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The consolidation characteristics of peat as determined from the one-dimensional consolidation test Doyle, Ronald Glen 1963

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T H E C O N S O L I D A T I O N C H A R A C T E R I S T I C S O F P E A T as determined f r o m the one-dimensional consolidation t e s t by R O N A L D G L E N D O Y L E B . A . S c , T h e U n i v e r s i t y of B r i t i s h Columbia, I960 ) A T H E S I S - S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S O F T H E D E G R E E O F M a s t e r of Applied Science in the Department of Civil Engineering We accept t h i s t h e s i s as conforming t o the required standard T H E U N I V E R S I T Y O F B R I T I S H J u l y , 1963 C O L U M B I A In presenting th i s thesis in p a r t i a l fulf i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make i t freely avai lable for reference and study. I further agree that per-mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or p u b l i -cation of this thesis for f i n a n c i a l gain sha l l not be allowed without my written permission. Ronald G l e n D O Y L E Department of C i v i l Engineer ing The Univers i ty of B r i t i s h Columbia, Vancouver 8, Canada. Date J u l y 1, 1963 ii A B S T R A C T A detailed discussion of the consolidation process of peats is presented with suggested t e s t i n g procedures f o r determining the consolidation c h a r a c t e r i s t i c s , specific g r a v i t y , void r a t i o , moisture content, side f r i c t i o n and permeability. P a r t i c u l a r ' a t t e n t i o n is d i r e c t e d t o secondary consolidation e f f e c t s which are discussed with r e f e r e n c e t o t e s t r e s u l t s on two types of pe a t s . T he r e s u l t s f r o m t e n consolidation t e s t s consisting of seven t e s t s (2.5 inches diameter by 1 inch o r i g -inal height) on two types o f peat,.and t h r e e t e s t s ( 8 inches diameter by 5 inches original height) .on an amorphous peat are presented. A side f r i c t i o n measuring apparatus is des-cribed and experimental r e s u l t s of side f r i c t i o n measurements are presented. A pore p r e s s u r e probe is described and eval-uated as to experimental r e s u l t s o f pore pressure measure-ments, permeability measurements and a rapid method of pore pressure determination during secondary compression. A graphical method of separation of primary and secondary com-pression is presented and described. T h r e e topics are out-lined as possible f u t u r e r e s e a r c h t h a t will increase the under-standing o f the consolidation c h a r a c t e r i s t i c s of peat. iii A C K N O W L E D G E M E N T The writer wishes to express his appreciation and indebtedness to his supervisors, the Department of Civil Engineering ,• and the Department of Soil Science f o r their suggestions and assistance which facilitated the completion of the laboratory tests required for this thesis. Special thanks are due to Assistant Professor N.D. Nathan for his comments and suggestions f o r improvements to the thesis manuscript. The writer would also like to thank the Department of Civil Engineering and the National Research Council of Canada f o r funds which provided an assistant ship and laboratory equipment. T A B L E O F C O N T E N T S C H A P T E R P A G E I. T H E C O N S O L I D A T I O N C H A R A C T E R -I S T I C S O F P E A T 1 Introduction . . 1 Definitions 1 Tes t Numbering System . . . . . . . . 2 Primary Consolidation 2 Secondary Consolidation 6 I I . C O N S O L I D A T I O N T E S T P R O C E D U R E S 8 Introduction 8 Cutting and preparing samples 8 Load-increment ratio .•• 10 Load duration 11 Temperature E f f e c t s 13 Consolidation apparatus 13 I I I . S P E C I F I C G R A V I T Y , V O I D R A T I O A N D M O I S T U R E C O N T E N T 17 Introduction 17 Specific Gravity 18 Moisture Content . 2 1 Void Ratio 23 Ash Content 22+ V C H A P T E R P A G E IV. P E R M E A B I L I T Y ' 25 Introduction 25 Permeability: Experimental Results and Conclusions 31 Sample Calculation of Permeability. . . . 32 V. P O R E - W A T E R P R E S S U R E 34 Introduction 34 The E f f e c t of Permeability on Pore Pressure Measurement 36 Pore Pressure Measurment Apparatus . 36 A Method f o r Rapid Determination of Pore Pressure During Secondary Consolidation 37 Sensitivity of the Pore Pressure Probe. 40 Experimental Results ......... 40 Conclusions 41 V I . S I D E F R I C T I O N 43 Introduction 43 Side Friction Measuring Apparatus . . . 44 Experimental Results 45 Conclusions 46 V I I . G E O M E T R Y O F L I N E S ON A SEMI-L O G P L O T 48 vi C H A P T E R P A G E V I I I . E X P E R I M E N T A L R E S U L T S O F C O N S O L I D A T I O N T E S T S 51 Description of the Peat Used f o r T e s t s . 51 Consolidation T e s t s 53 Void ratio-pressure Relationship 55 Coefficient of Secondary Compression . . 62 Coefficient of Secondary Compression: Conclusions 70 I X . C U R V E - F I T T I N G A N D I N T E R P R E T A T I O N 71 Introduction 71 Separation of Primary and Secondary Consolidation by a Graphical Method . . 72 Conclusions 76 X. P O S S I B L E F U T U R E R E S E A R C H T O P I C S 78 Permeability 78 Pore pressure measurement with a probe . 79 Secondary Consolidation 79 X I . SUMMARY O F C O N C L U S I O N S 81 N O T A T I O N . 85 R E F E R E N C E S 90 P H O T O S U P P L E M E N T 94 vii C H A P T E R P A G E C O M P R E S S I O N V E R S U S L O G - T I M E C U R V E S F O R C O N S O L I D A T I O N T E S T S 100 L I S T O F T A B L E S T A B L E P A G E I. Typical values of C N in log-cycles past t Q or t ' 0 50 I I . Properties of peats used f o r con-solidation tests 52 I I I . Initial sizes and characteristics of peat tests 54 I V . Calculation of t values f o r f i r s t trial of curve fittings 75 L I S T O F F I G U R E S F I G U R E P A G E 1. Trimming samples with a knife . . 8a 2. Showing "optimum" f i t of sample in the consolidation ring 8a 3. E f f e c t of changes in temperature and side friction on the rate of consolidation, during t e s t 3-A-4 13a 4. Loading system used f o r testing large samples (8 inches diameter by 5 inches original height) 14a 5. Two rings a f t e r a consolidation t e s t . . . . 14a 6. Apparatus f o r specific gravity determination of peat 19 7. The variation of moisture content f o r 3 samples of Sperling Avenue Peat caused by drying, at different temperatures . . 20a 8. Apparatus used f o r the consolidation t e s t when permeability is to be determined. . 28a 9. Relationship between the void ratio and the logarithm of permeability f o r t e s t 3-A . . 31a 10. Relationship between a function of the void ratio, e /{1+e), and the permeability f o r t e s t 3-A 32a X F I G U R E P A G E 1 1 . Consolidation as a function of depth and time factor 3 4 a 1 2 . Excess pore pressure at mid-depth 3 4 a 1 3 . Probe apparatus f o r pore pressure measure-ment 3 7 a 1 4 . Modified pore pressure probe 3 7 a 15. Plot to determine if the rate of movement of the null point is linear 3 8 a 1 6 . Plot used to determine the hydrostatic excess pressure at the probe tip, as determined by the rate of movement of the null point 3 8 a 17. Excess pore pressure at mid-depth, as measured with a pore pressure probe . . . 4 l a 18. Side friction weighing apparatus . . . . . . 4 4 a 19. Relationship between side friction coefficient and total stress 4 5 a 20. Relationship of maximum side friction force per load increment to total effective pressure 4 5 a 21. Showing coefficient of friction of peat on greased polished brass compared with peat on polished brass 45t> xi F I G U R E P A G E 22.. The ef f e c t of multiplying a function by a constant as shown by its semi-log plot . 48a 23. Plot of the function 48a 24. Semi-logarithmic plot of primary line and other compression lines 57a 25. Plot showing the ef f e c t of secondary consolidation on the e vs log P curve . . 57a 26. e100 v s *°£> ^» Sperling Avenue Peat . . . 59 27^ e100 v s F » S p e r l i n g Avenue Peat . . . 60 28. e100 v s l - , u ^ u Island Peat Si 29. Log C g vs log P, Sperling Avenue Peat . 65 ,30. Log C s vs log P, Sperling Avenue Peat . 66 31. Log C s vs log P, Lulu Island Peat . . . 67 32. Log C s vs log P, Sperling Avenue Peat . 68 33. Log Co^vs Void ratio, Sperling Avenue Peat 69 34. Compression vs log time, t e s t 3-A-7 . . . 70a 35. Types of compression versus logarithm of time curves 72a 36. Time f a c t o r , T M , versus b/ A ^ r p j . . . . 72a 37. Curve showing primary and secondary compression 72a d = d Q - b log - (I0 n -1) xii F I G U R E P A G E 38. Graphical method f o r separation of primary and secondary consolidation 73a 39. Colour Photographs of Sperling Avenue Peat 95 i+0. Consolidation machine with 6000 lb capacity at the loading head 96 41. Fulcrum adjustment 96 42. Side friction weighing apparatus in position on the consolidation machine . . . . . . . . 96 43. Consolidation t e s t in progress 97 44. Pore pressure probe 97 45. Pore pressure probe in position through the loading plate and porous stone 97 46. Pore pressure probe in sample during t e s t . 98 47. Consolidation ring showing pore pressure probe and thermometer in position . . . . 98 48. Consolidation ring and porous stones (8 inches in diameter) 98 49,. Shear machine used to determine the coeffic-ient of friction between peat and brass. . 98 50. L a t h f o r cutting 8 inch diameter samples . . 99 51. L a t h f o r cutting 2.5 inch and 6 cm diameter samples 99 F I G U R E Xlll P A G E 52. Consolidation machine used fo r small L I S T O F T E S T S T E S T P A G E 1- A Compression vs log time 101 2- A Compression vs log time 102 3 - A Compression vs log time 103 1- 4 Compression vs log time 104 2- 2 Compression vs log time 105 2- 3 Compression vs log time 106 3 - 4 Compression vs log time 107 0-1 Compression vs log time 108 0-2 Compression vs log time . 109 0-3 Compression vs log time 110 C H A P T E R I T H E C O N S O L I D A T I O N C H A R A C T E R I S T I C S O F P E A T as determined from the one-dimensional consolidation test Introduction One-dimensional consolidation tests are widely used f o r determining the parameters used to predict settlements of soils. The consolidation of peat is similar to that of clays, since as compression occurs there must be an escape of pore-water. Interpretation of the one-dimensional consolidation test requires consideration of permeability variation, secondary consolidation rate and side friction e f f e c t ; also the determin-ation of specific gravity of the soil particles, void ratio and water content. These considerations will be discussed in subsequent chapters. Notation:- The letter symbols used in this paper are defined where they f i r s t appear. They are assembled alpha-betically, f o r convenience, in the Appendix. Definitions Some of the terms and definitions used in soil mechanics have a variety of meanings. The following will give the in-tended connotation of certain terms used in this paper. 2 consolidation - the decrease in volume of a soil due to an applied load, as a function of time. compression - the decrease in volume of a soil due to an applied load, as a function of load. load increment - a step increase in load which acts f o r a given time interval. load increment ratio - the ratio of a given load increment to the total load acting immediately before its application. peat - soil containing more than 30 per cent organic matter; the soil . being deposited in a saturated condition. peat particle - a unit of organic material (i.e. a piece of root, leaf, branch, etc.) T e s t numbering system The individual load increments will be referred to by three characters as follows: 1 - A - i+ (Test number) (Test series or (Load increment) apparatus used) A particular test will be referred to by only the f i r s t two characters. Primary consolidation One-dimensional primary consolidation is decrease in volume of a soil resulting from a decrease in volume of voids accompanied by a squeezing out of pore-water which occurs with strain in the vertical direction only. The rate of pri-mary consolidation is governed by the hydrodynamic effect as described by Terzaghi's theoretical equation (cf. Taylor, 1948, p. 225). The mechanics of primary consolidation are based on the premise that f o r every void ratio there exists a particular effective pressure that can be supported by the intergranular soil skeleton. If an applied pressure is in excess of the capacity of the soil skeleton at the existing void ratio, the excess pressure must be supported by the pore-water. The excess pore pressure is then dissipated by drainage of the pore-water. Drainage continues until the soil skeleton void ratio approaches the void ratio that will support the additional pressure. The consolidation rate of most clays conforms to that predicted by Terzaghi's theoretical equation. Since, as will be shown later, the rate of consolidation of peat does not conform to Terzaghi's equation, a review of the assumptions on which this equation is based will be useful. These assum-ptions are: 1. Homogeneous soil, 2. Complete saturation, 3. Negligible compressibility of soil grains and water, 4. One-dimensional compression, 5. One-dimensional flow, 6. The validity of Darcy's Daw, 4 7. Constant values f o r certain soil properties which actually vary somewhat with effective pressure, 8. The greatly idealized pressure-versus-void-ratio relationship, 9. No movement of the drainage boundary during con-sol idatiori;,- and 10. The time lag of .consolidation- is due entirely to the low permeability of the soil. Microscopically peat is nonhomogeneous, but it may be con-sidered macroscopically homogeneous. Peat deposits, in most cases, have stratification; the individual strata may be con-sidered homogeneous. The presence of gas in pore spaces is characteristic of organic soils in which plant residue is decom-posing. Above the water table the gas produced is chiefly carbon dioxide; below the water table it is methane with lesser amounts of nitrogen, carbon dioxide, or hydrogen sulfide (Moran, et al, 1958). The presence of gas in the pore spaces causes an immediate consolidation of the soil skeleton due to the compressibility of the free gas. Moran, et al, (1958) have developed a modification to the Terzaghi equation to take into account the e f f e c t of gas in the pore spaces on the rate of consolidation. However, many peats located below the water table are close to 100 per cent saturation, and there-fore may be said to conform to the second assumption. The third assumption, which is justified f or saturated clays, is not entirely applicable to peats. A s in clays the compressibility of (the water may be neglected, since the compressibility of the soil skeleton is large compared to that of water. The compressibility of the solids in the peat may be neglected, but since the peat particles are plant cells and membranes that contain water they may be deformed by an increase in pres-sure. Also the peat particles could be compressed due to diffusion of water out of the cells and membranes. This dif-fusion would be caused by a pressure differential between the pore water and the effective pressure on the particles. A s will be discussed later the diffusion of water out of the cells and membranes could be one of the reasons f o r secondary consolidation. The fourth and f i f t h assumptions are closely realized in the laboratory t e s t . The validity of Darcy's Law fo r the flow of water through soils has been verified by many investigators f o r the gradients present during consolidation; but it appears that a lower limiting value exists, as will be mentioned in the discussion of permeability. The coefficients of permeability and compressibility of the soil skeleton are not constant during the pressure increment. The great variations of permeability during consolidations will be demonstrated and discussed later, but the variation in compressibility can be seen from a natural plot of void ratio versus pressure. I f allowances are made for variations in permeability and com-pressibility, the differential equation defining the consolidation 6 process becomes more complex. The solution of this d i f f e r -ential equation would require a relaxation or iteration proce-dure. A s in the solution of the consolidation equation f o r clays, the only justification f o r assumption eight is that a more correct relationship would make the analysis unduly com-plex. The movement of the drainage boundary during con-solidation, due to large axial strains, could cause discrepan-cies in the predicted rates of consolidation. Moran, et al. (1958) show a difference equation solution f o r a case with variable void ratio during consolidation. They conclude: that including the effect of variable void ratio pro-duces no appreciable changes in the shape of. the con-solidation vs. time relations, although a slightly increased value of consolidation is indicated f o r any particular value of time. This shows that the con-ventional theory of consolidation is satisfactory, even f o r relatively large reductions in thickness of the clay layer. The above conclusion should also apply to the consolidation of peats. Assumption ten refers to the arbitrary definition of primary consolidation. In other words, the consolidation governed by the rate of escape of the pore water shall be known as primary, and the consolidation governed by other soil properties shall be secondary. Secondary consolidation In many consolidation tests,, it has been found, that when the excess pore pressures approach zero the peat or 7 i clay mass continues to decrease in volume; this decrease in volume has become known as secondary consolidation. It has been found that the rate of secondary consolidation f o r peats proceeds linearly with the logarithm of time (Buisman, 1 9 3 6 ; Thompson and Palmer, 1 9 5 1 ; L e a and Brawner, 1 9 5 9 ) . Taylo ( 1 9 4 2 ) attributed secondary compression to the plastic distor tion of grain groups or the squeezing of water from between very closely spaced flat colloidal sized soil particles. Wahls ( 1 9 6 2 ) similarly suggests that secondary compression is due t the viscous yielding and the viscous reorientation of the soil grains; he feels that the term "structural relaxation" des-cribes this process of secondary consolidation. Similar pro-cesses would cause the secondary consolidation of peats but also, since peat particles contain large quantities of water, the diffusion of water out of the peat particles through cell walls and organic membrances would contribute to the magni-tude of the secondary consolidation. C H A P T E R II C O N S O L I D A T I O N T E S T P R O C E D U R E S Introduction The one-dimensional consolidation t e s t procedure f o r peat can be similar to the t e s t for clay as described by Taylor (1948) or Lambe (1951). Departures from the stand-are procedure and precautions in experimental technique will be discussed under the headings of: cutting and preparing samples, load increment ratios, load duration, temperature e f f e c t s , and consolidation apparatus. Cutting and preparing samples Peat is a highly compressible mixture of partially decom-posed and disintegrated organic material characterized by its high water content (as high as 3232$ reported by Feustel and Byers, 1930). Radford (1952) describes sixteen categories of peat constituents based on the extent to which wood and fibres are present. The amorphous and non-woody fine fibrous peat can be cut with a sharp knife. Care must be taken to shape the sample in as few cuts as possible since trimming thin slices is virtually impossible. Cut the sample with knife strokes t o -wards the waste material as shown in Figure 1. This will give the fibres the greatest support so that they will be cut not 8a Trim with knife strokes in this direction in order to cut fibres Figure 1 Trimming samples with a knife £ «f this amount of peat i s dragged down by the ring for an "optimum" f i t of the sample i n the ring Figure 2 Showing "optimum" f i t of sample in the consolidation ring 9 torn. Samples should be cut so that the consolidation ring will slide on without having to be forced. The ease with which the consolidation ring slides on will be called "degree of f i t " (tight, optimum, or loose). The significance of the degree of f i t will be discussed under side friction. F i t is "tight" when the ring must be forced on the trimmed sample and the bottom edge of the ring tears and deforms the sam-ple. F i t is "optimum" if the ring will go on the sample under its own weight f o r large rings or with an easy push fo r small rings. In this case the ring slightly deforms the small arrises on the exterior of the sample (see Figure 2 ) . Any sample smaller in diameter than that f o r an "optimum" f i t will give a "loose" f i t . The coarse fibrous, granular, and fine fibrous peats with undecayed fibres, are more difficult to cut. Methods of cutting these types of peat are quick freezing, as men-tioned by Brawner ( i 9 6 0 ) , and with knife and scissors. The knife and scissors method of trimming samples requires del-icate technique to obtain an undisturbed sample with an opti-mum "degree of f i t " . The method is to trim the decayed and soft material with the knife; use the scissors to cut the tough roots and fibres. An objection to the quick freeze method is that the extent of alteration of the peat structure due to freezing is not known. 10 Load-increment ratio The load-increment ratio ( (P2 - Pj_)/P^, where P-|_ is the total load during the previous load-increment and Pg the total load in the present load-increment) recommended by Taylor (1948) or Lambe (1951) f o r the standard consolidation test is one. T e s t s performed with other load-increment ratios give considerable variation in the coefficients of con-solidation (Leonards and Girault, 1 9 6 l , and Taylor, 1942). To date (1963) very little research dealing with load-increment ratios f o r consolidation tests of peat has been reported. The load-increment ratio could be a very important factor in relating laboratory results to field predictions. Natural peat deposits usually have no overburden, the water table at or near the surface, and low insitu density. Thus the preconsolidation load of peat ranges from zero at the sur-face to a pressure equal to the effective overburden pressure at lower s t r a t a . The effective overburden pressure f o r peats may be as low as two pounds per square foot per foot of overburden (MacFarlane, 1959), if the water table is at the surface. The addition of overburden to a stratum of peat will cause an infinite load-increment ratio at the surface; the ratio will decrease with depth. The preconsolidation load of a peat stratum is difficult to determine since the seasonal and yearly variation of the water table causes consolidation e f f e c t s . 11 The preconsolidation load results from a hysteresis effect caused by all past variations in effective overburden pressure. Load duration Taylor (1948) and Lambe (1951) recommend that the duration of each load-increment be one day. The procedure of doubling, the load each day during a consolidation t e s t f o r clays has the advantages that the tes t can be completed in one week and that the ratio of primary to secondary consolidation re-mains large. The secondary consolidation of clays is .usually ignored since it is only a small percentage of the total consol-idation; whereas in peats the secondary consolidation is signif-icant in the consolidation analysis. Thus the rates of both primary and secondary consolidation of peats must be deter-mined. This requires that the duration of each load increment be long enough f o r the rate of secondary consolidation to be determined. To determine the rate of secondary consolidation at least three and preferably five or six points that, will give a straight tangent on the compression versus log-time plot are required. Thus a minimum requirement f o r determining the rate of secondary consolidation would be to continue the load-increment one log-time cycle past the "tangent intercept point" (the tangent intercept point as determined by Casagrande's construction, see Figure 37). This means that t e s t s which 12 reach the tangent intercept point (TI) in 100 to 12+0 minutes continue f o r one day and t e s t s that reach T I in 1 0 0 0 minutes continue f o r seven days. The desirability of continuing the load increment one log-cycle past T I can be demonstrated by comparing tests 1-A and 2-A (the compression vs log-time curves f o r tests are in the appendix); in te s t 1-A a definite trend is apparent whereas in 2-A the secondary rate is arbi-t r a r y since it is defined by only two or three points. The effect of load durations longer than those mentioned above and the e f f e c t of varying the load-increment ratio during the t e s t will be discussed with the experimental results in Chapter V I I I . The void-ratio at the T I is a unique value that depends on the effective stress and is independent of the duration of previous load-increments (Wahls, 1 9 6 2 ) , this statement will be discussed and verified later. Thus the e f f e c t of the duration of the previous load increment is to vary the ratio of primary to secondary consolidation during the primary phase of the cur-rent load increment. One method of reducing the significance of primary consolidation, in order to study secondary e f f e c t s , is to prolong the duration of the previous load increment. Similarly, as in tests f o r clays, the effects of secondary con-solidation can be reduced by using short load increment durations. 13 Temperature e f f e c t s Changes in temperature have no noticeable e f f e c t on the rate of consolidation during the primary phase, since dur-ing that phase large volume changes occur in a short period of time. Changes in temperature during secondary consolidation greatly influence the results (K.Y. Lo, 19&1). From Figure 3, which shows the compression during t e s t 3-A-4 and the temperature at the time of the compression readings, the rate of secondary appears to be influenced more by a change in temperature rather than by the actual temperature itself. Methods to avoid or reduce the e f f e c t of temperature changes on the consolidation results consist of either testing in a constant temperature room or insulation of the sample. Where a constant temperature room is not available, the following methods can be used to reduce the influence of tem-perature changes: a large water bath around the sample to modulate the temperature changes, a water bath around the sample with a temperature control and a heater, or insulation of the sample with a block of styro-foam or similar insulative material. Consolidation apparatus The basic consolidation apparatus consists of a loading device, a ring f o r confining the sample, a dial gauge, and a 13a cocj T I M E . . . ( M I N . ) on the rate of consolidation, during test 5-A-4 14 container around the sample that will prevent evaporation. Many modifications of this basic apparatus have been devised. Consolidation apparatus has been described and illustrated in detail by Taylor (1942, 1948) and Lambe (1951). A brief description of the apparatus used f o r testing peat will follow. The loading device f o r testing peats can be similar to the testing machines for clays. Due to the large strains dur-ing the consolidation of peats, the loading device must be able to accommodate a movement of 70 to 90 per cent of the orig-inal sample height. With a lever loading system, an adjustable fulcrum, as shown in Figure 4, will allow large strains during consolidation while keeping the consolidation load constant. Figure 4 shows a schematic view of the consolidation machine used fo r loading the 8-inch diameter by 5-inch original height peat samples. The one-inch original height samples were tested in a standard consolidation frame (Figure 52). A consolidation ring is required to maintain one dimen-sional consolidation and one dimensional drainage of the sample. Porous stones or a similar material are required top and bottom of the sample, to permit drainage and to transmit the consol-idation load to the sample. Rings must be of a non-corrosive metal or plastic, with the inner surface polished to reduce the effects of friction (friction will be discussed in another sec-tion). The rings used f o r the peat t e s t s were polished brass 14a J a"4> * SAMPLE. ' p. ft COUNTE-R WEIGHT. 4= 7" • 30' I-LOA.C7 FV\Kl Figure 4 Loading system used for testing large samples (8 inches diameter by 5 inches original height) 1 - showes corrosion above the point where peat was in contact with the ring due to exposure to iron oxide - no corrosion of ring Figure 5 Two rings after a consolidation test 15 lubricated with a mixture of Lubriplate* and molybdenum disul-fide. A n examination of the ring a f t e r a long term t e s t showed no corrosion at the contact of the peat sample and the ring; but above the sample in some cases the ring showed corrosion. Figure 5 shows two rings af t e r consolidation t e s t s ; the ring with corrosion was exposed to iron oxide caused by the rusting of a steel ball-bearing on the consolidation machine; the other ring, exposed to the pore water squeezed from the sample showed no sign of corrosion. Teflon and stainless steel are other non-corrosive materials used f o r consolidation rings. The porous stones must have a permeability higher than that of the sample if they are not to hinder the dissi-pation of the pore water. The porous stones used f o r the 8-inch diameter t e s t s were l/2 inch thick Norton 32A80 K 5 V B E . The stones used in the other t e s t s were of the same material but only 1/4 inch thick. F o r peats that have a high permeability, instead of porous stones, the use of plates of a brass filtering material (a very porous material composed of tiny brass spheres pressed together) is recommended. A dial gauge is used to indicate the strain as consol-idation progresses. A standard dial gauge of one-inch range that gives readings in .001 inches or .001 centimeters will trade name of a commercial lubricant. 16 give s a t i s f a c t o r y r e s u l t s f o r samples of one inch original height. F o r larger samples the same gauge may be used but it will require r e s e t t i n g a f t e r each load increment. A container is required to prevent the evaporation of the pore-water from the sample, evaporation causes the sam-ple t o consolidate due t o desiccation. The simplest method to prevent evaporation from the sample is t o put the consolidation ring into an open dish, then f i l l the dish with water t o above the top of the sample, and add water daily to replace t h a t which has evaporated. Another method is to seal the appar-atus in a plastic or rubber membrane. Figure 2+6 shows the plastic sack of water in which the 8-inch diameter samples were t e s t e d . T e s t s in which pore pressure and permeability are taken require special containers which will be described l a t e r . C H A P T E R III S P E C I F I C G R A V I T Y , V O I D R A T I O A N D M O I S T U R E C O N T E N T Introduction The specific gravity (S.G.), void ratio and moisture content are properties or conditions of clay or peat required for the interpretation of the consolidation t e s t . The three terms are inter-related, since the moisture content and spec ific gravity of the soil solids are used to determine the void ratio, by the following: e = V - Vs with Vs = Ws (l) Vs G Y w and e = wG (2) where w - moisture content as a percentage of soil solids (oven dried weight) Ws - weight of oven dried soil solids G - specific gravity of soil solids e - void ratio S - saturation, volume of gas as a percentage of the total volume occupied by water and gas V - measured volume of the soil V s - volume of soil solids _ - unit weight of water 2r w F o r the interpretation of a consolidation t e s t the void ratio 18 usually determined from equations ( l ) , while equation (2) is used to determine the saturation of the so i l . S pecific gravity In most cases the specific gravity of the solids in peat is greater than one. Due t o the gases entrapped in the peat and the high water content the bulk specific gravity is approximately one and some times less than one. The problem in an accurate determination of the spec-i f i c g ravity of the soil solids is the removal of the entrapped gases, thereby obtaining a sample at 100 per cent satu r a t i o n . A n experimental procedure f o r a s a t i s f a c t o r y method of deter-mining the specific gravity of peat solids is similar to t h a t described by Lambe (1951, pp. 15-21), with the following refinements: Apparatus - as shown in Figure 6, consisting of a volumetric f l a s k , de-aired. water, vacuum source, and vacuum hose. 19 1) t o vacuum pump 3) 2) 4 ) 5) pea t a t n a t u r a l w a t e r c o n t e n t o r oven d r y . T j o in t t o enable w a t e r t o ge t in to t h e p y c n o m e t e r while sample is u n d e r d i sh o f d e - a i r e d w a t e r 500 ml p y c n o m e t e r vacuum F I G U R E 6 A P P A R A T U S F O R S P E C I F I C G R A V I T Y D E T E R M I N A T I O N O F P E A T P r o c e d u r e - c u t t h e pea t (oven d r i e d o r a t n a t u r a l w a t e r c o n t e n t ) i n to smal l p ieces (cubes about 0 . 2 inches by 0 . 2 i n c h e s ) . L o o s e l y pour t h e s e p ieces in to t h e p y c n o m e t e r . D e - a i r t h e p y c n o m e t e r t o a high vacuum (26 t o 28 inches o f m e r c u r y ) . T h e n whi le s t i l l under vacuum f i l l t h e p y c n o m e t e r w i t h d e - a i r e d w a t e r , enough t o c o v e r t h e pea t b u t n o t more t h a n t h r e e - q u a r t e r s o f t h e p y c n o m e t e r . C o n t i n u e t o d e - a i r , occa s iona l l y shaking and t a p p i n g t h e f l a s k g e n t l y t i l l a l l bubbles a r e d i s s i p a t e d . D e - a i r i n g o f oven d r i e d samples may t a k e t h r e e t o f o u r days o f soak ing and i n t e r m i t t e n t a p p l i c a t i o n s o f v a c u u m , while t h e sample con ta in ing t h e n a t u r a l i n s i t u p o r e - w a t e r may be d e - a i r e d in 30 m inu te s t o one h o u r . F r o m t h i s po in t p r o -ceed as d e s c r i b e d by L a m b e . 20 The advantages of using an oven dried sample to deter-mine specific gravity are that the dry weight of solids is known prior to the determination and a larger weight of solids may be used f o r the determination. The use of peat at the natural water content f o r S.G. determination has the advan-tage of a fa s t e r de-airing procedure, but the disadvantage of a small dry weight of sample-. A small weight of dry sample tends to give errors in the calculated S.G, due to experi-mental inaccuracies. A s mentioned by Lambe (1951, p. 18) the soil particles contain absorbed water; therefore, the specific gravity obtained is dependent on the method of drying employed. The variation of moisture content of peat due to various drying temperatures is shown in Figure 7. Another method of specific gravity determination, sug-gested by Cook (1956),, uses the concept of ash content (the ash remaining from peat fired at 800 degrees centigrade expressed as a percentage of over dry weight) . This pro-cedure assumes that the ash is composed of clay minerals with a specific gravity of 2 .7 and that the organic material, burnt o f f during firing, has a specific gravity of 1.5. The average specific gravity of the peat solids is calculated from the * expression G = (1 - A S)1.5 + 2.7A S (3) where A s = ash content. 20a s 40 * : 1 1 1 1 1 1 .—l 100 •„.:..;/. iao ' : i&o . " /. ..: : iso * t a o 3 , 0 0 2.2.0. . _1TEM P E ' R A T U R E I Z I N C D E C , R E E S L I L F A W R E N W E I T Z Z Z H Figure 7 The variation of moisture content for 3 samples of Sperling Ave Peat caused by drying at different temperatures. 1 I 1 21 The assumption that the organic matter has a specific gravity of 1.50 is justified since peat is composed of lignin (S.G. of 1.46) and wood (S.G. of 1 .52) particles. Caution must be used when applying this method since the ash does not consist entirely of clay minerals. The following example shows the necessity, if this method is used, of checking the S.G. of the ash: use equation (3) to find the S.G. of Sperling Ave-nue Peat which has an ash content of 66 per cent; G = (1 - . 6 6 ) 1 . 5 0 - 2 . 7 0 ( . 6 6 ) = 2 . 2 9 but the S.G. of the ash from Sperling Avenue Peat is 2 . 2 3 ' and the average S.G. of the oven dry solids is 1.93''~, which indicates that the organic matter has a S.G. of 1 . 4 5 . F o r this extreme case, equation (3) gives an error of approx-imately 18 per cent. Moisture content The moisture content, an easily obtainable property, is very useful since it gives an indication of consolidation pressure and it can be used as a basis of comparison f o r other characteristics. The ability of peat to absorb and hold water has been ascribed to five different phenomena (Ostwald, see MacFarlane, 1 9 5 9 ) . The water is correspondingly found by the pycnometer method. I 22 classified as: ( l ) water of occlusion, held in pores one milli-meter or more in diameter; (2) capillary water; (3) colloid-ally bound or absorbed water; (2+) osmotically bound water; and (5) chemically combined water. The maximum moisture holding capacity represents a total of all forms. The moisture content, defined as the weight of water expressed as a per-centage of the weight of dry solids, will depend on the temper-ature at which the solids are dried (see Figure 7). Jackson (1958) suggests that the weight loss, from drying at temper-atures up to 100 degrees centigrade, be attributed to absorbed water; that the weight loss, due to drying between 100 de-grees and 800 degrees centigrade, be attributed to organic matter. A t present (1963) most reports of moisture con-tent are from samples dried at 105 degrees centigrade (the temperature at which the moisture contents of clays are determined). A drying temperature of 85 degrees centigrade has been suggested; the lower temperature reduces the haz-ard of burning o f f part of the organic matter. Drying at room temperature can be successfully performed by using a small fan to circulate air over the sample, but variations in humidity will influence the results. In order to obtain an average value of moisture content, and avoid local variations, a large representative sample must be used f o r moisture determinations. The minimum size of sample would contain at 2 3 least 1 0 grams of dry solids. Drying of large samples may require two to three days to come to a constant weight at a temperature of 1 0 5 degrees centigrade, and an even longer drying time is required at lower temperatures. The drying can be hastened by an increased circulation of air over the sample. Void ratio The void ratio gives an indication of the compressibility of a material; the higher the initial void ratio the greater the potential compressibility. Void ratios in peats have been reported as high as 2 5 (Hanrahan, 1 9 5 4 ) . The void ratios reported f o r peats are usually based on the weight of oven dry solids. A more rational void ratio would be obtained by using the following equation: e = V - NVs ( 4 ) NVs where N = the ratio of the weight of oven dry solids and combined water to the weight of oven dry solids. The e f f e c t of equation ( 4 ) is to define "voids" as spaces occupied by mobile water. Although it is difficult to find the void ratio defined in this way, since N may be constant or variable and at best difficult to determine, this definition will be useful in later discussion of permeability and consolidation. A s h content A s h content of peats may be determined by two methods of combustion. F i r s t , combustion of the organic matter can be accomplished by heating with a bunsen burner f o r three t o four hours or, b e t t e r , by heating in a muffled furnace at 800 degrees Centigrade f o r two hours. Second, a wet combustion method using hydrogen peroxide (HgOg) requires two to three days f o r complete combustion of the organic m a t t e r . The ash content is defined as the weight o ash as a ra t i o of the weight of oven dry solids. C H A P T E R I V P E R M E A B I L I T Y Introduction The applicability of Darcy's Law f o r the flow of water through a soil stratum has been demonstrated in many reports (cf. Leonards, 1962, pp. 107-139) Darcy showed experimentally that the rate of water (q) flowing through soil of cross-sectional area (A) was proportional to the im-posed gradient (i), or q = kiA where k is the "coefficient of permeability" or "permeability" expressed in units of velocity. Leonards (1962) gives r e f e r -ences and experimental evidence to establish the upper limiting value of flow rate above which Darcy's Law is no longer valid, but this upper limit is seldom reached in the consolidation of peats and clays; he also mentions that now there appears to be a lower limiting value. This lower limit has been called "initial gradient"; a gradient that must be exceeded before flow will take place. Hansbo ( i 9 6 0 ) demonstrates that flow at low gradients does not conform to Darcy's Law.. The soil properties that determine the coefficient of permeability have been suggested by many writers (cf. Scheidegger, i 9 6 0 ) . The Kozeny-Carman equation, 26 K = 1 n3 k Q k T U - n ) * S g (5) where k g - l / C s - shape f a c t o r of pores krp - t o r t u s o s i t y f a c t o r of pores n - porosity S s - s u r f a c e area of voids w e t t e d by flowing f l u i d / unit volume of solids, called specific s u r f a c e . K - k_ L n •y - unit weight of fluid n - c o e f f i c i e n t of v i s c o s i t y although presently (1963) d i f f i c u l t t o apply, is the most accep-table relationship between permeability and soil p r o p e r t i e s . The Kozeny-Carman equation shows permeability depends on the following soil p r o p e r t i e s : 1. The second power of a dimension r e p r e s e n t a t i v e of the average grain size; this is r e p r e s e n t e d by the t e r m S s , which in clays is almost constant f o r any given s o i l . In p e a t s , however, t h e r e is evidence t h a t the p a r t i c l e s change shape as well as size during consolidation. 2. The p r o p e r t i e s of the pore fluid are r e p r e s e n t e d by the t e r m y . In any given clay or peat this t e r m will be n nearly constant a t all times, f o r a given t e m p e r a t u r e . O t h e r prop e r t i e s of the pore fluid may enter the problem in the case of clays and p e a t s . I f the pore fluid contains impurities not in equilibrium with the adsorption complex of the soi l , base 27 exchange may alter the quantity of immobile water discussed under (3) below. The polarity of the molecules of the pore fluid may also be a significant variable. 3. The void ratio (e) is represented by the term /(l-n)2 which is equivalent to e3 /(e+l). Changes in void ratio will also e f f e c t the terms k and k m . In coarse O T grained inorganic soils the void ratio may be readily defined by equation (1) e = (V-Vs)/Vs A s mentioned previously, the void ratio f o r peat (and, to a somewhat lesser degree f o r clay) could be defined as: e = (V-NVs)/NVs where N - volume correction applied to oven dried solids to give the volume of solid materials and immobile water; N ^ l . 2+. The shape and arrangement of pores governs the terms k g and krp. 5. The amount of undissolved gas within the pore water and the amount of dead water (i.e. water in dead end pores or in pores connecting two other pores, that are under the same hydro static pressure) is represented in the term S s . The general methods f o r measuring the permeability of soils with respect to the flow of pore water are as follows: 1. Direct measurement by constant-head or falling-head permeameters. 28 2. Indirect measurement by capillary absorption in horizontal tubes. 3. Indirect from consolidation t e s t data (Terzaghi, 1925). i+. Direct measurement from rate of flow in a pore-pressure measuring probe. A direct determination of permeability can be performed during a consolidation t e s t . A typical apparatus f o r perme-ability measurement during the consolidation t e s t is shown in Figure 8. The consolidation apparatus is essentially similar to" standard fixed ring t e s t apparatus except f o r the container, which must confine the water so that it flows only through the sample. Double drainage may be permitted during consol-idation, but during the permeability determination the bottom drainage valve must be closed. Sample disturbance will be kept to a minimum if a constant gradient from the permeability apparatus is maintained throughout the consolidation t e s t . Another experimental method of permeability determin-ation can be performed using the pore pressure probe (shown in Figure 14 and described in the Pore-pressure Measurement Chapter). The procedure^consists of timing the rate of flow of pore water into or out of the pressure probe. The coef-ficient of permeability can be determined by the well-point equation given by Taylor (1948): 28a 1 - container 2 - screw ring used to compress the O-ring 3 - top porous stone 4 - consolidation ring 5 - bottom porous stone 6 - O-ring Photo of the consolidation apparatus used for permeability determinations loading head 5 1 .vx^xy^ij v u o—or falling-head or constant-head permeameter f bottom drainage Cross-section showing consolidation apparatus used for permeability determinations Figure 8 Apparatus used for the consolidation test when permeability i s to be determined. 29 q = S' k h t (6) where"--q = r a t e of flow. S' = coefficient governed by the shape of flow net at the probe t i p . h t = head loss between pore pressure and the pressure being maintained in the probe. r' = inside radius of the probe. o This equation assumes an infinite soil mass and isotropic permeability. A s s t a t e d by T a y l o r , since nearly all the head is lost near the pipe or probe entrance, the boundary condit-ions have l i t t l e e f f e c t i f they a r e f f i n i t e r a t h e r than i n f i n i t e . The pore-pressure probe used in t e s t 3—A (see Figure 14) had entrance conditions somewhere between Taylor's two examples: an. open end impermeable tube where S' = 5.7 (this gives the average v e r t i c a l permeability), and the closed end tube with permeable walls where S' = 13.7 (this givesi the average horizontal permeability). The c o e f f i c i e n t s of permeability found by using the pore-pressure probe will be a combination of v e r t i c a l and horizontal permeability. Since in peats ho r i z -ontal permeability is larger than v e r t i c a l permeability (Miyakawa, I 9 6 0 ) the coefficient of permeability determined by the probe will closely represent the average horizontal permeability at the vicinity of the probe t i p . Permeability can also be determined from indirect methods of time r a t e of consolidation as given by Terzaghi's 30 theory. The coefficient of permeability can be determined from consolidation test data by the following relationships: k = c v a v yw (7) o (1+e) where c = < — - coefficient of consolidation. v t 5 0 T^ yj- _ time factor f o r 50 per cent consolidation are given by Wahls (1962) in Figure 3 6 . 50 - sample depth, from mid point to drainage face fo r double drained tests or total depth f o r single drained samples, at 50 per cent consol-idation . 50 - time at 50 per cent consolidation (see Figure 3 7 ) . a v - coefficient of compressibility (cf. Taylor, 1948, p. 2 2 5 ) . ^w - unit weight of water. The values of permeability determined by this method will indicate the magnitude of the average permeability up to 50 per cent consolidation. F o r inorganic soils, that show small changes in permeability during consolidation, these values may be used as the average permeability; but f o r peats, which have large changes of permeability during consolidation, these values are only useful as an indication of the change in perm-eability f o r each load increment. Permeability determined by this method will be of the correct magnitude even if the irrational void ratio expression (equation ( l ) ) is used in the calculation. Since, particularly at high void ratios, the influence of the void ratio changes on k are balanced by their influence on a v . Permeability: Experimental Results and Conclusions Experimental results of permeability are only available from a few of the tests performed, since, in order to keep variables to a minimum, permeability determinations were omitted from the t e s t procedure. The permeability results available are from tests 3-A. The results from these tests and the permeability calculated from the consolidation data are shown in Figure .9. The plot of void ratio versus logarithm of permeability should be a straight line (cf. Taylor, 1942). The permeability calculated from the consolidation data con-forms reasonably well to a line on the semi-log plot. The permeability determined with the probe varies from a straight plot, due perhaps, to the low pressure gradients used to find the permeability in tests 3-A-3 and 3-A-4 (as mentioned prev-iously, the rate of flow at low gradients has been found to deviate from Darcy's Law); or to a change in the relation-ship between the vertical and the horizontal permeability. The values of permeability calculated from tests 3-A probably only approximate the actual permeability, but the values do indicate the great variation in permeability during consolidation of peat. 3 l a • ' 1 , ,- , „ . „ -Ml- — - , . • . • ., . , i | 1 1 Q ^3-A - 3 - > y permeat by cons at TT -i l i t y d< olidatic itermir »n datj ed -~r-———— X . / / / / 8 by equa —•-•/• tion (-7] / — / ! -/ s -\ / s / V s / • / / / / / / -r / / 3.9 pei pea meabili' e pre SKI by deter nv> pr<Yh nined >y rl-0 / / ••• * y / / / / y _dep 1 th by e< Ration — s • s >> / / / / 5 // / :SPEI ILING AV E PEAT h —- — D / * • void ratio vs i •TEST. 3-A 1 ... 1 i a; 0 < tt -8 7 10 2 4 7 10"*7 2 4 • 7 10~6 log permeability (k) in cm/sec. 7 10 -5 -•Figure 9 Relationship between the .void ratio and the logarithm of  permeability for test 3-A. 32 A plot of e3/( l + e) versus permeability will show nearly a stra i g h t line relationship i f the change in permeability is dependent mainly on the change in the void r a t i o . The plot in Figure 10 shows t h a t a change in permeability must be dependent on other f a c t o r s besides the void r a t i o . This means there must be large changes in the terms k g , and S g , suggesting t h a t there is a definite change in the shape and, possibly, a change in the size of the peat particles dur-ing consolidation. A change in the size of the peat particles would mean tha t the f a c t o r N (used in Equation (4)) varies during the consolidation t e s t . Sample Calculation of Permeability The following sample calculation shows the method used f o r determining permeability by use of the pore pressure probe, Re w r i t e equation ( 6 ) as follows: K k A (8) S» p rb S» r-J where - r a t e of flow per unit of pressure, this can be found from the slope of the ra t e versus pres-sure plot (as shown in Figure 1 6 ) . A - area of the capillary at the null point. F o r example in t e s t 3-A-5 as shown in Figure 1 6 , where = .02 cm/min. /inch of mercury, r ^ = .0525 cm and A = .0255 cm^; assume S* = 10 (average between 13.9 and 5 .7) then 3 2 a 80 70 60 50 40 30 20 10 • \ i i / \ / < SPERLING AVE EEAT I ' \ e 3 / ( l + e) ; VS ! . ; .permeability : 1 ; I-0.0 1.0 1.5 -6 2.0 2.5 Permeability (k) in IO*". cm/sec Figure 10 Relationship between a function of the void ratio, e / ( l + e), and the permeability for test 3-A. 33 k = .02 (.0255) = . 4 6 7 ( 1 0 " 6 ) cm/sec. 10(.0525) (60) (34.6) 1 Since the values of S', A and r^ remain nearly constant f o r a particular probe during a t e s t , permeabilities may be quickly determined by using k = K k K p (9) where -^p - probe constant = A/S'r^ Note: A s will be mentioned in the next chapter the flow into or out of the pore pressure probe must be small so that the pore pressure in the sample remains virtually undis-turbed. C H A P T E R V P O R E-WATER P R E S S U R E Introduction The classical consolidation theory as developed by Terzaghi shows that the pore pressure or hydrostatic excess pressure at any point is inversely proportional to the consol-idation at that point. The consolidation is a function of time and depth. Figure 11 shows the relationship between pore pressure, consolidation, depth and time factor ( T ) , while Figure 12 shows the theoretical pore pressure dissipation rate at mid-depth of a double drained layer. The classical theory assumes that permeability is constant during primary consolid-ation but in f a c t f o r peats permeability varies considerably with consolidation as was discussed in the previous chapter. Many methods of pore pressure measurement have been devised (Taylor, 1942; Bishop, I 9 6 0 ; Whitman et.al., 1 9 6 1 ) . The measurement of pore pressure must be arranged so that there is no interference with the consolidation process and no alteration of the normal drainage paths. This requires a probe with a porous tip or a porous stone to isolate the pore water at,a specified point in the sample. The water pressure is then measured, allowing no volume change, by an external pres-sure sensing device. The two main methods of pressure excess pore pressure ( —) as % .2 " .4 .6 , . Consolidation ratio (u) 8 .1.0 Figure 11 Consolidation as a function of deptli and time factor. from Taylor (1948) p 235 1-.0-.8 .6 u .2 ifrom abc ve at . ~ - 1 V H 1' o. \ • .01 .02 .05 .1 !• log T .5 1.0 Figure 12 Excess pore pressure at mid-depth. 35 measurement are the null point, indicator and the transducer. The null point method balances the pore pressure against a known water or air pressure, the determination of pressure requiring that the pore-water-air interface (Taylor, 1942) or a pore-water-mercury interface. (Bishop, i 9 6 0 ) be held con-stant at a null (or no-movement) point. A small movement at the null point is required in order to determine the precision of pressure measurement; this will be discussed later. The transducer is a device (mechanical or electrical) that will measure pressures with very little movement of the interface between the transducer and the pore-water (Whitman et. al. , I 9 6 I ) . According to the classical theory, the initial excess pore pressure in saturated soils should be equal to the applied load increment, but there have been cases reported where the maximum measured pore pressure was much less than this value. Whitman et. a l . ( l 9 6 l ) suggest two causes f o r this discrepancy: flexibility in the pore pressure measuring system or low compressibility of the mineral skeleton (i.e. the com-pressibility of the skeleton approaching that of the pore-water). Another cause would be the presence of gas in the soil voids. 36 The E f f e c t of Permeability on Pore Pressure Measurement Pore pressure measurement would be independent of permeability if the pressure sensing devices did not require a slight movement of pore water into or out of the sample in order to determine the pressure. F o r example, the null point, when this method is used on a very impermeable soil, could appear to be balanced when it is actually moving at an imper-ceptible rate. Thus f o r an accurate measurement of pore pressure a large surface at the sample, a long term balancing period, or a magnification of the null point movement is required. A large area in contact with the soil can be accom-plished by a tes t with drainage at the top stone and measure-ment of the pore pressure at the bottom stone, but with a probe it is impossible to increase the end area without increasing the probe diameter. A long term balancing period is impractical during primary consolidation since pore pressure is changing rapidly with time, and during secondary consolidation results will be affected by temperature changes. A fine capillary tube or an optical device will give magnification of the null point movements. Pore Pressure Measurement Apparatus Pore pressure measurements were taken during tests 1-A and 3-A-. The five inch initial height of these tests 37 required double drainage during consolidation in order f o r p r i -mary consolidation to be completed in a reasonable time (less than one day). With double-drainage tests pore pressures must be measured with a probe since the top and bottom drainage faces have zero pore pressure. The probe assembly used f o r pore pressure measurement is shown in Figure 13. - A. "Soil T e s t PP25" pore pressure and permeability panel was used for pressure measurements during t e s t 1-A. F o r te s t 3-A the probe was modified to that shown in Figure 12+ (also see photos Figures 44 and 45 in the Appendix). The null point was moved from the pore pressure panel to the top of the probe. Advantages of the null point at the probe or as close to it as possible are that this: 1. simplifies de-airing of the apparatus, 2. reduces the ef f e c t of volume change in the water between the probe tip and the null point' caused by temperature change and pressure changes in the pore water, 3. reduces possible leaks of water out of the system or air into the system during a long term t e s t . A Method f o r Rapid Determination of Pore Pressure During Secondary Consolidation  An accurate reading of pore pressure during secondary consolidation, especially when the sample has a low permeability, 37a my' y&*7~7'A "*2T 2 3 _±JL •I T A t J l ^ WA5;W£.R Figure 13 Probe apparatus for pore pressure measurmeiit "i — V A t - V E ^ . . . . . -N v ^ 7 TIP" 'Figure 14 Modified pore pressure probe 38 may require up to 12 hours f o r balancing of the null point. In order to obtain an approximate pore pressure reading in a short period of time a method was devised to estimate the pore pressure from the rate of movement of the null point. This method is based on the folio wing ' assumptions : 1. Darcy's Law will hold, that is the rate of flow will be directly proportional to the unbalanced pressure. 2. Small changes in the pore water, volume would not appreciably e f f e c t the pore pressure. 3. The actual pore pressure is the pressure for no flow (i.e. no movement of the null point). 2+. Constant permeability during the pore pressure determination. The following sample calculation, which will include a discus-sion of the applicability of the above assumptions, will show the method used to determine pore pressure. Figure 15 gives a plot of volume change (or null point movement) versus, time; the slope of this curve is the rate of flow f o r a given pressure. A s can be seen in the figure the average rate can be calculated by determining the slope between the origin and the last point on each curve. A plot of the rate (in cm/ minute) versus the pressure (in inches of mercury), as shown in Figure 16, indicates the pressure at no flow would be -0.2 38a -3.3MHg .8 F2.1"Hg C o a. 3 c 0 •P <<-O a* o Z -.8 2 ^ * — . . . 10 15 Time in minutes •Figure 5 Plot to determine i f the rate of movement of the null point i s linear 4.2"Hg -4.1"Hg .1 -4 -2 Pressure (inches of mercury) Figure 16 Plot used to determine the hydrcstatic pore ? pressure probe ^•null point < SAMPLE correction by ,35"Hg to find hydrostatic excess pressure at the probe tip, as determined by the rate of movement of the null point. 39 inches of mercury, which would then be the balancing pressure at the null point. A correction (in this case 0.35 inches of mercury) f o r the head of water between the null point and tail water and also a correction f o r the capillary head at the null point should be added to the balancing pressure in order to determine the excess hydrostatic pressure at the probe-tip. Figure 16 indicates the excess hydrostatic pressure at the probe-tip is (.35 - .2 - .03) = 0.12 inches of mercury, where -.03 inches of mercury is the capillary correction. The circled numbers on Figures 15 and 16 indicate the order in which the readings were taken. The discrepancy between points 1 and 4 of Figure 16 could be due to experimental error or to changes in the values assumed constant in the above assumptions. When this method is used the best results are obtained by using pressures of approximately equal amounts above and below the actual pore pressure. Movement of the null point need not be as large as that shown in Figure 15, where large movements were used to determine whether the rate of flow would remain constant over a long period of time and whether large volumes of water flowing into or out of the sample, would aff e c t the rate of flow. A few words of caution: if the sample contains large volumes of gases this method of pore pressure determination should not be used; also it must be remembered that the flow 2+0 into, or out of the sample must be small in order to prevent i n t e r f e r e n c e with the consolidation process and a l t e r a t i o n of the drainage paths. S e n s i t i v i t y of the P o r e P r e s s u r e Probe A n estimate of the s e n s i t i v i t y of the pore pressure probe may be determined as follows: the time ( t ) required f o r a perceptible movement of the null point ( A r ) with an e r r o r in balancing pressure of (p') is t = A r (10) P1 K k where K^. - slope of the -rate versus pressure p l o t . F o r example in F i g u r e 16 where = .OS cm/min./inch of mercury and assuming A r = 0.1 cm and p» = 0.1 inches of mercury t = 2j_i— = 50 minutes .02 ( . l ) B y using the above described rapid pore pressure measuring procedure pore p r e s s u r e s of approximately the same accuracy ( i .1 inches of mercury) can be obtained in 10 t o 20 minutes. A s shown in C h a p t e r I V the slope of the r a t e versus p r e s -sure plot (K^) can also be used to determine the permeability. Experimental R e s u l t s A complete s e t o f pore pressure readings was not taken during the t e s t s . The readings taken were to check" 41 the correlation between the theoretical pressure dissipation during primary consolidation and the measured values, to deter-mine the pore pressures during secondary consolidation, and to evaluate the pore pressure measuring equipment. The results of pore pressures measured during test 3-A are plotted in Figure 17 as a percentage of the increment of applied stress C^0-) . The theoretical pore pressure at mid depth is also shown on Figure 17 as a basis f o r comparison. Although the pore pressure did not dissipate in the theoretical manner, it is of interest to note that: the maximum pore pressure did approach the increment of applied load, and all tests had a pore pressure dissipation curve of similar shape. The scatter of the pore pressure values during secondary con-solidation could be caused by changes in temperature during the tes t or errors in pore pressure measurement. Conclusions The dissipation of excess pore pressure, as shown by Figure 17, does not conform to the theoretical rate of dissi-pation, but dissipation rate is similar f o r all t e s t s . This sim-ilarity could be due to the time lag of the apparatus. There-fore, it would be necessary to measure the pore pressure with other types of apparatus before definite conclusions may be reached. tFigure 17 Excess pore pressure at mid-depth, as measured  with a pore pressure probe. The measurement of pore pressure during secondary-consolidation requires a more sensitive pore pressure probe or the method outlined above may be used t o give approximate values of pore pressures. C H A P T E R V I S I D E F R I C T I O N Introduction In order to determine the average e f f e c t i v e p r e s s u r e on" the sample during a consolidation t e s t i t is necessary t o determine a side f r i c t i o n c o r r e c t i o n f o r the applied p r e s s u r e s , or t o eliminate the e f f e c t s of side f r i c t i o n , as .discussed by T a y l o r (1942) , K.Y. L o ( I 9 6 l ) and Le o n a r d s and G i r a u l t (1961). T a y l o r (1942). derived an equation f o r the side f r i c -tion c o e f f i c i e n t ft = F d (ID 4H ( P - n F ) where f - side f r i c t i o n c o e f f i c i e n t , which is the product of the c o e f f i c i e n t of l a t e r a l p r essure and the c o e f f i c i e n t of f r i c t i o n . F. - t o t a l side f r i c t i o n t r a n s m i t t e d to the consolidation ring d - diameter of the consolidation ring. H - t o t a l height of the sample P - t o t a l applied load n - distribution f a c t o r (approximately - . 5 ) . T h i s equation gives the c o e f f i c i e n t of side f r i c t i o n when the excess pore pressure is ze r o . T o find the c o e f f i c i e n t of side f r i c t i o n at any time during a consolidation t e s t , use "P instead of P, where 'P is the average in t e r granular p r e s s u r e : 44 P = P ± i U A P (12) where P^ - total pressure of the previous load increment. U - consolidation ratio from Terzaghi's equation A P - additional load Leonards and Girault (I96l) compare side friction results by the ratio AFjyj / A^H, where AFJVJ is the change in max-imum friction force f o r the load increment; this relationship is useful since it is not the total side friction that influences the consolidation during a load increment but the changes in total side friction during that load increment. Side Friction Measuring Apparatus The measurement of side friction requires a device that will weigh the friction force transmitted to the consol-idation ring. Two such devices are described by Taylor (1942) and Leonards and Girault (1961). A simple type of side friction measuring apparatus is shown in Figure 18. This apparatus, although .not as elegant as those mentioned above, will give reliable values of total side friction. The apparatus consists essentially of a proving ring and an assembly to sup-port the consolidation ring. The correct position of the con-solidation ring is gauged by using a spacer block under the edge of the ring. The top adjustment is turned slowly to raise the proving ring till the spacer block will just slide under the edge of the consolidation ring. 44a 1 - adjustment to compensate for deformation of side friction measuring apparatus 2 - proving ring 3 - adjustment of support rods 4 - support rods 5 - porous stone 6 - consolidation ring 7 - loading head 8 - spacer block 9 - hook Figure 18 Side friction weighing apparatus 4 5 Experimental Results Side friction was measured during all the series A t e s t s (peat samples 8 inches in diameter by 5 inches original height). Values of f are shown in Figure 19 and the ratio A F M / A , F H is shown and compared with Leonards and Girault's results in Figure 2 0 . Polished brass rings lubricated with a mixture of "Lubriplate" and molybdenum disulfide were used f o r all con-solidation t e s t s . Values of f were calculated near the 100 per cent primary consolidation with the values of F and H at that point. The sample f o r t e s t 1-A was cut tora "tight" f i t ("degree of f i t " is defined in Chapter II under "Cutting Sam-ples") while samples for tests 2-A and 3-A were cut to an "optimum" f i t . T e s t s were performed with.a direct shear machine to determine the efficiency of the lubrication. The shear box used was similar to that shown by Lambe ( 1 9 5 1 , - p. 9 2 ) except that the lower half of the box was covered with a brass plate. The upper half of the shear box was filled with a block of undisturbed peat. The test procedure of shearing the peat on the brass was similar to that outlined by Lambe ( 1 9 5 1 ) f o r the "Direct Shear T e s t of Cohesionless Soils;" except that only . 0 3 inches of strain was permitted f o r each consolidation! load. Figure 2 1 shows the coefficient of friction between peat and polished brass compared with the coefficient -16 .14-u. i a x .08 .o(, .04 .02 1 /«\pp/°.e>crus~N<aT-F ^ N C T I ONI W ^ P R O P E R L V - .04.. .07 . JI;: -\0 ' •r .4- .7 i-o .Figure 19 Relationship between side friction coefficient and total stress. QJ X Si ft .10 .05 1 I 1 1 0 -! 1 * I t • i 1 * l \ L E O N A R D S MEXICO ClTr q R £ . A S £ D . T ; \ G I R A U L T : * 1.5" H T . — CLAV IN A ' — — — — i \ + V ~~ ~~ — —a —B . —« Sifi 0 y>KPPARA7 •""^ JvUNCT'OMC •\}%-;ncrr ~: uc; : PR.OPE.RJ .Y o e <i- & a :: .TOTAUT-£FFeCTivE.: P : R E s s U RE..(X^/cm ) Figure 20 Relationship of maximum side friction force per load  increment to total effective pressure. 45b .4-0 .30 2 V1 0 a li 0 r Z m ^ .20 u. u. ul 0 0 (D 0 CD — 0 - O . -C_j= » E . A X . : t > ' : B R A S S " i O N . C R E A S E D _PQt . \ . S ^ E D _ B R A 5 S 1 ,1* .1 • e s 1.0 • 2. Figure 21 Showing coefficient of friction of peat on greased polished brass compared with peat oh polished brass. 46 of friction of peat and lubricated polished brass. The num-bers by the points on the plot indicate the number of days each consolidation load was left on before shearing. The values are the maximum determined from shearing at a rate of .0001 inches per second. The values of ' A F M / A P H f o r the 8 inch diameter tests appear to be much lower than those reported by Leonards and Girault. This difference is due to the difference in size of the consolidation ring. Equation (11) may be rewritten as follows: F = 1 (13) P H d _ + n H 4f From this it is obvious that f o r low values of the side f r i c -tion coefficient ( f ) the diameter of the ring determines the influence of. side friction on a consolidation test more than does the height of the ring. Conclusions The following conclusions may be drawn from the data: The degree of f i t influences the magnitude of the side f r i c -tion; an "optimum f i t " gives lower values of side friction than a "tight" f i t . Lubrication of the consolidation ring results in a significant reduction in side friction. Side friction increases during a long duration load increment. kl A n understanding of the effects and magnitude of side friction are required for the interpretation of consolidation t e s t s . If the magnitude of side friction remained constant during a load increment there would be no problem. But friction varies with effective stress, this change during a load increment, gives rise to changes in the average effective load increment. The best solution to the problem is to elim-inate or reduce to insignificance the magnitude of the side friction. C H A P T E R V I I G E O M E T R Y O F L I N E S O N A S E M I - L O G P L O T A study of the geometry of lines on a semi-log plot gives valuable insight f o r the i n t e r p r e t a t i o n of consolidation versus log-time curves. F i r s t consider the plot of the functions d 1 = f ( t ) and d g = C f ( t ) . On a semi-log plot, as shown in Fig u r e 22, the curves dj_ and dg are identical in shape; but curve d2 is a constant horizon-t a l distance (log C ) f r o m the curve d^. T h i s is one of the relationships used f o r f i t t i n g the t h e o r e t i c a l consolidation curve to the experimental curve. Next consider the curve d = d c - b ( l o g t - log t Q ) = d Q - b log t _ (14) which plots on a semi-log plot as a s t r a i g h t line. i . e . d (d) = -b f o r all values of t . d(log t ) Suppose several such curves are to be compared each s t a r t i n g f r o m a d i f f e r e n t origin in time but otherwise identical. L e t us plot them with r e s p e c t t o a variable t' which s t a r t s f r o m one fixed point in time. Then :the general equation may be w r i t t e n 48a . locv t " ~ iFigure 22 The Effect of multiplying a function by a constant as shown by i t s semi-log plot . Figure 2J Plot of the1 function d o d - b log [7 - (lO n- l) 0 L "C d = d Q -b log 't« - t 0 ( I 0 n - 1) 49 d Q -blog j t ' / t 0 (I0 n - l7 | (15) where the starting time f o r each curve, when d= d Q is t' Q = t Q ( 1 0 n ) and t' = t + t o ( l 0 n - l ) . When n is an integer the time at d Q will be moved n log-cycles to the l e f t or right of t Q (see Figure 23). Now d(log t») (d) = -b ( 1 6 ) See Figure 23 f o r plots of equation ( 1 5 ) with values of n varying as integers between - 2 and + 2 . By changing the reference or zero time two types of plots occur, thos.e with slopes less than and those with slopes greater than the orig-inal plot (with n=0 and slope of -b) . It will be noticed however that all the plots eventually approach a slope of -b. Figure 23 is plotted with t Q = 1 0 0 ; but as mentioned above the curves can be moved horizontally, without changing their shape, by multiplying the function by a constant. L e t us now find the point at which equation ( l 6 ) approaches within N per cent of slope -b. This is given very nearly by the value of t' to make ifl ( 1 0 n - 1) t' N 100 ( 1 7 ) or T , . 100 ( 1 0 n _ 1 } 50 Then the slope from equation (16) will be approximately N per cent of -b at C ^ log-cycles past t Q ) where Table I gives typical values of C^. f o r N of 1 and 5 per cent T A B L E T Y P I C A L V A L U E S O F C N IN L O G - C Y C L E S P A S T t Q OR t' 0, n C N (log-cycles past t Q ) N = 5% N = 1% C' (log-cycles past t'Q ) N = 5% N = - 1 -10 + 1 + 10 1.25 1.3 2.25 11.3 1.95 2.0 2.95 12.0 2.25 11.3 1.25 1.3 2.95 12.0 1.95 2.0 C H A P T E R V I I I E X P E R I M E N T A L R E S U L T S OF C O N S O L I D A T I O N T E S T S Description of the Peat Used f o r T e s t s Consolidation tests were performed with two types of peat, which will be designated as Sperling Avenue Peat and Lulu Island Peat. The sample were hand cut blocks obtained from open excavations. Sperling Avenue Peat, obtained from the excavation f o r the Greater Vancouver Water and Sewer Pump Station on Sperling Avenue, Burnaby, British Columbia, may be described as follows: an amorphous peat with horizon-tal bedding planes of reeds and vertical root holes (approx-imately 2 to 3 per square inch) , colour insitu an olive green changing to a dark green when exposed to air, with nonorganic odor but rather an earthy smell. Lulu Island Peat, obtained from Northern Peat Products L t d . , Number 8 Road and River Road, Richmond, British Columbia, may be described as follows: an amorphous peat with few distinguishable bed-ding planes, some partially decayed roots visible, colour dark brown, and nonorganic odor. Table II gives some of the physical and chemical properties of these peats. See Figure 39 f o r colour photographs of Sperling Avenue Peat. 52 T A B L E I I P R O P E R T I E S O F P E A T S U S E D F O R C O N S O L I D A T I O N T E S T S Peat designation Sperling Avenue Lul u Island depth of sampling 7 to 8 f e e t 5 to 6 f e e t * ground water elevation unkno wn at present surface initial void ratio 10 to 12 11 to li+ natural water content 500 to 600 per cent 750 t o 950 per cent ash content 60 to 70 per cent 2 to 4 per cent specific gravity of solids ** 1.93 1.44 specific gravity of ash 2.23 — per cent SiOg in ash 90 to 92 per cent — pH 5.5 5.6 * 5 to 6 f e e t below original peat s u r f a c e , 1 f o o t below present surf a c e . ** calculation based on solids dried at 100° Centigrade. Sperling Avenue Pe a t warrants a few additional com-ments due to i t s high ash content. The low specific gravity of the ash caused concern t i l l i t was determined t h a t the ask contained silicate (Opal) r a t h e r than clay minerals. 53 A gravimetric chemical analysis showed the ash to contain 90 to 92 per cent silicate by weight ( c f . J a c k s o n , 1958, p. 300 f o r the analytical p r o c e d u r e ) . A s h obtained by a wet com-bustion using hydrogen peroxide (H^Og) was examined under a microscope. The ash consisted of mainly plant s t r u c t u r e opal and a small percentage of diatoms. C h a r a c t e r i s t i c s of opal are as follows ( c f . B e r r y e t . a l i , I960): chemical composition - S i O g "nHgO specific g r a v i t y - 2.0 t o 2.2 c r y s t a l system - none, amorphous water content - 3 t o 10 per cent Consolidation T e s t s T h e following is a summary describing the consolidation t e s t s p e r f o r m e d . The compression-log-time plots of each load increment are included in the appendix. T e s t s were performed on peat samples t h a t had initial sizes and charac-t e r i s t i c s as shown in Table I I I . The load increment r a t i o of one, as suggested by T a y l o r (1948), was used f o r all t e s t s . P o r e pressure meas-urements were taken during t e s t s 1-A and 3-A. Side f r i c t i o n was measured in all series A t e s t s . The t e s t i n g machines used f o r the t e s t s have been discussed previously (in C h a p t e r I I ) ; see F i g u r e 4 f o r the machine used in series A t e s t s ; F i g u r e 52 T A B L E III I N I T I A L S I Z E S A N D C H A R A C T E R I S T I C S OF P E A T T E S T S Initial T e s t Number water . content void ratio height satur-ation * sample diameter load duration type., of peat** 1-A 5 0 5 % 9 . 9 3 5 In. 9 8 % 8 In. 3 - 5 days Sperling Ave. 2-A 5 7 5 1 1 . 3 3 1 9 8 1 1 . 5 - 2 days 3-A 5 5 5 1 0 . 3 0 ti 9 9 1 2 - 7 weeks 1-4 5 7 0 1 1 . 1 2 1 In. 9 9 2 . 5 In. 1 . 5 - 3 days » 2 - 2 573 1 1 . 6 5 1 9 5 6 cm 3 days » 2 - 3 6 0 5 1 2 . 0 4 n 9 5 1 3 days » 3 - 4 6 0 8 1 1 . 7 0 1 • 1 0 0 2 . 5 l a 1 . 5 - 3 weeks » 0 - 1 733 1 1 . 2 0 ti 9 0 1 3 - 4 days Lulu Island 0 - 2 7 4 0 11.28 11. 9 4 . 5 6 cm. 1 day to 2 . 5 months 1 0 - 3 9 6 0 1 4 . 1 0 n 9 8 1 1 1 all t e s ts on undisturbed samples except test 0 - 3 ; test 0 - 3 on remoulded sample. * calculated from equation ( 2 ) 55 shows a machine similar to that used fo r the other t e s t s . The load f o r the initial load increments varied from .063 kg/sq.cm to .25 kg/sq.cm. The load increment durations varied from one day to two and one-half months. The inten-tion of this variation was to determine the e f f e c t s of this variable on the rate of secondary consolidation. Void ratio-pressure relationship The theory of primary consolidation is based on the premise that f o r every void ratio there exists a particular effective pressure that can be supported by the soil skeleton. In soils that have large secondary compression, such as peat, the void ratio-pressure relationship is indeterminate since com-pression at constant effective pressure continues f o r an indefinite time. A. useful relationship f o r these types of soils is a plot of e^oo (the void ratio at 100 per cent primary con-solidation as defined by Casagrande's construction) versus the logarithm of total pressure. This plot will indicate, for a particular total load, the void ratio at which primary compres-sion is essentially completed. If the void ratio is less than e100 ^" o r a &iven load, settlement occurring under any load not greater than the given load, will consist essentially of secon-dary consolidation with only an insignificant amount of primary consolidation. 56 Two relationships should be considered at this point to justify the value of an e-^QQ-log pressure relationship. F i r s t , as mentioned previously, the void ratio as determined from the weight of dry solids is used as a convenience to indicate the possible potential consolidation. What is the e f f e c t on the e -log pressure curve if the void ratio is determined by 100 equation (4)? Second, what is the e f f e c t of secondary con-solidation on the ~^°S pressure relationship? If N is a constant during the consolidation test the e100 v s ^ curve would be essentially the same f o r equa-tion (4) or equation ( l ) ; that is both curves would be the same shape but the ordinate (e) would be to different scales. The scale factor would be as follows: e = V - Vs (1) Vs V - NVs . e» = v4; NVs from (1) and (4) V = NVs (e» + 1) = Vs (e + l ) E ' = IT + W ' 1 ( 1 8 ) But if N varies during the consolidation t e s t the e^QO vs log F curve obtained by using equation (l) would have slight irreg-ularities which would depend on the effective pressure and the time of application of all preceeding load increments. These 57 irregularities in the e^QO v s 1°6 ^ curve will be discussed later. Since, at present ( 1 9 6 3 ) , the value of N would be very difficult to determine the only practical void ratio is that which is. calculated by equation ( 1 ) . An approach similar to Taylor's (1942) idealized curves (see Figure 24), that give the change in the void ratio-log pressure curve considering the effects of secondary consoli-dation, will be discussed. Suppose, instead of the curves at one day, one month, etc., as given by Taylor, we consider curves at times in relation to the time ( t r p j ) required to reach the tangent intersection point (the intersection of the tangents in Casagrande's 100 per cent primary consolidation construction). The void ratio-log pressure curve f o r time = 10 t r p j m a y be constructed by subtracting (from the e^QO values) : Ae = Hs where Hs - height of dry solids in the consolidation ring Ae - the change in void ratio per log cycle due to secondary consolidation b - rate of secondary compression per one cycle of log time A similar curve f o r time = 100 may be constructed by subtraction of 2 A e from the ^-^00 ~1°£ pressure curve, see Figure 2 5 . The validity of these void ratio-pressure relation-ships and the extrapolation of experimental data to obtain the 57a Or o > - P R I M A d V 1.1 N S -IO - © A V L I N E . T E N - YEAZ. M N E . L O G figure 24 Semi-logarithmic plot of primary line and other compression lines - . : ; after Taylor (1942) 7 f 5 P £. R L I N G A V E - P £ A"T T E . S T 8 * INCH D l ^ . 3 - A ' . •* S I W C H T . O R I G I N A L - H T . Figure 25 Plot showing the effect of secondary consolidation on the e vs log P curve . 0 7 L O < 5 .1 .2 P R E S S U R E . K f l / c o » l .4- .7 58 curves will be discussed later. The e^QQ-log pressure relationships, as shown in Figures 26, 27 and 28, su'mmarize all the tests performed. Even though there was slight variation in initial void ratios and water contents (see Table I I I ) , the e^oo -log pressure relationships give very consistent results. This consistency is indicated by the similarity in shape of all the curves and the tendency of all points in any one tes t to plot as a smooth curve. There is a tendency, however, f o r the points that occur af t e r a' load increment of long duration to have lower void ratios (S-LOQ); f ° r example, the point at 1.0 kg/cm in test 0-2 and at 4.0 kg/cm in test 0 -3 . This trend to lower void ratios (e±oo) is also shown by comparing tests 1-A and 3-A; many of the points in t e s t 3-A. coincide with those of test 1-A, but due to higher initial void ratio and moisture content should have, a higher eJ_QQ. 5 9 12 10 B A i o \ > V •e \ t f • ; 1 i i V6 . • U pa P •. • . — \ _ . -tf H-mrru u * &" W " *WAR-S-6 x 1 - A ' ' . . 1-£ rf 3 - A . .:. ' . -£^-£>-' pA£ 2^ $ 53 t=ogu T&^-T OP Tuf r e ^ T -1 1 1 --— sr-iC2 . :ce> , , : l ' „ Figure 26 60 61 62 C o e f f i c i e n t of Secondary Compression The r a t e of secondary compression can be defined by two essentially similar c o e f f i c i e n t s , as follows: Cc( = —J2 (from Wahls, 1962) (19) H i n i t i a l b C = (from Miyakawa, i 9 6 0 ) (20) H t where Ce<and C s = c o e f f i c i e n t of secondary compression ^ i n i t i a l = the t o t a l initial height of the sample = the t o t a l height of the sample at the time b is measured b = r a t e of secondary compression per one cycle of log time In clays, due to smaller t o t a l deformations during a consoli-dation t e s t , the c o e f f i c i e n t o f secondary compression will be essentially the same i f calculated by either equation (19) or (20), but in peats where the height of sample changes si g n i f -icantly during the t e s t the c o e f f i c i e n t of secondary compres-sion calculated by these equations will vary g r e a t l y . Wahls presents his data as a plot of Ce( versus void r a t i o (e ^ o o ^ while Miyakawa plots log C g versus log p r e s s u r e . Since log pressure has nearly a linear relationship to void r a t i o (e ^ g o ) the abscissa of the two plots are similar, with a change in scale only. The advantage of plotting a log scale on the ordin-ate is t h a t values of a constant plus or minus percentage f r o m a given line plot as lines parallel to the given line; whereas in 63 a natural plot the constant plus or minus percentage would, plot as diverging or converging lines. Summaries of the coefficients of secondary compres-sion from all tests are shown in Figures 29, 30 and 31; these are plotted arid calculated by a method similar to Miyakawa's (see equation (20) above). The plot of Miyakawa's average values is shown on these plots as a basis f o r comparison of the test results. The conclusions, that can be derived from the log C -log pressure plots in Figures 29, 30 and 31 are as follows: 1. Although there is a slight scatter of values f o r the individual t e s t s , the trend is f o r higher C s values at • higher pressures. This trend is similar to that shown by Miyakawa. 2. A s suggested by Miyakawa (i960) and Wahls (1962), there is a sharp break in the log C g -log pressure curves at the preconsolidation pressure. The break in the C s curve may be seen in all tests that had loads below the preconsolidation pressure. 3. T e s t s with short load increment durations give unre-liable C s values. This is demonstrated by te s t 2-A where the rate of secondary compression has been determined from only two or three consolidation read-ings . 4. The comparison of Sperling Avenue Peat to Lulu Island Peat shows that variations in physical and chemical properties influence the value of the coeffic-ient of secondary compression; 5. Long durations of load increments appear to have little e f f e c t on the coefficient of secondary compression; except in the case of a long duration load increment preceded by short duration load increments. In this case, as shown by t e s t s 0-2-4, 0-3-5 and 3-4-4, C s tends to increase with time. 64 6. The values of C s show no definite trend due to the original height of the sample. To further - verify this independence of height, tests 1-4, 3-4, 1-A and 3-A have been replotted in Figures 32 and 33 by both Miyakawa's method and Wahl's method. On figure 32, it can be seen that most of the points vary from average values by less than plus or minus 20 per cent. These limits are shown by the dashed lines. 65 [Figure; 29 66 iFigure1 30 Figure 31 Figure 32 • tf 5 : 1 1 lj 1 1 I , L_J I £ i > O u> j o o O o • . © ~ 1.. .-XIZ~ [ Figure 33 70 C o e f f i c i e n t of Secondary Compression: Conclusions The t e s t s show a tr e n d in the relationship between the coef f i c i e n t of secondary compression and pressure, but other, variables t h a t could e f f e c t the ra t e of secondary consolidation have not been considered. Some of these variables are load increment r a t i o , past loading h i s t o r y , side f r i c t i o n and tem-perature. Two examples will be given to indicate t h a t the above variables can and do a f f e c t the r a t e of secondary con-solidation. F i r s t , as shown by t e s t 3-A-7 (as replotted in Figure 34) increasing the load by load increment ra t i o s of .01 and .02 causes no change in the ra t e of secondary consolidation, but an increase in the load by a load increment ra t i o of .04 causes a slight increase in the r a t e of secondary consolidation. Second, as shown by t e s t 3-A - 4 in -Figure 3 , a f t e r a change in temperature the r a t e of secondary compression changes; the side f r i c t i o n also depends on the temperature. Since the change in side f r i c t i o n is only equivalent to less than a 1.5 per cent change in the t o t a l load this e f f e c t would probably cause l i t t l e change in the ra t e of secondary consolidation. A change in the temperature r a t h e r than the actual temperature appears to be the cause of deviations in the r a t e of secon-dary consolidation. 70a Figure 34 Compression vs log time, test 3-A-7 C H A P T E R IX C U R V E - F I T T I N G AN D I N T E R P R E T A T I O N Introduction When the load in a saturated soil specimen is increased from P-j_ to Pg» the intergranular pressure increases to the new value only over a period of time, at a rate governed by hydrodynamic lag. When the intergranular pressure reaches Pg volume change continues in the form of secondary consol-idation at a decreasing rate such that, f o r many soils, one-dimensional settlement plots against log-time as a straight line. That this is actually the case f o r peat, has been shown by a great many laboratory t e s t s , with samples of various sizes and various types of peat, and field observations (Thompson • and Palmer, 1951; Lea and Brawner, 1959; Buisman, 1936; and Miyakawa, i 9 6 0 ) . In order to separate the primary (hydrodynamic) consolidation from the secondary consolidation, Terzaghi's theoretical primary consolidation curve has to be fi t t e d to the observed curve. Logarithmic and square-root fitting methods are mainly used; many variations of these fitting methods have been suggested by Naylor and Doran (1948), Matlock and Dawson (1952), Hansen (1961), L o (1961), and Wahls (1962). The earlier methods assumed that there was virtually 72 no secondary consolidation proceeding during the f i r s t 90 per cent of primary s e t t l e m e n t . T h a t is to say, they assumed t h a t the secondary curve f o r P^ r e s t a r t e d f r o m time zero at the application of Pg, was sensibly horizontal during early primary consolidation, in the manner discussed in C h a p t e r V I I when n is less than z e r o . However, with peat, where secon-dary consolidation is so large, this is not good enough. A. f i t -t ing method must be devised which will separate the secondary consolidation corresponding t o the intergranular p r essure (somewhere between P^ _ and Pg) which is acting a t any time during primary consolidation, f r o m the primary consolidation. Wahls (1962) describes a c u r v e - f i t t i n g procedure, based on the primary consolidation conforming to Terzaghi's equation and secondary as a s t r a i g h t line on a semi-log plot, t h a t will separate the t o t a l consolidation curve into a primary and a secondary curve. A graphical modification of Wahls 1 procedure is suggested here f o r deriving the secondary curve if the p r i -mary consolidation does not conform to Terzaghi's equation. S e p a r a t i o n of P r i m a r y and Secondary Consolidation by a Graphical Method  T h i s graphic method may be used f o r Wahls' type I consolidation curves (see F i g u r e 35a), but t h e r e is doubt as to i t s applicability f o r Wahls' type I I consolidation curves (see F i g u r e 35b). F o r t e s t s with small load increment r a t i o s , 72a i~cc&zx\W/< OFT-— a) Type I curve S-^Ct AEUTHAA C?p T..v.:.r-ib) Type II curve 1 Figure 35 Types of compression versus logarithm of time curves Ct. / A &-p b./A tZ-TI Figure 36 Time factor, T^, versus V ^ R j j (from Wahls, 1962) Figure 37 Curve showing primary and secondary compression 73 as can be seen f r o m the replot of t e s t 3-A-7 in F i g u r e 34, it is impossible to determine, f r o m the geometry of the con-solidation plot, the end of primary consolidation or to d e t e r -mine if any primary consolidation has actually o c c u r r e d . R e s u l t s of t e s t 3-A—3 will be used to demonstrate the graphical separation of the primary and secondary curves f r o m the t o t a l consolidation curve. The method is as follows: T he experimental curve and graphical c o n s t r u c t i o n are shown in F i g u r e 38. 1. F i n d c o r r e c t e d zero ( R s ) by a separate plot of R versus square r o o t time ( t ) . A separate plot is required since inconsistent r e s u l t s are obtained by using the log t plot. 2. F i n d the tangent i n t e r c e p t point (Rrpj) by C a s a -grande's c o n s t r u c t i o n . T h i s is supposed to indicate the 100 per cent primary consolidation reading; but, usually, this point does not correspond to the time a t which primary con-solidation is completed. 3. Calculate A R m T = R - R T I T I s 4. Calculate R M = K s + 1, A ^ T I a n o - ^ i n d f r o m the 2 experimental curve the corresponding time coordinate, t ^ . 5. Determine the slope (b) of the secondary curve. 6. F i n d the time f a c t o r T M corresponding t o tjy[. Since t h i s is the f i r s t approximation, T M = .197 (derived f r o m the t h e o r e t i c a l equation) may be used. I f the primary 73a L O G ' T I M E . ( M l N . )-Z 4 7 10 4-0 . 7 o i o ' C O M F R E - S S I O M 3-A.-S-I-.45 f -•50; — R-> tS.E'4-'&«"CC.A1P PT .^V-.r. ".SECOHOft.RV.T.c u.ay £ °" JT=.?r..8 > r—o-R s - ' l • IS .2.1 . .. I : R i « . na . : ; .. R . « . 4-<=>2.;'"" "~':".-r. R M » I 7 Z -.-42.?.= . 352 . b = . O S 7 ... i n ' -—1—— — 1 ~ ; • • X .1 1 \ • | \ 1-\ •t \ 1 1 > i . \ K D M > L 0 l ! \ \ 1 i I X, r ~ l \ PRIMARY CONSOLTPAXION T '! ..THC0fc.E.TlCAl-' . CURV/S.". . FIMT. AP^»*iMA-rTaN: v "AND v Figure'38 Graphical method for separation of G -3E-tO*i C^PPR.tfKlMA-nO'W ' 1.0-primary and secondary consolidation 74 consolidation conforms to Terzaghi's equation then a one step fitting is possible using Wahls' curves in Figure 36 to find Tjyj. These curves- give T-^ f o r many ratios of b/ A ^ T I * 7. Tabulate, as in Table IV, per cent consolidation (U) and the corresponding time ( t ^ ) ; these values are obtained from Terzaghi's equation. 8. Construct, as in Figure 38, the average slopes of the secondary consolidation between the tabulated times t^-j. A s stated above the slope of the secondary curve is directly proportional to the primary consolidation completed. 9. Starting from t^g on the secondary curve draw a line of the average slope to t^Q, from t draw the average slope to tgQ, etc. Continue construction of the secondary curve through all tabulated points. The curve constructed is a f i r s t approximation of the consolidation due to secondary e f f e c t s . 10. Construct a primary curve directly below the experimental curve by plotting values of d (d defined as shown in Figure 37). If A R is the total primary compres-P sion due to the load increment and g the primary compres-sion completed at any time. Now we will prove that R = A R - d & P P P Then as shown in Figure 37, where £ s is the secondary 75 T A B L E IV C A L C U L A T I O N O F t V A L U E S F O R F I R S T T R I A L O F C U R V E F I T T I N G u T t .99 2.0 454 .93 1.0 227 .9 .848 190, .8 .576 126 .7 .403, 90 .6 .287 64 .5 .197 ' 44 .4 .126 28 .298 .07 15.6 .225 .04 8.9 .160 .02 4.5 .111 .01 2.3 .095 .007 1.6 .050 .004 .9 76 compression completed at any time and d^_ = j f g we may write the relationship d + d. - s p t s d P P Thus Figure 38 gives a f i r s t approximately of the primary compression. curve repeat 8 and 9 but instead of the theoretical equation use the curve constructed in 10 f o r the relation between U and t-Q. This can be done by constructing the per cent con-solidation scale on the primary curve. Then using the same slopes as in 8 and the new values of t-y construct a corrected secondary curve. 12. Primary curve is constructed by the same method as described in 10. 13. There should be no need f o r a third approximation. Conclusions Terzaghi's theoretical curve has been f i t t e d at t^Q on the primary curve obtained from the above construction, in Figure 38. The discrepancy between the experimental and the theoretical curve could be caused by the following: 11. F o r the second approximation of the secondary 77 1. L a r g e variations in permeability during the load increment. 2. Boundary conditions applied to Terzaghi's equation are not considered t o be valid f o r peat as large axial s t r a i n s indicate a moving boundary (S h r o e d e r and Wilson, 1962). -As mentioned in C h a p t e r I, the e f f e c t of the moving boundary is probably negligible. 3. S i d e - f r i c t i o n varies during the load increment since it is a f u n c t i o n of the intergranular p r e s s u r e . T h i s will cause variation in the average load during the load increment. C H A P T E R X P O S S I B L E F U T U R E R E S E A R C H T O P I C S The object of this thesis was to determine if the stan-dard consolidation tests are applicable f o r the testing of peat. The tests performed were in the nature of pilot t e s t s ; many more such tests are required in order to develop standard testing techniques f o r peats. This chapter will outline some of the possible future test programs that would be useful fo r continuing the research of peat consolidation. Permeability A study of the ef f e c t on the consolidation process of large changes in permeability during consolidation; such research could include the following: - Relate the permeability determined from the direct method, through bottom porous stone, to the permeability deter-mined by the pore pressure probe at different points in the sample and the permeability as calculated from con-solidation data. - Determine the effect on the permeability of varying the load increment ratio, duration of the load increment, and temperature. - Derive by an iteration procedure, similar to that used by •-79 Moran e t . a l . (1958) f o r s a t u r a t i o n , a t h e o r e t i c a l con-solidation versus time curve t h a t would r e s u l t if perm-eability varied during consolidation. P o r e pressure measurement with'a probe The probe method of pore pressure measurement is desirable f o r peat consolidation t e s t s since a double drainage t e s t allows primary consolidation to be more quickly completed, and is t h e r e f o r e p r e f e r r e d . A probe with higher sen s i t i v i t y than t h a t of the probe previously described is needed. R e s e a r c h could include the following: - Derive a relationship between the r a t e of movement of the null point and the pore pressure if t h e r e were no movement. - Measure pore p r e s s u r e s at d i f f e r e n t points in the sam-ple during consolidation. - Determine the e f f e c t on the r a t e of pore pressure d i s -sipation caused by a change in the permeability during consolidation. Secondary Consolidation P e r f o r m t e s t s to determine whether the compression versus log time curve will t u r n downwards if a load increment is l e f t on f o r a longer period of time than the previous load increments. T h i s downward t r e n d would indicate t h a t , as 80 s t a t e d by Buisman (1942), the ultimate r a t e of secondary settlement is the sum of the r a t e s of all the preceding secon-dary compressions. A l s o determine the e f f e c t on secondary compression r a t e of various load increment r a t i o s , load increment durations, and t e m p e r a t u r e s . C H A P T E R XI SUMMARY O F C O N C L U S I O N S This chapter will summarize the conclusions from all sections of the thesis. T e s t Procedures: The consolidation test procedures for peats may be similar to those used f o r testing clays, but the e f f e c t s of the large strains, permeability variation, secon-dary consolidation and side friction must be considered when determining experimental procedure and when specifying t e s t -ing equipment. Void Ratio: A rational expression for void ratio (e = V - NVs ^ which defines "voids" as spaces occupied by NVs mobile pore water is given in Chapter I I . This definition of void ratio is useful f o r the evaluation of permeability variation and interpretation of the consolidation process. Permeability: T e s t s indicate that there are large permeability changes in a peat stratum during consolidation. These large variations indicate that the peat particles change shape and size during consolidation. Pore pressure: The dissipation of excess pore pres-sure, during the consolidation of the peats tested, does not 82 conform to the. theoretical rate of dissipation, but dissipation rate was similar f o r all t e s t s . This similarity could be due to the time lag of the pore pressure measuring apparatus. Therefore it would be necessary to measure the pore pres-sure with other types of apparatus before definite conclusions may be reached. The measurement of pore pressure during secondary consolidation requires a more sensitive pore pressure probe or the method outlined in Chapter V may be used to give an approximate value of pore pressure. Side friction: The degree of f i t influences the mag-nitude of the side friction; an "optimum f i t " gives lower values of side friction than a "tight f i t " . Lubrication of the consolidation ring results in a significant reduction of side frict i o n . Side friction increases during a long duration load increment. An understanding of the effects and magnitude of side friction is required f o r the interpretation of consolidation t e s t s . I f the magnitude of side friction remained constant during a load increment there would be no problem. But f r i c -tion varies with effective stress, which changes during p r i -mary compression; this gives rise to changes in the average net load during the load increment. The best solution to 83 the problem is to eliminate or reduce to insignificance the magnitude of the side f r i c t i o n . C o e f f i c i e n t of Secondary Compression: The t e s t s show a trend in the relationship between the co e f f i c i e n t of secondary compression and pressure, but other variables t h a t could e f f e c t the r a t e of secondary consolidation have not been considered. Some of these variables are load increment r a t i o , past loading h i s t o r y , side f r i c t i o n and temperature. Two examples are given t o indicate that the above variables can and do a f f e c t the r a t e of secondary consolidation. A change in the temperature r a t h e r than the actual temperature appears to be the cause of deviations in the r a t e of secondary com-pression . C u r v e - f i t t i n g and I n t e r p r e t a t i o n : The discrepancy between the experimental and Terzaghi's theoretical consol-idation curve could be caused by the following: 1. L a r g e variations in permeability during the load increment. 2. Boundary conditions applied t o Terzaghi's equation are not considered to be valid f o r peat as .large axial s t r a i n s indicate a moving boundary (Shroeder and Wilson, 1962). A s mentioned in Chapter I , the e f f e c t of the moving boundary is probably negligible. 84 3. Side friction varies during the load increment since it is a function of. the intergranular pressure. This will cause variation in the average load during the load increment. N O T A T I O N 86 N O T A T I O N A - cross sectional area a v - coefficient of compressibility (cf. Taylor, 194-8, p. 225) A s - ash content b - rate of secondary compression per one cycle of log time C - constant C-^ - log cycles past a particular point C s - coefficient of secondary compression Co( - coefficient of secondary compression c v - coefficient of consolidation d - diameter of the consolidation ring d - primary consolidation as defined in Figure 37 d s - secondary consolidation as defined in Figure 37 e - void ratio e100 ~ v°id ratio at 100 per cent primary consolidation, as defined by Casagrande's construction F - total side friction transmitted to the consolidation ring f - side friction coefficient, which is the produce of the coefficient of lateral pressure and the coefficient of friction f ( t ) - function of t G - specific gravity of soil solids H - total height of the sample 87 Hs - height of dry solids in the consolidation ring H-f. - the total height of the sample at the time b is measured ^initial ~ ^ n e total initial height of the sample H ^ Q - sample depth, from mid point to drainage face f o r double drained tests or total depth f o r single drained samples, at 50 per cent consolidation H ^ Q Q - same as above but at 100 per cent primary consol-idation- as defined by Casagrande's construction h|_ - head loss between pore pressure and the pressure being maintained in the probe i - imposed gradient K - k £ •n - rate of flow per unit of pressure Kp - probe constant K Q - l / C S - shape factor of pores Krp - tortuosity factor of pores k - coefficient of permeability N - the ratio of the weight of oven dry solids and com-bined water to the weight of oven dry solids N - per cent of slope -b (Chapter V I I ) n - porosity n - distribution factor (approximately =.5), Chapter V I n - variable (Chapter V I I ) P - total applied load P ^ - total pressure of the previous load increment P o - total pressure of the present load increment 88 p1 - error in balancing pressure q - rate of flow R - compression reading (Chapter IX) Rjyj- - compression reading, as defined in Figure 37 R r p j - compression reading at the tangent intercept point R 0 - corrected zero reading r 1 - inside radius of the probe o S - saturation S' - coefficient governed by the shape of flow net at the probe tip S Q surface area of voids wetted by flowing fluid/unit volume of solids, called specific surface S.G. - specific gravity T - time fa c t o r Tjyj- - time factor f o r 50 per cent consolidation as given by Wahls (1962) see Figure 36 t - time tj-Q - time at 50 per cent consolidation, see Figure 37 tjj - time at U per cent consolidation tgo> tgQ, etc. - time at 90, 80, etc., per cent consolidation U - consolidation ratio from Terzaghi's equation V - measured volume of the soil V s - volume of soil solids Ws - weight of oven dried soil solids w - moisture content 89 y - unit weight of fluid irw - unit weight of water n - coefficient of viscosity &e - change in void ratio ^v- - increment of applied stress /\Fjyj - change in maximum friction force for the load, increment A P - additional load A R i p i - consolidation to tangent intercept point, as defined in Figure 37 A R p - total primary compression due to the load increment A r - movement of the null point gp - primary compression at any time, as defined in Figure 37 - secondary compression at any time, as defined in Figure 37 R E F E R E N C E S 91 R E F E R E N C E S Berry, L . 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D e p t . o f t h e N a v y , B u r e a u o f Y a r d s and. D o c k s . N a y l o r , A . H . and I . G . D o r a n (1948). " P r e c i s e D e t e r m i n -a t i o n o f P r i m a r y C o n s o l i d a t i o n . " P r o c e e d i n g s , S e c o n d I . C . S . M . F . E . , R o t t e r d a m , V o l . 1, p . 34. R a d f o r t h , N . W . (1952). " S u g g e s t e d C l a s s i f i c a t i o n o f M u s k e g f o r t h e E n g i n e e r . " T h e E n g i n e e r i n g J o u r n a l , V o l . 35, N o . 11, p p . 1194-1210. 93 Scheidegger, A . E . ( i 9 6 0 ) . The Physics of Flow Through, a  Porous Media. University of Toronto Press. Shroeder, J . and N.E.' Wilson (1962). "The Analysis of Secondary Consolidation of Peat." Proceedings Eighth Muskeg Research Conference, National Research Council of Canada, A.C.S.S.M. Tech. Memo. 74, Ottawa. Taylor, D .W. (1942). "Research on Consolidation of Clays." Serial 82, Dept. of Civil and Sanitary Engineering, Mass. Inst, of Tech., Cambridge, Mass. , (1948). Fundamentals of Soil Mechanics. John Wiley and Sons, Inc., New York. Terzaghi, K. (1925). "Principles of Soil Mechanics: IV, Settlement and Consolidation of Clay." Engineering  News Record, Vol. 95, No. 22, p. 847. Thompson, J . B . and L.A. Palmer (1951). "Report on Consolidation T e s t s with Peat." A S T M Spec. Tech. Pub. No. 126, p. 4. Wahls, H.E. (1962). "Analysis of Primary and Secondary Consolidation," Journal of the Soil Mechanics and  Foundation Division, A S C E , Vol. 88, No. SM6, Proceedings Paper 3373. Whitman, R.V., A.M. Richardson and K.A. Healy (1961). "Time-Lags in Pore Pressure Measurements," Proceedings , F i f t h I .C . S .M ,F .E . , . Paris , Vol. 1. P H O T O S U P P L E M E N T 95 a) H o r i z o n t a l s e c t i o n s p l i t a long bedding plane b) V e r t i c a l s e c t i o n c u t w i t h k n i f e , bedding planes r u n l e f t t o r i g h t c ) H o r i z o n t a l s e c t i o n showing r o o t holes F i g u r e 39 C o l o u r pho tog raphs o f S p e r l i n g A v e n u e P e a t ( same sca le f o r al l p h o t o g r a p h s ) 96 Figure 40 Consolidation machine with 6000 lb. capacity at the loading head 1- counter weight 2- counter weight height adjustment 3- fulcrum adjustment (see Figure 41) 4- load pan Figure 41 Fulcrum adjustment 1- knife edge 2- load lever 10:1 3- wheel f o r fulcrum adjust-ment 4- threaded lead screw Figure 42 Side friction weighing apparatus in position on consolidation machine 1- adjustment for raising entire side fricition apparatus 2- proving ring 3- adjustment f o r ring supports 4- compression dial gauge 5- consolidation ring, 8 inches in diameter 97 Figure 43 Consolidation t e s t in pro-gress 1- pore pressure panel 2 - mercury manometer 3- weights on pan 4- plastic bag of water around the sample Figure 44 Pore pressure probe 1- water inlet at tip 2 - washer to keep sample from squeezing into the porous stone 3- fitting screwed into loading head 4- O-ring 5- seal cap 6- valve 7 - null point 8 - calibrated capillary tube 9 - fitting f o r tubing to man-ometer Figure 45 Pore pressure probe in position through the load-ing head and porous stone legend same as Figure 44 10- loading head 11- porous stone 98 Figure 1+6 Pore pressure probe in sample during test 1 - probe apparatus 2- Soil T e s t PP-25, pore pressure panel 3- manometer 4- plastic bag of water Figure 47 Consolidation ring show-ing pore pressure probe and thermometer in position 1 - pore pressure probe 2- thermometer Figure 48 Consolidation ring and porous stones (8 inches diameter) 1 - loading plate 2- top porous stone 3- consolidation ring 4- bottom porous stone Figure 49 Shear machine used to determine the coeffic-ient of friction between peat and brass 99 F i g u r e 50 L a t h f o r c u t t i n g 8 inch d i a -m e t e r samples 1- adjus table s t r a i g h t edges 2 - h a c k s a w w i t h blade sha rpened t o a k n i f e edge 3- r o t a t i n g t a b l e , 7.96 inches d i a m e t e r in o r d e r t o give c l e a r ance f o r blade F i g u r e 51 L a t h f o r c u t t i n g 2 . 5 inch and 6 c m . d i a m e t e r samples 1- ad jus table s t r a i g h t edges 2 - h a c k s a w w i t h blade sha rpened t o a k n i f e edge 3- pea t sample 4- r o t a t i n g t ab l e 5 - t o p b lock t o s t e a d y sample du r ing t r i m m i n g F i g u r e 52 C o n s o l i d a t i o n machine u s e d f o r sma l l t e s t s C O M P R E S S I O N V E R S U S L O G T I M E C U R V E S F O R T E S T S IN S P E R L I N G A V E N U E P E A T AND L U L U I S L A N D P E A T X^OCA T\M&>~ M I N U T E ^ .2 .4 .7 vo UO- . iw. 1 U(cux>) 1 u. 1 - A - O 1 - A - V. 4.067 4. 3o3> ~4Tf»>& 9.7 5 S>. &4 To3 4 • \-A--4 4.7fo& . a o?i 4.22>fc> &-77 r - A - 4 - -Si*-? 7" 6 2 &.44~ .0Z50 - .1 - A - S s I T A - 4e .S>l 1 /2 r 2.e>lS> io5r2<& - 1 • A . - 7 .4<bfe ^ . 4 ^ 1 ' 4-S'Z. .CT7<b .03.(4- .-t T E S T 1 — A - ca.hh?zj^j\ou Y £ i^oc 10" lc>4 . 2 .4 -7 i-<? t .2 | L<3Ai? u o i I i. t i -2-A-O L ! 1 4.874 j i r . l& f .o&ee, \.oo\'s. 1 • \z>oe? . 4,717 4.7&7 i leas' | .oi~[ 1.0S&7 4,'2fo7 . <5>o\ 3.kS>4 \s-1^fl i &45> 1-114 •;-oso2 -• 3S>5 3.1*7 i 7.0O-. { .o&3 j .o€fcie> 1.93 3-51 ' -2' 23'2 | 4 . e o j :o7t ] -o^ i & -~f~ [ • i " T E ST 2 ~A < 2 O M I ^ £ - ^ ' | £ ^ J u?c- -fiM&" o <2 H i IKJ • ItJ . 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