4  Joint Alteration Number Ja φ r (approx.) (deg) a) Rock wall contact Tightly healed, hard, non-softening, impermeable filling A 0.75 (-) i.e. quartz or epidote B Unaltered joint walls, surface staining only 1.0 (25-35) Slightly altered joint walls. Non-softening mineral 2.0 (25-35) C coatings, sandy particles, clay-free disintegrated rock, etc. Silty, or sandy-clay coatings, small clay fraction (non3.0 (20-25) D softening) Softening or low friction clay mineral coatings, i.e. kaolinite, mica. Also chlorite, talc, gypsum and E 4.0 (8-16) graphite etc., and small quantities of swelling clays. (Discontinuous coatings, 1-2mm or less in thickness) b) Rock wall contact before 10cm shear F Sandy particles, clay-free disintegrated rock etc. 4.0 (25-30) Strongly over-consolidated, non-softening clay mineral 6.0 (16-24) G fillings (continuous, <5mm in thickness) Medium or low over-consolidation, softening, clay 8.0 (12-16) H mineral fillings (continuous, <5mm in thickness) Swelling clay fillings, i.e. montmorillonite (continuous, <5mm in thickness). Value of Ja depends on percent J 8.0-12.0 (6-12) of swelling clay-size particles, and access to water etc. c) No rock wall contact when sheared K,L, Zones or bands of disintegrated or crushed rock and 6.0, 8.0 or (6-24) M clay (see G, H, J for description of clay condition) 8.0-12.0 Zones or bands of silty or sandy clay, small clay N fraction (non-softening) 5 O,P, Thick, continuous zones or bands of clay (see G, H, J 10.0, 13.0 or (6-24) 13.0-20.0 R for description of clay condition) 5  Joint Water Reduction Factor  Jw  Approx. water pressure (kg.cm2)  A  Dry excavations or minor inflow, i.e. <5 l/min. locally Medium inflow or pressure occasional outwash of joint fillings Large inflow or high pressure in competent rock with unfilled joints Large inflow or high pressure, considerable oitwash of joint fillings Exceptionally high inflow or water pressure at blasting, decaying with time Exceptionally high inflow or water pressure continuing without noticeable decay  1.0  <1  0.66  1.0-2.5  0.5  2.5-10.0  0.33  2.5-10.0  0.2-0.1  >10.0  0.1-0.05  >10.0  B C D E F  Note: i) Values of (φ)r are intended as an approximate guide to the mineralogical properties of the alteration products, if present  Note: i) Factors C to F are crude estimates. Increase Jw if drainage measures are installed ii) Special problems caused by ice formation are not considered  12  Table 6: Descriptions and Ratings for the Parameter SRF (after Barton et al. 1974) 6 Stress Reduction Factor SRF a) Weakness zones intersecting excavation, which may cause loosening of rock Note: mass when tunnel is excavated i) Reduce these values of SRF by 25-50% if the relevant Multiple occurances of weakness zones containing clay or chemically A 10.0 shear zones only influence but disintegrated rock, very loose surrounding rock (any depth) do not intersect the Single weakness zones containing clay, or chemically disintegrated rock B 5.0 excavation (depth of excavation ≤50m) ii) For strongly anisotropic Single weakness zones containing clay, or chemically disintegrated rock C 2.5 stress field (if measured): (depth of excavation >50m) D Multiple shear zones in competent rock (clay free), loose surrounding 7.5 when 5<σ1/ σ3<10, reduce σc E Single shear zones in competent rock (clay free) (depth of excavation 5.0 and σt to 0.8σc and 0.8σt ; F Single shear zones in competent rock (clay free) (depth of excavation 2.5 when / >10, reduce and σ1 σ3 σc G Loose open joints, heavily jointed or "sugar cube" etc. (any depth) 5.0 σt to 0.6σc and 0.6σt b) Competent rock, rock stress problems where: σc = unconfined σ /σ σ /σ c  H Low stress, near surface J Medium stress High stress, very tight structure (usually favourable to K stability, may be unfavourable to wall stability) L M  N O P R  1  >200 200-10  t  1  >13 2.5 13-0.66 1.0 0.660.5-2.0 10-5 0.33 0.335-10 Mild rock burst (massive rock) 5-2.5 0.16 Heavy rock burst (massive rock) <2.5 <0.16 10-20 c) Squeezing rock; plastic flow of incompetent rock under the influence of high rock pressures 5-10 Mild squeezing rock pressure 10-20 Heavy squeezing rock pressure d) Swelling rock; chemical swelling activity depending on presence of water 5-10 Mild swelling rock pressure 10-15 Heavy swelling rock pressure  compression strength, σt = tensile strength (point load), σ1 and σ3 = major and minor principal stresses iii) Few case records available where depth of crown below surface is less than span width. Suggest SRF increase from 2.5 to 5 for such cases (see H)  13  # of Joint Sets  Jn  # of Joint Sets  Intact Rock No Joints  0.5  1  Few Random Joints Only  1 Set  2  3  1 Set + Random  2 Sets  4  6  2 Sets + Random  3 Sets  9  12  3 Sets + Random  > 4 Sets Heavily Jointed  15  20  Earthlike, Crushed Rock  Figure 2: Number of Joint Sets, Jn (after Barton et al. 1974) Jr  Large Scale:  Planar  Undulating  Discontinuous  0.5  1.5  2.0  1.0 <1/100cm  2.0 >2/100cm  3.0  Rough JRC > 10  1.5  3.0  4.0  Gouge-Filled No Wall Contact  1.0  1.0  1.5  Small Scale:  Jr (Critical Set)  Slickensided  Smooth JRC < 10  Figure 3: Joint Roughness Number, Jr (after Barton et al. 1974)  Typical Description (Critical Joint Set)  Ja  Tightly Healed  0.75  Sruface Staining Only  1.0  Slightly Altered Joint Walls, Sparse Mineral Coating  2.0-3.0  Low Friction Coating (Chlorite, Mica, Talc, Clay) < 1 mm thick  3.0-6.0  Thin Gouge, Low Friction or Swelling Clay 1 - 5 mm thick Thick Gouge, Low Friction or Swelling Clay > 5 mm thick Surface can be scratched with a knife Ja = 1 to 1.5 Surface can be scratched with a fingernail Ja = 2.0 - feels slippery Surface can be dented with a fingernail Ja = 4.0 - feels slippery  6.0-10.0 10.0-20.0  Figure 4: Joint Alteration Number, Ja (after Barton et al. 1974)  14  2.1.6 Modified Rock Tunneling Quality Index, Q’ Q’ is a modification of the Rock Tunneling Quality Index, Q. Q’ is identical to Q with one exception, the SRF term is excluded (Potvin, 1980):  RQD   J r  ×  Q ' =   Jn   Ja    × J w   Equation 3  Use of the original Q system will give conservative answers (Potvin, 1980) as it was designed and is used for tunneling. For mining purposes where the in situ and induced stress regimes vary considerably from that of tunneling situations, the SRF term is dropped and stress is considered separately from the rock mass.  2.1.7 Relating RMR and Q Based upon 111 case histories from around the world, a relationship between RMR and Q has been formed (Bieniawski, 1976). The relationship is presented as the following:  RMR= 9 ln Q + 44  Good  Exceptionally  Extremely Good  Very Good  Good  Fair  Poor  Very Poor  Extemely Poor  Poor  Exceptionally  100  Equation 4  Very Good Rock Mass Rating, RMR  80 Good 60 Fair 40 Poor 20  RMR = 9*LNQ + 44 Very Poor  0 0.001  0.01  0.1  1  10  100  1000  Rockmass Tunelling Index, Q  Figure 5: Relationship between RMR and Q (after Bieniawski, 1976)  15  Tunnelling Quality Index, Q 0.001 - 0.01 0.01 - 0.1 0.1 - 1 1-4 4 - 10 10 - 40 40 - 100 100 - 400 400 - 1000  Rock Mass Description Exceptionally Poor Extremely Poor Very Poor Poor Fair Good Very Good Extremely Good Exceptionally Good  Rock Mass Rating 0% - 3% 3% - 23% Area of interest 23% - 44% 44% - 56% 56% - 65% 65% - 77% 77% - 85% 85% - 98% 98% - 100%  Figure 6: Descriptive comparison between RMR and Q (after Bieniawski, 1976)  2.1.8 Mining Rock Mass Rating (MRMR) Laubscher introduced the Mining Rock Mass Rating (MRMR) system in 1974. It is based upon Bieniawski’s RMR system and has been modified to focus on mining operations, most specifically to block caving operations. The upper limit of what would be considered as caveable would be the lower limit of what would be considered as a stable span. In Laubscher’s 1990 paper, the author states that “A classification system must be straightforward and have a strong practical bias so that it can form part of the normal geological and rock-mechanics investigations to be used for mine design and communication. Highly sophisticated techniques are time-consuming, and most mines cannot afford the large staff required to provide complex data…” This is ironic because in this author’s opinion, the MRMR method requires a high degree of subjectivity, is a method where extensive data collection and manipulation is required and is time consuming. There is also a 98 percent correlation between the MRMR and RMR systems (Laubscher, 1990) which leads to note the ease of use of the RMR system. For these reasons, a brief overview of this method will be presented. For descriptions of the equation criteria and a more in depth look at the MRMR system, refer to Laubscher’s 1990 paper. The MRMR system is based upon the intact rock strength (IRS), the joint/fracture spacing and the joint condition/water with various adjustment factors and is calculated as follows: MRMR = IRS +  FF + 40[ A × B × C × D ] × adjustments m  Equation 5  Or,  16  MRMR = IRS + [RQD + JS ] + 40[ A × B × C × D ] × adjustments Where,  Equation 6  IRS = Intact Rock Strength FF/m = Fracture Frequency per Meter RQD + JS = Spacing of Fractures based upon RQD and Joint Spacing A = Large-scale joint expression B = Small-scale joint expression C = joint wall alteration D = joint infilling Adjustment factors include weathering, joint orientation, mining-induced stresses and blasting effects. A stability/instability design graph relating MRMR against the hydraulic radius was created based upon case histories. These case histories were divided into three categories of Stable (requiring key-block stabilization only), Caving and a Transition Zone (requiring more intensive support to maintain stability). Since the hydraulic radius is presented, as opposed to the span, this curve cannot be compared to the RMR and Q design curves that will be presented later (Lang, 1994).  2.2 Weak Rock Underground Excavation Failure Mechanisms Underground rock failures occur in one or a combination of the following three forms; 1. Stress Induced Failure 2. Structural Failure 3. Rock Mass Failure In a weak rock environment, the most typical type of failure encountered is the rock mass failure and can frequently include a number of small structural failures. However, the overall rock mass failure is what is most prevalent. Due to the broken up nature of a weak rock environment, stress is typically not an issue and is looked at separately. For the purpose of this thesis, rock mass failure, and more specifically weak rock mass  17  failures, will be focused upon. Rock mass failure has been studied for decades and many relationships have been established. An overview of these relationships can be found in Section 2.2.3.1. The Span Design Curve (Lang, 1994, Wang et al. 2002) is widely used throughout the mining industry and is the focus of this thesis. The weak rock mass portion of the original (Lang, 1994) and expanded (Wang et al. 2002) database has very little data in the RMR76 range below 55. The research focus on the weak rock mass range will expand the available usage of the Span Design Curve providing a user friendly tool for span design in these weak rock mass environments. A brief discussion of stress and structural failures will also be presented.  2.2.1 Stress When the mining induced stress of an area exceeds the strength of the rock, stress induced failure of the rock occurs. In highly competent (massive and elastic) rock, rockbursting may be the result of the higher stresses. In weak or highly jointed rock, gradual yielding or movement along joint planes may occur. Typically in weak rock environments, stress induced failures are not a concern due to the yielding nature of the rock mass. However, modeling may be done if there are any concerns. Most modeling programs follow either Mohr-Coulomb or Hoek-Brown failure criterion.  Good  summaries of these criterions may be found in Goodman, 1989 and Hoek and Brown, 1980, respectively.  2.2.2 Structure Structurally controlled failures involve wedges and/or blocks that can either fall due to gravity or slide along a plane. Wedges and blocks are identified by mapping (core logging and/or underground mapping) and are most commonly evaluated using stereonets and/or computer aided analyses. Other methods of evaluating structurally controlled failures in “blocky” ground (weak rock environment) include “Block Theory” (Goodman, 1989) and Voussoir Arch Failure (Evans, 1941 and Beer and Meek, 1982).  2.2.2.1 Stereonet Analysis A quick and easy initial assessment of potential wedge failure in the back can be done using stereonets. This method is typically the initial method used. A good summary on the use of stereonets is provided by Hoek and Brown, 1980. The use of stereonets aids in 18  the identification of wedge forming structures. From mapping data, the prominent joint sets are plotted on an equal angle, lower hemisphere stereonet. Tetrahedral wedges will form with three (3) intersecting structures and the roof of the excavation. A gravity “free fall” wedge is indicated by having the centre of the stereonet lying within the triangle created by the three great circles of the corresponding joint sets (Figure 7). A sliding wedge is indicated by having a triangle created by the three great circles of the corresponding joint sets without having the centre of the stereonet lying inside the triangle, while also allowing the wedge to slide along one of the joint planes.  To  determine if sliding will occur, one or more of the joint planes must lie within the corresponding friction circle (Figure 8). If the triangle should lie outside of this centre area, the wedge is stable.  Gravity Wedge  Figure 7: Gravity Wedge Failure (after Lang, 1994)  Sliding Wedge  Figure 8: Sliding Wedge Failure (after Lang, 1994)  19  2.2.2.2 Computer Aided Analysis Computer programs are available that aid in the visualization of intersecting joint planes in an underground excavation.  One such program is UNWEDGE provided by  Rocscience, 2006. Potentially unstable wedges are identified and factors of safety are calculated. Support requirements may be entered and factors of safety are updated. This program, and others like it, allow for quick identification and determination of wedges and support requirements needed to achieve a stable excavation.  2.2.2.3 “Block Theory” In weak rock/highly jointed ground conditions, movement or extraction of certain blocks/wedges may allow other blocks to move. Unsupported, movement of these “key blocks” could drastically alter the final dimensions of the planned excavation. Identification and support of these blocks prior to their movement will prevent subsequent block movements.  Six types of blocks are identified in “block theory”  (Figure 9).  VI V IV II  I  I  II  III  Figure 9: Types of Blocks in "Block Theory" (after Goodman, 1989)  Type I, II and III blocks are finite and removable. Type I blocks are key blocks. The movement of key blocks will allow potential movement of other blocks. These blocks require support as their geometry will allow for movement (gravity and sliding blocks). Type II blocks are potential key blocks in that movement of these blocks will also allow for potential movement of other blocks. However, movement of the initial block is 20  unlikely due to their geometry. Type III blocks are stable also due to their geometry (in this case, stable due to gravity). Type IV and V blocks are stable blocks unless they are undermined due to the movement of key blocks (Goodman, 1989).  2.2.2.4 Voussoir Arch Failure The Voussoir arch theory was first considered by Evans, (1941) and later modified by Beer and Meek, (1982). A good summary of the Voussoir arch theory can be found in Brady and Brown, (1985). The theory of the Voussoir arch is that lateral thrust through a beam is not uniformly distributed, and that it traces an approximate parabolic arch through the beam. Three failure mechanisms have been identified by Beer and Meek, (1982); 1. Shear failure at the abutments, 2. Crushing at the hinges formed in the upper portion of the centre of the beam and at the lower abutment contacts, 3. Buckling of the roof beam with increasing eccentricity of lateral thrust giving rise to a snap-through mechanism. The following assumptions are also made (Lang, 1994); -  The rock mass is assumed to be composed of discrete blocks, cut by linear discontinuities trending along strike.  -  No horizontal compressive stress is being transferred to the beam from the surrounding rock.  -  There is no tensile strength between the blocks.  -  The load distributions over the abutments, surfaces of the beam and at the central section of the beam act in a triangular fashion illustrated in (Brady and Brown, 1985)  2.2.3 Rock Mass Failure of a rock mass is characterized by the caving of the immediate area. The extent of caving may be small and may cease once a stable geometry has been reached or may continue until the void has been filled (Figure 10). Rock mass failure has been studied  21  for decades and many relationships have been established. These empirical designs all rely on rock mass classification and are therefore significantly dependant on the major parameters as outlined in Section 2. Several of these designs are detailed below. These empirical designs are used as tools to determine the stability, stand-up time and support requirements of an excavation. Many of these designs are based upon civil engineering case histories that have higher factors of safety than are generally used in mining. Unfortunately this can produce conservative estimates for mining applications. There are two systems that have become “standard” in the mining industry, Barton’s Q system and Bieniawski’s RMR system.  Rock mass failure may stop when a stable shape has been attained  Caving may continue until the void is filled  Figure 10: Extent of Rock Mass Failures  2.2.3.1 History of Span Excavation Studies Several relationships relating rock mass and underground span openings have been developed. Many of them have been inspired from civil engineering and tunneling practices which require greater factors of safety. In recent history, there has been an emphasis on establishing such relationships for underground excavations. This section describes a selection of these studies.  Unal – Coal Mine Roof Control The main area of work done by Unal is in the design and roof control of underground coal mines.  From his work, an estimate of support load and rock load height can be  applied in hard rock conditions as well as coal. The support load can be determined as follows (Unal, 1983):  P=  100 − RMR γB = γht 100  Equation 7  22  where P is the support load; RMR is the rock mass rating from Bieniawski’s Geomechanics Classification; γ is the density of the rock, kg/m3;  B is the drift width in m. This gives the rock load height as:  100 − RMR  ht =  B 100    Equation 8  Lauffer’s Stand-Up Time vs. Span Relationship While others have discussed the time dependence stability/instability of excavations, Lauffer was the first to propose that the stand-up time of an active span is related to the rock mass quality of the excavation (Figure 11), with the classes of rock mass corresponding to Terzaghi’s classification; A being very good rock and G being very poor rock (Lauffer, 1958). The stand-up time is the length of time which the excavation will stand unsupported once it has been excavated. The active span is the width of the excavation or the distance from the face to the support if this is less than the excavation width.  ACTIVE SPAN - m  10  1.0 Area of Interest  0.1  G 1 min  F 10 min 1 hour  E  D  1 day 1 week 1 mth STAND-UP TIME  C  B  A  1 year 10 years 100 years  Figure 11: Relationship between Active Span and Stand-Up Time (after Lauffer, 1958)  23  Equivalent Dimension, De, of Excavation (Barton) Barton et al. (1974) determined a relationship between the span of an opening with regards to the Tunneling Index, Q (Figure 12). They are related using the following parameter;  De =  Excavation Span or Height (m) ESR  Equation 9  where, De = Equivalent Dimension ESR = Excavation Support Ratio The ESR is a reflection of the Factor of Safety that is required for the opening based upon its final use. An ESR of 3 to 5 is recommended for mining applications. A list of ESR values based upon the observations of Barton et al. (1974) can be found in Table 7.  Area of Interest  100  Exceptionally Poor  Extremely Poor  Very Poor  Poor  Fair  Good  Very Good  Ext. Good  Exc. Good  Equivalent Dimension, De  De = 2Q0.4 Support Required 10  No Support Required 1  0.1 0.001  0.01  0.1  1  10  100  1000  NGI Tunnelling Quality, Q  Figure 12: Relationship between Q and the Equivalent Dimension, De (after Barton et al. 1974)  24  The boundary of “No Support Required” and “Support Required” can be approximated by the following equation; De ' = 2Q 0.4  Equation 10  where, De’ = Equivalent Dimension Q = rock mass quality Table 7: Excavation Support Ratios (after Barton et al. 1974) Type of excavation A. Temporary mine openings etc. B. Vertical shafts: i) circular section ii) rectangular.square section C. Permanent mine openings, water tunnels for hydro power (exclude high pressure penstocks), pilot tunnels, drifts and headings for large excavations etc. D. Storage rooms, water treatment plants, minor road and railway tunnels, surge chambers, access tunnels, etc. (cylindrical E. Power stations, major road and railway tunnels, civil defence chambers, portals, intersections, etc. F. Underground nuclear power stations, railway stations, sports and public facilities, factories, etc.  ESR 3-5 2.5 2.0  No. of cases (2) (0) (0)  1.6  (83)  1.3  (25)  1.0  (79)  0.8  (2)  This chart has been updated by Grimstad and Barton (1993) in reflection of the increased use of fiber reinforced shotcrete in underground openings and is shown in Figure 13 and Table 8. Table 8: Reinforcement Categories (after Grimstad and Barton, 1993) REINFORCEMENT CATEGORIES 1) Unsupported 2) Spot Bolting 3) Systematic bolting 4) Systematic bolting with 40-100mm unreinforced shotcrete  5) Fibre reinforced shotcrete, 50-90mm, and bolting 6) Fibre reinforced shotcrete, 90-120mm, and bolting 7) Fibre reinforced shotcrete, 120-150mm, and bolting 8) Fibre reinforced shotcrete, > 150mm, with reinforced ribs of shotcrete and bolting 9) Cast concrete lining  25  Area of Interest  100  Extremely Poor  Very Poor  Poor  Fair  Good  Very Good  Ext. Good  Exc. Good  20 10  50  Span or Height in m / ESR  7 20  5  10  3  5  2.4  2  1.5  1 0.001  0.004 0.01  0.04 0.1  0.4 1  4  40  10  100  Bolt Length in m for ESR = 1  Exceptionally Poor  400 1000  Figure 13: Estimate Support Categories based on the Tunneling Index, Q (after Grimstad and Barton, 1993)  Bieniawski’s Stand-Up Time vs. RMR Following Lauffer’s Stand-up time graph, Bieniawski related the stand-up time for maximum stable openings for given RMR (Figure 14). This graph is applicable to tunnels, chambers and mine openings (Bieniawski, 1989). 1d  30 Immediate Collapse  10 8 Roof Span, m  1mo 70  20  1yr  10yr 90  80  60 50  40  6 5 4 3  1wk  30  Area of Interest  20  80  70  60 50  2 40  1  No Support Required  30  20  10-1  100  101  102  103  104  105  106  Stand-up Time, hrs  Figure 14: Relationship between the stand-up time and span for various RMR classes (after Bieniawski, 1989)  26  Span Design Curve The “critical span curve” has undergone modifications since its development in 1994 by Lang and the University of British Columbia. The span curve, including updates, has been widely accepted in the North American mining community, and provides a quick and simple tool to estimate a maximum span that may be designed based upon the observed RMR value. The initial curve was developed to evaluate back stability in cut and fill mines and consists of two straight lines that divide the graph into three zones (Stable, Potentially Unstable and Unstable) (Figure 15). The database for this graph consisted of 172 points from the Detour Lake mine owned by Placer Dome Inc. with most of the points having RMR76 values of 60 to 80 (Lang 1994). The database was expanded to 292 observations in 2000 with case histories from an additional six mines (Table 9). The expanded database includes RMR76 values from 24 to 87, with 63% of the cases in the range of 60 to 80 (Wang et al. 2002). Less than 10% of RMR76 values in the updated database fall below an RMR76 value of 40 and less than 20% fall below a value of 55 (Figure 16 and Figure 17)(Brady et al. 2003). The updated curve (Figure 17) has uncertainties below RMR76 values of 50 and above RMR76 values of 80. At the lower RMR76 range (and in the Unstable zone), it has been shown in mining operations that openings can remain stable with only local support (Ouchi et al. 2004).  27  Span Design Curve 45 40  Uncertainties  Design Span (m)  35 30  Unstable  25 20 15 10  Stable  5 0 0  10  20  30  40  50  60  70  80  90  100  Rock Mass Rating  Figure 15: Critical Span Curve (after Lang 1994) Table 9: Case history data sources (after Wang et al. 2002) Mine  Number of data cases Stable Potentially unstable 94 37 10 0 0 6 4 1 5 3 35 10 12 2 160 59  Total  Detour Lake mine, 1994 Detour Lake mine, 1999 Photo Lake mine Olympias mine Brunswick Mining Musselwhite mine Snip Operations Summary  172 22 6 13 17 46 16 292  Unstable 41 12 0 8 9 1 2 73  30 Number (%)  25 20 15 10 5 0  0 0 0 0 5  15  3 25  1 0 35  5 4 5 6  45  55  8  20 18 14 11 3 65  75  85  1 0 0 95  Rock Mass Rating  Figure 16: RMR distribution  28  < 10% of data  < 20% of data  Figure 17: Updated Critical Span Curve (after Wang et al. 2002)  2.2.3.2 Extent of Failure The extent of failure for rock mass failures is not addressed in the previously discussed empirical designs. Different methods have been used to determine the possible depth of failure that an excavation will experience. Further assessment of two ‘rules of thumb’ will be presented; a computational study and empirical design of caving depth estimation. Two typical ‘rules of thumb’ are used and are as follows; In the absence of prevailing stress and/or structure, -  A wedge shaped failure with the apex at a distance equivalent to 1/2 the span of the excavation (Figure 18).  -  A tabular volume across the entire width of the excavation with a height equal to 1/3 of the width of the excavation (Figure 19).  These rules are confirmed by bolting support guidelines (lengths of 30-50% x span) recommended for RMR values of 80 to 20 (Bieniawski, 1989)  29  zone of potential failure  ½ Span Span Opening  Figure 18: ½ span zone of rock mass failure influence  zone of potential failure  1/3 Span Span Opening  Figure 19: 1/3 span zone of rock mass failure  Studies regarding the extent of failure of an excavation of lower RMR conditions have been recently completed (MacLaughlin et al., 2005).  The study conducted was a  parametric study of failure modes using Itasca’s distinct element method, UDEC, software. Conclusions from the study indicate that there is a correlation between RMR, friction angles and symmetry of jointing with the type of failure observed. Excavations in rock where asymmetrical jointing (Figure 20) and where symmetrical jointing (Figure 21 and Figure 22) was present experienced local failures with failure extents based on wedge geometry. Excavations in rock with symmetrical jointing and RMR values less than 55% experienced deep seated failure (Figure 23).  Excavations in rock with  symmetrical jointing and given friction angles of 25 degrees or less also experienced deep seated failure. It is, however, noted in the study that further work is required in the variation and persistence of the jointing input to obtain a better correlation to real world conditions (real world conditions rarely display perfect symmetry). Deep seated failures do happen and are documented, but are not as prevalent as this study might indicate.  30  Figure 20: Asymmetrical jointing of 60º and 30º and Friction angle of 10º (after MacLaughlin et al., 2005)  Figure 21: Local Failure Mode with symmetrical jointing of 30º and Friction angle of 40º (after MacLaughlin et al., 2005)  Figure 22: Symmetrical jointing of 60º and Friction angle of 40º (after MacLaughlin et al., 2005)  31  Figure 23: Deep Seated Failure Mode with symmetrical jointing of 30º and Friction angle of 10º (after MacLaughlin et al., 2005)  Empirical caving data is another method that may be used in the determination of the extent of failure that an excavation may experience. The most extensive observations of the relationship between the geomechanical state of a rock mass and its potential for caving has been reported by Laubscher (Brady and Brown, 1992). The origins of this data is from caving mines where caving is desired and not accidental. Therefore, caution should be used when applying this empirical method to an area that is not designed for caving (i.e. weak rock mass). However, it can give a good indication of the extent of failure that may occur if the installed ground support is insufficient. Laubscher’s caving design is based on the MRMR classification system (Table 10). Table 10: The Angle of Cave and the Failure Zone (after Laubscher, 1990) MRMR Class Very Good 100-81  Good 80-61  Fair 60-41  Poor 40-21  Very Poor 20-0  Cave Angle (degrees) Depth (m) Unres Res 100 70-90 85-95 500 70-80 80-90 Extent of Failure Zone Depth (m) Surf U/G 100 10m 10m 500 10m 20m Unres = No lateral restraint  Unres 60-70 60-70  Res 75-85 70-80  Unres 50-60 50-60  Surf U/G Surf 20m 20m 30m 20m 30m 30m Res = Lateral restraint  Res 65-75 60-70  U/G 30m 50m Surf = At  Unres 40-50 40-50  Res 55-65 50-60  Unres 30-40 30-40  Res 45-55 40-50  Surf U/G Surf U/G 50m 50m 75m 100m 50m 100m 75m 200m surface U/G = Underground  32  For the purposes of this study, the ‘rule of thumb’ of ½ span (Figure 18) is used since the exact orientations and number of joints sets for the data obtained are not known.  33  3  Methodology  There are many methods available to analyse data sets. Some are more accurate and are better at reflecting reality, while some achieve quicker results with more generalities applied. In the past, more accuracy implied longer computation times. There are now computer programs that make the computation process quick and simple, and still achieve accurate results. Care must be taken to choose and balance the amount of accuracy required and the time and resources involved. The results will only be as accurate as the data used. If the input data is preliminary and, at best, a rough estimate, an in depth and involved analytical method may not be necessary.  Three methods  available for tunnel/underground design are discussed. These methods are as follows; Observational methods, Analytical methods and Empirical methods.  3.1 Observational Method The observational method is exactly that, based upon observations made in the field. This method is most often reactionary.  The observational method is best suited to  established operations with the monitoring of existing excavations through visual observations and ground movement monitoring systems.  3.2 Analytical Methods Analytical methods include physical and numerical modeling. Using these methods, the stresses around an excavation, the deformation of the rock and the overall stability (Factor of Safety) of the excavation can be determined. With the increase of computer power and technology, numerical modeling has become easy to use, and less time consuming and has thus gained popularity in the industry. There are many simple and economic software programs available in both 2D and 3D. 2D methods are used for quick and simple approximations while 3D methods are used for more in depth analysis.  3.3 Empirical Methods Empirical methods use statistical analysis to determine the applicability of a given database to a given situation. The statistical analysis can be done using typical methods such as regression, or with a specifically designed statistical analysis computer software 34  program, also known as an expert system or neural network, may be used. Neural networks have evolved with the increase in computer power and technology and are now widely used in a variety of engineering applications. The most notable advantage of these systems over conventional statistical analysis is that an average user can analyze data that previously required extensive knowledge of mathematics and statistical analysis. Statistical analysis software programs are simple to use and can be used on any of today’s computers. Neural networks are based upon the biological network of the human brain. A neural network builds a system of “neurons” to make decisions, classifications and forecasts. Training of a network determines linear relationships between inputs and outputs, assigns weights to the links between neurons, creates additional hidden neurons and layers to determine non-linear relationships (Figure 24). Single layer networks are typically used for basic input/output optimization problems while multi layered networks are used for more complicated problem solving.  Inputs  Hidden  Output Neurons  Links Figure 24: Simple Network Structure  A network trains/learns by adjusting weightings throughout the network. Re-iteration of these adjustments occurs until a stable set of weights is achieved. Through training, neurons that don’t significantly influence the decision making will be eliminated and new neurons with appropriate weightings will be created. A network is trained on a set of data and verified on a smaller set of data before being used to make future predictions. In training a network, accuracy is determined through values of r-squared, average error and correlation, with correlation and r-squared values of 1.0 and an average error of zero being “perfect”.  35  Neural networks have been applied to numerous mining problems. The most relevant of these problems would be the update of the original span design curve done by J. Wang (Wang et al. 2002). The use of Ward System’s Neuroshell Predictor software (Ward, 2003) is applied to the database for the empirical design of this project. Within the Ward System Neuroshell Predictor software Neural and Genetic training are used. Neural training will extrapolate the data and Genetic will interpolate the data. For the purposes of this research, Genetic training has been applied.  36  4  Span Design  From 12 mines across North America, 463 case study data points were collected. Each record consists of the mine, span, RMR76 or Q’, stability and support employed. From the type of support employed and the associated Factor of Safety, the records were split into one of four (4) categories. Span, stability and support definitions are described in this chapter.  4.1 Span, Stability and Support Definitions This section outlines definitions used in this study and in the previous span design studies. The critical span of an opening will be defined along with that of standard support. The different stability cases will also be defined. This study separates the database into four (4) support categories. These four (4) categories are defined in Section 4.1.4.  4.1.1 Definition of Span The term “critical span” used by design methods/graphs refers to the largest circle that can be drawn within the boundaries of the excavation when viewed in plan (Figure 25a). This definition of span includes the overhang area that has not been supported by other means (i.e. fill from lifts below) (Figure 25b). Span  Post Pillar Span = Diameter of Largest Circle which can be drawn between Pillars and Walls a) Span Definition in Plan View  Span Includes Hanging Wall Overhang b) Span Definition in Section View  Figure 25: Span Definition (after Pakalnis and Vongpaisal 1993)  37  4.1.2 Definition of Stability The stability of an excavation is classified into three categories: 1) Stable Excavations a. No uncontrolled falls of ground b. No observed movement in the back c. No extraordinary support measures implemented 2) Potentially Unstable Excavations a. Extra ground support has been installed to prevent potential falls of ground b. Movement in the back of 1mm or more in 24 hours has been observed (Pakalnis 2002) c. Increase in the frequency of popping and cracking indicating ground movement 3) Unstable Excavations a. Area has collapsed b. The depth of failure of the back is 0.5 times the span (in absence of structure related failure) c. Support was not effective in maintaining stability When evaluating areas with shallow dipping or flat joints, a correction factor of minus 10 is applied to the final calculation of RMR76. This correction factor is usually applied in high stress environments where these flat lying joints typically develop. In the weak rock environment, typically heavily jointed, it is expected that the addition of a flat lying joint set will play a minor role in the overall stability of the opening. Due to the amorphic nature of the already weak rock mass, the application of this correction factor for flat lying joints is questionable. Where structures of discrete wedges have been identified, these must be supported prior to employing the critical span curve.  38  4.1.3 Definition of Standard Support The term “design span” refers to spans that have no support and or spans that have used limited local support consisting of pattern bolting (1.8m long mechanical bolts on a 1.2m x 1.2m pattern). Local support is deemed as support that is used to confine potential blocks/loose that may open/fall due to subsequent mining activities in surrounding areas (Pakalnis and Vongpaisal 1993). Due to the dynamic nature of weak rock environments, alternate and/or increased support is typically used. Friction bolts (i.e. Split Sets and Swellex) provide yielding/passive support and shotcrete provides a rigid/active support to the opening. This research looks into the use of these different support methods and evaluates their efficacy in terms of rock quality and span. Spans with a Factor of Safety of less than 1.2 are deemed “Unsupported” and can be compared to the original span design database of Lang (1994). Spans with a Factor of Safety greater than 1.2 are deemed “Supported.”  4.1.4 Definitions of Weak Rock Support Categories The database was split into four (4) support categories. These support categories were created to be able to compare similar support types with similar resultant factors of safety. Figure 26, Figure 27, Figure 28 and Figure 29 present typical bolt installation for Categories A, B, C and D respectively. Other configurations are possible and are used.  39  4.1.4.1  Category A  This category is comprised of spans that were pattern bolted (typically 1.2m x 1.2m or 0.9m x 0.9m) solely with frictions sets (Split Sets and/or Swellex). For rock with a specific gravity of 3.0, the calculated average Factor of Safety of a dead weight failure for the typical installation described in Figure 26 is 0.34. With the Factor of Safety being less than 1.0 for this category, it can be considered as “Unsupported” as was the initial graph by Lang (1994). More on the Factor of Safety can be found in Section 5.4.1. Direction of Advance  PLAN VIEW  0.9-1.2m 0.9-1.2m  Friction Bolt - Friction (Split Sets and/or Swellex) type bolts - 1.5m minimum, 2.4m maximum length - 0.9 to 1.2m square spacing  0.9-1.2m  SECTION VIEW Face  Figure 26: Typical Bolt Installation for Category A  40  4.1.4.2  Category B  This category is comprised of spans that were pattern bolted (typically 1.2m x 1.2m or 0.9m x 0.9m) with frictions sets (Split Sets and/or Swellex) along with spot bolting using resin grouted rebar. For rock with a specific gravity of 3.0, the calculated average Factor of Safety of a dead weight failure for the typical installation described in Figure 27 is 6.76. With the Factor of Safety of this category being significantly greater than 1.0, this category cannot be compared side by side with the original span graph by Lang (1994). More on the Factor of Safety can be found in Section 5.4.2. Direction of Advance  PLAN VIEW  0.9-1.2m  0.9-1.2m  Friction Bolt Grouted Rebar - Friction (Split Sets and/or Swellex) type bolts - 1.5m minimum, 2.4m maximum length - 0.9 to 1.2m square spacing - Fully grouted rebar - 2.4m length - Spot bolt as per diagram  0.9-1.2m  Face  SECTION VIEW  Figure 27: Typical Bolt Installation for Category B  41  4.1.4.3  Category C  This category is comprised of spans that were pattern bolted (typically 1.2m x 1.2m or 0.9m x 0.9m) with frictions sets (Split Sets and/or Swellex) and pattern bolted (typically 1.2m x 1.2m or 0.9m x 0.9m) with resin grouted rebar. For rock with a specific gravity of 3.0, the calculated average Factor of Safety of a dead weight failure for the typical installation described in Figure 28 is 7.32.  With the Factor of Safety of this category  being significantly greater than 1.0, this category cannot be compared side by side with the original span graph by Lang (1994). More on the Factor of Safety can be found in Section 5.4.3. Direction of Advance  PLAN VIEW  0.9-1.2m  0.9-1.2m  Friction Bolt Grouted Rebar - Fully grouted rebar - 2.4m length - 0.9 to 1.2m square spacing - Friction (Split Sets and/or Swellex) type bolts - 1.5m minimum, 2.4m maximum length - 0.9 to 1.2m square spacing in between grouted rebar 0.9-1.2m  Face  SECTION VIEW  Figure 28: Typical Bolt Installation for Category C  42  4.1.4.4  Category D  This category is comprised of spans that were bolted with cablebolts or that were supported using another engineering designed support system such as cemented rock fill (underhand cut and fill mining), a significant application of shotcrete (typically 76mm), spiling or timber sets. For rock with a specific gravity of 3.0, the calculated average Factor of Safety of a dead weight failure for the typical installation described in Figure 29 is 9.55. With the Factor of Safety of this category being significantly greater than 1.0, this category cannot be compared side by side with the original span graph by Lang (1994). More on the Factor of Safety can be found in Section 5.4.4 and Appendix A: Entire Database.  43  Direction of Advance  PLAN VIEW  0.9-1.2m  Friction Bolt  0.9-1.2m  Grouted Rebar Cable Bolt - Fully grouted cables - 7m length - Spot bolt as per diagram - Fully grouted rebar - 2.4m length - 0.9 to 1.2m square spacing - Friction (Split Sets and/or Swellex) type bolts - 1.5m minimum, 2.4m maximum length - 0.9 to 1.2m square spacing in between grouted rebar  0.9-1.2m  SECTION VIEW  Face  Figure 29: Typical Bolt Installation with Cablebolts for Category D  44  5  Database  Empirical design is only as good as the data that is used. While it is important to have a significant quantity of data cases, it is also important that the data used is reliable and representative of what is seen in industry. The more reliable and representative the data, the more applicable the design is to a wide range of mining situations.  The data  collection techniques and statistics are also presented in this section.  5.1 Data Collection More than 500 cases were collected from twelve (12) mines across Canada and the United States. The mines from which the data originated are as follows; Cameco’s Rabbit Lake mine, Barrick’s Carlin East, Eskay Creek and Rodeo mines, Newmont’s Deep Post and Midas mines, Placerdome’s (now Barrick) Getchell and Turquoise Ridge mines, Yukon Nevada Gold’s (Queenstake) Jerritt Canyon mine, Breakwater Resources’ Myra Falls mine, Goldcorp’s Red Lake mine and Stillwater Mining Company’s Stillwater mine. The location of each mine and the distribution of data from each mine are shown in Figure 30 and Figure 31 respectively.  45  Eskay Creek  Cameco  Myra Falls  Red Lake Stillwater  Turquoise Ridge and Getchell  Jerritt Canyon, Midas, Carlin East, Rodeo and Deep Post  Figure 30: Mine Locations in North America  Cameco, 0.9% Carlin East, 0.6% Deep Post, 0.6% Eskay Creek, 5.4% Getchell, 0.4% Jerritt Canyon, 0.2% Midas, 1.3% Myra Falls, 1.1% Red Lake, 8.2% Rodeo, 2.8% Stillwater, 77.5% Turquoise Ridge, 0.9%  Figure 31: Database Mine Distribution  46  At each mine, the span, RMR76 or Q’ value, stability and installed ground support were collected for each case history along with any relevant comments.  The span was  collected in feet or meters and converted to meters for the final database. The RMR76 or Q’ values were determined by experienced rock mechanic engineers and converted to RMR76 for the final database. The RMR76 system was chosen because of its visual ease of being displayed linearly. Due to the experienced personnel involved and the industry acceptance of the reliability of the RMR76 and Q systems, the variability of rock quality ratings between different mines and between different rock mechanic engineers can be assumed to be minimal and negligible. The stability was rated as “Stable” where the mine opening showed no signs of deterioration, as “Potentially Unstable” where mine openings showed some signs of deterioration where rock bolt plates were bent, where there was excessive loose confined by the mesh or where there was evidence of extensive cracking in the walls and back or shotcrete lining of the walls and back, or as “Unstable” where there had been a fall of ground. The installed report was recorded as length and pattern of bolts used for primary and secondary support. The use of mesh and/or mats was also recorded. For Category D where extensive ground support systems were used, a detailed description was recorded. Data was collected in the fall of 2003 with a visit to the Rodeo, Midas, Deep Post, Getchell and Turquoise Ridge mines in Northern Nevada. The Stillwater mine data was provided by Rad Langston of the Stillwater Mining Company and the remaining data was provided by Rimas Pakalnis with permission from the respective mines. The data collection trip to Northern Nevada was to gather data pertaining to weak rock masses and to raise awareness of the research being conducted on weak rock masses and how it may apply to the respective operations. Discussed at each mine were the mining method employed, the stope dimensions/critical span, the ground support installed and the ground conditions. RMR76 calculations were also taken underground. Examples can be seen in Figure 32.  47  Location: 220 Topcut Stope Span: 18ft ROCK MASS RATING 1) Strength R1-R2 2) RQD 25% 3) Spacing in + 4) Condition soft 5) Water dry Flat Joints or Bursting Rating Design  2-4 3-8 5-10 6-12 10 26-44% 35-40%  Location: Top of Spiral 2 – development Span: 15ft ROCK MASS RATING 1) Strength R1 2 2) RQD 25% 3-8 3) Spacing inches 5 4) Condition open 0-6 5) Water dry 10 Flat Joints or Bursting Rating 20-26% Design 20-25%  Location: Spiral 4 5400 North – back Span: 8ft ROCK MASS RATING 1) Strength R1-R2 2 2) RQD 25% 3 3) Spacing inches 5 4) Condition gouge 0-6 5) Water dry 10 Flat Joints or Bursting Rating 20-26% Design 20% Location: Ore Span: 10ft ROCK MASS RATING 1) Strength 2) RQD 3) Spacing 4) Condition 5) Water Flat Joints or Bursting  R1-R2 <25% inches slight/slick dry  2 3 5 6 10  Rating Design  26% 25%  Figure 32: Weak Rock RMR76  48  5.2 Database Construction Cases where instability was a result of stress, structure or poor mining practices (i.e. undercutting of ribs resulting in a larger and not fully supported span) were removed, 463 data points remained. Data from each of these mines consists of rock mass classification in either RMR76 or Q’. For data collected as Q’, it was converted into RMR76 using the formula discussed in Section 2.1.7. For the purposes of this study, the RMR76 values were limited to values of 60 and below. This was done to concentrate the design on weak rock masses. The span of the openings was recorded along with the stability of the openings that was rated according to the descriptions in Section 4.1.2. The type of support used (including the use of mesh and/or mats) was also recorded. The Factor of Safety for a ½ span dead weight failure was calculated for each case (Appendix A: Entire Database). It was found that due to the range of the types of support used, that all the data could not be compared. For example, an opening supported with a pattern of Friction Sets, could not be compared to an opening supported with Cablebolts, the support capacities of each type of support is too different. The data was separated into four (4) support categories that could be compared; Category A: Pattern Friction Sets, Category B: Pattern Friction Sets with Spot Bolting of Rebar, Category C: Pattern Friction Sets with Pattern Rebar Bolts and Category D: Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill under Cemented Rock Fill.  5.3 Factor of Safety The Factor of Safety was calculated for the ½ span failure capacity of each data point. The Factor of Safety was calculated by dividing the support capacity of the system, against the weight of a wedge that is ½ of the span as described in Section 2.2.3.2. A specific gravity of 3.0 was used for each data point as it was not collected in the field. The yield and bond capacities of the system were determined from industry accepted values shown in Table 11. Both the yielding strength of the system and the bond strength (length beyond the wedge) of the system were calculated and the lesser of the two was used. A Factor of Safety above 1.0 indicates that the support system is sufficient to hold up the mass of a potential wedge failure. A Factor of Safety of 1.2 for short term  49  development is the rule of thumb used in the mining industry. A Factor of Safety less than 1.2 is considered “Unsupported.” Table 11: Support Properties (Brady et al. 2005 and Dehn 2007)  Rock Bolt Properties Bolt Type  Yield Strength  (tonnes) 5/8 inch mechanical 6.1 Split Set (SS-33) 8.5 Split Set (SS-39) 12.7 Standard Swellex N/A Yielding Swellex N/A Super Swellex N/A 20mm rebar (#6) 12.4 22mm rebar (#7) 16 25mm rebar (#8) 20.5 #6 Dywidag 11.9 #7 Dywidag 16.3 #8 Dywidag 21.5 #9 Dywidag 27.2 #10 Dywidag 34.6 1/2 inch Cable Bolt 15.9 5/8 inch Cable Bolt 21.6 1/4" X 4" Strap (MS) 25 #6 refers to 6/8", #7 refers to 7/8" diameter etc  Breaking Strength (tonnes) 10.2 (Grade 690MPa) 10.6 14 11 9.5 22 18.5 23 30.8 18 24.5 32.3 40.9 52 18.8 25.5 39  SCREEN - BAG STRENGTH 4ft X 4ft PATTERN 4x4" Welded wire mesh (4 gauge) Bag Strength = 3.6 tonne 4x4" Welded wire mesh (6 gauge) Bag Strength = 3.3 tonne 4x4" Welded wire mesh (9 gauge) Bag Strength = 1.9 tonne 4x2" Welded wire mesh (12 gauge) Bag Strength = 1.4 tonne 2" chainlink (11 gauge bare metal) Bag Strength = 2.9 tonne 2" chainlink (11 gauge galvanized) Bag Strength = 1.7 tonne 2" chainlink (9 gauge bare metal) Bag Strength = 3.7 tonne 2" chainlink (9 gauge galvanized) Bag Strength = 3.2 tonne 4 gauge=.023" diam., 6gauge=0.20", 9 gauge=0.16" diam. 11 gauge=0.125", 12 gauge=0.11" diam. 2 shotcrete shear strength=2MPa=200tonnes/m  BOND STRENGTH Bolt Type  Bond Strength  39mm Split Set Weak Ground Standard Swellex Weak Ground Cable Bolt Weak Ground #6 Rebar Weak Ground #6 Rebar Hard Ground  (tonnes/m) 0.75-3.6 8.1-13.8 24 13.6 (Dehn 2007) 59  50  5.4 Database Statistics From twelve (12) different mines across Canada and the United States, 463 data points were collected (Figure 33). The Stillwater mine contributed 77.5% (359 cases) of the data. This database has been divided up into four (4) support sub-categories as described in section 4.1.4. Statistics for theses categories are discussed separately.  400 350  22  # of Cases  300  86  250  Unstable  200  Potentially Unstable  150  Stable  252  100 2 0 2  Turquoise Ridge  2 4 7  Stillwater  6 15 17  Rodeo  0 2 3  Red Lake  1 0 5  Myra Falls  0 1 0  Midas  0 2 0  Jerritt Canyon  1 7 16  Getchell  1 0 2  Eskay Creek  0 2 1  Deep Post  Cameco  0  0 1 3  Carlin East  50  Mine  Figure 33: Database Stable/Potentially Unstable/Unstable Distribution  5.4.1 Category A (pattern friction sets) Statistics This category is comprised of spans that follow the description provided in section 4.1.4.1. Category A consists of 47 points from seven (7) mines distributed as shown in Figure 34. Most, 40%, of the data comes from the Stillwater mine. The Red Lake mine contributed 19% of the data, Midas contributed 13% and Eskay Creek contributed 11%. The remaining 17% of the data came from the Carlin East mine, the Turquoise Ridge mine and the Rodeo mine.  51  Cameco, 0% Carlin East, 6.4% Deep Post, 0% Eskay Creek, 10.6% Getchell, 0% Jerritt Canyon, 0% Midas, 12.8% Myra Falls, 0% Red Lake, 19.1% Rodeo, 4.3% Stillwater, 40.4% Turquoise Ridge, 6.4%  Figure 34: Category A Data Source Distribution  Stable cases comprise of 66% of the entire database with 31 cases that come from all seven (7) mines in this database. Potentially Unstable cases comprise of 21% of the database with 10 cases that come from three (3) of the seven (7) mines. Unstable cases comprise of 13% of the database with six (6) cases that come from five (5) of the seven (7) mines. Even though there are only 47 points in this database, there is a very good distribution over the different stability cases and very good representation of different mining situations with the distribution over seven (7) mines (Figure 35).  This  distribution increases the credibility of the results in this category.  52  20 18 16 # of Cases  14 12  Unstable  10  Potentially Unstable Stable  8 6 4 2 Turquoise Ridge  Stillwater  Rodeo  Red Lake  Myra Falls  Midas  Jerritt Canyon  Getchell  Eskay Creek  Deep Post  Carlin East  Cameco  0  Mine  Figure 35: Category A Stable/Potentially Unstable/Unstable Distribution  The RMR76 data range for the Category A data is from 20 to 60 (Figure 36). The Stable cases range from 26 to 60, the Potentially Unstable cases range from 40 to 59 and the Unstable cases range from 20 to 48. There is a good distribution of data with 23% of the data of an RMR76 of 40 or less and 51% of the data of an RMR76 of 50 or less. The Unstable cases have 67% with RMR76 values of 30 or less. The Stable cases have 65% with RMR76 values over 50.  53  18 16  Frequency  14 12 Unstable Potentially Unstable  10 8  Stable  6 4 2 96-100  91-95  86-90  81-85  76-80  71-75  66-70  61-65  56-60  51-55  46-50  41-45  36-40  31-35  26-30  21-25  16-20  11-15  6-10  1-5  0  RMR76  Figure 36: Category A RMR76 Distribution  The span data range for the Category A data is from 1.8m to 12.2m (Figure 37). The Stable cases range from 1.8m to 9m, the Potentially Unstable cases range from 2.7m to 12.1m and the Unstable cases range from 3m to 12.2m. The higher frequency of the span is between 2m and 4m at 64% of the data. The high range of the data, 11m to 12.2m, is either Potentially Unstable or Unstable.  54  20 18 16 Frequency  14 12  Unstable  10  Potentially Unstable Stable  8 6 4 2 12.1-13  11.1-12  10.1-11  9.1-10  8.1-9  7.1-8  6.1-7  5.1-6  4.1-5  3.1-4  2.1-3  1.1-2  0  Span (m)  Figure 37: Category A Span Distribution  Based on the Category A database, a series of statistical parameters was calculated. These values are shown in Table 12. It is shown that there is a good range over the RMR76 values and the span values represented in this database. The majority of cases have a ½ span failure Factor of Safety of less than 1.0. The Stable points have an average Factor of Safety of 0.59 with the lowest value at 0.0 and the highest value at 3.3, the Potentially Unstable points have an average Factor of Safety of 0.73 with the lowest value at 0.18 and the highest value at 2.7 while the Unstable points have an average Factor of Safety of 0.34 with the lowest value at 0.0, where the span failed prior to the installation of support, and the highest value at 0.82. Table 12: Category A Summary of Statistics Stable RMR Span (m) FS # of cases 31 Minimum 26 1.8 0 Maximum 60 9 3 Range 34 7.2 3 Mean 49.94 3.87 0.59 Variance 80.90 3.09 0.33 Std. Dev. 8.99 1.76 0.58 Covariance 2.07 2.07 N/A Std. Error 1.77 9.06 N/A Median 54.4 3.20 0.51  Potentially Unstable RMR Span (m) FS 10 40 2.7 0.18 59 12.1 2.7 19 9.4 2.52 48.09 5.75 0.73 40.42 12.60 0.52 6.36 3.55 0.72 1.21 0.32 N/A 3.18 2.31 N/A 48.2 4.58 0.55  Unstable RMR Span (m) 6 20 3 48 12.2 28 9.2 32.20 5.49 105.49 11.88 10.27 3.45 3.98 3.98 3.82 11.38 30.0 4.45  FS 0 0.82 0.82 0.34 0.08 0.28 N/A N/A 0.33  55  5.4.2 Category B (pattern friction sets with spot bolting of rebar bolts) Statistics This category is comprised of spans according to the description provided in section 4.1.4.2. Category B consists of 176 points from seven (7) mines distributed as shown in Figure 38. Almost all, 90%, of the data comes from the Stillwater mine. The Red Lake mine contributed 4.5% of the data, Myra Falls contributed 2.3%, Deep Post contributed 1.1% and Cameco, Eskay Creek and Rodeo contributed 0.6% each.  Cameco, 0.6% Carlin East, 0% Deep Post, 1.1% Eskay Creek, 0.6% Getchell, 0% Jerritt Canyon, 0% Midas, 0% Myra Falls, 2.3% Red Lake, 4.5% Rodeo, 0.6% Stillwater, 90.3% Turquoise Ridge, 0%  Figure 38: Category B Data Source Distribution  Stable cases comprise of 75% of the entire database with 132 cases that come from six (6) of the seven (7) mines in this database. Potentially Unstable cases comprise of 21.5% of the database with 38 cases that come from four (4) of the seven (7) mines. Unstable cases comprise of 3.5% of the database with six (6) cases that come from three (3) of the seven (7) mines. An overwhelming majority of the data, 90%, is from one mine. There are also very few Unstable cases. This data set is heavy on the Stable cases and is predominately from one mine (Figure 39). As such, mines using this database should be  56  cautious due to this.  It would be advisable for a mine to add data from its own  experiences to verify the applicability of this database. 180 160  # of Cases  140 120 Unstable  100  Potentially Unstable  80  Stable  60 40 20 Turquoise Ridge  Stillwater  Rodeo  Red Lake  Myra Falls  Midas  Jerritt Canyon  Getchell  Eskay Creek  Deep Post  Carlin East  Cameco  0  Mine  Figure 39: Category B Stable/Potentially Unstable/Unstable Distribution  The RMR76 data range for the Category B data is from 30 to 60 (Figure 40). The Stable cases range from 30 to 60, the Potentially Unstable cases range from 36 to 60 and the Unstable cases range from 40 to 48. Seven percent (7%) of the data is of an RMR76 of 40 or less and 48% of the data is of an RMR76 of 50 or less. All of the Unstable cases have RMR76 values of 50 or less. The Stable cases have 45% with RMR76 values over 50.  57  80 70  Frequency  60 50  Unstable  40  Potentially Unstable Stable  30 20 10  86-90 91-95 96-100  61-65 66-70 71-75 76-80 81-85  36-40 41-45 46-50 51-55 56-60  11-15 16-20 21-25 26-30 31-35  1-5 6-10  0  RMR76 Figure 40: Category B RMR76 Distribution  The span data range for the Category B data is from 1.5m to 10m (Figure 41). The Stable cases range from 1.5m to 10m, the Potentially Unstable cases range from 1.8m to 10m and the Unstable cases range from 1.5m to 9.1m. The highest frequency of the span is between 2m and 3m at 47% of the data.  58  90 80 70 Frequency  60 Unstable  50  Potentially Unstable  40  Stable  30 20 10 12.1-13  11.1-12  10.1-11  9.1-10  8.1-9  7.1-8  6.1-7  5.1-6  4.1-5  3.1-4  2.1-3  1.1-2  0  Span (m)  Figure 41: Category B Span Distribution  Based on the Category B database, a series of statistical parameters was calculated. These values are shown in Table 13. It is shown that there isn’t a good representation of RMR76 values less than 40 in the database. However, the span distribution is well represented in this database. The majority of cases have a ½ span failure Factor of Safety greater than 1.0. The cases that have a ½ span failure Factor of Safety of 1.0 or less are those that were bolted with only resin rebar. The reason for this is that the resin rebar was the only bolt type used in the support system for these spans and was installed in an approximately 1m2 pattern. The spans in this study that have more than one type of bolt installed, have each type installed on an approximately 1m2 pattern, thus installing more bolts to a given area than spans employing only one type of bolt. The Stable points have an average Factor of Safety greater than 10 with the lowest value at 0.54, the Potentially Unstable points have an average Factor of Safety greater than 6 with the lowest value at 0.54, and the Unstable points have an average Factor of Safety greater than 6 with the lowest value at 1.0 and the highest value at 16.3.  59  Table 13: Category B Summary of Statistics Stable RMR Span (m) FS # of cases 132 Minimum 30 1.5 0.54 Maximum 60 10 22 Range 30 8.5 21.46 Mean 50.83 3.68 10.02 Variance 34.88 3.65 29.58 Std. Dev. 5.91 1.91 5.44 Covariance 4.54 4.54 N/A Std. Error 1.75 5.42 N/A Median 54.4 3.05 10.15  Potentially Unstable RMR Span (m) FS 38 36 1.8 0.54 60 10 22 24 8.2 21.46 46.32 3.64 3.64 58.83 3.02 3.02 7.67 1.74 1.74 5.63 5.63 N/A 1.59 7.01 N/A 42.0 3.35 3.35  RMR 40 48 8 45.72 9.84 3.14 5.44 2.62 46.5  Unstable Span (m) 6 1.5 9.1 7.6 5.44 9.81 3.13 5.44 2.62 5.81  FS 1.0 16.3 15.3 6.76 46.70 6.83 N/A N/A 3.62  5.4.3 Category C (pattern friction sets with pattern rebar bolts) Statistics This category is comprised of spans according to the description provided in section 4.1.4.3. Category C consists of 152 points from two (2) mines distributed as shown in Figure 42.  Again, most (87%) of the data comes from the Stillwater mine. The Red  Lake mine contributed 13% of the data.  Cameco, 0% Carlin East, 0% Deep Post, 0% Eskay Creek, 0% Getchell, 0% Jerritt Canyon, 0% Midas, 0% Myra Falls, 0% Red Lake, 13.2% Rodeo, 0% Stillwater, 86.8% Turquois e Ridge, 0%  Figure 42: Category C Data Source Distribution  60  Stable cases comprise of 57% of the entire database with 87 cases that come from both mines in this database. Potentially Unstable cases comprise of 31% of the database with 10 cases that come from both mines. Unstable cases comprise of 12% of the database with 18 cases that come from both mines. With 152 cases in the database, there is a very good distribution over the different stability cases. However, there are only two (2) mines included in this database questioning the applicability over a wide range of mining situations (Figure 43). As such, mines using this database should be cautious due to this. It would be advisable for a mine to add data from its own experiences to verify the applicability of this database.  140  # of Cases  120 100 Unstable  80  Potentially Unstable  60  Stable  40 20 Turquoise Ridge  Stillwater  Rodeo  Red Lake  Myra Falls  Midas  Jerritt Canyon  Getchell  Eskay Creek  Deep Post  Carlin East  Cameco  0  Mine  Figure 43: Category C Stable/Potentially Unstable/Unstable Distribution  The RMR76 data range for the Category C data is from 36 to 60 (Figure 44). The Stable cases range from 42 to 60, the Potentially Unstable cases range from 36 to 60 and the Unstable cases range from 36 to 54. 7% of the data is of an RMR76 of 40 or less and 62% of the data is of an RMR76 of 50 or less. The Unstable cases have 4% with RMR76 values of 45 or less. The Stable cases have 26% with RMR76 values over 50.  61  70 60  Frequency  50 Unstable  40  Potentially Unstable 30  Stable  20 10  91-95  96-100  81-85 86-90  76-80  66-70 71-75  61-65  51-55 56-60  41-45 46-50  36-40  26-30 31-35  21-25  11-15 16-20  6-10  1-5  0  RMR76  Figure 44: Category C RMR76 Distribution  The span data range for the Category C data is from 1.8m to 11m (Figure 45). The Stable cases range from 1.8m to 7.6m, the Potentially Unstable cases range from 3m to 11m and the Unstable cases range from 1.8m to 10.7m. The higher frequency of the span is between 2m and 5m at 59% of the data. The high range of the data, 8m to 11m, is either Potentially Unstable or Unstable.  62  40 35  Frequency  30 25  Unstable Potentiallly Unstable  20  Stable  15 10 5  12.1-13  11.1-12  10.1-11  9.1-10  8.1-9  7.1-8  6.1-7  5.1-6  4.1-5  3.1-4  2.1-3  1.1-2  0  Span (m) Figure 45: Category C Span Distribution  Based on the Category C database, a series of statistical parameters was calculated. These values are shown in Table 14. It is shown that there is a very narrow range over the RMR76 values and that the span values are well represented in this database. Every case has a ½ span failure Factor of Safety greater than 1.0. The Stable points have an average Factor of Safety greater than 10 with the lowest value at 2.3, the Potentially Unstable points have an average Factor of Safety greater than 6 with the lowest value at 1.1 while the Unstable points have and average Factor of Safety greater than 7 with the lowest value at 1.1 and the highest value at 29.2.  63  Table 14: Category C Summary of Statistics Stable  RMR # of cases Minimum Maximum Range Mean Variance Std. Dev. Covariance Std. Error Median  42 60 18 50.17 23.01 4.80 3.75 1.07 48.2  Span (m) 87 1.8 7.6 5.8 4.06 1.75 1.32 3.75 3.86 3.66  Potentially Unstable  FS  RMR  2.3 29.2 26.9 10.75 30.95 5.56 N/A N/A 10.09  36 60 24 48.30 48.57 6.97 7.95 1.43 48.2  Span (m) 47 3 11 8 5.83 3.35 1.83 7.95 5.43 5.79  Unstable  FS  RMR  1.1 14.5 13.4 6.70 13.53 3.68 N/A N/A 5.86  36 54 18 46.05 43.25 6.58 13.79 1.32 48.2  Span (m) 18 1.8 10.7 8.9 6.63 6.56 2.56 13.79 3.38 7.32  FS 1.1 29.2 28.1 7.32 63.67 7.98 N/A N/A 4.05  5.4.4 Category D (cablebolts, CRF, shotcrete, spiling and timber) Statistics This category is comprised of spans according to the description provided in section 4.1.4.4. Category D consists of 88 points from 10 mines distributed as shown in Figure 46.  Most, 57%, of the data comes from the Stillwater mine. The Eskay Creek mine  contributed 21% of the data, Rodeo contributed 11%, Cameco contributed 3.4% and Getchell contributed 2.3%.  Deep Post, Jerritt Canyon, Myra Falls, Red Lake and  Turquoise Ridge contributed 1.1% each.  Cameco, 3.4% Carlin East, 0% Deep Post, 1.1% Eskay Creek, 20.5% Getchell, 2.3% Jerritt Canyon, 1.1% Midas, 0% Myra Falls, 1.1% Red Lake, 1.1% Rodeo, 11.4% Stillwater, 56.8% Turquoise Ridge, 1.1%  Figure 46: Category D Data Source Distribution  64  Stable cases comprise of 66% of the entire database with 58 cases that come from nine (9) of the 10 mines in this database. Potentially Unstable cases comprise of 28% of the database with 25 cases that come from two (2) of the 10 mines. Unstable cases comprise of 6% of the database with five (5) cases come from two (2) of the 10 mines. With 88 cases, there is also a very good representation of different mining situations with the distribution over 10 mines. However, the distribution of the different stability cases is isolated to two (2) mines in each of the Potentially Unstable and Unstable cases. The database is also weak in the number of Unstable cases (Figure 47).  Mines using this  database should be cautious due to this. It would be advisable for a mine to add data from its own experiences to verify the applicability of this database.  60  40 Unstable Potentially Unstable  30  Stable 20 10  Turquoise Ridge  Stillwater  Rodeo  Red Lake  Myra Falls  Midas  Jerritt Canyon  Getchell  Eskay Creek  Deep Post  Carlin East  0 Cameco  # of Cases  50  Mine  Figure 47: Category D Stable/Potentially Unstable/Unstable Distribution  65  The RMR76 data range for the Category D data is from 15 to 55 (Figure 48). The Stable cases range from 15 to 55, the Potentially Unstable cases range from 36 to 55 and the Unstable cases range from 36 to 54. 30% of the data is of an RMR76 of 40 or less and 74% of the data is of an RMR76 of 50 or less. The Potentially Unstable and Unstable cases are all within the RMR76 values of 36 to 55.  25  Frequency  20 15  Unstable Potentially Unstable Stable  10 5  1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60 61-65 66-70 71-75 76-80 81-85 86-90 91-95 96-  0  RMR76 Figure 48: Category D RMR76 Distribution  The span data range for the Category D data is from 2.1m to 13.1m (Figure 49). The Stable cases range from 2.1m to 13.1m, the Potentially Unstable cases range from 2.1m to 12m and the Unstable cases range from 4.6m to 10m. The higher frequency of the span is between 2m and 5m at 61% of the data.  66  25  Frequency  20 15  Unstable Potentially Unstable Stable  10 5  13.1-14  12.1-13  11.1-12  10.1-11  9.1-10  8.1-9  7.1-8  6.1-7  5.1-6  4.1-5  3.1-4  2.1-3  1.1-2  0  Span (m)  Figure 49: Category D Span Distribution  Based on the Category D database, a series of statistical parameters was calculated. These values are shown in Table 15. It is shown that there is a good range over the RMR76 values however the distribution of the different stability cases is concentrated at the higher RMR76 values. The span values are well represented in this database with a good distribution of the different stability cases over the span range. The ½ span failure Factor of Safety is difficult to compare in this database due to the wide variety of support systems employed. The majority of cases have a ½ span failure Factor of Safety greater than 1.0 with only a small number of data points with values below 1.0. The Stable points have an average Factor of Safety greater than 9 with the lowest value at 1, the Potentially Unstable points have an average Factor of Safety greater than 6 with the lowest value at 0.8 while the Unstable points have and average Factor of Safety of 2.2 with the lowest value at 0.75 and the highest value at 2.2.  67  Table 15: Category D Summary of Statistics Stable RMR Span (m) FS # of cases 58 Minimum 15 2.1 1 Maximum 55 13.1 CRF Range 40 11 N/A Mean 42.85 4.76 9.55 Variance 94.38 4.74 22.80 Std. Dev. 9.71 2.18 4.77 Covariance 4.66 4.66 N/A Std. Error 2.14 9.55 N/A Median 45.00 4.57 8.55  Potentially Unstable RMR Span (m) FS 25 36 2.1 0.83 55 12 7.7 19 9.9 6.87 46.98 6.02 11.45 42.38 8.51 48.27 6.51 2.92 6.95 11.85 11.85 N/A 2.27 5.05 N/A 48.21 6.10 9.16  RMR 36 54 18 47.12 60.22 7.76 48.18 2.82 46.08  Unstable Span (m) 5 4.6 10 5.4 6.27 6.10 2.47 2.13 8.87 4.57  FS 0.75 2.2 1.45 9.55 22.80 4.77 N/A N/A 8.55  68  6  Weak Rock Span Design  The span curve database has been augmented with a total of 463 points in the RMR76 range of 15-60. The weak rock data has been collected from twelve (12) mines across Canada and the US. This weak rock database has been divided into four support type categories as described in Section 4.1.4. These categories were created to be able to compare similar support types/capacities. For each category, several neural network analyses (Section 3.3) were performed. The Neuroshell Predictor program from Ward Systems was used (Ward 2003). For the spanRMR76 relationship for each category, the networks were trained on approximately 60% of the data and verified with the remaining 40%. Genetic analyses were preformed to obtain interpolation results. Stable points were given values of 1, Potentially Unstable points were given values of 2 and Unstable points were given values of 3. The categories that achieved an acceptable correlation and error, the networks were used to make stability predictions on a grid that covered an RMR76 range from 20 to 60 and a span range from 1.5m to 13m.  From this data, the transitions from 1 to 2 mapped the  Stable/Potentially Unstable transition line and the transitions from 2 to 3 mapped the Potentially Unstable/Unstable transition line.  To determine the suitability of the  calculated ½ span failure Factor of Safety in the prediction of stability, neural network analyses (genetic analysis) were performed on the entire database for each category to determine the “importance of inputs.” Relationships between span, RMR76 and FS, span and FS and RMR76 and FS were performed. “Unsupported” refers to spans with a calculated Factor of Safety less than 1.2. The rock mass design is valid for these spans, however, care must be taken to ensure that potential structural failure planes are not present. “Supported” refers to spans with a calculated Factor of Safety that is greater than 1.2 and are supported in terms of structurally controlled failures that encompass ½ span.  69  6.1 Category A (pattern friction sets) The Category A database includes 47 points from seven (7) mines across North America. RMR76 values range from 20 to 60 with spans from 1.8m to 12.2m.  To ensure  interpolation of data, only genetic analyses were preformed for training, verification and predictions. A neural network analysis was performed on thirty (30) cases and verified with seventeen (17) cases. The neural network training analysis obtained a correlation of 0.90, R-squared of 0.80 and average error of 0.18 with the verification obtaining a correlation of 0.95, R-squared of 0.90 and average error of 0.06. The entire database obtained a correlation of 0.91, R-squared of 0.83 and average error of 0.14. A perfect correlation relationship is 1.0 and an acceptable correlation is above 0.80, Category A yields very good results. With this trained network, a grid of RMR76 values of 25 to 60 and span values of 2m to 12m was trained to predict stability values (Appendix B: Grid Prediction Data).  The transitions between values of 1 (Stable) and 2 (Potentially  Unstable) were plotted to determine the transition curve of Stable to Potentially Unstable. The transitions between values of 2 (Potentially Unstable) and 3 (Unstable) were plotted to determine the transition curve of Potentially Unstable to Unstable. Caution had to be used when determining these transitions as it seemed that the predictor reverted to a value of 1 when it was making predictions outside of the value ranges of the database. Due to the factors of safety of this database being on average less than 1.0, it is fair to say that it can be compared to the original “Unsupported” database of Lang (1994). Figure 50 shows the updated weak rock curves overlaid with the 2002 updated curve.  70  50  2002 Stable-PU Unstable 2002 PU-Unstable Weak Rock Stable-PU Line Weak Rock Stable-PU Projection Weak Rock PU-Unstable Line Weak Rock PU-Unstable Projection Stable Potentially Unstable Unstable  40  Span (m)  30  20  10  0 0  20  40  RMR76  60  80  100  Figure 50: Category A (Pattern Friction Sets) Updated Weak Rock Curves – “Unsupported” FS<1.2  The resultant weak rock Stable/Potentially Unstable and Potentially Unstable/Unstable curves duplicate what is seen in the field. It is known that Stable excavations are possible at lower RMR76 values with smaller spans (Ouchi et al. 2004). However, once a certain span is exceeded, the span typically fails. This is shown with the weak rock transition curves.  As the RMR76 values decrease, the transition between Stable, Potentially  Unstable and Unstable really becomes a drastic transition, at an RMR76 of 25, between Stable and Unstable with a very small to non-existent Potentially Unstable zone where spans typically have warning signs prior to failure. On the graph, the maximum stable span at an RMR76 of 25 is 3m. This database only has 47 cases. Typically a database this small would not be sufficient. However, these cases are well distributed (section 5.4.1) over seven (7) mines and can be said to represent what is seen in weak rock 71  environments in the North American mining industry. That being said, due to the small database, it is recommended that mines use caution around this lower end of the weak rock database and augment this database with site specific data (Ouchi et al. 2008).  6.1.1 Comparison with Barton’s Relationship between Q and De The comparison between Barton’s graph (Section 3.3.1.3) and the weak rock mass curves (Figure 50) is shown in Figure 51.  The recommended ESR values for temporary  openings such as those in mining applications of 3 and 5 are used. In this comparison it is shown that the weak rock mass update (Category A) of the span design curve is approaching Barton’s relationship. 50 2002 PU-Unstable Existing PU-Unstable 2002 Stable-PU Existing Stable-PU Weak Rock Stable-PU New Stable-PU LineLine Weak Rock Stable-PU Projection New Stable-PU Projection Weak Rock PU-Unstable New PU-Unstable LineLine Weak Rock PU-Unstable Projection New PU-Unstable Projection ESR =3 ESR=3 ESR =5 ESR=5  40  Span (m)  30  20  10  0 0  20  40  RMR76  60  80  100  Figure 51: Comparison of Span Design Curves and Barton's Relationship between Q and De  72  6.2 Category B (pattern friction sets with spot bolting of rebar bolts) The Category B database includes 176 points from seven (7) mines across North America. RMR76 values range from 30 to 60 with spans from 1.5m to 9.1m. To ensure interpolation of data, only genetic analyses were preformed for training, verification and predictions. A neural network analysis was performed on 150 cases and verified with 26 cases. The neural network training analysis obtained a correlation of 0.89, R-squared of 0.80 and average error of 0.12 with the verification obtaining a correlation of 0.92, Rsquared of 0.84 and average error of 0.12. The entire database obtained a correlation of 0.90, R-squared of 0.80 and average error of 0.12. A perfect correlation relationship is 1.0 and an acceptable correlation is above 0.80, Category B yields very good results. With this trained network, a grid of RMR76 values of 25 to 60 and span values of 2m to 12m was trained to predict stability values (Appendix B: Grid Prediction Data). The transitions between values of 1 (Stable) and 2 (Potentially Unstable) were plotted to determine the transition curve of Stable to Potentially Unstable. The transitions between values of 2 (Potentially Unstable) and 3 (Unstable) were plotted to determine the transition curve of Potentially Unstable to Unstable. Caution had to be used when determining these transitions as it seemed that the predictor reverted to a value of 1 when it was making predictions outside of the value ranges of the database. Even though this category is significantly more supported and cannot be properly compared to the original database of Lang (1994), Figure 52 shows the updated weak rock curves overlain with the 2002 updated curve.  73  50 2002 Stable-PU Line 2002 PU-Unstable Line Weak Rock Stable-PU Line Weak Rock Stable-PU Projection Weak Rock PU-Unstable Line Stable Potentially Unstable Unstable  40  Span (m)  30  20  10  0 0  20  40  RMR 76  60  80  100  Figure 52: Category B (pattern friction sets with spot bolting of rebar bolts) Updated Weak Rock Curves – “Supported” FS>1.2  The results from this category are similar to those from Category C and will be discussed in concurrence with those from Category C.  6.3 Category C (pattern friction sets with pattern rebar bolts) The Category C database includes 152 points from 2 mines across North America. RMR76 values range from 26 to 60 with spans from 1.8m to 10.7m.  To ensure  interpolation of data, only genetic analyses were preformed for training, verification and predictions. A neural network analysis was performed on 115 cases and verified with 37 cases. The neural network training analysis obtained a correlation of 0.92, R-squared of 0.85 and average error of 0.15 with the verification obtaining a correlation of 0.90, R-  74  squared of 0.80 and average error of 0.14. The entire database obtained a correlation of 0.92, R-squared of 0.84 and average error of 0.15. A perfect correlation relationship is 1.0 and an acceptable correlation is above 0.80; thus, Category C yields very good results. With this trained network, a grid of RMR76 values of 25 to 60 and span values of 2m to 12m was trained to predict stability values (Appendix B: Grid Prediction Data). The transitions between values of 1 (Stable) and 2 (Potentially Unstable) were plotted to determine the transition curve of Stable to Potentially Unstable. The transitions between values of 2 (Potentially Unstable) and 3 (Unstable) were plotted to determine the transition curve of Potentially Unstable to Unstable Caution had to be used when determining these transitions as the predictor seemed to revert to a value of 1 for predictions outside of the database value range.  Even though this category is  significantly more supported and therefore cannot be properly compared to the original database of Lang (1994), Figure 53 shows the updated weak rock curves overlaid with the updated curve.  75  50  2002 Stable-PU Line 2002 PU-Unstable Line Weak Rock Stable-PU Line Weak Rock Stable-PU Projection Weak Rock PU-Unstable Line Weak Rock PU-Unstable Projection Stable Potentially Unstable Unstable  40  Span (m)  30  20  10  0 0  20  40  RMR 76  60  80  100  Figure 53: Category C (pattern friction sets with pattern rebar bolts) Updated Weak Rock Curves “Supported” FS>1.2  The resultant weak rock Stable/Potentially Unstable and Potentially Unstable/Unstable curves for Categories B and C are a little surprising (Figure 54 and Figure 55). The Stable/Potentially Unstable curve does move up indicating that stable excavations are possible down to RMR76 values of 35. However, it has not moved up as much as the same curve for Category A (Figure 54). Also, one would suppose that the Potentially Unstable/Unstable curve would fit closer to or to the left of the existing curve due to the increased yield and bond strengths of rebar as compared to friction sets (Figure 55). The RMR76 range of the databases for Categories B and C have a lower range of about 35 (Figure 52 and Figure 53) as compared to 20 for Category A (Figure 50). This could  76  contribute to the unexpected results at the RMR76 range less than 40.  The trends  exhibited in Categories B and C indicate that data in the RMR76 20-25 range for both graphs would be Unstable (Ouchi et al. 2008).  50  Existing Stable-PU 2002 Stable-PU Line Line 2002 PU-Unstable Line Line Existing PU-Unstable Category Line CategoryAAStable-PU Stable-PU Line Category Projection CategoryAAStable-PU Stable-PU Projection Category Line CategoryBBStable-PU Stable-PU Projection Category B Stable-PU Projection Category B Stable-PU Projection Category Line CategoryCCStable-PU Stable-PU Line Category Projection CategoryCCStable-PU Stable-PU Projection  40  Span (m)  30  20  10  0 0  20  40  RMR 76  60  80  100  Figure 54: Comparison of Categories A, B and C Weak Rock Stable-PU Lines  77  50  Existing Stable-PU 2002 Stable-PU Line Line Existing PU-Unstable 2002 PU-Unstable Line Line Category PU-Unstable Category AA PU-Unstable LineLine Category Category AA PU-Unstable PU-Unstable Projection Projection Category BB PU-Unstable LineLine Category PU-Unstable Category BB PU-Unstable Projection Category PU-Unstable Projection Category C PU-Unstable Line Category C PU-Unstable Line Category CC PU-Unstable Projection Category PU-Unstable Projection Projection  40  Span (m)  30  20  10  0 0  20  40  RMR 76  60  80  100  Figure 55: Comparison of Categories A, B and C Weak Rock PU-Unstable Lines  It has been observed that resin grouted rebar is difficult to install in weak rock (Ouchi et al. 2008). Full resin coverage of the bolt is difficult to achieve due to the jointed nature of the rock mass. This incomplete coverage, leaving the toe of the bolt ungrouted, would result in a decrease in effective length of the rebar bolts. This could be a reason why there are so many spans in the previous Potentially Unstable zone that have failed. The use of resin grouted rebar in weak rock environments could give an operator a false sense of security if the bolts are not installed properly. Therefore it would be imprudent to rely on the results of Categories B and C. Installation and quality control issues pertaining to resin grouted rebar is discussed further in Section 8.  78  6.4 Category D (cablebolts, CRF, shotcrete, spiling and timber) The Category D database includes 88 points from 10 mines across North America. RMR76 values range from 15 to 55 with spans from 2.1m to 13.1m.  To ensure  interpolation of data, only genetic analyses were preformed for training, verification and predictions. A neural network analysis was performed on 57 cases. The neural network training analysis obtained a correlation of 0.55, R-squared of 0.29 and average error of 0.43. This category did not achieve acceptable statistical results with the neural network analysis. This is most likely due to the varied engineered support systems which act differently on the rock mass resulting in distinct support mechanisms with different factors of safety. The data is displayed in Figure 56 to show that spans in the Unstable zone of the original “Unsupported” database of Lang (1994) may be supported with detailed engineering support design.  79  50 2002 Stable-PU Line 2002 PU-Unstable Line Stable - Cables Potentially Unstable - Cables Unstable - Cables CRF-Shotcrete-Spiling-Timber  40  Span (m)  30  20  10  0 20  40  RMR76  60  80  100  Figure 56: Category D (cablebolts, CRF, shotcrete, spiling and timber) Points on Span Design Curve (no weak rock interpretation) - “Supported” FS>1.2  6.5 Factor of Safety A neural network analysis was performed for each category to determine the suitability of the calculated ½ span failure Factor of Safety in the prediction of stability. Each entire database was used and the “importance of inputs” outcome was chosen. The variables span, RMR76 and FS (Factor of Safety) were compared. The outcomes and comparison for each category are discussed in this section.  6.5.1 Category A (pattern friction sets) In the relationship between the span, RMR76 and the FS, the span and the RMR76 were the most relevant with 51% and 49% relevancy respectively (Appendix C: Neural 80  Network Results). The FS was found to be completely irrelevant (0%) compared to the span and the RMR76 in the prediction of stability. The relationship of the three variables together obtained a correlation of 0.54 and R-squared of 0.28 indicating that the relationship is not as well suited to predict stability as the relationship between the span and RMR76. To confirm these results, analyses were preformed relating span and FS and RMR76 and FS separately. In the relationship between the span and FS, the span was 100% more relevant than the FS and in the relationship between RMR76 and FS, the FS obtained 68% relevancy as compared to 32% for the RMR76. However, even though the importance of the FS is greater than that of the RMR76, the relationship between the RMR76 and the FS is still not a good relationship in the prediction of stability as the correlation is below acceptable values at 0.5 with an R-squared of 0.12.  6.5.2 Category B (pattern friction sets with spot bolting of rebar bolts) In the relationship between the span, RMR76 and the FS, the span and the RMR76 were the most relevant with 52% and 47.8% relevancy respectively (Appendix C: Neural Network Results). The FS was found to be virtually irrelevant (0.2%) compared to the span and the RMR76 in the prediction of stability. The relationship of the three variables together obtained a correlation of 0.62 and R-squared of 0.34 indicating that the relationship is not as well suited to predict stability as the relationship between the span and RMR76. To confirm these results, analyses were preformed relating span and FS and RMR76 and FS separately. In the relationship between the span and FS, the span was 100% more relevant than the FS and in the relationship between RMR76 and FS, the RMR76 obtained 81% relevancy as compared to 19% for the FS.  6.5.3 Category C (pattern friction sets with pattern rebar bolts) In the relationship between the span, RMR76 and the FS, the span and the RMR76 were the most relevant with 54% and 46% relevancy respectively (Appendix C: Neural Network Results). The FS was found to be completely irrelevant (0%) compared to the span and the RMR76 in the prediction of stability. The relationship of the three variables together obtained a correlation of 0.87 and R-squared of 0.75. Even though the correlation for the relationship between the three variables is above acceptable values, the relationship between the span and RMR76 alone has a correlation of 0.92 (section 6.3) and 81  is more suitable to comparison. To confirm these results, analyses were performed relating span and FS and RMR76 and FS separately. In the relationship between the span and FS, the span was 97% relevant as compared to 3% for the FS. In the relationship between RMR76 and FS, the RMR76 obtained 57.5% relevancy as compared to 42.5% for the FS. However, even though the importance of the FS is comparable to that of the RMR76, the relationship between the RMR76 and the FS is still not a good relationship in the prediction of stability as the correlation is below acceptable values at 0.65 with an Rsquared of 0.39.  6.5.4 Category D (cablebolts, CRF, shotcrete, spiling and timber) In the relationship between the span, RMR76 and the FS, the RMR76 and the FS were the most relevant with 77.5% and 22.5% relevancy respectively (Appendix C: Neural Network Results). The span was found to be completely irrelevant (0%) compared to the RMR76 and the FS in the prediction of stability. The relationship of the three variables together obtained a correlation of 0.18 and R-squared of -0.03 indicating that the relationship is not well suited to predict stability. To confirm these results, analyses were preformed relating span and FS and RMR76 and FS separately.  In the relationship  between the span and FS, the span was completely irrelevant (0%) compared to the FS and in the relationship between RMR76 and FS, the RMR76 obtained 77% relevancy as compared to 23% for the FS. However, even though the importance span is irrelevant in the relationship between the span and the FS, it is still not a good relationship in the prediction of stability as the correlation is well below acceptable values at -0.10 with an R-squared of -0.32.  6.5.5 General Comments on FS As seen from the best fit lines (no regression) from each category (Figure 57), the calculated FS increases as the support Categories B and C incorporate support mechanisms with greater yield and bond strengths. Category D, however, does not follow this observation.  82  30 Category A Category B Category C Category D  FS  20  10  0 0  4  8 Span (m)  12  16  Figure 57: FS Comparison of Categories  From the observations of Figure 57, Categories B and C would be approximately 20 times more supported than Category A for small spans.  This increase in support  decreases with span length until the span becomes greater than 10m, after which point all 4 categories support a similar amount. Category D is approximately eight times more supported than Category A for small spans. Categories A, B and C are blanket patterns of different support systems that are applied to all spans within the respective databases. Small spans within these databases would most likely not require the type of support installed, but the mine “minimum standard” would still be applied. In Category D, most all cases were carefully designed to minimize the use of costly support mechanisms while still achieving a desired Factor of Safety. This  83  explains why Category D has a lower calculated Factor of Safety than Categories B and C for a given span. Categories B and C have very large FS values for small spans and the FS values approach those of Category A as the span increases to over 10m.  From the installation  observations made in Section 6.3, it would be difficult and imprudent to rely on the results of the calculated FS for Categories B and C. The actual/in situ bond strength of resin grouted rebar may not be as assumed for the FS calculation. The FS results for these categories, as well as the results of the weak rock span design curve (Sections 6.2 and 6.3), could give the operator a false sense of security if the bolts are not installed properly. Category A remains fairly constant at an FS of just less than 1 and reflects similar “Unsupported” conditions of the original span database (Lang, 1994).  With the  calculated FS being on average less than 1.0, the operator must take care in identifying potential wedge structures that will require additional support beyond what pattern friction sets provide. From the observations above, one cannot entirely rely on the results of Categories B and C and cannot say that these categories would be approximately 20 times more supported than Category A for small spans. Categories A and D can still be compared and it is still possible to say that Category D is approximately eight times more supported than Category A for small spans. For large spans greater than 10m, all four categories support a similar amount.  84  7  Application of the Weak Rock Span Curve  Based upon the results of the weak rock span design and the support mechanisms available, the “Unsupported” Weak Rock Updated Span Design Curve (Category A: pattern friction sets) (Figure 58) was employed as a design tool at Barrick’s Goldstrike mine during 2008 (Figure 59) and was used in the design of 17 headings (Table 16). In addition to these spans, seven existing spans that exhibited signs of instability (Table 16), requiring rehabilitation, were also added to the database shown in Figure 59. 50  40  Span (m)  30  20  10  0 0  20  40  RMR 76  60  80  100  Figure 58: "Unsupported" Weak Rock Updated Span Design Curve (pattern friction sets, FS < 1.2)  85  50  Goldstrike - Stable Goldstrike - Potentially Unstable 40  Span (m)  30  20  10  0 0  20  40  RMR 76  60  80  100  Figure 59: Goldstrike use of the Weak Rock Updated Span Design Curve  86  Table 16: Goldstrike Category A weak rock mass span design database RMR  stability  meters  FS  Primary Type of Support  42 49 51 53 57 57 52 45 56 45 59 73 64 65 46 62 45 29 38 30 37 33 31 44  Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable Stable PU PU PU PU PU PU PU  5.2 5.2 5.2 6.1 5.2 7.6 4.6 6.1 5.2 4.6 9.1 7.6 7.6 7.6 6.1 5.8 5.2 5.8 6.1 6.1 5.2 5.2 4.6 4.6  0.8 0.8 0.8 0.7 0.8 0.3 0.2 0.7 0.8 0.2 0.8 0.3 0.3 0.3 0.7 0.9 0.8 0.9 0.7 0.7 0.8 0.8 0.2 0.2  Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets Split Sets  Secondary Type of Support Swellex Swellex Swellex Swellex Swellex Swellex Swellex Swellex Super Swellex Swellex Swellex Swellex Swellex Swellex Swellex Swellex Swellex Swellex Swellex Swellex  Length of Spacing of Length of Spacing of Primay Secondary Secondary Primary Support Support Support Support 6 6 6 6 6 6 6 6 6 6 8 6 6 6 6 6 6 6 6 6 6 6 6 6  1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2  8 8 8 8 8 8  1.8 1.8 1.8 1.8 1.8 1.8  8 8  1.8 1.8  12 8 8 8 8 8 8 8 8 8 8 8  1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8  The Goldstrike mine uses various standard patterns depending on the span and the quality of the ground encountered. Of the designed spans, 14 spans between 5m and 8m in width had ground support installed consisting of 2.4m long 39mm Split Sets on a 1.2m x 1.2m square pattern with 2.4m long standard Swellex bolts on a 1.8m x 1.8m square pattern. One span was 9m wide requiring longer support and was supported with 2.4m long standard Swellex on a 1.2m x 1.2m square pattern with 4m long Super Swellex bolts on a 1.8m x 1.8m square pattern. This larger span may also use the Category A weak rock span design curve as it still employed friction type bolts. Four spans that were less than 5m in width were supported with 2.4m long 39mm Split Sets on a 1.2m x 1.2m square pattern. Of the Potentially Unstable spans, the five spans between 5m and 8m in width had ground support installed consisting of 2.4m long 39mm Split Sets on a 1.2m x 1.2m square pattern with 2.4m long standard Swellex bolts on a 1.8m x 1.8m square pattern and two spans that were less than 5m in width were supported with 2.4m long 39mm Split Sets on a 1.2m x 1.2m square pattern. These spans were all bolted according to the  87  mined spans. However, the RMR76 of these spans indicated that all but one of the spans would be Potentially Unstable or Unstable. As shown in section 6.4, these Potentially Unstable points can remain stable with additional designed support resulting in a greater Factor of Safety. The use of the Category A (pattern friction set) weak rock span design curve is an easy and useful tool for operators to use in the determination of appropriate span design and ground support application. The calculated FS of these spans are all less than a value of 1.2 and can be considered “Unsupported”. This is consistent with what is shown in section 6.5. None of the spans in this Goldstrike database had any identified structure that would indicate potential for a structural failure.  88  8  Lessons Learned  In Section 6.3 it was noted that resin grouted rebar is difficult to install in weak rock. As mines are moving away from having operators work only a meter or two away from unsupported ground (“face” miners), more mechanized methods of drilling and ground support installation are being implemented. In weak rock ground support installation, it has been observed that resin grouted rebar is difficult to install. Two difficulties have been observed; the first being that the actual diameter of the hole is greater than expected, thus requiring more resin to fully encapsulate the rebar and the second being that the resin cartridges tend to either get caught in open fissures of the rock mass, breaking the tubes part way into the hole or that the resin spins out into the surrounding rock mass thus resulting in incomplete coverage of resin along the length of the bolt. “Face” miners are able to manually insert the resin cartridges that are used. The manual insertion minimizes the risk of tearing the plastic casing of the cartridge upon insertion. The miner is also able to visually gauge the amount of resin that is required for the hole and ensure that the cartridges have reached the toe of the hole. Mechanized installation requires experienced operators who can judge the required amount of resin that is required in the hole and who have the patience to correctly install the rebar. With mechanized installation of resin grouted rebar, there is no way to ensure that the resin has reached the toe of the hole, especially if the cartridges have broken during insertion. One has to assume that if the correct number of cartridges are installed and that there is resin at the collar once the rebar is installed, that there is full encapsulation of the rebar bolt. There is no non-destructive method of testing to ensure full encapsulation of the rebar bolt. Incomplete coverage, leaving the toe of the bolt ungrouted, would result in a decrease in the effective length of the rebar bolts. Therefore, the use of resin grouted rebar in weak rock environments could give an operator a false sense of security if the bolts are not installed properly. On the design side of support installation for weak rock masses, engineers must be aware of the significant decrease in the bond capacity of resin grouted rebar in weak rock (Table 11). It is important that weak rock mass awareness is circulated within the mining community to avoid the use of generally established hard rock values for support  89  calculations. This is currently being undertaken by the author, Dr. Rimas Pakalnis and NIOSH in the presentation of conference papers and the initiation of short courses in areas of weak rock mass mining such as northern Nevada. It has also been observed that the North American mining industry is moving away from the use of resin grouted rebar in weak rock masses and switching to frictions sets. Barrick’s Goldstrike mine no longer uses resin grouted rebar due to the installation difficulties and Barrick’s Turquoise Ridge mine is in the process of changing the ground support from resin grouted rebar with Split Sets to a pattern of only Swellex type bolts. Mines are also switching from Split Set type bolts to Swellex type bolts as has been observed at both of the above mentioned mines.  90  9  Conclusions and Recommendations  The University of British Columbia Geomechanics group and the NIOSH Spokane Research Laboratory have been conducting research in the development of safe and costeffective underground design guidelines in weak rock environments with RMR76 in the range of 20 to 60. An update of the Span Design Curve was conducted for this weak rock mass range. A total of 463 points were added to the database. Ground support is almost always used in weak rock environments to ensure a stable work environment. The type of support used can vary widely. The development of the weak rock augmented Span Design Curve has been separated into four different support categories; Pattern Friction Sets (A), Pattern Friction Sets with Spot Bolting of Rebar (B), Pattern Friction Sets with Pattern Rebar Bolts (C) and Cablebolting, Shotcrete, Spiling, Timber Sets or Underhand Cut and Fill under Cemented Rock Fill (D). Category D includes cablebolts and other engineering designed support systems such as cemented rock fill (underhand cut and fill mining), significant application of shotcrete (typically 76mm), spiling or timber sets. Neural network analyses were conducted on the span-RMR76 relationship for these four support categories. Approximately 60% of each database was used to train the network and the remaining 40% was used to verify the network. Categories A, B and C obtained acceptable correlation. Category D, however, did not. This is most likely due to the varied engineered support systems which act differently on the rock mass resulting in distinct support mechanisms with different factors of safety. Category A incorporates 47 additional weak rock (RMR76 20-60) cases from 7 different mines across North America. Category A yields good results and follows what is seen in the field. These results also fit well with Barton’s relationship between Q and De. At and RMR76 value of 25, the maximum stable span is 3m. However, at an RMR76 of 25, there is a drastic transition between the Stable/Potentially Unstable zones and the Potentially Unstable/Unstable zones. There is a very small to non-existent Potentially Unstable zone. Caution should be used when at these low RMR76 values due to this lack of Potentially Unstable zone. Openings can very quickly go from being Stable to Unstable. Even though the database represents the North American mining industry well with 7  91  mines participating in the database, caution should be used as the dataset is small with 47 points. Categories B and C yielded similar results with the Stable/Potentially Unstable line moving up on the graph (increased span values).  However the Potentially  Unstable/Unstable line moved towards the right on the graph (increased RMR76 values). This is unexpected, but may be explained by the difficulty experienced in the installation of resin grouted rebar. Due to this uncertainty in the accuracy of the data of Categories B and C, it would be imprudent to rely on the data interpretation in span design for these categories. Category D, the “heroic” category did not obtain positive results from the neural networks analysis, but still demonstrates that spans can be stable at lower RMR76 values with detailed engineering support design. The calculated ½ span failure Factor of Safety was found not to be significantly relevant in any category when applied to the prediction of stability in the relationship between the span and the RMR76. In comparing the calculated Factor of Safety of all four categories, it was found that small spans in Category D were approximately eight times more supported (FS is eight times greater) than the corresponding small spans in Category A. As the span increased, the difference in the support capacities of the two categories diminished. At a span greater than 10m the difference in the support capacities became negligible. Due to the uncertainties identified previously, it would be imprudent to relate Categories B and C. Category A is deemed “Unsupported” with the Factor of Safety being less than 1.2. The rock mass design is valid for these spans, however, care must be taken to ensure that potential structural failure planes are not present. Category D is deemed “Supported” with the Factor of Safety being greater than 1.2 and is supported in terms of structurally controlled failures that encompass ½ span. It has been observed that resin grouted rebar is difficult to install in weak rock. Full resin coverage of the bolt is difficult to achieve due to the jointed nature of the rock mass. This incomplete coverage, leaving the toe of the bolt ungrouted, would result in a decrease in effective length of the rebar bolts. This could be a reason why there are so many spans in the previous Potentially Unstable zone that have failed. The use of resin grouted rebar in weak rock environments could give an operator a false sense of security  92  if the bolts are not installed properly. It has also been observed that the North American mining industry is moving away from the use of resin grouted rebar in weak rock masses and switching to frictions sets. The author’s contribution to the weak rock mass knowledge base of the mining community is in the understanding of span stability in the RMR76 range below 60 and the awareness of the potential detrimental effects of using resin grounted rebar in weak rock masses and the false sense of security that the use of resin grouted rebar may instill. Confirmation of the author’s general observations of spans in this range remaining stable in contradiction to the previously updated span design curve are shown empirically with the “Unsupported” Weak Rock Updated Span Design Curve. It is also shown that spans in the “Unstable” zone of the new “Unsupported” Weak Rock Updated Span Design Curve can possibly be stabilized if detailed engineering design is applied to obtain “Supported” status (FS>1.2).  The “Unsupported” Weak Rock Updated Span Design  Curve was applied to span design at Barrick’s Goldstrike mine during 2008 and was successful. Efforts to increase industry awareness of the hazards of working in and the available best practices for weak rock mass environments is currently being undertaken by the author, Dr. Rimas Pakalnis and NIOSH in the presentation of conference papers and the initiation of short courses in areas of weak rock mass mining such as northern Nevada. As with any empirical design, it is important to understand the data behind the design. These designs are for rock mass only. They do not incorporate design based upon structure and/or stress states.  Small scale structure and/or changes in stress states may  lead to a change in the RMR76 of a given area. A new RMR76 calculation may be done to reflect the change(s) and allow these empirical studies to remain valid. The empirical design graphs presented in this paper are intended to aid the experienced operator in making safe and economical design decisions. Further work would be to increase the Category A database, to determine the “actual” bond strength and applicability of resin rebar in weak rock and to determine the ideal deduction due to flat joints to the RMR76 rating.  A suggestion to determine the  applicability of resin rebar in weak rock would be to overcore an installed rebar to determine the resin coverage of the rebar and the mixing consistency of the resin.  93  References Barton, N., Lien, R and Lunde, J. (1974). Engineering classification of rock masses for the design of tunnel support. Rock Mechanics, Vol. 6, 189-236. Beer, G. and Meek, J.L. (1982). Design Curves for Roofs and Hangingwalls Based on Voussoir Beam and Plate Solutions.  Transactions of the Institute of Mining and  Metallurgy, Vol. 91, London. Bieniawski, Z.T. (1976). Rock Mass Classifications in Rock Engineering. Proceedings: Symposium on Exploration for Rock Engineering, Johannesburg, S. Africa, 97-106. Bieniawski, Z.T. (1989). 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Unwedge. http://www.rocscience.com Terzaghi, K. (1946). Rock Defects and Loads on Tunnel Support. Rock Tunneling with Steel Supports, eds. R.V. Proctor and T. White. Commercial Shearing Co., Youngstown, Ohio. Unal, E. (1983). Design Guidelines and Roof Control Standards for Coal Mine Roofs. Ph.D. Thesis, Pennsylvania State University. Wang, J., Milne, D. and Pakalnis, R. (2002). Application of a Neural Network in the Empirical Design of Underground Excavation Spans. Transactions of the Institution of Mining and Metallurgy, London, Vol. 111, A73-A81.  96  Ward Systems Group (Frederick, MD). (2003).  Neuroshell Predictor Version 2.01.  http:www.wardsystem.com. Wickham, G. E., Tiedemann, H. R. and Skinner, E. H. (1971). Support Determinations Based on Geological Predictions. RETC Proceedings, Vol. 1, 43-64.  97  Appendices Appendix A: Entire Database  98  CAPACITIES USED support capacity Swellex std Split set (39) rebar #7 cables mechanical  bond (tonne/m) 10.89 1.35 13.62 24 0  Assumed Rock SG 3  t/m  yield (tonne) 11 8.5 16.3 15.9 6.1  3  FACTOR OF SAFETY SAMPLE CALCULATION Span = 3.6m, Pattern 1.8m length 39mm Split Sets on 0.9m x 0.9m pattern, Stable Calculation of weight of ½ span wedge Base x height x ½ x advance x specific gravity = 3.6m x 1.8m x ½ x 0.9m x 3t/m3 = 8.748 tonnes Calculation of number of bolts across the back Span / spacing = 3.6m / 0.9m = 4 Calculation of Yield Strength of System Number of bolts x 8.5tonnes = 34 tonnes Length of bolts past the ½ span wedge = {bolt length–[spacing–(spacing x ½)] + bolt length–[spacing+(spacing x ½)]}x2 = {1.8m – [0.9m - (0.9m x ½)] + 1.8m – [0.9m + (0.9m x ½)]} x 2 = 3.6m Calculation of Bond Strength of System = length of bolts past the ½ span wedge x bond capacity = 3.6m x 1.35 tonnes/m = 4.86 tonnes Factor of Safety calculation = weaker of the bond and yield strengths / weight of the ½ span wedge = 4.86 tonnes / 8.748 tonnes = 0.5556  99  50  50  55  60  3.6  6.0  2.7  2.7  S  S  S  S  S  S  S  S  S  S  S  PU  PU  S  PU  S  S  S  S  S  U  PU  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  7  7  32  9  11  5  6  6  5  8  6  5  5  9  8  9  6  8  8  8  6  8  6  1.2  1.2  1.2  0.9  1.2  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  1.2  1.2  1.2  0.9  1.2  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  1.8  1.8  1.8  1.8  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.3  1.5  2.8  2.8  3.2  4.9  3.4  3.0  2.4  2.4  3.0  3.9  2.4  3.0  3.0  3.3  3.9  3.1  2.4  3.9  3.9  3.9  2.4  3.9  1.8  4.3  17.0  17.0  42.5  34.0  25.5  25.5  25.5  25.5  25.5  34.0  25.5  25.5  25.5  34.0  34.0  34.0  25.5  34.0  34.0  34.0  25.5  34.0  25.5  34.0  2.8  2.8  3.2  4.9  3.4  3.0  2.4  2.4  3.0  3.9  2.4  3.0  3.0  3.3  3.9  3.1  2.4  3.9  3.9  3.9  2.4  3.9  1.8  4.3  0.4  0.4  0.1  0.6  0.3  0.6  0.4  0.4  0.6  0.5  0.4  0.6  0.6  0.4  0.5  0.3  0.4  0.5  0.5  0.5  0.4  0.5  0.3  0.6  6ft SS, straps  6ft SS, straps  6ft SS, straps  6ft SS on 3ft pattern, 9gauge weld mesh, straps  6ft SS, straps  1+  1  1  1+  1+  1  1+  1+  1  1  1  1+  1  1  1  1  1 2-  1+  1+  Support  Eskay Creek Eskay Creek Eskay Creek Eskay Creek  55  54  54  54  54  36  48  42  3.5  2.7  Stillwater  54  2.7  Stillwater  54  48  2.7  3.6  Stillwater  Stillwater Eskay Creek  3.4  Stillwater  54  3.0  3.7  Stillwater  54  54  3.0  3.0  Stillwater  Stillwater  3.4  Stillwater  59  Stillwater  3.4  Stillwater  54  48  2.7  3.4  Stillwater  RMR  Stillwater  3.0  Stillwater  Stability  59  Support Category  3.0  3.4  Stillwater  1/2 span dead weight (t) 7  Depth of support pattern (m)  A  primary  A  spacing of primary  S  length of primary  S  bond  58  yield  54  support capacity (t)  3.4  3.0  FS  Stillwater  3.2  Mine  Stillwater  n  n  n  y  n  y  n  n  n  y  n  y  y  y  y  y  y  y  y  y  y  y  y  y  Mesh  Stillwater  Span (m)  Stillwater  y  y  y  y  y  n  n  n  n  n  y  Mats  length of secondary  spacing of secondary  secondary  100  1.8  3.0  4.3  5.8  3.7  Rodeo  TR  TR  TR  Red Lake  6.1  6.1  6.1  3.0  6.1  9.1  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Stillwater  12.2  3.0  Rodeo  Red Lake  3.0  Midas  11.9  7.6  Midas  12.2  4.6  Midas  Red Lake  2.1  Midas  Red Lake  2.1  56  33  8  33  33  25  134  100  95  12  23  12  6  0  0  6  52  19  3  3  0.9  1.2  1.2  1.2  1.2  0.9  1.2  0.9  0.9  1.2  0.9  0.9  0.9  0.9  1.2  1.2  0.9  0.9  0.9  0.9  split sets  mechanical  mechanical  mechanical  mechanical  swellex  mechanical  swellex  swellex  swellex  split sets  split sets  split sets  split sets  swellex  split sets  split sets  split sets  split sets  split sets  split sets  0.9  1.2  1.2  1.2  1.2  0.9  1.2  0.9  0.9  1.2  0.9  0.9  0.9  0.9  1.2  1.2  0.9  0.9  0.9  0.9  0.9  1.5  1.8  1.8  1.8  1.8  2.4  2.4  2.4  2.4  2.4  1.8  1.8  1.8  1.8  2.4  2.4  1.2  1.2  1.8  2.4  2.4  rebar  secondary  B  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  A  33  24  0.9  1.8  spacing of secondary  S  S  S  PU  S  S  PU  U  PU  PU  U  U  S  S  U  S  S  U  S  S  A  A  55  2.4  2.4  length of secondary  59  60  45  41  52  54  57  40  51  50  20  30  30  30  30  45  55  25  26  45  S  PU  A  0.9  80.6  0.0  0.0  0.0  0.0  75.3  0.0  81.9  62.5  44.8  3.8  5.4  3.6  0.0  0.0  3.6  43.6  5.3  1.6  1.6  5.4  9.7  8.5  8.1  182.8  24.4  18.3  24.4  24.4  77.0  24.4  154.0  143.0  33.0  51.0  42.5  25.5  0.0  0.0  25.5  66.0  34.0  17.0  17.0  68.0  59.5  85.0  51.0  80.6  24.4  18.3  24.4  24.4  75.3  24.4  81.9  62.5  33.0  3.8  5.4  3.6  0.0  0.0  3.6  43.6  5.3  1.6  1.6  5.4  9.7  8.5  8.1  1.4  0.7  2.2  0.7  0.7  3.0  0.2  0.8  0.7  2.7  0.2  0.4  0.6  0.0  0.0  0.6  0.8  0.3  0.5  0.5  0.2  0.4  0.2  0.4  1+  Mechanical Bolts  Mechanical with WWM  mechanical with chainlink  Mechanical with WWM  Swellex  Mechanical with WWM  8' Swellex WWM  8' swellex with chain link  8' Swellex  6ft SS39 on 3ft pattern with mesh  6ft SS39 on 3ft pattern with mesh  6ft SS39 on 3ft pattern with mesh  unsupported (prior to placement of support)  Caved prior to placement of support  6ft SS39 on 3ft pattern with mesh  8ft SS46 on 4ft pattern  8ft SS46 on 4ft pattern  4ft SS39 on 3ft pattern with mesh  4ft SS39 on 3ft pattern with mesh  6ft SS39 on 3ft pattern with mesh  Standard Support  Standard Support  Standard Support  y  y  y  y  y  y  y  y  y  y  y  n  n  y  y  y  Mesh  40  Midas  Mine  40  Span (m)  7.0  RMR  6.0  Stability  Midas  Support Category  S  1/2 span dead weight (t)  45  Depth of support pattern (m)  9.0  primary split sets  spacing of primary  0.9  length of primary  20  bond  A  yield  PU  support capacity (t)  45  FS  5.5  Support  Carlin East Carlin East Carlin East  Mats  101  6.1  3.0  3.7  2.4  2.4  6.1  4.0  4.6  2.4  1.5  1.8  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  2.4  Stillwater  Stillwater  2.7  Stillwater  2.4  1.5  Stillwater  Stillwater  3.7  Stillwater  7.6  1.8  Stillwater  2.4  2.4  Stillwater  Stillwater  3.7  Stillwater  RMR  Stillwater  3.7  Stillwater  52  52  48  52  59  59  52  54  48  48  52  58  59  54  54  59  38  42  46  59  40  59  42  52  Stability  S  S  S  S  S  S  S  PU  PU  S  S  PU  S  S  S  S  PU  S  U  S  PU  PU  PU  PU  S  Support Category  59  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  1/2 span dead weight (t)  3.7  6.1  Stillwater  2  2  4  14  11  25  4  4  9  6  25  4  39  4  9  9  4  5  2  9  2  4  9  9  25  Depth of support pattern (m) 0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  primary  4  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  42  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  B  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  B  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  spacing of secondary  U  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  length of secondary  PU  67.8  25.5  60.2  56.7  68.5  66.6  60.2  60.2  115.2  50.7  66.6  60.2  72.5  60.2  115.2  75.1  60.2  55.5  25.5  75.1  67.8  60.2  75.1  115.2  66.6  60.2  65.7  bond  46  49.6  33.3  58.1  91.4  82.9  124.7  58.1  58.1  115.5  58.1  124.7  58.1  149.5  58.1  115.5  82.9  58.1  58.1  33.3  82.9  49.6  58.1  82.9  115.5  124.7  58.1  158.0  yield  48  49.6  25.5  58.1  56.7  68.5  66.6  58.1  58.1  115.2  50.7  66.6  58.1  72.5  58.1  115.2  75.1  58.1  55.5  25.5  75.1  49.6  58.1  75.1  115.2  66.6  58.1  65.7  support capacity (t)  3.7  2.4  22.0  16.3  14.5  4.0  6.5  2.7  14.5  14.5  12.8  8.1  2.7  14.5  1.9  14.5  12.8  8.3  14.5  10.9  16.3  8.3  22.0  14.5  8.3  12.8  2.7  14.5  1.5  FS  Stillwater  7.9  Mine  Stillwater  2  2  2-  2- 1  1  1  2-  2  2  2  1  2-  1  2-  2-  1+  2+  2+  2+  1+  2+  2-  1+  2  1+  2+  1+  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  n  y  y  y  y  y  y  y  y  y  y  y  Mesh  Stillwater  Span (m)  Stillwater  y  Mats  Support  102  Span (m)  2.1  3.7  2.4  3.7  4.6  7.9  1.5  3.4  9.1  3.0  2.4  9.1  2.7  2.7  2.7  3.0  2.7  2.7  2.4  6.1  1.5  2.4  2.0  2.4  1.8  3.4  2.4  Mine  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  RMR  46  48  59  40  48  54  36  48  48  48  42  54  42  52  54  54  39  54  56  48  36  59  54  Stability  48  S  S  S  S  U  S  S  S  S  S  S  PU  S  PU  S  S  S  PU  S  S  S  S  S  PU  Support Category  S  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  1/2 span dead weight (t)  52  4  8  2  4  3  4  2  25  4  5  5  6  5  5  5  56  4  6  56  8  2  42  14  9  4  Depth of support pattern (m) 0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  primary split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  0.9  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  0.9  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  3  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  0.9  1.8  0.9  1.8  spacing of secondary  9  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  length of secondary  B  60.2  47.4  67.8  60.2  65.5  60.2  25.5  66.6  60.2  55.5  55.5  50.7  55.5  55.5  55.5  80.6  60.2  50.7  80.6  47.4  25.5  65.7  122.7  115.2  60.2  115.2  63.2  bond  B  58.1  66.6  49.6  58.1  49.6  58.1  33.3  124.7  58.1  58.1  58.1  58.1  58.1  58.1  58.1  182.8  58.1  58.1  182.8  66.6  33.3  158.0  140.3  115.5  58.1  115.5  49.6  yield  S  58.1  47.4  49.6  58.1  49.6  58.1  25.5  66.6  58.1  55.5  55.5  50.7  55.5  55.5  55.5  80.6  58.1  50.7  80.6  47.4  25.5  65.7  122.7  115.2  58.1  115.2  49.6  support capacity (t)  PU  14.5  6.2  22.0  14.5  18.7  14.5  16.3  2.7  14.5  10.9  10.9  8.1  10.9  10.9  10.9  1.4  14.5  8.1  1.4  6.2  16.3  1.5  8.7  12.8  14.5  12.8  16.1  FS  42  2  2  2  2  2+  2  2  2  1  2  2  2  2-  2  2  2+  1  2+  2  1  2  2+  1  2-  2-  2-  2  y  y  y  y  n  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  Mesh  54  n  y  Mats  Support  103  3.0  3.0  2.7  2.4  2.7  2.7  3.0  3.0  2.7  3.7  2.7  4.0  3.7  1.8  3.7  3.7  6.1  2.3  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  2.4  Stillwater  3.7  3.0  Stillwater  RMR  Stillwater  2.4  Stillwater  48  54  42  52  52  42  48  48  42  48  54  59  48  54  42  54  48  54  54  48  42  52  54  58  Stability  S  S  PU  PU  S  PU  PU  S  S  S  S  PU  S  S  S  S  S  S  S  S  PU  S  S  S  S  Support Category  56  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  1/2 span dead weight (t)  2.7  2.4  Stillwater  4  25  9  9  2  9  11  5  9  5  6  6  5  5  4  5  6  6  9  2  5  4  6  4  4  Depth of support pattern (m) 0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  primary  2  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  B  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  B  1.8  1.8  1.8  0.9  1.8  0.9  1.8  1.8  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  spacing of secondary  S  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  length of secondary  S  62.2  66.6  75.1  115.2  67.8  115.2  68.5  55.5  115.2  55.5  50.7  50.7  55.5  55.5  60.2  55.5  50.7  50.7  115.2  67.8  55.5  60.2  50.7  60.2  60.2  67.8  55.5  bond  51  58.1  124.7  82.9  115.5  49.6  115.5  82.9  58.1  115.5  58.1  58.1  58.1  58.1  58.1  58.1  58.1  58.1  58.1  115.5  49.6  58.1  58.1  58.1  58.1  58.1  49.6  58.1  yield  54  58.1  66.6  75.1  115.2  49.6  115.2  68.5  55.5  115.2  55.5  50.7  50.7  55.5  55.5  58.1  55.5  50.7  50.7  115.2  49.6  55.5  58.1  50.7  58.1  58.1  49.6  55.5  support capacity (t)  1.8  1.8  16.0  2.7  8.3  12.8  22.0  12.8  6.5  10.9  12.8  10.9  8.1  8.1  10.9  10.9  14.5  10.9  8.1  8.1  12.8  22.0  10.9  14.5  8.1  14.5  14.5  22.0  10.9  FS  Stillwater  2.7  Mine  Stillwater  2  1-  1+  2  2  2-  1+  2  2-  2  2+  2+  2  2-  2  2  2  2  2  2+  2  2  2  2  2  2  2  y  n  y  n  y  y  y  y  y  y  y  y  y  y  n  y  y  y  y  n  y  y  y  y  y  y  n  Mesh  Stillwater  Span (m)  Stillwater  y  y  n  n  n  Mats  Support  104  Span (m)  2.7  3.7  3.0  3.7  2.6  7.3  1.5  2.4  2.0  2.0  2.9  2.1  6.1  4.0  9.1  6.1  6.1  6.1  3.7  7.6  3.7  3.7  3.7  2.7  3.7  2.4  3.0  Mine  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  RMR  42  54  36  48  54  54  57  54  57  54  54  42  54  54  48  36  54  36  36  42  48  48  42  Stability  48  PU  S  PU  S  S  S  S  S  S  S  S  S  S  S  S  PU  S  PU  PU  S  S  U  S  S  Support Category B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  1/2 span dead weight (t)  PU  6  4  9  5  9  9  9  39  9  25  25  25  56  11  25  3  6  3  3  4  2  36  5  9  6  Depth of support pattern (m)  42  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  primary split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  0.9  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  0.9  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  9  1.8  1.8  1.8  1.8  0.9  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  spacing of secondary  5  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  length of secondary  B  50.7  60.2  75.1  55.5  115.2  115.2  75.1  72.5  75.1  66.6  66.6  66.6  80.6  68.5  66.6  63.2  53.1  65.5  65.5  60.2  25.5  81.5  57.9  75.1  50.7  75.1  56.4  bond  B  58.1  58.1  82.9  58.1  115.5  115.5  82.9  149.5  82.9  124.7  124.7  124.7  182.8  82.9  124.7  49.6  58.1  49.6  49.6  58.1  33.3  149.5  58.1  82.9  58.1  82.9  58.1  yield  S  50.7  58.1  75.1  55.5  115.2  115.2  75.1  72.5  75.1  66.6  66.6  66.6  80.6  68.5  66.6  49.6  53.1  49.6  49.6  58.1  25.5  81.5  57.9  75.1  50.7  75.1  56.4  support capacity (t)  S  8.1  14.5  8.3  10.9  12.8  12.8  8.3  1.9  8.3  2.7  2.7  2.7  1.4  6.5  2.7  16.1  9.4  18.7  18.7  14.5  16.3  2.3  12.8  8.3  8.1  8.3  11.6  FS  54  2+  2  1  2  2  2  1  1+  1-2  1  1  1  1  1+  1  2+  2-  2+  2+  2  2  1  2  1  2  1+  2-  y  y  y  y  y  y  n  y  y  y  y  y  n  n  n  y  y  y  y  y  n  n  y  y  n  y  y  Mesh  48  y  y  y  y  y  y  y  y  n  y  y  n  Mats  Support  105  2.4  3.0  3.0  3.0  3.0  3.0  2.4  2.1  2.1  3.0  3.0  2.4  3.7  6.1  4.0  3.7  3.7  3.7  2.1  6.1  2.4  3.0  3.0  3.7  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Mine  Stillwater  Span (m)  Stillwater  RMR  54  42  54  54  54  42  54  42  42  48  54  54  42  54  54  54  42  42  54  54  54  42  42  42  42  Stability  2.4  S  S  S  S  S  S  S  S  PU  S  S  S  S  S  S  S  S  S  S  S  S  S  S  S  S  Support Category  Stillwater  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  1/2 span dead weight (t) 9  6  6  4  25  3  9  9  9  11  25  9  4  6  6  3  3  4  6  6  6  6  6  4  4  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  Depth of support pattern (m)  4  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  primary  39  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  B  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  B  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  S  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  spacing of secondary  S  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  length of secondary  54  115.2  50.7  50.7  60.2  66.6  63.2  75.1  75.1  115.2  68.5  66.6  75.1  60.2  50.7  50.7  63.2  63.2  60.2  50.7  50.7  50.7  50.7  50.7  60.2  60.2  60.2  72.5  bond  48  115.5  58.1  58.1  58.1  124.7  49.6  82.9  82.9  115.5  82.9  124.7  82.9  58.1  58.1  58.1  49.6  49.6  58.1  58.1  58.1  58.1  58.1  58.1  58.1  58.1  58.1  149.5  yield  7.6  115.2  50.7  50.7  58.1  66.6  49.6  75.1  75.1  115.2  68.5  66.6  75.1  58.1  50.7  50.7  49.6  49.6  58.1  50.7  50.7  50.7  50.7  50.7  58.1  58.1  58.1  72.5  support capacity (t)  2.4  12.8  8.1  8.1  14.5  2.7  16.1  8.3  8.3  12.8  6.5  2.7  8.3  14.5  8.1  8.1  16.1  16.1  14.5  8.1  8.1  8.1  8.1  8.1  14.5  14.5  14.5  1.9  FS  Stillwater  1  2  2+  2  2  1  2 3  1+ - 2  1  2  1  1+  1  2  2-  2-  2  2  2+  2  2  2  2  2  2  2  2  y  y  n  n  n  y  y  n  y  y  y  n  n  y  y  y  y  y  n  y  y  y  y  y  y  n  y  Mesh  Stillwater  y  y  y  y  y  y  y  n  Mats  Support  106  42  60  4.9  4.0  6.1  3.0  3.0  3.0  3.0  3.7  2.4  2.4  2.4  2.4  3.7  2.4  3.7  2.4  2.4  3.7  7.6  2.4  5.0  4.3  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater Eskay Creek  Deep Post  Mine  Stillwater  Span (m)  Stillwater  RMR  U  S  S  S  S  S  S  PU  S  S  S  S  S  S  S  S  S  PU  S  S  PU  PU  S  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  B  17  17  4  39  9  4  4  9  4  9  4  4  4  4  9  6  6  6  6  25  11  16  2  1.2  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  0.9  1.2  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.5  1.8  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  2.4  3.6  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  2.4  112.2  102.2  60.2  72.5  75.1  60.2  60.2  75.1  60.2  75.1  60.2  60.2  60.2  60.2  115.2  50.7  50.7  50.7  50.7  66.6  68.5  50.3  25.5  67.8  115.2  82.9  97.8  58.1  149.5  82.9  58.1  58.1  82.9  58.1  82.9  58.1  58.1  58.1  58.1  115.5  58.1  58.1  58.1  58.1  124.7  82.9  91.4  33.3  49.6  115.5  82.9  97.8  58.1  72.5  75.1  58.1  58.1  75.1  58.1  75.1  58.1  58.1  58.1  58.1  115.2  50.7  50.7  50.7  50.7  66.6  68.5  50.3  25.5  49.6  115.2  12.8  5.0  5.8  14.5  1.9  8.3  14.5  14.5  8.3  14.5  8.3  14.5  14.5  14.5  14.5  12.8  8.1  8.1  8.1  8.1  2.7  6.5  3.1  16.3  22.0  2  y  6ft SS39 on 4ft pattern, 12ft #8 rebar on 6ft x 4ft pattern with mesh  n  n  n  n  y  y  n  y  y  n  y  y  n  y  y  y  y  y  y  y  y  y  2  3  y y  2 2.4m #6 rebar on 0.9mx0.9m pattern with 9gauge weld mesh  1  1  2  2  1  2  1  2  2  2  2+  2  2  2  2  2  1 2  1  1  2  2  Support  45  54  54  54  54  42  48  48  42  42  42  48  48  54  54  42  54  54  54  54  42  Stability  1.5  Support Category  Stillwater  1/2 span dead weight (t) 0.9  Depth of support pattern (m)  9  primary  2  spacing of primary  B  length of primary  B  secondary  S  spacing of secondary  S  length of secondary  42  bond  42  yield  3.7  support capacity (t)  1.8  FS  Stillwater  Mesh  Stillwater  n  y  y  y  y  y  y  y  y  y  Mats  107  RMR  Span (m)  Mine  6.1  2.4  6.1  Stillwater  Stillwater  7.9  Stillwater  Stillwater  7.3  Red Lake  4.6  9.1  Red Lake  Stillwater  5.2  Red Lake  3.7  3.0  Red Lake  6.1  4.6  Red Lake  Stillwater  4.5  Red Lake  Stillwater  4.5  5.0  Cameco  2.7  55  9.0  Red Lake  59  10.0  Red Lake  54  10.0  46  58  46  54  40  42  45  59  60  47  57  38  57  59  59  PU  S  S  PU  U  S  PU  PU  U  S  PU  S  S  PU  PU  S  PU  S  PU  C  C  C  C  C  C  C  B  B  B  B  B  B  B  B  B  B  B  B  B  25  4  25  14  25  9  42  48  75  24  8  19  18  7  18  23  73  90  90  90  29  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.8  split sets  split sets  split sets  split sets  split sets  split sets  split sets  rebar  rebar  rebar  swellex  rebar  rebar  rebar  rebar  mechanical  rebar  rebar  rebar  rebar  rebar  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.2  1.2  1.2  2.4  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.2  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  2.1  2.4  2.1  2.4  2.1  2.1  1.8  1.8  2.4  2.3  2.3  2.3  2.3  2.4  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  split sets  rebar  0.9  0.9  0.9  0.9  0.9  0.9  0.9  2.4  1.8  0.9  1.8  3.0  2.4  3.0  3.0  3.0  2.4  3.0  2.1  2.4  2.4  3.6  147.0  76.3  147.0  171.7  147.0  115.2  145.7  45.9  77.8  35.7  57.9  44.0  45.6  28.0  36.6  46.3  76.3  49.0  49.0  49.0  63.0  123.6  173.6  74.4  173.6  140.3  173.6  115.5  223.2  97.8  130.4  65.2  43.6  65.2  65.2  32.6  65.2  73.3  130.4  130.4  130.4  130.4  99.9  74.4  147.0  74.4  147.0  140.3  147.0  115.2  145.7  45.9  77.8  35.7  43.6  44.0  45.6  28.0  36.6  73.3  76.3  49.0  49.0  49.0  63.0  74.4  5.9  18.5  5.9  9.9  5.9  12.8  3.4  1.0  1.0  1.5  5.2  2.3  2.6  4.1  2.0  3.3  1.0  0.5  0.5  0.5  2.2  6.0  2  3  2  2  2  3-  2  7ft rebar and WWM  rebar with chainlink  7ft rebar with WWM  Swellex with 7ft rebar  7ft rebar with chainlink  7ft rebar with chainlink  Rebar and Chainlink  rebar/swellexwith chainlink  2.3m resin rebar 2.4m mechanical on 1.2m pattern with rebar  2.3m resin rebar  2.3m resin rebar  n  y  y  y  y  y  y  y  y  y  y  y  y  y  6ft SS39 on 4ft pattern, 12ft #8 rebar on 6ft x 4ft pattern with mesh 8ft rebar on 6ft x 5ft pattern and 8ft SS39 in 3ft x 3ft pattern 2.3m resin rebar  y  Support  S  B  1.8  Mesh  52  56  Stability  10.0  Support Category  PU  1/2 span dead weight (t)  45  Depth of support pattern (m)  4.6  primary  Rodeo Myra Falls Myra Falls Myra Falls Myra Falls  spacing of primary 1.2  length of primary  split sets  secondary  1.2  spacing of secondary  12  length of secondary  B  bond  S  yield  30  support capacity (t)  3.7  FS  Deep Post  y  y  Mats  108  4.6  7.9  3.7  2.1  3.7  4.6  3.0  5.5  4.0  7.3  6.1  4.6  6.1  4.9  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  7.6  Stillwater  Stillwater  6.1  Stillwater  3.7  6.1  Stillwater  4.3  4.6  Stillwater  Stillwater  4.6  Stillwater  RMR  Stillwater  4.0  Stillwater  54  54  48  36  54  54  56  42  36  42  42  48  52  49  48  48  48  42  56  50  56  54  48  48  Stability  54  S  S  PU  PU  S  S  S  S  PU  S  S  S  PU  S  PU  S  S  PU  S  PU  S  S  PU  PU  S  Support Category  4.9  5.2  Stillwater  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  1/2 span dead weight (t) 16  25  14  25  36  11  20  6  14  18  3  18  42  14  9  12  12  16  39  25  25  14  14  11  18  0.9  Depth of support pattern (m) 0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  rebar  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  primary  9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  2  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  2.4  1.5  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  C  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  C  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of secondary  S  3.0  2.4  2.4  3.6  2.4  3.0  3.0  2.4  3.6  3.6  2.4  3.6  3.0  3.6  2.4  3.0  3.0  3.0  2.4  2.4  3.0  2.4  3.0  2.4  2.4  2.4  2.4  length of secondary  S  158.5  97.9  122.7  203.5  120.8  145.3  174.6  99.1  220.7  181.5  81.4  181.5  145.7  220.7  115.2  136.4  136.4  158.5  107.7  97.9  147.0  122.7  171.7  104.4  98.6  115.2  88.0  bond  46  140.3  173.6  140.3  173.6  214.7  115.5  165.1  90.7  140.3  114.1  65.9  114.1  223.2  140.3  115.5  124.0  124.0  140.3  214.7  173.6  173.6  140.3  140.3  115.5  148.8  115.5  65.9  yield  46  140.3  97.9  122.7  173.6  120.8  115.5  165.1  90.7  140.3  114.1  65.9  114.1  145.7  140.3  115.2  124.0  124.0  140.3  107.7  97.9  147.0  122.7  140.3  104.4  98.6  115.2  65.9  support capacity (t)  4.3  3.7  8.7  3.9  8.7  6.9  3.3  10.9  8.1  14.5  9.9  6.3  21.4  6.3  3.4  9.9  12.8  10.1  10.1  8.7  2.7  3.9  5.9  8.7  9.9  9.9  5.4  12.8  29.2  FS  Stillwater  1.8  Mine  Stillwater  3+ 4  2  2-  2-  2+  2-  2  2  3  23  34  3  3+  2  2+  3  2  2  2  2-  2-  2  2-  2  2+  2-  2+  y  y  y  y  y  n  y  y  y  y  y  n  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  Mesh  Stillwater  Span (m)  Stillwater  n  n  y  Mats  Support  109  2.7  3.7  4.0  3.0  2.7  2.7  3.7  6.1  6.7  2.1  7.6  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  5.5  Stillwater  Stillwater  6.1  Stillwater  5.5  3.4  Stillwater  Stillwater  4.9  Stillwater  4.0  3.7  Stillwater  3.4  4.3  Stillwater  Stillwater  2.4  Stillwater  RMR  Stillwater  9.1  Stillwater  54  42  54  48  48  36  48  48  48  58  42  54  54  42  54  54  54  54  42  48  48  54  49  54  Stability  PU  S  PU  PU  S  U  S  S  S  S  S  S  S  S  PU  S  S  S  S  PU  PU  S  S  U  S  Support Category  48  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  1/2 span dead weight (t)  3.8  3.7  Stillwater  39  3  30  25  9  5  5  6  11  18  5  20  11  8  36  10  20  25  8  16  9  12  4  56  9  Depth of support pattern (m) 0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  primary  25  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  36  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  C  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  C  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of secondary  S  3.0  2.4  3.0  3.0  2.4  2.4  2.4  2.4  2.4  3.6  2.4  2.4  3.0  2.4  3.0  2.4  2.4  3.0  2.4  3.6  2.4  3.0  2.4  2.4  2.4  2.4  2.4  length of secondary  PU  159.2  81.4  160.0  147.0  115.2  108.0  108.0  99.1  104.4  181.5  108.0  122.1  145.3  91.6  176.4  109.8  122.1  147.0  91.6  207.6  115.2  136.4  76.3  119.5  115.2  97.9  120.8  bond  54  214.7  65.9  189.9  173.6  115.5  90.7  90.7  90.7  115.5  114.1  90.7  165.1  115.5  99.2  214.7  115.5  165.1  173.6  99.2  140.3  115.5  124.0  74.4  264.3  115.5  173.6  214.7  yield  54  159.2  65.9  160.0  147.0  115.2  90.7  90.7  90.7  104.4  114.1  90.7  122.1  115.5  91.6  176.4  109.8  122.1  147.0  91.6  140.3  115.2  124.0  74.4  119.5  115.2  97.9  120.8  support capacity (t)  7.3  6.1  4.1  21.4  5.3  5.9  12.8  17.9  17.9  14.5  9.9  6.3  17.9  6.0  10.9  12.1  4.9  11.2  6.0  5.9  12.1  8.7  12.8  10.1  18.5  2.1  12.8  3.9  3.3  FS  Stillwater  7.3  Mine  Stillwater  2  3  2  2  2  2  2+  3  2-  3  3  2-  2  3  2  2-  2-  2  3  2+  2+  2  3  2-  2  2-  1+  y  y  y  y  y  y  y  y  y  n  y  y  y  n  y  y  y  n  y  n  y  y  y  y  n  y  y  Mesh  Stillwater  Span (m)  Stillwater  y  n  n  y  n  y  n  n  n  n  Mats  Support  110  4.0  1.8  3.7  7.3  8.2  3.7  3.7  4.6  6.1  3.7  8.8  2.7  5.8  5.5  5.8  4.3  5.0  7.3  3.7  3.2  7.6  7.6  3.0  3.7  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Mine  Stillwater  Span (m)  Stillwater  RMR  48  48  48  54  54  42  54  48  36  42  54  48  36  36  36  48  54  48  54  54  54  42  54  48  36  Stability  1.8  S  S  U  PU  S  PU  U  PU  PU  U  S  PU  U  PU  PU  PU  S  S  S  PU  PU  PU  S  S  U  Support Category  Stillwater  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  1/2 span dead weight (t) 9  6  39  39  7  9  36  17  12  23  20  23  5  53  18  25  14  9  18  46  36  9  2  11  2  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  Depth of support pattern (m)  18  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  rebar  split sets  split sets  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  rebar  primary  18  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  C  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  2.4  1.5  1.5  1.5  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  2.4  length of primary  C  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  PU  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  spacing of secondary  PU  2.4  2.4  2.4  3.0  2.4  2.4  3.0  2.4  3.0  3.0  2.4  2.4  2.4  3.0  3.6  3.0  3.0  2.4  3.6  3.0  2.4  2.4  2.4  3.0  2.4  3.6  3.6  length of secondary  48  115.2  99.1  107.7  159.2  96.0  115.2  176.4  105.2  136.4  159.4  122.1  108.9  108.0  145.1  181.5  147.0  171.7  115.2  181.5  175.6  120.8  115.2  88.0  145.3  88.0  196.6  181.5  bond  48  115.5  90.7  214.7  214.7  99.2  115.5  214.7  148.8  124.0  165.1  165.1  165.1  90.7  248.0  114.1  173.6  140.3  115.5  114.1  239.5  214.7  115.5  65.9  115.5  65.9  148.8  114.1  yield  3.7  115.2  90.7  107.7  159.2  96.0  115.2  176.4  105.2  124.0  159.4  122.1  108.9  90.7  145.1  114.1  147.0  140.3  115.2  114.1  175.6  120.8  115.2  65.9  115.5  65.9  148.8  114.1  support capacity (t)  5.2  12.8  14.5  2.7  4.1  13.9  12.8  4.9  6.2  10.1  7.0  6.0  4.8  17.9  2.8  6.3  5.9  9.9  12.8  6.3  3.8  3.3  12.8  29.2  10.9  29.2  8.2  6.3  FS  Stillwater  3+  3  3  2-  2  2  3  2  2-  2  2  2-  2-  3  2  3  2  2  2+  3  2  2-  2+  3  2  3  2+  y  y  y  y  y  y  n  y  y  y  y  y  y  y  y  y  y  n  y  y  n  y  y  y  y  y  n  Mesh  Stillwater  y  y  n  n  Mats  Support  111  Span (m)  4.9  2.7  5.8  4.6  3.4  4.3  3.0  4.6  4.3  3.4  4.3  3.7  8.5  7.6  6.1  6.1  4.3  5.2  4.0  3.0  3.7  3.7  2.4  2.4  4.6  3.0  3.7  Mine  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  RMR  48  42  48  54  48  48  48  42  48  48  45  54  54  54  48  42  36  42  54  48  48  48  48  Stability  48  S  S  PU  S  S  S  S  S  S  PU  PU  S  S  PU  U  S  PU  S  S  S  S  S  S  S  Support Category C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  1/2 span dead weight (t)  PU  18  6  14  4  4  9  9  6  11  18  12  25  25  39  49  18  12  8  12  14  6  12  8  14  23  Depth of support pattern (m)  48  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  primary rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  0.9  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  0.9  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  secondary  5  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of secondary  16  3.6  2.4  3.0  2.4  2.4  2.4  2.4  2.4  3.6  2.4  3.0  3.0  3.0  2.4  3.0  3.6  3.6  2.4  3.6  3.6  2.4  3.0  2.4  2.4  2.4  2.4  3.0  length of secondary  C  181.5  99.1  171.7  76.3  76.3  115.2  115.2  99.1  186.1  98.6  136.4  147.0  147.0  107.7  158.4  181.5  177.3  91.6  177.3  220.7  99.1  136.4  91.6  122.7  108.9  108.0  158.5  bond  C  114.1  90.7  140.3  74.4  74.4  115.5  115.5  90.7  115.5  148.8  124.0  173.6  173.6  214.7  239.5  114.1  124.0  99.2  124.0  140.3  90.7  124.0  99.2  140.3  165.1  90.7  140.3  yield  S  114.1  90.7  140.3  74.4  74.4  115.2  115.2  90.7  115.5  98.6  124.0  147.0  147.0  107.7  158.4  114.1  124.0  91.6  124.0  140.3  90.7  124.0  91.6  122.7  108.9  90.7  140.3  support capacity (t)  PU  6.3  14.5  9.9  18.5  18.5  12.8  12.8  14.5  10.9  5.4  10.1  5.9  5.9  2.7  3.2  6.3  10.1  12.1  10.1  9.9  14.5  10.1  12.1  8.7  4.8  17.9  8.7  FS  48  3-4  3+  2  3  3  2  2-  3  2+  1+  2  2  2  2-  2  3  2+  3  2+  2+  3  2  3  2-  2-  3  2  y  y  y  y  y  y  n  y  y  y  y  y  n  y  y  y  y  n  y  y  y  n  y  y  y  y  n  Mesh  42  y  y  y  y  y  y  y  y  y  y  y  n  Mats  Support  112  48  3.4  Red Lake  7.3  9.1  11.0  Red Lake  Red Lake  Red Lake  6.4  7.3  Red Lake  Red Lake  6.1  9.1  6.6  Stillwater  Red Lake  6.1  2.4  Stillwater  Red Lake  54  2.4  Stillwater  59  49  52  50  48  59  57  53  55  42  48  PU  U  U  PU  PU  PU  S  U  S  S  S  S  S  S  S  S  U  U  S  S  U  PU  PU  S  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  C  108  75  48  46  42  75  10  48  42  29  4  8  9  9  9  6  77  39  4  30  39  6  9  8  1.2  1.2  1.2  1.5  1.5  1.2  1.2  1.2  1.5  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  split sets  swellex  swellex  rebar  rebar  rebar  swellex  rebar  rebar  rebar  split sets  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  0.9  1.2  1.2  1.2  1.5  1.5  1.2  1.2  1.2  1.5  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.5  3.0  3.6  1.8  2.1  2.1  3.0  1.8  1.8  1.8  1.5  1.5  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  rebar  rebar  rebar  swellex  swellex  swellex  rebar  swellex  swellex  swellex  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  0.9  1.2  1.2  1.2  1.5  1.5  1.2  1.2  1.2  1.5  0.9  0.9  1.8  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  2.4  2.1  2.1  1.8  2.4  2.4  2.1  1.8  1.8  2.4  3.0  2.4  3.6  2.4  2.4  2.4  2.4  3.0  3.6  2.4  2.4  3.6  2.4  2.4  2.4  2.4  90.7  151.7  194.0  80.9  94.5  105.2  154.8  67.9  80.9  97.1  168.5  76.3  162.1  115.2  115.2  115.2  103.5  143.8  224.5  76.3  108.3  224.5  99.1  115.2  91.6  76.3  262.0  218.4  174.8  120.2  120.2  218.4  81.9  174.8  120.2  189.9  74.4  81.5  115.5  115.5  115.5  90.7  297.6  214.7  74.4  189.9  214.7  90.7  115.5  99.2  74.4  198.4  90.7  151.7  194.0  80.9  94.5  105.2  154.8  67.9  80.9  97.1  168.5  74.4  81.5  115.2  115.2  115.2  90.7  143.8  214.7  74.4  108.3  214.7  90.7  115.2  91.6  74.4  2.6  1.4  2.6  1.7  2.0  2.5  2.1  6.7  1.7  2.3  5.8  18.5  10.2  12.8  12.8  12.8  16.0  1.9  5.5  18.5  3.6  5.5  14.5  12.8  12.1  18.5  1+  2  10ft swellex + 7ft rebar  12ft swellex + 7ft rebar  Chain link Rebar and Swellex  Rebar swellex and Chain link  Rebar swellex and Chain link  10ft swellex, 7ft rebar + chainlink  rebar/swellex with WWM rebar/swellex with chainlink+straps  6ft rebar/swellex/5x5 pattern  2  2+  3 4  2  2+  2 3  3  2  2 3  2+  1+  2+  3  3+  2-3  3  Support  Red Lake  48  3.7  Stillwater  48  48  42  3.7  2.9  Stillwater  3.7  10.7  Stillwater  48  Stillwater  7.6  Stillwater  48  54  48  48  42  Stillwater  6.7  2.4  7.6  Stillwater  Stillwater  3.0  Stillwater  3.7  Mine  Stillwater  Span (m)  Stillwater  RMR  48  Stability  3.4  Support Category  Stillwater  1/2 span dead weight (t) 0.9  Depth of support pattern (m)  4  primary  35  spacing of primary  C  length of primary  C  secondary  U  spacing of secondary  U  length of secondary  48  bond  36  yield  7.2  support capacity (t)  2.4  FS  Stillwater  y  y  y  y  y  y  n  n  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  Mesh  Stillwater  y  y  y  y  y  n  y  y  y  Mats  113  Span (m)  4.9  6.1  4.9  8.2  8.2  2.7  6.4  8.2  4.3  4.6  3.0  3.0  7.3  2.4  4.9  2.6  2.7  3.0  6.1  7.6  7.6  6.1  2.7  2.1  3.7  4.6  2.7  Mine  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Red Lake  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  RMR  45  42  54  42  30  55  48  48  50  54  55  25  40  54  54  36  55  52  52  50  57  57  60  Stability  60  S  PU  PU  PU  S  S  PU  PU  S  S  S  S  S  S  S  S  S  S  S  U  S  S  PU  PU  Support Category D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  C  C  C  C  C  C  C  C  C  1/2 span dead weight (t)  S  5  14  9  3  5  25  39  39  25  6  5  5  16  4  36  6  8  19  16  61  46  7  61  61  21  Depth of support pattern (m)  55  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.2  1.2  1.2  1.2  1.5  1.2  1.2  1.2  1.2  primary split sets  rebar  rebar  split sets  rebar  rebar  rebar  rebar  rebar  split sets  split sets  split sets  split sets  split sets  rebar  split sets  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  rebar  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  1.2  1.2  1.2  1.2  1.5  1.2  1.2  1.2  1.2  1.5  1.2  spacing of primary  rebar  1.5  2.4  2.4  1.5  2.4  2.4  2.4  2.4  2.4  1.5  1.5  1.5  1.5  1.5  2.4  1.5  1.8  1.8  1.8  1.8  2.1  1.8  1.8  1.8  1.8  2.1  1.8  length of primary  1.5  cables  cables  cables  cables  cables  cables  cables  cables  cables  rebar  cables  cables  rebar  rebar  cables  rebar  swellex  swellex  swellex  swellex  swellex  swellex  swellex  swellex  swellex  swellex  swellex  secondary  1.2  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  1.8  0.9  1.8  1.8  1.8  0.9  1.8  0.9  1.2  1.2  1.2  1.2  1.5  1.2  1.2  1.2  1.2  1.5  1.2  spacing of secondary  42  6.7  6.7  6.7  6.7  6.7  6.7  6.7  6.7  6.7  2.4  6.7  6.7  2.4  2.4  6.7  2.4  1.8  1.8  1.8  1.8  2.4  1.8  1.8  1.8  1.8  2.4  1.8  length of secondary  21  303.0  485.5  497.2  316.0  367.4  617.2  676.3  676.3  617.2  99.1  303.0  305.6  50.0  76.3  705.4  99.1  79.1  66.9  77.7  67.2  94.5  68.1  67.2  67.2  82.2  105.2  82.2  bond  C  57.3  129.2  112.9  48.8  80.7  177.7  209.9  209.9  177.7  90.7  57.3  57.3  91.4  74.4  209.9  90.7  81.9  109.2  109.2  191.1  120.2  65.6  191.1  191.1  120.2  120.2  120.2  yield  C  57.3  129.2  112.9  48.8  80.7  177.7  209.9  209.9  177.7  90.7  57.3  57.3  50.0  74.4  209.9  90.7  79.1  66.9  77.7  67.2  94.5  65.6  67.2  67.2  82.2  105.2  82.2  support capacity (t)  S  11.6  9.2  12.5  15.9  16.4  7.1  5.4  5.4  7.1  14.5  11.6  12.6  3.1  18.5  5.8  14.5  9.5  3.6  4.7  1.1  2.0  9.7  1.1  1.1  3.8  2.5  3.8  FS  S  2 and cables  4  4  3 and cables  34  4  4  4  4  3  2 and cables  2 and cables  2  3  4  3  rebar/swellex/chainlink  rebar/swellex/chainlink  rebar/swellex/chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  rebar, swellex with chainlink  Support  55  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  y  Mesh  58  n  y  n  y  y  n  n  Mats  114  5.0  7.3  6.1  2.7  2.1  3.0  6.1  6.1  7.0  4.6  4.9  2.1  2.7  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  Stillwater  4.6  Stillwater  7.3  4.6  Stillwater  Stillwater  5.0  Stillwater  Stillwater  4.6  Stillwater  2.1  Stillwater  4.6  2.7  Stillwater  RMR  Stillwater  2.7  Stillwater  45  36  48  46  40  30  50  46  45  30  30  48  25  40  40  35  30  42  36  45  40  42  45  30  Stability  42  S  PU  S  U  S  S  S  S  S  S  S  S  S  S  S  S  S  S  U  S  S  PU  S  S  PU  Support Category  4.5  4.9  Stillwater  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  1/2 span dead weight (t) 5  3  16  14  33  25  25  6  3  5  25  36  36  17  14  14  17  14  14  7  14  3  5  5  16  0.9  Depth of support pattern (m) 0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  rebar  split sets  rebar  rebar  rebar  split sets  rebar  rebar  split sets  split sets  split sets  split sets  rebar  split sets  split sets  split sets  split sets  rebar  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  split sets  primary  5  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  0.9  spacing of primary  4  2.4  1.5  2.4  2.4  2.4  1.5  2.4  2.4  1.5  1.5  1.5  1.5  2.4  1.5  1.5  1.5  1.5  2.4  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  1.5  length of primary  D  cables  rebar  cables  cables  cables  cables  cables  cables  rebar  cables  rebar  rebar  cables  rebar  cables  cables  rebar  cables  rebar  rebar  cables  rebar  cables  cables  rebar  rebar  rebar  secondary  D  1.8  0.9  1.8  1.8  1.8  1.8  2.4  1.8  0.9  1.8  0.9  0.9  1.8  1.2  1.8  1.8  0.9  1.8  1.2  1.2  1.8  0.9  1.8  1.8  0.9  0.9  1.2  spacing of secondary  S  6.7  2.4  6.7  6.7  6.7  6.7  6.7  6.7  2.4  6.7  2.4  2.4  6.7  2.4  6.7  6.7  2.4  6.7  2.4  2.4  6.7  2.4  6.7  6.7  2.4  2.4  2.4  length of secondary  PU  367.4  81.4  464.7  485.5  574.0  527.0  472.0  352.0  82.1  303.0  97.8  120.8  706.9  96.9  406.2  407.3  106.5  485.5  74.6  66.6  410.0  81.4  303.0  303.0  109.5  76.3  78.6  bond  38  80.7  65.9  129.2  129.2  324.4  123.1  161.8  80.7  65.9  57.3  173.6  214.7  209.9  132.5  90.2  90.2  148.8  129.2  107.7  82.9  90.2  65.9  57.3  57.3  140.3  74.4  74.4  yield  45  80.7  65.9  129.2  129.2  324.4  123.1  161.8  80.7  65.9  57.3  97.8  120.8  209.9  96.9  90.2  90.2  106.5  129.2  74.6  66.6  90.2  65.9  57.3  57.3  109.5  74.4  74.4  support capacity (t)  3.3  2.4  16.4  21.4  8.0  9.2  9.8  4.9  6.4  12.9  22.1  11.6  3.9  3.3  5.8  5.7  6.3  6.4  6.3  9.2  5.3  9.1  6.6  21.4  11.6  11.6  6.8  18.5  15.1  FS  Stillwater  2.7  Mine  Stillwater  2+ and cables  4  3  4  4  5  3 and cables  3+  4  3  2 and cables  3  3  4  2+ and cables  3 and cables  1 and cables  3  4  3-  2+ and cables  2 and cables  3  2 and cables  3 and cables  3  3  n  y  y  y  y  n  y  y  y  y  y  y  y  n  y  n  n  y  y  y  y  y  y  y  y  y  y  Mesh  Stillwater  Span (m)  Stillwater  y  y  y  y  y  y  n  y  y  y  y  y  n  y  y  n  Mats  Support  115  54  36  48  54  54  54  42  52  48  48  45  45  48  54  5.5  6.1  3.4  3.7  6.1  9.1  6.1  3.7  9.1  4.6  4.6  2.7  3.8  4.3  4.6  Cameco  Red Lake Eskay Creek Eskay Creek Eskay Creek Eskay Creek Eskay Creek Eskay Creek Eskay Creek Eskay Creek Eskay Creek Eskay Creek  RMR  54  55  42  9.1  12.0  10.7  Stability  S  PU  PU  PU  U  S  S  S  S  S  S  PU  PU  PU  PU  Support Category  S  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  1/2 span dead weight (t)  D  42  18  15  33  Depth of support pattern (m)  S  1.5  1.8  1.8  1.2  primary SHOT  SHOT  SHOT  CRF  CRF  CRF  CRF  CRF  CRF  CRF  CRF  CRF  CRF  cables  cables  cables  cables  rebar  1.5  2.4  2.3  2.1  0.9  0.9  spacing of primary  split sets  6.0  5.0  5.0  5.0  2.4  1.5  length of primary  0.9  rebar  rebar  cables  rebar  secondary  0.9  1.2  1.2  1.8  0.9  spacing of secondary  5  5.0  6.0  6.7  2.4  length of secondary  20  320.5  464.5  424.1  241.3  634.9  70.5  bond  D  63.6  97.0  80.7  95.4  161.4  74.4  yield  D  63.6  97.0  80.7  95.4  161.4  70.5  support capacity (t)  S  SHOT  SHOT  SHOT  CRF  CRF  CRF  CRF  CRF  CRF  CRF  CRF  CRF  CRF  1.5  5.4  5.3  2.9  7.9  14.3  FS  PU  3  6ft SS, straps, screen, shotcrete  6ft SS, screen, straps, shotcrete  CRF 2.4m rebar on 1.2m pattern with 76mm shotcrete  CRF CRF, 6ft SS, straps, screen, shotcrete  CRF  CRF  CRF  CRF  CRF  CRF  CRF  Cabled  cables and rebar  2.3m resin rebar and 6m cables  5 cablebolts on 4ft x 7ft pattern, 0.6cm dia cable - 30 tonne  Support  Cameco Eskay Creek Eskay Creek  42  2.7  Mine  Stillwater Deep Post Myra Falls  y  y  y  n  y  Mesh  35  Span (m)  Stillwater  y  y  y  y  Mats  116  7.6  9.1  Rodeo  5.5  4.1  Rodeo  4.6  2.7  48  9.1  Rodeo  48  7.3  Cameco Eskay Creek Eskay Creek Eskay Creek Eskay Creek  4.3  54  10.7  Rodeo  5.0  54  9.1  Rodeo  Rodeo  55  6.1  Rodeo  Rodeo  48  7.6  55  50  45  45  54  54  54  48  42  52  3.7  6.1  Mine  Getchell Jerritt Canyon  Span (m)  Getchell  RMR  36  Stability  3.7  S  S  S  S  S  S  S  S  S  S  PU  PU  PU  PU  PU  PU  PU  Support Category D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  D  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  primary  PU  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  SHOT  FS  48  Standard Support  Standard Support  bolts, mesh and shotcrete  6ft SS, straps, shotcrete 8ft swellex on 5ft x 2ft pattern, mesh and 2" shotcrete 8ft swellex on 5ft x 2ft pattern, mesh and 2" shotcrete  6ft SS, straps, screen, shotcrete  6ft SS, straps, screen, shotcrete  6ft SS, straps, screen, shotcrete  8ft rebar on 6ft x 5ft pattern and 8ft SS39 in 3ft x 3ft pattern and shotcrete 8ft swellex on 5ft x 2ft pattern, mesh and 2" shotcrete shotcrete + 16ft cables/swellex + 8ft SS39 on 3ft pattern and mesh 2.4m rebar on 1.2m pattern with 76mm shotcrete  Standard Support 7ft SS on 4ft pattern with mesh and shotcrete  6ft SS, straps, screen, shotcrete 8ft SS39 on 4ft pattern with mesh and shotcrete  6ft SS, straps, screen, shotcrete  Support  4.0  y  y  y  n  y  y  y  y  y  y  y  y  y  Mesh  Eskay Creek Eskay Creek  y  y  y  y  y  y  Mats  support capacity (t)  yield  bond  length of secondary  spacing of secondary  secondary  length of primary  spacing of primary  Depth of support pattern (m)  1/2 span dead weight (t)  117  25  40  10.0  4.6  2.7  13.1  7.6  Rodeo  Stillwater  Stillwater  TR  Stillwater  Span (m)  6.4  Mine  54  25  45  42  U  S  S  S  U  S  S  S  Stability  Stillwater  RMR  15  D  D  D  D  D  D  D  D  SHOT  TIMBER  SPILE  SPILE  SPILE  SHOT  SHOT  SHOT  SHOT  TIMBER  SPILE  SPILE  SPILE  SHOT  SHOT  SHOT  Standard Support  Timber  4 5 15ft rebar inclined +flat, no resin, straps at anchor.  3  6ft SS, straps, screen, shotcrete 12ft swellex on 5ft x 2ft pattern, mesh and 2" shotcrete  3  n  n  y  y  y  y  y  Mesh  40  Support Category  3.7  primary  2.7  FS  Rodeo  Support  Stillwater  n  y  n  y  y  n  Mats  support capacity (t)  yield  bond  length of secondary  spacing of secondary  secondary  length of primary  spacing of primary  Depth of support pattern (m)  1/2 span dead weight (t)  118  Appendix B: Grid Prediction Data  119  Category A Grid Prediction Data Span (m) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3  RMR 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36  Predictions 1.00 1.00 1.00 1.02 1.03 1.03 1.03 1.03 1.03 1.03 1.01 1.01 1.06 1.42 1.87 1.90 1.74 1.45 1.19 1.07 1.04 1.08 1.23 1.53 1.83 1.92 1.49 1.07 1.01 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.31 1.70 1.92 1.98 2.00 2.00 2.00 1.96 1.67 1.14 1.01 1.00  Span (m) 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4  RMR 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48  Predictions 1.00 1.05 1.40 1.87 1.93 1.81 1.56 1.34 1.41 1.78 2.14 2.30 2.27 2.03 1.44 1.07 1.01 1.00 1.00 1.03 1.11 1.21 1.26 1.27 3.00 2.99 2.98 2.96 2.96 2.96 2.96 2.96 2.92 2.58 1.51 1.06 1.01 1.00 1.05 1.35 1.51 1.29 1.25 1.46 1.74 1.85 1.81 1.72  Span (m) 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  RMR 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60  Predictions 1.65 1.60 1.52 1.33 1.11 1.02 1.01 1.05 1.25 1.64 1.88 1.95 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.69 2.02 2.00 2.00 2.00 2.00 2.00 2.00 2.00 1.99 1.89 1.78 1.76 1.73 1.61 1.34 1.10 1.02 1.00 1.00 1.00 1.01 1.06 1.31 1.78  120  Span (m) 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 7 7 7  RMR 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.95 2.04 1.83 1.87 1.91 1.94 1.96 1.97 1.98 1.99 1.99 1.99 2.00 2.00 2.00 1.94 1.06 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 3.00 3.00 3.00 2.93 1.11 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.01  Span (m) 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8  RMR 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50  Predictions 1.01 1.02 1.03 1.04 1.06 1.08 1.12 1.17 1.24 1.31 1.06 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 2.63 1.02 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00  Span (m) 8 8 8 8 8 8 8 8 8 8 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 10 10 10  RMR 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27  Predictions 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.01 1.03 1.10 3.00 3.00 3.00  121  Span (m) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11  RMR 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.97 2.03 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00  Span (m) 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  RMR 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.97 2.03 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.97 2.03 2.00 2.00 2.00 2.00  Span (m) 12 12 12 12 12 12 12  RMR 54 55 56 57 58 59 60  Predictions 2.00 2.00 2.00 2.00 2.00 2.00 2.00  122  Category B Grid Prediction Data Span (m) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3  RMR 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36  Predictions 1.00 1.00 1.00 1.00 1.00 1.94 1.98 1.98 1.98 1.98 1.98 1.98 1.98 2.00 2.09 2.08 1.20 1.00 1.00 1.04 1.66 1.60 1.05 1.00 1.00 1.00 1.00 1.00 1.03 1.04 1.04 1.07 1.46 1.25 1.04 1.01 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.50 2.00 2.00 2.00  Span (m) 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4  RMR 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48  Predictions 2.00 2.00 2.00 1.71 1.54 1.54 1.54 1.54 1.49 1.10 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.86 1.99 2.00 2.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.50 2.00 2.00 2.00 2.00 2.00 1.63 1.57 1.57 1.57 1.58 2.75 2.96 2.46 1.39 1.38  Span (m) 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  RMR 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60  Predictions 1.38 1.47 2.00 1.95 1.35 1.27 1.27 1.08 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.50 2.00 2.00 2.00 2.00 2.00 1.00 1.00 1.20 2.00 2.01 2.01 2.01 2.00 2.00 2.00 1.02 1.00 1.00 1.01 1.48 1.99 1.98 1.04 1.00 1.00 1.00 1.00  123  Span (m) 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 7 7 7  RMR 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37  Predictions 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.49 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00  Span (m) 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8  RMR 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50  Predictions 1.00 1.00 1.00 1.00 1.00 1.00 1.10 3.00 3.00 3.00 3.00 3.00 3.00 2.64 1.00 1.00 1.00 1.00 1.00 1.15 1.66 1.95 2.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.04 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00  Span (m) 8 8 8 8 8 8 8 8 8 8 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 10 10 10  RMR 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27  Predictions 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.01 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 1.00 1.00 1.02 1.15 1.56 1.26 1.03 1.00 1.00 1.00 1.00 2.99 3.00  124  Span (m) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11  RMR 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.01 2.00 2.00 2.00 1.99 1.50 1.01 1.00 1.00 1.00 1.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00  Span (m) 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  RMR 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.67 2.00 2.00 2.00 2.00 2.00 1.99 1.50 1.01 1.00 1.00 1.00 1.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00  Span (m) 12 12 12 12 12 12 12  RMR 54 55 56 57 58 59 60  Predictions 1.99 1.50 1.01 1.00 1.00 1.00 1.00  125  Category C Grid Prediction Data Span (m) 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 3  RMR 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.99 2.17 1.02 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00  Span (m) 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4  RMR 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48  Predictions 3.00 2.95 1.46 1.03 1.03 1.03 1.03 1.03 1.06 1.14 1.16 1.16 1.16 1.15 1.14 1.02 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 1.99 1.86 1.69 1.60 1.58 1.56 1.48 1.35 1.21 1.16 1.16  Span (m) 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5  RMR 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60  Predictions 1.16 1.15 1.06 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.01 2.01 2.02 2.02 2.01 1.94 1.88 1.86 1.84 1.79 1.69 1.36 1.01 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00  126  Span (m) 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 7 7 7  RMR 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37  Predictions 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.01 2.65 2.99 3.00 3.00 3.00 2.99 2.39 2.00 2.00 2.00 2.00 2.00 1.84 1.17 1.02 1.01 1.02 1.08 1.40 1.79 1.95 1.99 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00  Span (m) 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8  RMR 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50  Predictions 2.01 2.51 2.99 3.00 3.00 3.00 2.99 2.85 2.84 2.84 2.83 2.81 2.86 2.79 2.48 2.15 1.96 1.86 1.72 1.46 1.46 1.85 1.98 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.95 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00  Span (m) 8 8 8 8 8 8 8 8 8 8 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 10 10 10  RMR 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27  Predictions 2.91 2.38 2.08 1.99 1.86 1.54 1.48 1.90 1.99 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.25 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.97 2.97 2.97 2.96 2.86 2.11 2.00 2.00 2.00 2.00 2.00 2.00  127  Span (m) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 11 11 11 11 11 11 11 11 11 11 11 11  RMR 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36  Predictions 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.01 2.99 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.88 2.12 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00  Span (m) 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  RMR 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45  Predictions 2.00 2.00 2.02 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.89 2.12 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.03 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00  Span (m) 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12  RMR 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60  Predictions 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 2.99 2.01 2.00 2.00  128  Appendix C: Neural Network Results  129  130  Category A Stability Neural Network Training Data  131  Category A Stability Neural Network Verification Data  132  Category A Stability Neural Network Entire Data  133  Category B Stability Neural Network Training Data  134  Category B Stability Neural Network Verification Data  135  Category B Stability Neural Network Entire Data  136  Category C Stability Neural Network Training Data  137  Category C Stability Neural Network Verification Data  138  Category C Stability Neural Network Entire Data  139  Category D Stability Neural Network Training Data  140  Category A Factor of Safety Neural Network Relevance of Inputs, Span/RMR/FS  141  Category A Factor of Safety Neural Network Relevance of Inputs, RMR/FS  142  Category A Factor of Safety Neural Network Relevance of Inputs, Span/FS  143  Category B Factor of Safety Neural Network Relevance of Inputs, Span/RMR/FS  144  Category B Factor of Safety Neural Network Relevance of Inputs, RMR/FS  145  Category B Factor of Safety Neural Network Relevance of Inputs, Span/FS  146  Category C Factor of Safety Neural Network Relevance of Inputs, Span/RMR/FS  147  Category C Factor of Safety Neural Network Relevance of Inputs, RMR/FS  148  Category C Factor of Safety Neural Network Relevance of Inputs, Span/ FS  149  Category D Factor of Safety Neural Network Relevance of Inputs, Span/RMR/FS  150  Category D Factor of Safety Neural Network Relevance of Inputs, RMR/FS  151  Category D Factor of Safety Neural Network Relevance of Inputs, Span/FS  

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