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Sources and receivers with the seismic cone test Laing, Nancy Louise 1985

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SOURCES AND RECEIVERS WITH THE SEISMIC CONE TEST by NANCY LOUISE LAING B . A . S c , The U n i v e r s i t y of B r i t i s h Columbia, 1983 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of C i v i l Engineering We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June 1985 © Nancy Louise La ing , 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of I C ^ ' A - g e ^ / ^ The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date M / DE-6 (3/81) i i ABSTRACT D i f f e ren t types of sources and rece ivers used with the seismic cone penetrat ion t e s t were i n v e s t i g a t e d . The sources inves t iga ted were mechanical shear and compression wave sources c o n s i s t i n g of a hammer-and-weighted-plank source; an on-shore Buf fa lo gun source u t i l i z i n g shotgun s h e l l s ; an o f f - shore seismic cap source; and an o f f - s h o r e embedded blade with seismic cap source. The rece ivers invest igated were hor i zonta l and v e r t i c a l geophones and accelerometers. The hammer shear source used prev ious ly with the seismic cone (Rice , 1984), was used as a standard f o r comparison. The hammer P-wave source was not used success fu l l y with the seismic cone, because the v e r t i c a l rece ivers used in the cone do not represent the s o i l response and thus can not be used with any source, and because the amplitude of the P-waves produced by the source was not large enough to detect on the hor izonta l r e c e i v e r s . The Buf fa lo gun source d id not give repeatable or accurate shear wave v e l o c i t i e s fo r depths l e s s than 12 meters, but d id appear repeatable and accurate below 12 meters. The seismic cap sources i n c l u d i n g the embedded blade source were found to give reasonable shear wave v e l o c i t i e s and reasonable compression wave v e l o c i t i e s i f the depth at which the seismic cap was f i r e d was kept constant . Both hor izonta l geophones and accelerometers were found to give s i m i l a r shear wave v e l o c i t i e s fo r the hammer shear source, but f o r the Buf fa lo gun source the accelerometers give d i f f e r i n g r e s u l t s from the geophones probably because of a var iab le phase s h i f t assoc ia ted with the f i l t e r i n g of the accelerometer. V e r t i c a l rece ivers were not success fu l l y used with the seismic cone because they do not give a response representat ive of the s o i l response, because of the v e r t i c a l s t i f f n e s s of the cone and rods. The use of compression and shear wave v e l o c i t i e s to determine Po isson ' r a t i o gave reasonable resu l t s i f the s t r a i n l eve l and type of compression wave were taken in to account. A pre l iminary determination of the material damping r a t i o gave r e s u l t s whtich were higher than expected, probably i n d i c a t i n g the seismic wave rece ive rs were responding to the cone-so i l system, rather than to the s o i l a lone . i v TABLE OF CONTENTS Abstract i i Table of Contents 1v L i s t of F igures v i i Acknowledgements x 1. Introduct ion 1 2. Seismic Wave Theory and Conventional In S i tu Methods.. 3 2.1 Introduction . . . . 3 2.2 Types of Seismic Waves and The i r C h a r a c t e r i s t i c s 3 2.3 Seismic Wave V e l o c i t i e s and the E l a s t i c Moduli 8 2.3.1 Development of E l a s t i c Moduli 8 2.3.2 C a l c u l a t i n g Seismic Wave V e l o c i t i e s 11 2.4 Conventional In S i t u Methods f o r Seismic Measurement 13 3. Equipment and Procedures 16 3.1 Introduct ion 16 3.2 The Seismic Cone Penetrometer . . . 16 3.3 Seismic Wave Sources and Related T r igger ing Systems 19 3.3.1 Introduct ion 19 3.3.2 Mechanical Sources 21 3.3.3 Tr igger ing System fo r the Mechanical Sources 22 3.3.4 On-Shore Explos ive Source 22 3.3.5 Tr igger ing System f o r the On-Shore Explos ive Source 25 3.3.6 Off-Shore Explos ive Sources 27 3.3.7 Tr igger ing System f o r the Off-Shore Explos ive Sources 29 3.4 Seismic Wave Detect ion and Recording 29 3.4.1 Introduct ion 29 3.4.2 Geophones 32 3.4.3 Accelerometers . .34 3.4.4 Signal F i l t e r i n g 37 3.4.5 Recording Osc i l l oscope 43 3.5 F i e l d Procedures 44 V 4. F i e l d Invest igat ions 48 4.1 McDonalds Farm S i t e 48 4.2 Beaufort Sea S i tes 49 4.2.1 Schoolhouse S i t e 49 4.2.2 Swimming Po int S i t e 51 4.2.3 Richards Is land S i t e 51 4.2.4 TuktOyaktuk Harbour S i t e 52 5. Eva luat ion of D i f f e r e n t Sources 53 5.1 Evaluat ion of the Mechanical Sources 53 5.1.1 Hammer Shear Wave Source 53 5.1.2 Hammer P-wave Source 53 5.2 On-Shore Explosive Source 56 5.3 Off-Shore Explosive Sources . .62 5.3.1 Seismic Cap Source 62 5.3.2 Embedded Blade with Seismic Cap Source 64 5.4 Comparison of D i f f e r e n t Sources . . . . . 6 8 5.4.1 Buffa lo Gun Source versus Hammer Shear Wave Source 68 5.4.2 Seismic Cap Source versus Hammer Shear Wave Source 72 5.4.3 Embedded Blade Source versus Seismic Cap Source ..72 6. Eva luat ion of D i f f e r e n t Seismic Receivers 76 6.1 Geophones versus Accelerometers 76 6.2 Horizontal versus V e r t i c a l Receivers 81 7. Eva luat ion of Compression Wave Data 85 8. Eva luat ion of Damping C h a r a c t e r i s t i c s 89 8.1 Introduct ion 89 8.2 Accelerometers to obtain S o i l Damping 89 8.3 Waveform Ana lys i s to determine S o i l Damping 92 8.3.1 Results of Manual Waveform A n a l y s i s 93 vi 9. Conclusions 96 References 99 Appendix A 102 v i i LIST OF FIGURES 2.1 Charac te r i s t i c s of a Compression Wave 5 2.2 Charac te r i s t i c s of a Shear Wave 6 2.3 P a r t i t i o n of E l a s t i c Wave at Inter face between Two E l a s t i c Media 7 2.4 Schematic View of the Radiat ion Pattern of a V e r t i c a l and Horizontal Surface Point Source 9 2.5 Determination of Seismic Wave V e l o c i t y 12 2.6 Conventional In S i tu Methods f o r Seismic Measurement.. 14 3.1 15 sq . cm Seismic Cone Penetrometer 17 3.2 10 s q . cm Seismic Cone Penetrometer . .18 3.3 CPT Seismic Equipment Layout f o r Mechanical S o u r c e s . . . . 20 3.4 E l e c t r i c a l Step T r igger C i r c u i t fo r Hammer Source . . . 2 3 3.5 Buf fa lo Gun and i t s Operation 24 3.6 Tr igger ing Systems fo r Bu f fa lo Gun Source 26 3.7 Geophone Tr igger Response to Bu f fa lo Gun Source 28 3.8 Operation of Seismic Cap Source 30 3.9 Schematic of Mass-spring Type of V ibrat ion-measur ing Transducer 31 3.10 Schematic of Geophone 33 3.11 Geophone S p e c i f i c a t i o n s 35 3.12 Schematic of Strain-gage Acclerometer 36 3.13 Unamplif ied and Ampl i f ied Accelerometer Responses 38 3.14 F i l t e r e d and U n f i l t e r e d Accelerometer Responses 39 3.15 Attenuation and Phase S h i f t C h a r a c t e r i s t i c s of the Low Pass F i l t e r s . . 4 1 3.16 E f f e c t of D i f f e r e n t F i l t e r Cu t -o f f Frequencies on Accelerometer Response 42 3.17 Schematic of the E l e c t r o n i c s Set-up f o r Seismic Test ing 45 4.1 Location Map for Beaufort Sea S i t e s 50 vi i i 5.1 Horizontal Geophone Response P r o f i l e f o r Hammer Shear Source 54 5.2 V e r t i c a l Accelerometer Response to Hammer P-Wave S o u r c e . . . . 55 5.3 Horizontal Accelerometer Response to Hammer P-Wave Source 57 5.4 Horizontal Accelerometer-Response P r o f i l e f o r Buf fa lo Gun 58 5.5 V a r i a t i o n of Accelerometer Response with P o s i t i o n of Buf fa lo Gun Source 60 5.6 Comparison of Shear Wave V e l o c i t y P r o f i l e s from Buf fa lo Gun S o u r c e . . . . 6 1 5.7 Comparison between True and Pseudo Interval Measurement 63 5.8 Horizontal Geophone P r o f i l e Response f o r Seismic Cap Source f i r e d j u s t below Ice 65 5.9 Comparison of Shear Wave V e l o c i t y P r o f i l e s f o r the Seismic Cap Source f i r e d j u s t below Ice at Swimming Po int S i t e 66 5.10 Horizontal Geophone Response P r o f i l e f o r Seismic Cap Source f i r e d at Mudline 67 5.11 Horizontal Geophone Response P r o f i l e f o r Embedded Blade Source 69 5.12 Shear Wave Ve loc i t y P r o f i l e s from the Horizontal Accelerometer f o r Hammer and Buf fa lo Bun Sources 70 5.13 Shear Wave V e l o c i t y P r o f i l e s from the Horizontal Geophone fo r Hammer and Buf fa lo Gun Sources 71 5.14 Shear Wave V e l o c i t y P r o f i l e s f o r Hammer and Seismic Cap Sources 73 5.15 Shear Wave Ve loc i ty P r o f i l e s f o r Seismic Cap Source f i r e d j u s t below Ice and at Mudline 74 5.16 Seismic Wave V e l o c i t y P r o f i l e s f o r Embedded Blade and Seismic Cap Sources 75 6.1 Hor izontal Geophone and Accelerometer Responses to Hammer Shear Source 77 6.2 Horizontal Geophone and Accelerometer Responses to the Buf fa lo Gun Source 79 6.3 Shear Wave Ve loc i t y P r o f i l e s from the Horizontal Geophone and Accelerometer fo r the Hammer and Buf fa lo Gun Sources 80 6.4 Hor izontal Geophone Response to the Seismic Cap Source f i r e d j u s t below Ice 82 6.5 V e r t i c a l Geophone Response P r o f i l e f o r Seismic Cap Source 84 ix 7.1 Ca l cu la ted Po lsson 's Ratios f o r School house S i te a) Depth 0 to 15 meters 86 b) Depth 15 to 30 meters 87 7.2 Ca lcu la ted Po isson 's Ratios fo r Tuktoyaktuk Harbour S i t e 88 8.1 D e f i n i t i o n of Log Decrement from Horizontal Accelerometer Response to Hammer Shear Source 90 8.2 Damping Rat ios from Accelerometer Response versus Depth 91 8.3 Geophone Waveforms de f in ing Quant i t i es f o r Damping C a l c u l a t i o n 94 8.4 Damping Rat ios from Manual Waveform A n a l y s i s versus Depth 95 ACKNOWLEDGEMENTS x I wou ld l i k e to e x p r e s s my s i n c e r e t h ank s t o D r . Campane l l a f o r h i s s u p p o r t , s u g g e s t i o n s and g u i d a n c e t h r o u g h o u t t h e c o u r s e o f t h i s s t u d y . Many t h a n k s , a l s o , t o D r . R o b e r t s o n , whose a s s i s t a n c e and s u g g e s t i o n s were i n v a l u a b l e . S p e c i a l t h ank s t o Mr . Don G i l l e s p i e and Mr . John Howie f o r t h e i r h e l p i n t he f i e l d and w i t h a n a l y s i s and f o r t h e i r c r i t i c a l comments on t he t e x t . The p r o j e c t wou ld no t have been p o s s i b l e w i t h o u t t h e f i n e t e c h n i c a l s u p p o r t and workmansh ip o f Me s s e r s A r t B r o o k e s , G l e n n J o l l y , and D i c k P o s t g a t e . The a s s i s t a n c e o f M r . P e t e r Brown, Mr . B ruce O ' N e i l l and Mr . M i k e D a v i e s i n t h e f i e l d i s a p p r e c i a t e d . S p e c i a l t h a n k s t o Mr . J i m G r e i g f o r h i s h e l p w i t h c ompu t e r s . I wou ld l i k e t o thank t he G e o l o g i c a l Su r vey o f Canada and Dr . J . A . H u n t e r , Head, S e i s m i c Method S e c t i o n , f o r p r o v i d i n g t h e In S i t u T e s t i n g Group a t U .B .C . w i t h t he o p p o r t u n i t y t o p e r f o r m s e i s m i c cone t e s t i n g o f f -s h o r e . The h e l p o f Dr . P . J . K u r f u r s t , Mr . N i x o n , and Mr . B. Gagne o f t h e G . S . C . w h i l e i n t h e B e a u f o r t was g r e a t l y a p p r e c i a t e d . F i n a n c i a l s u p p o r t f r om N a t u r a l S c i e n c e s and E n g i n e e r i n g Re s ea r c h C o u n c i l o f Canada and Ene rgy , M ines and R e s o u r c e s , Canada i s g r a t e f u l l y a c know l edged . L a s t l y , v e r y s p e c i a l t h ank s go t o my husband , Doug, f o r h i s s u p p o r t and h e l p w i t h p r e s e n t a t i o n . 1. INTRODUCTION 1 In recent y e a r s , the study of s o i l dynamics has been assuming an Increas ingly important ro l e in geotechnical engineer ing s i t e i n v e s t i g a t i o n s . So i l dynamics i s used to analyze and design f o r dynamic loading of s o i l s , which inc lude earthquakes, ocean waves, and v i b r a t i n g machinery. As dynamic ana lys i s of s o i l s becomes more complex, more accurate dynamic s o i l parameters are necessary. Small s t r a i n dynamic e l a s t i c moduli o f a s o i l can be determined i f s o i l density and compression and shear wave v e l o c i t i e s in the s o i l are known. At present, the downhole and crosshole seismic t e s t i n g methods are used, most commonly, f o r determining in s i t u compression and shear wave v e l o c i t i e s . These methods may be c o s t l y and time consuming, because they invo lve the d r i l l i n g and cas ing of one or more boreholes . The seismic cone penetrat ion t e s t i s a r e l a t i v e l y new technique fo r determining i n s i t u compression and shear wave v e l o c i t i e s . This technique i s being inves t iga ted at U . B . C . , a n d was f i r s t researched by Rice (1984). Rice found that the seismic cone penetrat ion t e s t "can provide a r a p i d , accurate assessment of shear moduli at s i t e s where cone penetrat ion can be c a r r i e d out ." Rice a l so found the seismic cone penetrat ion t e s t to have d i s t i n c t advantages over the downhole and crosshole t e s t methods, because i t was f a s t e r and needed only one uncased t e s t h o l e . The main ob jec t i ve of t h i s t h e s i s was to evaluate the use of d i f f e r e n t sources and rece ivers of seismic body waves with the seismic cone penetrometer. S i m i l a r studies have been done fo r the downhole and crosshole techniques ( P a t e l , 1981; Warrick, 1974; Stokoe and Hoar, 1978). Invest igat ion of sources and rece ivers was c a r r i e d out both on and o f f - s h o r e , with mechanical and explos ive sources. The r e c e i v e r types inves t iga ted were 2 horizontal and v e r t i c a l geophones and accelerometers. Secondary ob jec t ives of t h i s t h e s i s were, f i r s t to determine Po isson 's r a t i o using the compression and shear wave v e l o c i t i e s obtained from the t e s t i n g , and second, to take an i n i t i a l look at damping r a t i o f o r the s o i l using the seismic cone penetrometer data . The t h e s i s w i l l begin with a b r i e f review of seismic wave c h a r a c t e r i s t i c s , e l a s t i c moduli determinat ion, and conventional in s i t u seismic t es t ing methods. Then, the equipment used during the research , inc lud ing sources, t r i g g e r s , rece ivers and recording instruments, w i l l be described i n d e t a i l , fo l lowed by a b r i e f descr ip t ion of each t e s t s i t e . The r e s u l t s of the eva luat ion of d i f f e r e n t sources w i l l be presented. Each source w i l l be evaluated a lone, and then compared to other sources, where p o s s i b l e . A f t e r t h i s fo l lows a comparison of the d i f f e r e n t seismic rece iver types used. Determination of Po isson 's r a t i o and damping r a t i o are then presented. F i n a l l y , the major conclusions of the t h e s i s w i l l be summarized. 3 2. SEISMIC WAVE THEORY AND CONVENTIONAL IN SITU TESTING METHODS 2.1 Introduct ion This chapter w i l l b r i e f l y review the re levant theory assoc iated with seismic wave types and wave-propagation. I t w i l l then ou t l i ne the development of e l a s t i c constants as re la ted to seismic wave v e l o c i t i e s . F i n a l l y , the conventional methods fo r determining seismic wave v e l o c i t i e s w i l l be very b r i e f l y reviewed. Richart et al (1970), Mooney (1974) and Borm (1977) have wr i t ten ample d iscuss ions on seismic waves, t h e i r c h a r a c t e r i s t i c s , and the r e l a t i o n of seismic wave v e l o c i t i e s to dynamic e l a s t i c modul i . These references were used extens ive ly i n preparing Sect ions 2 .2 . and 2 .3 . L i t e ra tu re reviews of c rosshole and downhole seismic t e s t i n g methods have been c a r r i e d out by Patel (1981) and Rice (1984) and w i l l not be repeated here. Instead, the re levant c h a r a c t e r i s t i c s and procedures fo r each t e s t w i l l be b r i e f l y o u t l i n e d , with an emphasis on sources and rece ivers used. 2.2 Types of Seismic Waves and The i r C h a r a c t e r i s t i c s Seismic waves observed in engineer ing s tud ies f a l l i n to two c a t e g o r i e s ; body waves and surface waves. Body waves t rave l i n to the I n t e r i o r of the earth in the form of compression waves and shear waves. Surface waves propagate only near the surface and do not extend to any great depth. The two forms of surface waves are Rayleigh and Love waves. Although Raylelgh waves have been used in engineering seismic s t u d i e s , they were not used in t h i s research and so nei ther they, nor Love waves w i l l be descr ibed f u r t h e r . Compression waves (a lso known as d i l a t a t i o n a l waves, long i tud ina l waves, or primary waves (P-waves)).cause p a r t i c l e s to move p a r a l l e l to the ray path 4 of the wave, in the d i r e c t i o n of wave propagation (see F igure 2 . 1 ) . Compression waves can t rave l through both sol Ids and f l u i d s . In order to detect compression waves, a r e c e i v e r must be a l igned p a r a l l e l to the d i r e c t i o n of wave propagat ion, s ince p a r t i c l e motion i s i n t h i s d i r e c t i o n (see Figure 2 . 1 ) . Therefore , f o r a source which generates v e r t i c a l l y propagating compression waves, a v e r t i c a l detector must be used. Shear waves (a lso known as d i s t o r t i o n a l waves, transverse waves or secondary waves (S-waves)), cause p a r t i c l e s to move i n a plane perpendicular to the ray path of the wave. The d i r e c t i o n of motion with in t h i s perpendicular plane depends mainly on the d i r e c t i o n of the seismic source. For convenience shear waves can be reso lved i n t o two components. The shear wave component i s denoted SV when both p a r t i c l e motion and wave propagation are in the same plane, genera l ly a v e r t i c a l plane (see Figure 2 . 2 ) . The shear wave component i s denoted SH i f p a r t i c l e motion i s i n a plane transverse to the plane de f in ing the SV component, genera l ly a hor izonta l plane (see F igure 2 . 2 ) . Since f l u i d s can not develop a shearing r e s i s t a n c e , shear waves can not t rave l through f l u i d s . Therefore , shear waves can only t rave l through s o l i d s . For detect ion of both SV and SH-waves, a r e c e i v e r must be a l igned in the plane perpendicular to the d i r e c t i o n of wave propagat ion. Thus, as can be seen from Figure 2.2, f o r a v e r t i c a l l y propagating shear wave, hor izonta l rece ivers must be used. Each type of body wave behaves d i f f e r e n t l y when i t s t r i k e s a geologic boundary. As can be seen from Figure 2 .3a, when a compression wave s t r i k e s a boundary between two mediums with d i f f e r e n t P-wave v e l o c i t i e s , P and SV-waves are r e f l e c t e d and r e f r a c t e d . No SH-waves are generated. S i m i l a r l y , when a SV-wave s t r i k e s a boundary, SV and P-waves are r e f l e c t e d and re f rac ted (see Figure 2 .3b) . Again , no SH-waves are generated. However, when an SH-wave 5 Figure 2.1 C h a r a c t e r i s t i c s of a Compression Wave coordinate axes a) SV-wave j ^ v e r t i c a l plane (not necessarily in xz-plane) d i r e c t i o n of SV-wave p a r t i c l e motion perpendicular to di r e c t i o n of wave propagation di r e c t i o n of S-wave propagation detector aligned with the directi o n of p a r t i c l e motion coordinate axes b)SH-wave ^ h o r i z o n t a l plane (not necessarily * perpendicular to di r e c t i o n of wave propagation) — d i r e c t i o n of SH-wave p a r t i c l e motion perpendicular to di r e c t i o n of wave propagation r T d i r e c t i o n of S-wave propagation detector aligned with d i r e c t i o n of p a r t i c l e motion Figure 2.2 C h a r a c t e r i s t i c s of a Shear Wave 7 p P-Pl sv / P-SV1 ^ / / ^ Medium 1 \ SV-SV1 SH ^ SV-P1 \ Pl, V p l , V s l \ SH-SH1 \ \^ Medium 2 *Y P-P2 P-SV2 VS. p2,Vp2,Vs2 \ SV-P2 SV-SV2 SH-SH2 a) Incident P-wave b)Incident SV-wave c) Incident SH-wave Figure 2.3 P a r t i t i o n of E l a s t i c Wave at Interface between two E l a s t i c Media 8 s t r i k e s a boundary only SH-waves are r e f l e c t e d and r e f r a c t e d . No P or SV-waves are generated. (See F igure 2 . 3 c ) . A s i m i l a r phenomenon occurs with sources . A source e i t h e r generates predominantly P and SV-waves with no SH-wave component, or i t generates predominantly SH-waves with l i t t l e P and SV-wave components. F igure 2.4 shows schematical ly the rad ia t i on patterns of a hor izonta l and v e r t i c a l surface point source. This i l l u s t r a t e s the complete lack of SH-waves f o r a v e r t i c a l surface point source, and the lack of a v e r t i c a l component f o r the P and SV-waves fo r the hor izonta l surface po int source . Th is phenomenon i s an important cons iderat ion when designing a seismic source. C h a r a c t e r i s t i c a l l y , compression waves are f a s t e r than shear waves. The shear wave v e l o c i t y can be up to 70% o f the compression wave v e l o c i t y . Compression wave v e l o c i t i e s a l so tend to have a h igher frequency then shear waves. A fu r ther comment about SH-wave sources i s needed. Sources which produce SH-waves usua l ly have the a b i l i t y to reverse the p o l a r i t y of the SH-wave. P o l a r i z a t i o n of the SH-wave i s obtained by revers ing the d i r e c t i o n of the energy impulse which generates the SH-waves. Th is energy reversal gives rece ive r responses to the SH-wave, which are opposite in s i g n . However, P-waves generated by these sources w i l l not show p o l a r i z a t i o n . Th is property great ly a ids shear wave (SH) a r r i v a l i n t e r p r e t a t i o n . 2.3 Seismic Wave V e l o c i t i e s and the E l a s t i c Moduli 2.3.1 Development of E l a s t i c Moduli It has been found that one equation can descr ibe the behaviour of many v i b r a t i n g physical systems. That equation i s known as the wave equat ion. The development of t h i s equation can be found in many t e x t s , inc lud ing Richart e t a l , 1970, and w i l l not be inc luded here . 9 1 1 — . P " —1 - V — • 1 / s v No S H r r S H V e r t i c a l Source Horizontal Source Figure 2.4 Schematic View of the Radiation Pattern of a V e r t i c a l and Horizontal Surface Point Source (From Kahler and Meissner, 1983) Assuming i s o t r o p i c and homogeneous e l a s t i c i t y of the ground, the so lut ions to the wave equation using Hooke's laws, give the fo l lowing expressions for the v e l o c i t i e s of compression and shear waves: V p 2 = (X + 2G)/p V s 2 = G/p where Vp = compression wave v e l o c i t y Vs = shear wave v e l o c i t y \ = Lame's constant G = shear modulus and P = densi ty of propagation medium. Thus, i f the v e l o c i t y of the shear wave propagating through the s o i l and the density of the s o i l i s known, the shear modulus of the s o i l may be determined. I f the compression wave v e l o c i t y through the s o i l i s a l so known, then Lame's constant can be determined. Knowing the shear modulus and Lame's constant allows a l l other e l a s t i c moduli to be determined for a given s o i l . The e l a s t i c moduli obtained using the f i e l d methods out l ined in t h i s thes i s are small s t r a i n moduli ( s t r a i n s l e s s than .0001 percent ) . Since e l a s t i c moduli are s t r a i n dependent, comparison of moduli determined using d i f f e r e n t t e s t i n g procedures, must take Into account the s t r a i n leve l at which the t e s t s were performed. Thus, shear moduli determined using the seismic cone penetrat ion t e s t , are maximum or dynamic shear modul i , denoted Gmax because they are determined at very small s t r a i n s (Seed and I d r i s s , 1970). One other important e l a s t i c constant which w i l l be used in t h i s thes i s i s Poisson's r a t i o . Po isson 's r a t i o can be determined d i r e c t l y from the two wave v e l o c i t i e s as f o l l o w s : v = ( ( V P / V s ) 2 - 2) . 2 ( ( V p / V s ) 2 -1) where v = Po isson's r a t i o and Vp and Vs are as def ined p rev ious ly . The assumption of an i s o t r o p i c , homogeneous, e l a s t i c medium f o r s o i l 1s only a f i r s t approximation, and moduli determined using t h i s assumption should be used with caut ion . A lso the compression wave v e l o c i t y in saturated s o i l may not be the t rue compression wave v e l o c i t y of the s o i l and may 1n f a c t be the v e l o c i t y of the compression wave through the pore f l u i d (see R ichar t e t a l , 1970). Thus, the Po isson 's r a t i o determined using Vp should be used with caut ion and again, only as a f i r s t approximation. 2.3.2 C a l c u l a t i n g Seismic Wave V e l o c i t i e s The technique used for c a l c u l a t i n g v e l o c i t i e s of seismic waves from the seismic cone penetrat ion t e s t i s the pseudo i n t e r v a l technique. At each t e s t depth, the a r r i v a l time of the seismic wave (compression or shear) 1s recorded. Th is a r r i v a l time i s assumed to be the time f o r the wave to t rave l the path ATP shown in F igure 2 .5 . Each a r r i v a l time i s cor rec ted v e c t o r i a l l y , as shown, to the time taken to t rave l a v e r t i c a l path, T c o r r , as i f the source were located d i r e c t l y adjacent to the t e s t h o l e . For the pseudo in te rva l technique, the time to t rave l the in te rva l between t e s t depths, AT, i s c a l c u l a t e d by subt rac t ing the correc ted t rave l times f o r two adjacent t e s t depths. To c a l c u l a t e the v e l o c i t y , the depth i n te rva l AZ i s d iv ided by the in te rva l time AT, and the c a l c u l a t e d v e l o c i t y 1s taken to represent the average v e l o c i t y f o r that depth i n t e r v a l . The s t r a i g h t l i n e t rave l path of the wave from source to rece iver 1s an approximation. However, Rice (1984), found tha t t h i s assumption 1s s a t i s f a c t o r y f o r c a l c u l a t i o n of the seismic v e l o c i t i e s , e s p e c i a l l y i f the pseudo i n t e r v a l technique i s used and the angle of the t rave l path, o> (see 12 Signal Source Offset, |< Xn ATPn+1, Tmeas,n+1 >exsmometers ATPn Tcorr = Tmeas( Ve l o c i t y = AZ _ (Zn+1 - Zn) ATP ,n ) AT (Tcorr,n+1 - Tcorr,n) Figure 2.5 Determination of Seismic Wave V e l o c i t y Figure 2 . 5 ) , i s greater than 45 degrees. The i n t e r v a l technique tends to cancel out e r rors associated with equipment and t rave l path assumptions. The steep t rave l path angle minimizes the e r r o r due to r e f r a c t i o n of the waves along s o i l boundaries. 2.4 Conventional In S i tu Methods fo r Seismic Measurement There are three conventional methods of measuring seismic wave v e l o c i t i e s . These methods are: the seismic r e f r a c t i o n survey, the crosshole seismic method, and the downhole seismic method. The essent ia l elements of each of these methods w i l l be ou t l i ned in the fo l l owing paragraghs. The seismic r e f r a c t i o n survey c o n s i s t s of a s t r i n g of rece ivers set out in a s t r a i g h t l i n e from a source l o c a t i o n . The source emits body waves which are re f rac ted by boundaries between s o i l s of d i f f e r e n t v e l o c i t i e s , and detected by the rece ivers (see Figure 2 . 6 a ) . The r e l a t i o n s h i p between the a r r i v a l time and the o f f s e t d istance of the r e c e i v e r from the source ind icates l ayer v e l o c i t i e s and th icknesses as shown i n F igure 2 .6a. If compression wave v e l o c i t i e s are d e s i r e d , then v e r t i c a l rece ivers are used and sources which emit strong P-waves, such as exp los ive sources, are used. I f shear wave v e l o c i t i e s are d e s i r e d , then hor izonta l rece ivers are used and sources which emit predominantly shear waves, such as a hammer and weighted plank source, are used. The crosshole method, i l l u s t r a t e d in F igure 2.6b, c o n s i s t s of several boreholes i n which rece ivers are placed at the same e l e v a t i o n . Another borehole i s d r i l l e d f o r the source. When the source i s at the same e leva t ion as the r e c e i v e r s , i t i s ac t i va ted and the time f o r the body waves to t rave l between the source and rece ivers i s recorded. Knowing t h i s t rave l time and the t rave l d is tances , the v e l o c i t y of the l a y e r can be determined. This procedure i s repeated at successive depths to obta in a v e l o c i t y p r o f i l e . TIME [msec! |COl SOURCE i r- . x£o2 . x OFFSET (ra] GEOPHONE T 1 w^V^^,,... .i/C. v*! cSOOm/sec, v j s Z v ^ , V3 = 3 v i , hi =7.5rn, = 2hi s) Three-ltyer r t f r t c t lon time/distance »nd ny path di igru (from Borm,1977) ~m^~-— Gf T- 12II ( 3 . 7 m l — 4 — 1 2 I I ( 3 . 7 m ) — 4 — 7 1 1 (2.1 m ) - ^ 0 . -PLAH VIEW V e r t i c a l V e l o c i t y - V t r l i c o l ^-3-0 Velocity |N Transducer Wedged m Pk>ct (Not lo Scola) b . -CROSS-SECTIONAL VIEW b) C r o s s h o l e s e i s m i c m e t h o d . (from Stokoe and Hoar,1977) r- R t c a i v t r i B o r e h o t o a-PLAN VIEW (Not lo S c o n ) b . - C R O S S - S E C T I O N A L VIEW c) Downhole seismic method. (from Stokoe and Hoar,1977) Figure 2.6 Conventional In S i t u Methods for Seismic Measurement For compression wave v e l o c i t i e s , exp los ive sources are used, i f p o s s i b l e , because they generate sharper, l a r g e r i n i t i a l P-waves. However, mechanical sources are a lso used i f the t rave l path between source and rece iver i s r e l a t i v e l y short (Stokoe and Hoar, 1978). For shear wave v e l o c i t i e s , mechanical sources are genera l ly used. These sources can be impulse sources or tors iona l sources and are genera l ly revers ib le so that p o l a r i z a t i o n of the shear wave can be obta ined. The down-hole method, i l l u s t r a t e d in F igure 2.6c, cons i s t s of a s ing le borehole with the rece iver in the borehole and the source at the surface a short distance from the borehole. When the r e c e i v e r i s at the tes t depth, the source i s a c t i va ted , and the a r r i v a l time of the body waves i s recorded. The rece iver i s moved to the next t e s t depth, and the procedure i s repeated. The pseudo in te rva l technique, descr ibed in Sect ion 2 .3 .2 , i s general ly used to determine seismic wave v e l o c i t i e s . The seismic cone penetrat ion t e s t descr ibed i n t h i s thes i s i s , e s s e n t i a l l y , a downhole seismic t e s t method. For compression wave v e l o c i t i e s determined from the downhole t e s t , the same type of sources are used as f o r the crossho le method. For shear wave v e l o c i t i e s , a r e v e r s i b l e , mechanical , impulse source i s general ly used, such as a hammer and weighted plank. Generally a t r i a x i a l package of rece ive rs i s used f o r both the crosshole and downhole methods. In the crosshole method, a v e r t i c a l rece iver i s used to detect shear waves from an impulse source such as that shown in Figure 2.6b. A transverse hor izonta l rece iver i s used f o r a to rs iona l source. Horizontal rece ivers are used for the hammer and weighted plank source used fo r the downhole method. Genera l ly , P-waves are detected on v e r t i c a l rece ivers fo r both methods. 3. EQUIPMENT AND PROCEDURES 16 3.1 Introduct ion This chapter w i l l ou t l i ne and descr ibe the equipment and procedures used for t h i s t h e s i s . The chapter w i l l begin with a d e s c r i p t i o n of the seismic cone, inc lud ing i t s c a p a b i l i t i e s as a standard cone f o r cone penetrat ion t e s t s , and i t s add i t iona l c a p a b i l i t i e s f o r detect ing seismic waves. The U.B.C. In S i tu Test ing veh ic le w i l l then be b r i e f l y descr ibed . The fo l lowing sect ions w i l l go on to desc r ibe , s e q u e n t i a l l y , the equipment involved in the seismic t e s t i n g , i n c l u d i n g the seismic sources, the t r i g g e r s fo r the recording instruments, the seismic wave detectors , and the recording instruments themselves. The f i n a l sect ion w i l l ou t l i ne typ i ca l f i e l d t e s t i n g procedures. Both the ra t iona le behind the procedures and the mod i f i ca t ions to the i n i t i a l procedures w i l l be d iscussed when necessary. 3.2 The Seismic Cone Penetrometer The seismic cone penetrometers used fo r t h i s study had e i t h e r a 15 sq . cm or a 10 sq . cm base area . These cones are depicted in F igure 3.1 and 3 .2 . A l l UBC cones are capable of measuring bearing r e s i s t a n c e , f r i c t i o n res i s tance , and pore pressure, in add i t ion to temperature and i n c l i n a t i o n . These c a p a b i l i t i e s are descr ibed in f u l l de ta i l i n Campanella and Robertson (1981). The 15 sq . cm seismic cone was instrumented with a t r i a x i a l package of seismic wave r e c e i v e r s . These rece ivers were e i t h e r geophones or accelerometers. The two other seismic cones used (denoted UBC#6 and UBC#8) were 10 sq . cm cones, and each was instrumented with a s i n g l e , h o r i z o n t a l l y 17 s t r a i n gages for-f r i c t i o n load c e l l pressure transducer -porous p l a s t i c -small cavity-1 To 16 conductor cable a m p l i f i e r board ft - t r i a x i a l geophone or accelerometer package ( i n s t a l l e d at d i f f e r e n t times) -slope sensor •Quad r i n g 2qual end area f r i c t i o n sleeve ( 225 sq. cm area) •st r a i n gages for cone bearing load c e l l -rxngs -Quad r i n g -60* cone 43.7 mm O.D. Figure 3.1 15 sq. cm Seismic Cone Penetrometer strain gages for-friction load cell temperature sensor -pressure transducer --•wage fitting to lock 14 conductor cable porous plastic -•mall cavity —' wires spl iced to cable Inside tube - seismometer -•lope sensor -Quad ring -equal end area friction sleeve (150cm' area) -•train gages for cone bearing load cell -O-rlngs -Quad ring 60'cone 35.68mm O.D. Figure 3.2 10 sq. cm Seismic Cone Penetrometer 19 o r i en ted , seismic wave r e c e i v e r . The UBC#6 cone was Instrumented with a geophone, and the UBC#8 cone with an accelerometer. The cones were connected to the surface with a 16 conductor c a r r i e r cable which was threaded through one meter lengths of standard 20T Dutch cone rods. The conductor cable fed the analog data i n to a data a q u i s i t i o n system manufactured by Hogentogler & Co. Inc . and modif ied at U.B.C. The s igna l s from the cone were ampl i f ied in the cone, but d i g i t i z a t i o n of the bear ing , f r i c t i o n , and pore pressure was done at the surface by the Hogentogler data a q u i s i t i o n system. For the 15 sq . cm cone instrumented with accelerometers, the a m p l i f i e r s f o r the temperature and i n c l i n a t i o n were used in the cone to ampl i fy the accelerometer output. The accelerometer output was not d i g i t i z e d by the Hogentogler data aqu is t ion system, but came out of the system as an analog signal which went in to a recording o s c i l l o s c o p e (see Sect ion 3 . 4 . 5 ) . The cone was advanced in to the s o i l using the U.B .C . In S i tu Test ing veh ic le ( t r u c k ) . The truck shown i n F igure 3.3 weighs approximately 11 tons , and has two hydraul ic c y l i n d e r s with which the cone i s pushed in to the s o i l . To provide the react ion force needed to push the cone, the truck i s ra i sed on two hydraul ic pads as shown in the f i g u r e . Further d e t a i l s about the design of the truck are given in Campanella and Robertson (1981). 3.3 Seismic Wave Sources and Related T r igger ing Systems 3.3.1 Introduct ion Several d i f f e r e n t types of sources were Invest igated fo r t h i s study. The sources can be d iv ided in to three c a t e g o r i e s : mechanical sources, on-shore explos ive sources, and o f f -shore explos ive sources . In the fo l lowing sect ions these three categor ies and t h e i r r e l a t e d t r i g g e r i n g systems w i l l be d iscussed . 20 Figure 3.3 CPT Seismic Equipment Layout f o r Mechanical Sources (af t e r Rice, 1984) 21 The reason fo r Invest igat ing d i f f e r e n t exp los ive sources of seismic waves stems from the a p p l i c a t i o n of the cone to o f f - s h o r e i n v e s t i g a t i o n s . Explos ive sources are used o f f -shore to avo id employing a cos t l y mechanical seabed dev ice . The explos ive sources used on-shore were researched for two reasons. F i r s t , f a m i l i a r i t y with i n t e r p r e t i n g exp los ive sources was desired before o f f -shore work was undertaken. Second, because explos ive sources input a l a r g e r amount of energy in to the ground, the use of these sources fo r deep on-shore cone work was i n v e s t i g a t e d . 3.3.2 Mechanical Sources For t h i s study, the generation of both P and S waves was des i red . As d iscussed in Chapter 2, compression wave sources a l so generate shear waves. The a r r i v a l of the shear wave from t h i s type of source i s often d i f f i c u l t to i n t e r p r e t because of the add i t ion of the two wave types . Thus, to allow accurate a r r i v a l time est imates , two d i f f e r e n t mechanical sources were t r i e d - one to generate SH-waves, and one to generate P-waves. A good mechanical source f o r generat ing large amplitude shear (SH) waves with l i t t l e or no compressional wave component c o n s i s t s of a plank weighted to the ground and impacted on one end (Mooney, 1974). Th is type of mechanical shear source (hammer shear source) was used fo r t h i s study. The rear hydrau l i c pad of the UBC In S i tu Tes t ing vehic le was used as the weighted plank fo r the hammer shear source (see F igure 3 . 3 ) . Since the truck i s ra i sed on i t s two hydrau l i c pads during t e s t i n g , the pads are in good mechanical contact with the ground. To prevent damage to the pads, one inch th ick metal p lates were welded onto the ends of the rear hydraul ic pad. These p la tes were struck h o r i z o n t a l l y with a 7 kg sledge hammer. Po la r i zed shear waves were e a s i l y generated by s t r i k i n g opposi te ends of the pad. The use of the rear pad e l iminated the necess i ty of having a second vehic le on 22 s i t e to weigh down a p lank. A s i m i l a r system, using the rear hydrau l i c pad of the truck and a sledge hammer, was used to generate P-waves. A steel p l a t e , 2.5 cm t h i c k , 0.45 m wide and 1.2 m long, was placed part way under one s ide of the rear hydrau l i c pad and the pad was lowered on top of i t (see Figure 3 . 3 ) . Approximately 0.5 meters of the p late protruded out beyond the end of the pad and t h i s was struck with a blow, d i rec ted v e r t i c a l l y downward, from the 7 kg sledge hammer. The r e s u l t s obtained from these mechanical sources w i l l be d iscussed i n Chapter 5. 3 .3.3 T r igger ing System fo r the Mechanical Sources An accurate , r e l i a b l e t r i g g e r i s essent ia l for .any seismic t e s t i n g . D i f f e r e n t t r i g g e r s for the mechanical source used in conjunct ion with the U.B.C. seismic cone have been invest igated prev ious ly by Rice (1984). Rice found an e l e c t r i c a l step t r i g g e r , recommended by Hoar and Stokoe (1978) to be the most accurate . The t r i g g e r c i r c u i t i s shown i n F igure 3 .4 . I t has a s ignal r i s e time of l e s s than 1 microsecond. 3.3.4 On-Shore Explos ive Source The on-shore explos ive source used for t h i s study was a "Buf fa lo gun" o r i g i n a l l y designed by the Geological Survey of Canada f o r engineering surface seismic surveys (Pul lan and MacAulay, 1984). The 12-gauge Buf fa lo gun c o n s i s t s of a 1.0 to 1.5 meter length of standard 3/4 inch water pipe and f i t t i n g s as shown i n F igure 3 .5a . Winchester 12-gauge AA Trapload s h e l l s with a 7/8 oz . load were used. The s h e l l s f i t t e d snugly between the n ipp le and the coupler and d id not move when the shot was f i r e d . A handle was attached to the top of the pipe as shown, to a id in p lac ing the gun 1n the ground. A 1 1/4 inch diameter auger was used to d r i l l a hole f o r the Buf fa lo gun. The gun was then lowered in to t h i s ho le , with the she l l end down, u n t i l 23 Volts = 6V Rise Time =0.1 us Hammer Impulse a) Trigger Signal .Time 1=1.1(R)(C) A 5 - 14 Volts D.C. LM555 I.C to o c i l l o s c o p e t r i g g e r input b) C i r c u i t Diagram Figure 3.4 E l e c t r i c a l Step Trigger C i r c u i t f o r Hammer Source S T E E L DROP ROD — r^ n ci ~ m r>—PND C A P m ^ T E E ^ ^ N I P P L E 3/4" PIPE F I R I N G PIN Q*-N 12 GAUGE S H E L L Drop Rod Buffalo Trigger and Flange Prebored Hole \ ^ a) Schematic of Buffalo Gun (from Pullan and MacAulay, 1984) S h e l l Ready to F i r e Detonated b) Operation of Buffalo Gun Figure 3.5 Buffalo Gun and i t s Operation ro I t was f i rm ly seated past the end of the augered hole (genera l ly , 0.75 meters deep). The f i r i n g rod (or drop rod) , with pin end down, was then lowered down the center of the gun u n t i l i t was approximately 0.3 meters above the s h e l l . The f i r i n g rod was then re leased and the she l l detonated (see Figure 3 .5b) . A f t e r the she l l was detonated, the gun was pu l l ed out of the ground, and re loaded, a new hole was dug, and the procedure repeated with the cone at the next t e s t depth. Results obtained from t h i s source w i l l be d iscussed in Chapter 5. 3.3.5 T r igger ing System for the On-Shore Explos ive Source Two t r i g g e r i n g systems were used with the Buf fa lo gun. The f i r s t system cons i s ted of a geophone. The second system cons i s ted of a hammer switch. These systems w i l l be descr ibed below. A geophone, i d e n t i c a l to those descr ibed in d e t a i l i n Sect ion 3.4.2 below, was used to t r i g g e r the recording instruments. The geophone was o r i g i n a l l y attached to the gun using a hose clamp (see Figure 3 . 6 a ) . This method f o r at taching the geophone was found to be inadequate because the leads coming from the geophone were not rugged enough to be exposed in t h i s manner. The geophone was then mounted on a f lange that was attached to the rods (see F igure 3 .6b ) . This f lange was dual purpose. F i r s t , i t served as a mount f o r the geophone, and second, i t prevented any debr is from shooting out of the hole and i n j u r i n g the operator when the she l l was detonated. The f lange was r i g i d l y attached to the gun with a set-screw as shown i n Figure 3.6b and t h i s provided good mechanical coupl ing between the gun and the geophone. The geophone i t s e l f was exc i ted by the compression wave t r a v e l l i n g back up the gun a f t e r the she l l exploded. Th is compression wave t r a v e l l e d up the gun at a speed of approximately 5100 meters per second, prov id ing a f a i r l y Geophone Buffalo Gun Set Screw— Flange c Buffalo Gun Hose Clamp a)Geophone with Hose Clamp .Geophone Case -Geophone i n Case ' O I—'*• i I.L b; Geophone with Flange Figure 3.6 Triggering Systems f o r Buffalo Gun Source cons is tent t r i g g e r (see Figure 3 . 7 ) . P r e t r i g g e r i n g d id occur however, when the f i r i n g rod was lowered into the gun, or when the f i r i n g rod was f a l l i n g through the gun before i t h i t and detonated the s h e l l . The f i r s t p re t r i gger ing problem was e a s i l y remedied. The gun operator would simply check with the recording operator to ensure the t r i g g e r was ready before dropping the f i r i n g pin the f i n a l 0.3 m and detonat ing the s h e l l . The second p re t r i gger ing problem was mostly overcome by decreas ing the s e n s i t i v i t y of the t r i g g e r c i r c u i t . The second system cons is ted of a hammer switch manufactured by EG & G Geometries. The hammer switch was ac t i va ted by the compression wave t r a v e l l i n g up the gun a f t e r the she l l exploded. The switch c i r c u i t r y created a s t e p - l i k e increase in voltage over a per iod of l e s s than one microsecond, but a delay occurred between the detonation of the shotgun s h e l l and the t r i g g e r i n g of the recording instrument. Th is delay was v a r i a b l e and unknown. Thus, t h i s t r i g g e r was found to be inadequate. Rice (1984) used t h i s t r i g g e r with the hammer shear source and found i t i n c o n s i s t e n t . 3.3.6 Off-Shore Explos ive Sources The exp los ive sources used fo r t h i s study were Seismlcap Mark II seismic caps, which were detonated with a Geometrix b l a s t e r box. The seismic caps were used in a va r i e ty of ways 1n an attempt to generate a wave t r a i n from which both P and S waves cou ld be e a s i l y i n t e r p r e t e d . The seismic caps were i n i t i a l l y lowered to tnudline and f i r e d . Next, they were lowered to a pos i t i on j u s t below the i c e and f i r e d (see Sect ion 4.2 f o r s i t e d e s c r i p t i o n ) . When f i r e d j u s t below the i c e , the seismic caps were e i t h e r weighted with a chain or attached to a pole of f ixed length before being lowered. T h i r d , the seismic caps were f i x e d to the side of a blade and t h i s blade was subsequently embedded i n the sea f l o o r with the seismic cap fac ing away from the cone and rods . Once the blade was embedded, Time of Detonation-111 ^ Response of Geophone— Trigger to Buffalo Gun Source \ V McDonalds Farm i i -30 •20 •10 0 10 Time (milliseconds) 20 30 40 Figure 3.7 Geophone Trigger Response to Buffalo Gun Source 29 the seismic cap was detonated. F igure 3.8 i l l u s t r a t e s the d i f f e r e n t seismic cap sources. Results obtained from these sources w i l l be d iscussed i n Chapter 5. 3.3.7 T r igger ing System fo r the Off-Shore Explos ive Sources The Geometrix b l a s t e r box was used to t r i g g e r the recording instrument. The b l a s t e r box detonated the seismic cap by sending a 5 Vo l t step signal to the cap . Th is same 5 Vo l t step signal was used to t r i g g e r the recording instrument. The r i s e time fo r the step signal was much l e s s than 10 microseconds. Th is t r i g g e r i n g system was found to be very r e l i a b l e and accurate. 3.4 Seismic Wave Detect ion and Recording 3.4.1 Introduct ion Two d i f f e r e n t types of transducers were used f o r t h i s t h e s i s to detect seismic waves - geophones and accelerometers. Geophones are v e l o c i t y transducers and accelerometers are a c c e l e r a t i o n t ransducers . The theory descr ib ing how the transducers work i s , however, the same and a b r i e f review of t h i s theory f o l l ows . Both v e l o c i t y and acce lera t ion transducers can be modelled by the mass-spring system i l l u s t r a t e d in F igure 3 . 9 . (The system may or may not be damped). The mass 1s attached to the transducer case by the s p r i n g . The transducer case moves with the s t ruc ture to which i t i s attached and motion 1s i n f e r r e d by the r e l a t i v e motion between the mass and the case . The transducers convert t h i s mechanical motion i n t o an e l e c t r i c a l s ignal which can be Interpreted by the e l e c t r i c a l recording instrument. Depending on the natural frequency of the mass-spring system and the frequency of the e x c i t a t i o n s i g n a l , the r e l a t i v e motion between the mass and To In s i t u Testing Vehicle Figure 3.8 Operation of Seismic Cap Source 31 transducer case. viscous damper spring mass /;///////;/// „ MOVING PART r e l a t i v e motion between mass and case 'motion to be measured Figure 3.9 Schematic of Mass-spring Type of Vibration-measuring Transducer the s t ructure w i l l be proport ional to e i t h e r displacement, v e l o c i t y or a c c e l e r a t i o n . The undamped natural frequency of a system i s given by: 2 UJ = (k/m) where w=the natural frequency k=the spr ing s t i f f n e s s and m=the mass. Systems with a low natural frequency with respect to the e x c i t a t i o n signal (low spr ing s t i f f n e s s and high mass), are v e l o c i t y t ransducers . Systems with a high natural frequency with respect to the e x c i t a t i o n signal (high spr ing s t i f f n e s s and low mass), are acce le ra t ion t ransducers . This sect ion w i l l describe the geophones and accelerometers used f o r t h i s t h e s i s . Further transducer theory w i l l . b e inc luded where necessary. The f i l t e r i n g required w i l l a lso be out l ined and the per t inent information about the recording osc i l l oscope reviewed. 3.4.2 Geophones Geophones were i n s t a l l e d in both the 10 and 15 sq . cm cones. The 15 sq . cm cone was instrumented with a t r i a x i a l package of geophones, while the 10 sq . cm cone (UBC#6) had a s ing le hor izonta l geophone. The o r i e n t a t i o n of t h i s geophone was marked on the outside of the UBC#6 cone, and a s i m i l a r marking was made for one of the hor izonta l geophones in the 15 sq . cm cone. The purpose of these markings was to enable the geophone to be favourably or iented fo r a d i rec ted shear wave source. The geophones cons is ted of a permanent magnet with a wire c o i l suspended from l e a f springs as shown i n F igure 3 .10 . An e l e c t r i c current i s generated in the c o i l when r e l a t i v e movement e x i s t s between the magnet and the c o l l . Thus, the magnet i s act ing as the transducer case , the c o i l as the mass, and the l e a f spr ing as the spr ing described in the mass-spring system of Sect ion 3 . 4 . 1 . The output voltage created by the current in the c o i l Is d i r e c t l y 33 Figure 3.10 Schematic of Geophone proport ional to the s o i l p a r t i c l e v e l o c i t y . The geophones were GSC-14-L3 min iature v e l o c i t y transducers manufactured by Geospace Corporat ion . The manufacturer's s p e c i f i c a t i o n s are shown in Figure 3 .11. The geophones were 1.7 cm in diameter, 2.0 cm h igh, and weighed 19 grams. The i r natural frequency was approximately 28 Hz. They were smal l , rugged and operated in any o r i e n t a t i o n . A m p l i f i c a t i o n of the geophone signal was not necessary fo r shallow on-shore t e s t i n g . However, f o r o f f - shore t e s t i n g the geophone signal was ampl i f i ed at the surface in some cases . The a m p l i f i e r used was the model AD521 manufactured by Analog Devices . The response of the geophones w i l l be d iscussed in Chapter 6. 3.4.3 Accelerometers Accelerometers were i n s t a l l e d in both 10 and 15 sq . cm cones. Geophones and accelerometers were i n s t a l l e d at d i f f e r e n t times in the 15 sq . cm cone. The 10 sq . cm cone (UBC#8) had a s i n g l e , h o r i z o n t a l l y or iented accelerometer. As mentioned above, the o r i e n t a t i o n of the hor izonta l accelerometers was marked on the outside of the cone so that the accelerometer could be favourably o r i en ted . During most of the research , only the marked hor izonta l and the v e r t i c a l accelerometers in the 15 sq . cm. cone were connected, because only two amp l i f i e r s were a v a i l a b a l e . A m p l i f i e r s were necessary fo r reasons out l ined below. The accelerometers used fo r t h i s study were of the s t r a i n gage type shown i n F igure 3.12. The accelerometers were model TGY-155-10 manufactured by K u l i t e Semiconductor Products Inc. The natural frequency of the accelerometers was approximately 550 Hz. The theory f o r the mass-spring transducer can be app l ied to the s t r a i n gage t ransducer . The wires of the s t r a i n gage are elongated or relaxed in response to the r e l a t i v e displacement between the wire and the transducer case . As the wire changes length , the GSC-1U-L3 SEISMOMETER The GSC-Ht-13 Is a very small, extremely rugged seismometer. It Is designed • nd built to maintain performance characteristics even after being subjected to high shock forces. Principal applications Include intrusion detection, military use and vibration monitoring. Standard natural frequency Is 28 Hz, with t i l t angle of operation up to 180°. Standard Natural Frequency Standard Coll Resistance P 25°C Intrinsic Voltage Sensitivity Normalized Transduction Constant T i l t Angle of Operation Open Circuit Damping Moving Mass Operating Temperature Dimensions: Diameter Height Height With Terminals Weight SPECIFICATIONS 28 Hz t 5 Hz 570 Ohms t 5% .29 V/in/sec t 15% .012 /Tc " (V/ In/ sec) 180° 18 of Cr i t ica l 1 .04 2.15 g -30°F to +160°F .66 in (1.7 cm) .70 In (1.8 cm) .80 In (2.0 cm) 19 9 3 O .30 .25 .19 .12} OSO .040 .OJO .on 20 21 SO 40 SO CO ISO 200 250 3O0 4QQ SOO SHUNT _0_PEN DAM PMC l*%l laooo. 9200, I30-J l _ J _ J | _ S S E I S M I C 01 OUT :TE PUT DE ) e=_)l_r— CTOR R E S P O N S E CURVE VS F R E O U E N C Y 1 TYPE NATU COIL 0SC-I4 TECTON. HOOEL L3 ! »»L UNDAMPED FREQUENCY RESISTANCE STO OMUS A H e i r I f k t i l i v l l r 7» 2> HI T 2 5* C V/IN/SEC OF CNITICAL 1 1 1 1 OPEN CIOCUIT OAMPING 1* X • 10 IS 20 23 30 FREQUENCY (Hi) Figure 3.11 Geophone S p e c i f i c a t i o n s ( a f t e r Geo Space Corp.) 36 r e s i s t o r s viscous damper transducer case Ar = change i n resistance « 6 6 = r e l a t i v e motion between mass and case r e s i s t o r s Figure 3.12 Schematic of Strain-gage Accelerometer res is tance of the wire changes. The change 1n res i s tance i s proport ional to the s o i l p a r t i c l e a c c e l e r a t i o n . The change i n res i s tance of the s t r a i n gage wire 1s inverse ly proport ional to the square of the natural frequency. Since the natural frequency of the accelerometers i s h igh , the change i n res i s tance upon e x c i t a t i o n i s very small and the output s ignal i s very s m a l l . Thus the output signal must be a m p l i f i e d . The d i f f e rence between the ampl i f i ed and unampli f led s ignal i s shown i n F igure 3 .13 . A m p l i f i c a t i o n of the accelerometer s igna l s was done using AD522 p r e c i s i o n IC instrumentat ion a m p l i f i e r s , manufactured by Analog Dev ices . Because the natural frequency of the accelerometer i s h igh , high frequency s igna l s w i l l cause the accelerometer to resonate. I t was found that a considerable amount of high frequency noise was accompanying the wave s i g n a l . Th is noise made i n t e r p r e t a t i o n d i f f i c u l t . In order to reduce t h i s no ise , f i l t e r i n g of the s ignal was employed. Th i s f i l t e r i n g w i l l be descr ibed in the fo l lowing s e c t i o n . The response of the accelerometer w i l l be d iscussed in Chapter 6. 3.4.4 Signal F i l t e r i n g Although s ignal f i l t e r i n g i s not recommended to be used fo r seismic wave v e l o c i t y i n v e s t i g a t i o n s , (Stokoe and Hoar, 1977), f i l t e r i n g of the accelerometer s igna l s was necessary f o r i n t e r p r e t a t i o n . F i l t e r e d and u n f i l t e r e d accelerometer responses to the mechanical hammer source are shown in Figure 3.14. One of the reasons signal f i l t e r i n g i s not recommended, 1s because f i l t e r i n g causes a phase s h i f t . A phase s h i f t 1s a s h i f t 1n time of the output signal with respect to the Input s i g n a l . The amount of phase s h i f t due to f i l t e r i n g depends on the frequency of the input s i g n a l , the c u t - o f f frequency of the f i l t e r , and the f i l t e r c h a r a c t e r i s t i c s . +.025. ) » — W W N A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A -.025. + Unamplified Response + +1.0-\ A A A A A A A A A % l i r ,1 -1.0. i l l ! ' Amplified Response . .i i McDonalds Farm Depth 2.0 meters U n f i l t e r e d Responses 10 20 30 40 50 Time (milliseconds) 60 70 80 Figure 3.13 Unamplified and Amplified Accelerometer Responses CO CO F i l t e r e d Signal Low pass f i l t e r with 300 Hz c u t - o f f frequency •Un f i l t e r e d Signal -4 McDonalds Farm Depth = 8.0 m Amplified Response 20 40 60 80 100 120 140 160 Time (milliseconds) Figure 3.14 F i l t e r e d and U n f i l t e r e d Accelerometer Responses CO 40 Di f fe rent analog f i l t e r s were used on and o f f - s h o r e . The f i l t e r used on-shore was the model 1022F Dual Hi/Lo f i l t e r , manufactured by Rockland Laborator ies , Inc. A low-pass f i l t e r was used. Th is means a l l frequencies of a s ignal passing through the f i l t e r above a set c u t - o f f frequency were attenuated by the f i l t e r , but a l l f requencies below the se t c u t - o f f frequency passed through the f i l t e r unattenuated. The attenuat ion c h a r a c t e r i s t i c s of the on-shore f i l t e r are shown in Figure 3.15. A range of d i f f e r e n t c u t - o f f frequencies was t r i e d with t h i s f i l t e r and the r e s u l t s are shown i n F igure 3 .16. The phase s h i f t caused by the d i f f e r e n t c u t - o f f frequencies can be c l e a r l y seen in t h i s f i g u r e . A cut-o f f frequency of 100 Hz was used fo r most of the data c o l l e c t i o n . The f i l t e r used o f f - shore was the model 2B31J manufactured by Analog Devices . The c u t - o f f frequency of t h i s f i l t e r was 100 Hz. The attenuat ion c h a r a c t e r i s t i c s of t h i s f i l t e r are a lso shown i n F igure 3 .15. As can be seen in the f i g u r e , the attenuat ion c h a r a c t e r i s t i c s of the o f f - s h o r e f i l t e r were smal ler than those of the on-shore f i l t e r . In f a c t , the o f f - s h o r e f i l t e r attenuated high frequency amplitudes by only h a l f as much as the on-shore f i l t e r . The r e s u l t s obtained by the two d i f f e r e n t f i l t e r s w i l l be d iscussed in Chapters 5 and 6. The accelerometer response can a l so be d i g i t a l l y f i l t e r e d . D i g i t a l f i l t e r i n g involves transforming the d i g i t i z e d response from the time domain to the frequency domain using a F o u r i e r transform, e l i m i n a t i n g se lected frequencies with in the response, and transforming the a l t e r e d response back to the time domain. The recording o s c i l l o s c o p e used fo r t h i s study (see Sect ion 3.4.5) 1s capable of d i g i t a l l y f i l t e r i n g a por t ion of a d i g i t i z e d response stored in i t s memory. A d i g i t i z e d response s tored in the o s c i l l o s c o p e has e i t h e r 15872, 41 N O R M A L I Z E D FREQUENCY - f/tc Figure 3.15 Attenuation and Phase Shift Characteristics of the Low Pass Filters (after Rockland Laboratories, Inc., 1969) Low Pass F i l t e r McDonalds Farm 8.0 m Depth in w -P o > <u T3 3 •P •H r-l shear wave a r r i v a l s " 4 Cut-off frequency = 20 Hz (delay due to phase s h i f t ) j 1 30 Hz 40 Hz 600 Hz 'W-/\A~./v> VUVwWVyW-. -~v~v-^nMA/vVv^^ 0 20 40 60 30 100 Time (milliseconds) 120 140 Figure 3.16 E f f e c t of D i f f e r e n t F i l t e r Cut-off Frequencies on Accelerometer Response 7936, or 3968 data points (see Sect ion 3 . 4 . 5 ) . The d i g i t a l f i l t e r program fo r the osc i l l o scope can only operate on 1024 data points at one t ime. Thus, the f i l t e r can only f i l t e r a small window of the s i g n a l , and not the e n t i r e response. This type of f i l t e r i n g could only be used i f the approximate a r r i v a l time was already known. The c a p a b i l i t y to d i g i t a l l y f i l t e r the large number of data points in a t yp i ca l accelerometer response requires a large amount of computer storage space. Thus, i n order to d i g i t a l l y f i l t e r an accelerometer response from the o s c i l l o s c o p e , the response must f i r s t be t rans fe r red to a computer with t h i s k ind of memory capac i ty . Once t r a n s f e r r e d , d i g i t a l f i l t e r i n g can be performed. The computer system needed fo r t h i s type of f i l t e r i n g i s s t i l l under i nves t iga t ion at U.B.C. 3 . 4 . 5 . Recording Osc i l l oscope The responses of the geophones and accelerometers to the seismic wave e x c i t a t i o n were d isp layed and recorded using a N i c o l e t 4094 d i g i t a l o sc i l l o scope with a CRT screen and a f loppy disk storage c a p a b i l i t y . A complete descr ip t ion of t h i s o s c i l l o s c o p e i s given by Rice (1984), and only the perta inent c h a r a c t e r i s t i c s of the o s c i l l o s c o p e , as they r e l a t e to t h i s study, w i l l be summarized here. The osc i l l oscope was an analog to d i g i t a l recorder , capable of recording a s i n g l e input signal to the nearest 10 microseconds, and two simultaneous input s igna l s to the nearest 20 microseconds. The double-s ided double-density f loppy d isks used for data storage in conjunct ion with the o s c i l l o s c o p e , were d iv ided in to 20 sec to rs . A s ing le signal could be stored in f u l l , h a l f or quarter sec tors , which could hold 15872, 7936, and 3968 data po ints r e s p e c t i v e l y . (Two simultaneously recorded s igna l s cou ld only be stored in h a l f or quarter s e c t o r s ) . Known t r i g g e r delays cou ld be preset on the o s c i l l o s c o p e . By using known t r i g g e r delays and maximum storage capac i t y , the maximum sampling rate could be used to greater depths. The data could be ampl i f ied on the screen and add i t ion or subtract ion of s igna l s could be performed. Disk programming packages used with the o s c i l l o s c o p e allowed signal smoothing, d i g i t a l f i l t e r i n g (see Sect ion 3 . 4 . 4 ) , and other operat ions . 3.5 F i e l d Procedures An important element f o r obta in ing accurate repeatable seismic data 1s a standard f i e l d procedure performed by w e l l - t r a i n e d personnel . Th is sec t ion w i l l ou t l i ne the bas ic f i e l d procedures used with the seismic cone f o r t h i s t h e s i s . Most of these procedures have been out l ined prev ious ly by Rice (1984) and w i l l be only b r i e f l y reviewed here. Special procedures, to be used with s p e c i f i c sources or r e c e i v e r s , have been out l ined prev ious ly in t h i s chapter or w i l l be inc luded in Chapters 5 and 6. The f i e l d procedure Involved several steps before seismic t e s t i n g cou ld beg in . F i r s t , the truck was ra i sed and l e v e l l e d on i t s hydraul ic pads, thus c r e a t i n g the plank fo r the mechanical shear wave source. I f a mechanical compression wave source was to be used, the stee l p la te was pos i t ioned under the rear hydrau l i c pad before the pads were lowered. Second, the i n i t i a l se t -up of the e l e c t r o n i c s and recording systems was made. Th is set-up i s shown schematical ly i n F igure 3 .17. T h i r d , the cone was saturated and the data a q u i s i t i o n system i n i t i a l i z e d (see Campanella and Robertson, 1981). Next, the cone, with seismic transducers favourably o r i e n t e d , was advanced i n t o the s o i l to the f i r s t t e s t depth. At each t e s t depth a s i m i l a r procedure fo r seismic t e s t i n g was fo l lowed. Th is procedure cons is ted o f : - s e t t i n g the o s c i l l o s c o p e to the c o r r e c t sampling r a t e s , maximum vo l tages , Seismic Cap Source Cone Data T to D.A.S. Power Supply to Cone Accelerometers or Geophones V Cone Trigger Conditioni Box^ 'Low Pass F i l t e r and/or Amplifier V e r t i c a l Input Geophones Switch Trigger Input Blaster Box I Seismic Cap Hammer Source Truck Pad r/ v> si— Sledge Hammer Buffalo Gun Source < h. Geophone HF Shotgun Shell Figure 3.17 Schematic of the Electronics Set-up f or Seismic Testing en and t r i g g e r delays; -removing the load from the cone and rods and turn ing the truck engine o f f i f necessary; -checking that the t r i g g e r i s working and a c t i v a t i n g i t ; - induc ing a seismic wave i n t o the ground with e i t h e r a mechanical or explos ive source; - s t o r i n g the wave s ignal on the o s c i l l o s c o p e f loppy disk recorder and not ing the t e s t information an a data sheet; - p o l a r i z i n g the s i g n a l , i f us ing a hammer shear source; -advancing the cone to the next t e s t depth and repeat ing the procedure; A few notes should be made about some of the t e s t s teps . When using the on-shore explosive source, to avoid unnecessary r e p e t i t i o n of the t e s t due to poorly chosen sca les , i t was found useful to use the hammer source as an i n d i c a t o r of the time and voltage sca les needed before detonating the point source. This technique could not be used for the o f f - shore explos ive sources . However, carefu l study of the previous s ignal c o u l d , with exper ience, help with se lec t ion of appropriate s c a l e s , although d i f f i c u l t i e s d id a r i s e i f the t e s t depths were a considerable distance apar t . Checking the t r i g g e r before f i r i n g the on-shore explos ive source, as mentioned in Sect ion 3 . 3 . 5 , was e s p e c i a l l y important, s ince the t e s t takes considerably more time to repeat than the mechanical source t e s t s , and many r e p e t i t i o n s could be c o s t l y due to the shotgun s h e l l s needed. The augering of the hole and loading of the Buf fa lo gun was done while the cone was being advanced, 1n order to save t ime. To reduce the amount of noise t r a v e l l i n g down the rods from the In s i t u t e s t i n g v e h i c l e , at each t e s t depth the rods were uncoupled from the t ruck . Th i s uncoupling was accomplished by removing the load from the rods and a l lowing the rods to stand free In the rod w e l l . I f excess noise in the wave signal was encountered a f t e r the uncoupling of the rods, then the truck engine was shut o f f while the wave s ignal was t r a v e l l i n g through the s o i l . The use of a f r i c t i o n reducer with the seismic cone (see Campanella and Robertson, 1981) to reduce f r i c t i o n along the rods, a l so helped prevent excess noise from t r a v e l l i n g in the rods . 4. FIELD INVESTIGATIONS 48 The data contained in t h i s t h e s i s was obtained from two s i t e s . The f i r s t s i t e was McDonalds Farm loca ted in the Fraser River D e l t a , near Vancouver, B.C. The second s i t e , c a l l e d the Beaufort Sea s i t e , cons is ted of four sub-s i t e s , a l l located near Tuktoyaktuk, N.W.T., 1n the McKenzie River D e l t a , and the Beaufort Sea. These s i t e s are descr ibed in d e t a i l below. Typical cone penetrat ion p r o f i l e s f o r a l l the s i t e s can be found in Appendix A. 4.1 McDonalds Farm S i te The McDonalds Farm s i t e was an abandoned farm located on the north side of Sea Is land , near the Vancouver Internat iona l A i r p o r t . Sea Is land i s located between the North Arm and Middle Arm of the Fraser R iver , on the north s ide of the main Fraser River D e l t a . The s i t e , from surface to a depth of 2 meters, cons is ted of s o f t , compressible c lays and s i l t s . The sand from 2 meters to 13 meters was a medium to coarse gra in s i z e with th in l ayers of medium to f i n e gra in s i z e . The sand genera l ly increased in dens i ty with depth. A th in t r a n s i t i o n l ayer of f i ne sand with some s i l t ex i s ted from 13 to 15 meters. The sand was under la in by a th ick deposi t of s o f t , normally conso l ida ted , c layey s i l t . The groundwater table was approximately 1 meter below the ground surface and pressures were approximately h y d r o s t a t i c . (Campanella et a l . , 1982). Seismic cone penetrat ion t e s t s were performed at McDonalds Farm with both the 10 and 15 sq . cm cones. The 10 sq . cm cones were Instrumented with e i t h e r a s i n g l e , hor izonta l geophone (UBC#6) or accelerometer (UBC#8). The 15 sq . cm cone was Instrumented at d i f f e r e n t times with a t r i a x i a l package of geophones and accelerometers. The on-shore f i l t e r descr ibed in sec t ion 3.4.4 was used in conjunct ion with the acce lerometers . Both the mechanical hammer 49 and Buf fa lo gun sources were used at the s i t e . 4.2 Beaufort Sea S i tes The l oca t ions of the Beaufort Sea s i t e s are shown i n F igure 4 . 1 . The four sub-s i t es are c a l l e d the School house s i t e , the Swimming Po int s i t e , the Richards Is land s i t e , and the Tuktoyaktuk Harbour s i t e . Test ing at these s i t e s was performed in l a t e March (1985). Ice was present at a l l the s i t e s and was approximately 2 meters t h i c k . These s i t e s w i l l be descr ibed below. The s i t e desc r ip t ions are summarized from Campanella et a l . (1985). 4.2.1 School house S i te The School house s i t e was located in the near o f f shore area west of Tuktoyaktuk (see F igure 4 . 1 ) . Depth of water and sea- i ce (depth to mudline) at the s i t e var ied from 2.5 to 4.25 meters, and was genera l ly inc reas ing with inc reas ing distance from the s h o r e l i n e . The s o i l at Schoolhouse s i t e cons i s ted of medium dense to dense, s i l t y , f i ne sand, genera l ly ending i n permafrost . The density of the sand and depth to permafrost appeared to increase with Increasing distance from the s h o r e l i n e . Seismic cone penetrat ion t e s t s were performed using both the 10 and 15 sq . cm cones. Both the UBC#6 and the UBC#8 cones were used. The 15 sq. cm cone was instrumented at d i f f e r e n t times with a b i a x i a l package of geophones and accelerometers. Unfortunate ly , the o f f - shore f i l t e r descr ibed in sec t ion 3.4.4 d id not adequately attenuate the unwanted frequencies from the accelerometer responses. Thus, the s igna l s from the accelerometers were not adequately f i l t e r e d , and could not be used. The seismic cap source was used exc lus i ve l y at the Schoolhouse s i t e . The three d i f f e r e n t con f igura t ions descr ibed in Sect ion 3.3.6 were a l l t r i e d ; that 1s, the seismic cap was lowered on a pole below the i c e , the seismic cap 135° 3C r=bo: 2C • i n 134° 5C rrfr-r 4C r-r+rr 3C 2C 133c 50 < '225' Hoooer-; ' " Island BELUGA BAY E A u f o ; ( A R C T 723 > P " " * n Vj'lsland R T I C O C E A SITE 3 RICHARDS ISL. A Y K U G M i \ L L I T ^ C ! ^I^V'.-.. Summer 70° S E A N J •>• - " ."" * • -JA--...•>•'Bay "V A Y j'jrtendrickson fa Topk.k Pt^- ^ -• Fisn - • i - • -Denis •225. , Ut - . • • - -Umiak' . V f r _ ..• Kitt igazuit •^ ••IsJand TuktoyaktukoJ•'•-> • SITE 1 SCHOOLHOUSE SITE 2 SWIMMING POINT l ' -Figure 4.1 Location Map for Beaufort Sea Sites was lowered f r e e l y to below the i ce and to the mudline, and the seismic cap was attached to a blade and embedded below the mudl ine. Unfortunate ly , the s o i l at the s i t e surface was too dense to al low the blade with the seismic cap to be embedded. Thus, no data was obtained from t h i s source at t h i s s i t e . 4.2.2 Swimming Point S i t e The Swimming Point s i t e was loca ted in the east channel of the McKenzie R iver , approximately 65 km south west of Tuktoyaktuk as shown in F igure 4 . 1 . The depth to mudline var ied from 1.75 meters to 11.0 meters depending on the d istance from shore. Close to shore, where the depth to mudline was l e s s than 2 meters, the i c e extended to the mudline. The upper s o i l s at the s i t e cons i s ted of predominantly s o f t , organic s i l t with l ayers that were more c layey or sandy. The c layey layers were s l i g h t l y overconsol idated. Underly ing these s o f t s o i l s was a gravel l a y e r . The th ickness of the s o f t s o i l s increased towards shore. Seismic cone penetrat ion t e s t s were performed with both the UBC#6 and 15 sq . cm cones. The 15 sq . cm cone was instrumented with a b i ax ia l package of geophones. The UBC#8 cone was used at t h i s s i t e , but , as at the Schoolhouse s i t e , the f i l t e r i n g was inadequate. Both the mechanical hammer source and the se ismic cap source were used at the Swimming Point s i t e . The hammer source was used where the 1ce extended to mudl ine. The seismic cap source was used where there was both water and i c e . The seismic cap source was used with the se ismic cap lowered f r e e l y to j u s t below the i ce or lowered to mudl ine. 4 .2 .3 Richards Is land S i t e The Richards Island s i t e was loca ted in Beluga Bay, west of North Po in t , Richards Is land (see Figure 4 . 1 ) . The i c e extended to mudline at Richards Is land and was 1.9 meters t h i c k . Water d id f low Into the hole through the Ice during penet ra t ion . The s o i l s a t the Richards Is land s i t e cons is ted mainly of s i l t y c lay with a l a y e r of dense sand between 4 meters and 8 meters. The c layey s o i l s were s l i g h t l y overconso l idated . Permafrost was encountered at a depth of 13.5 meters. The UBC#6 cone was used. The mechanical hammer source provided the source f o r seismic waves. The seismic cap source was not used at t h i s s i t e . 4 .2 .4 Tuktoyaktuk Harbour S i t e The Tuktoyaktuk Harbour s i t e was located wi th in the harbour near the hamlet of Tuktoyaktuk. (see F igure 4 . 1 ) . The depth to mudline was 6.6 meters. The s o i l s at Tuktoyaktuk Harbour cons i s ted of medium dense to dense f i n e sand with some t h i n lenses of s i l t y sand. The density of the sand appeared to decrease with depth. The UBC#6 cone was used. The seismic cap source generated the seismic waves. The seismic caps were e i t h e r lowered on a pole to below the i c e , or attached to a blade and embedded j u s t below the mudline. The s o i l at the surface of t h i s s i t e was s o f t , a l lowing the blade to be e a s i l y embedded. 5. EVALUATION OF DIFFERENT SOURCES 53 The main c r i t e r i a upon which a seismic source i s eva luated , are the source's r e p e a t a b i l i t y , strength and d i r e c t i o n a l i t y (Stokoe and Hoar, 1978). This chapter w i l l evaluate the use of three ca tegor ies of sources with the seismic cone penetrometer. These categor ies of sources, as out l ined in Chapter 3, are mechanical sources, on-shore exp los ive sources, and o f f -shore explosive sources. Each of the source types w i l l be looked at i n d i v i d u a l l y , and then they w i l l be compared with each o ther . 5.1 Evaluat ion of the Mechanical Sources 5.1.1 Hammer Shear.Wave Source The hammer shear wave source employed f o r t h i s study produced, as expected, s t rong, d i r e c t i o n a l , repeatable shear waves. F igure 5.1 shows po lar i zed hor izonta l geophone response p r o f i l e s from the hammer shear wave source. Eva luat ion of the use of t h i s source with the seismic cone penetrometer has been presented prev ious ly (R i ce , 1984), and w i l l not be repeated here. The main advantages of t h i s source are i t s ease of use, i t s p o l a r i z i n g c a p a b i l i t i e s , and i t s a b i l i t y to generate predominantly shear waves. These c h a r a c t e r i s t i c s make i t a standard to which other sources may be compared. 5.1.2 Hammer P-wave Source The hammer P-wave source was not s u c c e s s f u l l y used with the seismic cone. The hammer P-wave source generated a compression wave thats v e r t i c a l component was l a r g e r than i t s hor izonta l component, and thus was best detected by a v e r t i c a l r e c e i v e r . Typical v e r t i c a l accelerometer responses from the hammer P-wave source at two successive depths are shown in F igure 5 .2 . As can be seen from the 54 Time (milliseconds) Figure 5.1 Horizontal Geophone Response P r o f i l e f o r Hammer Shear Source V e r t i c a l Accelerometer (Low Pass F i l t e r Cut-off Frequency = 100 Hz) Hammer P-wave Source McDonalds Farm Time (milliseconds) Interval Time = 0.16 msec ===^  Ve l o c i t y = 6250 m/s, approximately Vp i n s t e e l Figure 5.2 V e r t i c a l Accelerometer Response to Hammer P-wave Source f i g u r e , the wave forms are not separated i n time as expected. For a v e l o c i t y of 1600 m/s, an average expected P-wave v e l o c i t y f o r t h i s s o i l type, the in terva l time would be 0.625 m i l l i s e c o n d s . The i n t e r v a l time between the two wave forms shown i s only 0.16 m i l l i s e c o n d s , i n d i c a t i n g a v e l o c i t y of 6250 m/s, which i s approximately the speed of a compression wave in s t e e l . A l s o , the d i r e c t a r r i v a l v e l o c i t y using the d i r e c t a r r i v a l time fo r 10 meters depth, gives a v e l o c i t y o f 1086 m/s, a slower v e l o c i t y than expected fo r saturated, inorganic s o i l . The reasons fo r the response of the v e r t i c a l rece iver not representing the s o i l response w i l l be discussed i n Chapter 6. Horizontal accelerometers were a lso used to detect the wave s ignal from the hammer P-wave source. F igure 5.3 shows the hor izonta l accelerometer responses at two successive depths. As can be seen from the f i g u r e , the amplitude of the i n i t i a l P-wave a r r i v a l i s very s m a l l , making i n t e r p r e t a t i o n d i f f i c u l t . Thus, because i n t e r p r e t a t i o n of the f i r s t a r r i v a l i s d i f f i c u l t , large e r ro rs in i n te rva l times and thus v e l o c i t i e s , can occur. I t i s poss ib le that i f several hor izonta l accelerometer responses from the hammer P-wave source were added together, the a r r i v a l time of the P-wave could be picked with more conf idence. 5.2 On-shore Explos ive Source The Buf fa lo Gun, the on-shore exp los ive source, was found to be a strong source of compression and shear waves. However, the Buf fa lo gun could not be p o l a r i z e d , and was not repeatable at shallow depths (depths l e s s than 12 meters) . These a t t r i bu tes of the Buf fa lo gun w i l l be d iscussed below. The Buf fa lo gun produced strong compression and shear waves. F igure 5.4 shows a t yp i ca l hor izonta l accelerometer response p r o f i l e f o r the Buf fa lo gun (Ver t i ca l rece ivers could not be used. See Chapter 6 ) . The compression wave 57 Hammer P-wave Source McDonalds Farm Horizontal Accelerometer Low Pass F i l t e r with Cut-off Frequency = 100 Hz 20 40 60 Time (milliseconds) Figure 5.3 Horizontal Accelerometer Responses to Hammer P-wave Source ure 5.4 Horizontal Accelerometer Response P r o f i l e for Buffalo Gun a r r i v a l i s e a s i l y picked as the f i r s t wave to a r r i v e . The shear waves are the s t rong, lower frequency waves with a much slower a r r i v a l time than the compression waves. At depths greater than about 10 meters, i t i s f a i r l y easy to pick the shear wave a r r i v a l s , although the compression wave i s more d i f f i c u l t to p i ck , because i t i s h igh ly attenuated. For depths l e s s than 10 meters, d i s t i n g u i s h i n g between the compression and shear wave i s d i f f i c u l t because of the add i t ion of the two waves. Explos ive sources are not d i rec t i ona l and thus can not be p o l a r i z e d . However, the amplitude and sign of the waveform rece ived from the Buf fa lo gun was a f fec ted by the alignment of the source and r e c e i v e r . The l a r g e s t amplitude s igna l s were obtained when the Buf fa lo gun was on the l i n e of the o r i e n t a t i o n of the hor izonta l rece iver , and the smal lest amplitude s igna l s when the Buf fa lo gun was in a l i n e perpendicular to the o r i e n t a t i o n of the rece iver (see F igure 5 . 5 ) . Because a hor izonta l rece iver was used, the s ign of the Buf fa lo gun response depended on which s ide of the truck the gun was f i r e d . The combined e f f e c t s of source and rece ive r alignment and the mul t ip le wave source made i n t e r p r e t a t i o n d i f f i c u l t . The r e p e a t a b i l i t y o f the Buf fa lo gun was only good below approximately 12 meters (see F igure 5 . 6 ) . Above 12 meters, the r e s u l t s v a r i e d , at some depths by as much as 50 percent . Some of t h i s v a r i a b i l i t y was due to the d i f f e r e n t types of rece ivers and t h i s w i l l be d iscussed i n Chapter 6. However, the v a r i a b i l i t y was mainly due to t r i g g e r i n g problems and/or t rave l path problems. These two fac tors w i l l be d iscussed below. Neither of the t r i g g e r i n g systems used with the Buf fa lo Gun were p a r t i c u l a r l y s u c c e s s f u l . This was because the t r i g g e r was ac t i va ted by the wave t r a v e l l i n g through the gun, and t h i s wave was not c o n s i s t e n t . Although the geophone t r i g g e r was used with some success, i t d id not allow compression wave a r r i v a l times to be picked cons i s ten t l y with conf idence . The a r r i v a l of Time (milliseconds) 40 60 80 100 120 60 160 (LI 00 O > 4-1 3 Cu •u 3 O cu co CO 4 J C - H O O co 6 Ph (-1 <D 4-1 CU B O J-l 0J i H 0) O O <: r 0 LlOO Location of Buffalo Gun • Shotholes Orientation of/ Horizontal Accelerometer McDonalds Farm Depth 10.5 meters Buffalo Gun Offset 4.5 meters Shothole Depth .75 meters Horizontal Accelerometer Low Pass F i l t e r Cut-off Frequency = 100 Hz Figure 5.5 V a r i a t i o n of Accelerometer Response with P o s i t i o n of Buffalo Gun Source 61 0 0-J s-a. a a 10 15-20 S - Wava V e l o c i t y (m/e) B u f f a l o Gun Source 100 I 200 300 400 I 500 O L E G E N D Caophonae Acca1sramatari AO O I A O _1_ McDonalds Farm Figure 5.6 Comparison of Shear Wave V e l o c i t y P r o f i l e s from Buffalo Gun Source 62 the slower shear wave was l e s s a f fec ted by the t r i g g e r i n g problems. However, c a l c u l a t e d compression wave a r r i v a l times were sometimes used to co r rec t the shear wave a r r i v a l times f o r the t r i g g e r i n g e r r o r . Th i s c o r r e c t i o n was, at t imes, as much as 2.5 m i l l i s e c o n d s . The c a l c u l a t i o n of t rave l path length fo r the Buf fa lo gun has to take in to account not only a hor izonta l o f f s e t from the cone rods, but a lso a v e r t i c a l o f f s e t from ground sur face . Both of these o f f s e t s were v a r i a b l e . To e l iminate some of t h i s v a r i a b i l i t y and thus ease i n t e r p r e t a t i o n , i t was decided to f i x the v e r t i c a l o f f s e t . This meant f i r i n g only one shot per ho le , s ince the gun could not be lodged f i rm ly at the same depth a second t ime. L imi t ing the use of the Buf fa lo gun to one shot per hole made the Buf fa lo gun a labor ious and r e l a t i v e l y slow technique to use. At depths l e s s than 6 meters, the t rave l path angle f o r the Buf fa lo gun can be l e s s than 60 degrees. Refract ion of the wave s ignal on s o i l boundaries may increase the e r r o r t rave l path length and thus the v a r i a b i l i t y i n v e l o c i t y (see Sect ion 2 . 3 . 2 ) . A l s o , re f rac ted waves may be adding to the d i r e c t waves, confusing i n t e r p r e t a t i o n . The Buf fa lo gun cou ld be considerably improved i f a true i n te rva l technique was used, ins tead of the pseudo in te rva l technique. The true in terva l technique ( inves t iga ted by R ice , 1984), i l l u s t r a t e d in F igure 5 .7 , would e l iminate t r i g g e r i n g and t rave l path problems, a l lowing both compression and shear a r r i v a l s to be picked with greater conf idence. 5.3 Off-shore Explos ive Sources 5.3.1 Seismic Cap Source The seismic cap source was found to be a s t rong , repeatable source of compression and shear waves. The seismic cap source was f i r e d e i t h e r j u s t 63 T r a v e l time c a l c u l a t e d by m o n i t o r i n g shear wave a r r i v a l from s e p a r a t e energy i m p u l s e s . f s O P S E U D O V I N T E R V A L o V a ) T r a v e l time c a l c u l a t e d by s i m u l t a n e o u s l y m o n i t o r i n g two s h e a r wave a r r i v a l s f rom a s i n g l e energy i m p u l s e . f S [Ol T R U E I N T E R V A L s Ol V b ) Figure 5.7 Comparison between True and Pseudo In t e r v a l Measurement (from Rice, 1984) below the i ce or at the mudline. These two methods of f i r i n g the seismic cap w i l l be considered separate ly . F igure 5.8 shows a t y p i c a l hor izonta l geophone response p r o f i l e f o r the seismic cap f i r e d j u s t below the i ce (lowered on a pole to a f i xed depth). The compression waves are d i s t ingu ished by being the f i r s t wave to a r r i v e . The shear waves are the l a t e r , lower frequency waves with f a i r l y high amplitudes. Interpretat ion of the shear wave a r r i v a l i s d i f f i c u l t . As with the Buf fa lo gun, use of the true i n t e r v a l technique would help great ly with i n t e r p r e t a t i o n , because the same waveform cou ld be compared at two successive depths. However, the seismic cap source was found to be f a i r l y repeatable, as seen i n F igure 5 .9 . It was found that in order to use the compression wave a r r i v a l s , the depth of the seismic cap below the i c e had to be c o n s i s t e n t . Several seismic cone penetrat ion soundings were done without proper ly c o n t r o l l i n g t h i s depth, and the compression wave v e l o c i t i e s cou ld not be determined. Some of the v a r i a b i l i t y of the S-wave v e l o c i t y shown in F igure 5.8 cou ld be from t h i s va r i ab le depth problem. Th is depth contro l would not have been necessary i f a true in te rva l technique were used. F igure 5.10 shows a t y p i c a l hor izonta l geophone response p r o f i l e f o r the seismic cap f i r e d at the mudline. Th is technique d id not have the same separat ion in time of the compression and shear waves as the technique of f i r i n g the seismic cap j u s t below the i c e , because of the t rave l path l ength . Interpretat ion of the shear wave a r r i v a l s was d i f f i c u l t , but not appreciably more d i f f i c u l t than that for f i r i n g the seismic cap j u s t below the i c e . Moreover, compression wave v e l o c i t i e s cou ld always be determined from t h i s technique because the p o s i t i o n of the seismic cap was cons i s ten t . 5 .3 .2 . Embedded Blade with Seismic Cap Source Although the embedded blade with seismic cap source was only used once Figure 5.8 Horizontal Geophone Response P r o f i l e f o r Seismic Cap Source f i r e d j u s t below Ice (Campanella et a l , 1985) 66 S - Wove V e l o c i t y <m/«> Seismic Cap Source 100 200 300 400 500 1 1 I I LEGEND GSC#5 o GSC06 GSDV8A o A A 0 o-i \ A 15-Swimming Point S i t e - Beaufort Sea Figure 5 . 9 Comparison of Shear Wave V e l o c i t y P r o f i l e s for the Seismic Cap Source f i r e d j u s t below Ice at Swimming Point S i t e Figure 5.10 Horizontal Geophone Response P r o f i l e f o r Seismic Cap Source f i r e d at Mudline to obta in a seismic cone pentrometer p r o f i l e , 1t appeared to be a s t rong, semi-d i rec t iona l source. F igure 5.11 shows the geophone response p r o f i l e f o r the embedded blade source. Th is source not only gives a strong compression wave a r r i v a l , but a lso shows a stronger shear wave then the seismic cap alone showed. The reason the embedded blade shows stronger shear waves could be because of i t s asymmetry. Mooney (1980) s tates that t h e o r e t i c a l l y a source must be unbalanced, d i r e c t i o n a l , and asymmetric to generate shear waves. The embedded blade source i s a r e l a t i v e l y slow technique to use since the blade must be l i f t e d up from mudline a f t e r each t e s t . 5.4 Comparison of D i f f e r e n t Sources 5.4.1 Buf fa lo Gun Source versus Hammer Shear Wave Source F igures 5.12 and 5.13 show shear wave v e l o c i t y p r o f i l e s f o r both the Buf fa lo gun and hammer source. The p r o f i l e s obtained from the accelerometer show s i m i l a r r e s u l t s f o r both methods below 12 meters, but above 12 meters the v e l o c i t i e s obtained from the two sources, vary by as much as 50 percent . The p r o f i l e obtained by the geophone shows the Buf fa lo gun to give v e l o c i t i e s which are genera l ly smal ler than those given by the hammer. Thus the Buf fa lo gun gives reasonable r e s u l t s f o r depths greater than 12 meters. A s t a t i s t i c a l a n a l y s i s , such as the one c a r r i e d out by Rice (1984) fo r the hammer shear source, should be performed with the Buf fa lo gun i n order to ascer ta in i t s r e l i a b i l i t y . Chapter 6 w i l l compare the geophone and accelerometer responses. For use on-shore, the hammer i s very much s impler than the Buf fa lo gun to use and to i n t e r p r e t , because i t 1s a wave generator which can be e a s i l y p o l a r i z e d . However, the hammer does not produce strong compression waves which can be detected by hor izonta l r e c e i v e r s , and thus Po isson 's r a t i o (see Chapter 7) can not be determined using the hammer source a lone. I f an Figure 5.11 Horizontal Geophone Response P r o f i l e f o r Embedded Blade Source Figure 5.12 Shear Wave Velocity P r o f i l e s from the Horizontal Accelerometer for the Hammer and Buffalo Gun Sources o 200 McDonalds Farm Figure 5.13 Shear Wave Vel o c i t y P r o f i l e s from the Horizontal Geophone for Hammer and Buffalo Gun Sources accurate t r i g g e r i n g c i r c u i t can be developed fo r the Buf fa lo gun, or i f a true in terva l technique i s used with the Buf fa lo gun, then i t would be a good source fo r compression waves fo r depths l e s s than 10 meters. As can be seen from Figure 5.4, the compression wave does attenuate f a i r l y rap id l y with depth. Th is problem could be a l l e v i a t e d by adding several s igna ls together at depth. Interpretat ion of shear waves produced by the Buf fa lo gun i s not d i f f i c u l t at depth because of the separat ion of the compression and shear waves. Thus i f very deep on-shore cone t e s t i n g i s necessary (depths greater than 40 meters) , the Buf fa lo gun cou ld be employed f o r depths below 10 meters. 5.4.2 Seismic Cap Source versus Hammer Shear Wave Source Figure 5.14 shows shear wave v e l o c i t y p r o f i l e s f o r the seismic cap source and hammer source. Both these sources show s i m i l a r r e s u l t s f o r shear wave v e l o c i t y . Th is ind i ca tes that the seismic cap source, although d i f f i c u l t to i n t e r p r e t g ives reasonable r e s u l t s . The pos i t i on at which the seismic cap i s f i r e d , e i t h e r j u s t below the ice or at the mudline, does not a f f e c t the r e s u l t s o f the shear wave v e l o c i t y c a l c u l a t i o n as can be seen from Figure 5.15. Although both pos i t ions give s i m i l a r r e s u l t s , f i r i n g , t h e cap j u s t below the i ce gives a greater separat ion between the P and S-wave, thus a id ing i n i n t e r p r e t a t i o n . 5.4.3 Embedded Blade Source versus Seismic Cap Source F igure 5.16 shows the P and S-wave v e l o c i t y p r o f i l e s obtained from both the embedded blade and seismic cap sources. The f i gure shows that very s i m i l a r r e s u l t s are obtained from both sources f o r P-wave v e l o c i t i e s . The shear wave v e l o c i t i e s obtained from the seismic cap source are c o n s i s t e n t l y smal ler than those obtained from the embedded blade source. Further research Is necessary to ascer ta in i f t h i s i s a cons is tent r e l a t i o n s h i p between the two sources. S - Wove V e l o c i t y (m/s) Hammer Source S - Wove V e l o c i t y (m/s) Seismic Cap Sourco 200 COME BEARING 0c (bar) 250 Swimming Point Site - CPT GSC//8A Figure 5.14 Shear Wave Velocity P r o f i l e s for Hammer and Seismic Cap Sources S - V e l o c i t y (m/s) Seismic Cop below i c e 100 I 200 I 300 i 400 L_ O LEGEND Shot-hole 1 Shot-hole 2 500 0 0 4 Ok i O 10' 15-S - Wave V e l o c i t y (m/s) Seismic Cop at mudline 100 I 200 I 3D0 I .400 I 500 CONC BEARING 0c (bar) LEGEND Shot-hole 1 Shot-hole 2 (>A OA Swimming Point Site - CPT GSC//7 Figure 5.15 Shear Wave Velo c i t y P r o f i l e s f o r Seismic Cap source f i r e d j u s t below Ice and at Mudline Wove V a l o c l t y (m/«0 S - Wave V e l o c i t y (m/«) CONE BEARING Bo (bar) 1000 1500 2000 2500 0 100 200 300 400 500 0 Tuktoyaktuk Harbour Site - "CPT GSC//12 Figure 5.16 Seismic Wave Velo c i t y P r o f i l e s for Embedded Blade and Seismic Cap Sources 6. EVALUATION OF DIFFERENT SEISMIC RECEIVERS 76 This chapter w i l l present the r e s u l t s of a comparison between d i f f e r e n t rece ive rs . As mentioned in chapter 3, the types of rece ive rs used were hor izontal and v e r t i c a l geophones and accelerometers. 6.1 Geophones versus Accelerometers Geophones and accelerometers w i l l be examined in t h i s sec t ion with the object ive of determining t h e i r r e l a t i v e advantages and disadvantages. The important c h a r a c t e r i s t i c s o f each rece iver type w i l l be o u t l i n e d and compared, and conclus ions w i l l be drawn about the appropriateness of each to s p e c i f i c a p p l i c a t i o n s . Geophones are rugged, r e l a t i v e l y inexpensive seismic wave rece ivers which do not need to be amp l i f i ed or f i l t e r e d . When used with the mechanical hammer source, they produce c l e a r s igna l s as shown i n F igure 6 . 1 . Accelerometers are l e s s rugged, and more expensive then geophones. They must be ampl i f ied and f i l t e r e d before wave s igna l s can be d i s t i n g u i s h e d . However, once amp l i f i ca t i on and f i l t e r i n g i s done, the accelerometer produces a c l e a r signal when used with the hammer source (see Figure 6 . 1 ) , and i t can detect the hammer source to a cons iderab ly greater depth than the unampl i f ied geophone. Geophones can be a m p l i f i e d . Th is increases t h e i r expense and complexity, but al lows detect ion of seismic waves to greater depths. The ra t iona le behind the i n v e s t i g a t i o n of the use of accelerometers with the cone penetrat ion t e s t , stemmed from the a p p l i c a t i o n of the seismic cone to o f f -shore I n v e s t i g a t i o n s . Exp los ive sources are genera l ly used o f f - s h o r e , and these sources produce predominantly P and SV-waves. Thus, the wave s igna ls received are a combination of both P and SV-waves, and p ick ing the a r r i v a l time of the SV-wave can often be d i f f i c u l t . 77 T 1 1 1 1 r SH Geophone Accelerometer *(C.O.F. = 100Hz) Hammer Shear Source McDonalds Farm Depth = 10.0 m *Low pass f i l t e r cut-off frequency = 100 Hz 20 40 60 80 100 120 Time (milliseconds) 140 160 Figure 6.1 Horizontal Geophone and Accelerometer Responses to Hammer Shear Source Because the natural frequency of the geophones used in t h i s study was c lose to the frequency of the shear waves in the s o i l , the response of the geophone i s c l ose to resonance, and the in terna l damping of the geophone a f f e c t s i t s response to a large degree. The natural frequency of the accelerometers used in t h i s study, on the other hand, was well above the frequency of shear waves in s o i l , and the accelerometers were undamped. Thus, the accelerometers tend to show a response which more c l o s e l y represents the response of the s o i l . In conventional seismic t e s t i n g methods, geophones are genera l ly used. However, these geophones genera l ly have a very low natural frequency (5 to 15 Hz) and thus, are not exc i ted near resonance. Such low natural frequencies require a l a r g e r mass, and thus, genera l ly a l a r g e r s i z e . Th is type of geophone was too b ig to f i t in a 10 or 15 sq . cm cone. Figure 6.2 shows a comparison of hor izontal geophone and accelerometer responses to the Buf fa lo gun. Although i n t e r p r e t a t i o n of the f i r s t a r r i v a l of the shear wave i s d i f f i c u l t with t h i s source from both the accelerometer and geophone, the accelerometer tends to show more d e t a i l of the s o i l response. F igure 6.3 compares the shear wave v e l o c i t y p r o f i l e s of the hammer and Buf fa lo gun obtained using both geophones and accelerometers. The geophone and accelerometer show good agreement of shear wave v e l o c i t i e s obtained from the hammer shear source. V a r i a t i o n between the two can be mainly accounted for by a change i n bear ing res i s tance between the two soundings (compare Figures 5.12 and 5 .13) . Thus, f i l t e r i n g of the accelerometer s ignal appears to have a n e g l i g i b l e a f f e c t on the v e l o c i t y c a l c u l a t i o n f o r the hammer shear source. This i s as expected i f a source repeatedly produces shear waves of the same frequency, because the phase s h i f t w i l l be a constant . The use of the pseudo-Interval technique fo r c a l c u l a t i n g wave v e l o c i t i e s e l iminates the 79 Figure 6.2 Horizontal Geophone and Accelerometer Responses to the Buffalo Gun Source Wave V e l o c i t y <m/e> Hammar S o u r c e S - Wave V e l o c i t y (m/e) B u f f a l o Gun S o u r c e 100 I 10-a. a D 20-30-200 L_ 300 I 400 L_ 5C0 0 0 LEGEND G e o p h o n e A c c e 1 e r o m e t e r - 10-AO X 20-30-100 1_ 200 i 30G i . 400 I 500 CONE BEARING 0c (bar) LEGEND A G a o p h o n e O A c c e l e r o m e t e r AO A O 10 200 McDonalds Farm - CPT//21 Figure 6.3 Shear Wave Velocity P r o f i l e s from the Horizontal Geophone and Accelerometer for the Hammer and Buffalo Gun Sources e f f e c t of the constant phase s h i f t . For the Buf fa lo gun source, the geophone and accelerometer do not give as s i m i l a r r e s u l t s as f o r the hammer. Th is v a r i a t i o n cou ld be due to a combination of changes i n bearing res is tance between soundings, t r i g g e r incons i s tenc ies , and v a r i a t i o n in phase s h i f t of the accelerometer response due to add i t ion of compression and shear waves. The a d d i t i o n of compression and shear waves causes a frequency change i n the s ignal and thus a change in phase s h i f t . As can be seen from Figure 6 .3 , the v a r i a b i l i t y between the two receivers i s greater at the shal lower depths where the a r r i v a l s of compression and shear waves are c l o s e r together . Geophones were used with the seismic caps o f f - s h o r e . As with the Buf fa lo gun, the seismic cap produces predominantly P and SV-waves. In terpre ta t ion of the geophone response to the seismic cap was d i f f i c u l t . However, i t was found that i f the seismic cap was f i r e d from a p o s i t i o n j u s t below the i c e , greater separation occurred between the P and SV-wave s igna l s (see F igure 6 . 4 ) . Th is made the i n t e r p r e t a t i o n of the f i r s t a r r i v a l of the SV-wave somewhat e a s i e r . 6.2 Horizontal versus V e r t i c a l Receivers In conventional seismic t e s t i n g , both v e r t i c a l and hor izonta l rece ivers are used to detect compression and shear waves. These r e c e i v e r packages are wedged in the borehole in such a way, so that the rece ive rs move with the s o i l i n both the v e r t i c a l and hor izonta l d i r e c t i o n s . Both hor izonta l and v e r t i c a l detectors were i n s t a l l e d in the 15 sq . cm seismic cone penetrometer. The hor izonta l rece ivers s u c c e s s f u l l y detected SH-waves from the mechanical source, and P and SV-waves from the explos ive sources. Typica l responses of the hor izonta l rece ivers from each of the three source types are shown i n F igures 6 .1 , 6 .2 , and 6.4. Seismic Cap Source Schoolhouse S i t e - Beaufort Sea Depth = 6.0 m Figure 6.4 Horizontal Geophone Response to the Seismic Cap Source f i r e d j u s t below the Ice. The use of v e r t i c a l rece ivers in the seismic cone d id not meet with success. The rece ive r response d id not change apprec iably with depth. F igure 6.5 shows the response with depth of a v e r t i c a l geophone. As can be seen, ne i ther compression nor shear wave a r r i v a l s can be c o n s i s t e n t l y p icked. A poss ib le explanat ion fo r the response of the v e r t i c a l rece iver has to do with the v e r t i c a l s t i f f n e s s of the cone and rods . Because the cone i s weighted down by the rods above i t , and because i t i s made of a very s t i f f material in comparison with the s o i l , the cone can not respond as e a s i l y to v e r t i c a l s o i l motion as i t can to hor izonta l s o i l motion. Consequently, the v e r t i c a l r ece ive r does not represent the response of the s o i l to the body waves passing through i t . 84 Time (milliseconds) 0 50 100 150 200 250 300 350 400 r i 1 1 1 1 1 • 1 J I I I • • L Figure 6.5 V e r t i c a l Geophone Response P r o f i l e f o r Seismic Cap Source 7. EVALUATION OF COMPRESSION WAVE DATA 85 The a b i l i t y to generate and detect not only shear waves, but a l so compression waves, al lows the c a l c u l a t i o n of Po isson 's r a t i o f o r the s o i l . For example, both Beeston and McEv i l l y (1977) and Warrick (1974) have used in s i t u body waves to obtain Po isson 's r a t i o . Th is chapter w i l l b r i e f l y ou t l ine the r e s u l t s obtained using the o f f - shore explos ive sources to obtain Po isson 's r a t i o . The explos ive sources descr ibed i n Chapter 5, generate both compression and shear waves, and these waves can be detected and in te rp re ted with the seismic cone. Using the equation given in Chapter 2, Po isson 's r a t i o was c a l c u l a t e d fo r the Schoolhouse and Tuktoyaktuk Harbour s i t e s . F igures 7.1 and 7.2 show the P and S-wave v e l o c i t y p r o f i l e s with the c a l c u l a t e d Po i sson ' s r a t i o s f o r these s i t e s . The c a l c u l a t e d Po isson 's r a t i o s vary between 0.33 and 0.46 a t the two s i t e s . Po isson 's r a t i o obtained fo r sand from conventional t e s t i n g methods i s genera l ly around 0.33. Thus, the r e s u l t s obtained from the seismic cone seem to be h i g h . There are two fac tors which may exp la in t h i s d iscrepancy. F i r s t , the compression wave i s probably t r a v e l l i n g through the water in the s o i l , 1n which case i t s v e l o c i t y 1s only p a r t i a l l y a f f ec ted by the c o m p r e s s i b i l i t y of the s o i l ske le ton . Second, Po isson 's r a t i o 1s a f f e c t e d by s t r a i n l eve l and only those values obtained at the same s t r a i n l eve l should be compared. The r e s u l t s obtained using the seismic cone penetrat ion t e s t are s i m i l a r to r e s u l t s obtained by Beeston and McEv i l l y (1977) using a conventional downhole seismic t e s t in s i m i l a r s o i l s . Schoolhouse S i t e - CPT GSC//3 Figure 7.1 Calculated Poisson's Ratio for Schoolhouse S i t e a) 0 to 15 meters P - Wave V e l o c i t y (m/s) S e i s m i c Cap S o u r c e S - Wave V e l o c i t y (m/s) S e i s m i c Cop S o u r c e 500 CONE BEARING Oc (bar) 15 250 H 20 2S 30 • Schoolhouse S i t e - CPT GSC#3 Figure 7.1 Calculated Poisson's Ratio for Schoolhouse S i t e b) 15 to 30 meters Tuktoyaktuk Harbour S i t e - CPT GSC//12 Figure 7.2 Calculated Poisson's Ratio for Tuktoyaktuk Harbour S i t e co Co 8. EVALUATION OF DAMPING CHARACTERISTICS 89 8.1 Introduct ion The determination of 1n s i t u material damping great ly enhances the dynamic ana lys i s of s o i l s . Two d i f f e r e n t methods of obta in ing material damping using the seismic cone were b r i e f l y evaluated fo r t h i s study. F i r s t , undamped accelerometers were used in an attempt to obta in the true response of the s o i l and thus, s o i l damping. Second, t rue in terva l geophone data (obtained by R ice , 1984) was used in conjunct ion with a waveform ana lys i s suggested by Hoar and Stokoe (1984), i n an attempt to obta in material damping. These methods w i l l be d iscussed below. 8.2 Accelerometers to obta in So i l Damping As discussed in Chapter 6, accelerometers tend to show a response which more c l o s e l y represents the response of the s o i l . Thus, damping c h a r a c t e r i s t i c s of s o i l should t h e o r e t i c a l l y be a t ta inab le from accelerometer responses. Using accelerometer responses from the hammer shear source, the log decrement and thus damping r a t i o o f the response were determined. The log decrement of a c y c l i c response i s the natural logarithm of the r a t i o of the amplitude of two success ive peaks (see Figure 8 . 1 ) . The damping r a t i o , D, can be determined from the log decrement using the fo l lowing equat ion: D - 6 / ( < 5 2 + 4 ( T T ) 2 ) where & = log decrement. T y p i c a l l y , s o i l s have a damping r a t i o , D, of approximately .05 . Damping r a t i o s determined using the accelerometer responses are p lo t ted in F igure 8 .2 . The average value D i s 0.196, approximately 4 times the value expected. T y p i c a l Horizontal Accelerometer Response to Hammer Shear Source Time A Log Decrement 6 = In 1 A 2 Figure 8.1 D e f i n i t i o n of Log Decrement from Horizontal Accelerometer Response to Hammer Shear Source Damping R a t i o .05 .1 I L . 15 2 25 A A r a. o a 5- A ~ McDonalds Farm Hammer Shear Source Damping r a t i o s calculated from log decrement of h o r i z o n t a l accelerometer response. Figure 8.2 Damping Ratios From Accelerometer Response versus Depth A poss ib le explanat ion fo r the high damping r a t i o values obtained from the accelerometers i s that the accelerometers are not responding to the s o i l a lone. The accelerometer i s f i r m l y attached to the seismic cone penetrometer which i s i t s e l f coupled to the s o i l . The seismic cone penetrometer has i t s own response c h a r a c t e r i s t i c s to wave e x c i t a t i o n . Thus, the accelerometer response represents a combination of the cone and s o i l responses, rather than the s o i l response a lone . In order to determine the response of the s o i l a lone, the response of the cone to s p e c i f i c wave e x c i t a t i o n must be determined, and then subtracted from the to ta l response of the cone-so i l system seen by the accelerometer. 8.3 Waveform Ana lys i s to determine So i l Damping Determination of i n s i t u mater ia l damping has been attempted by Hoar and Stokoe, 1984, using the c rossho le seismic t e s t i n g method. Hoar and Stokoe state that other seismic f i e l d methods, such as downhole t e s t i n g , could be used to obtain in s i t u mater ia l damping, as long as two shear wave a r r i v a l s are monitored from a s i n g l e energy impulse. That i s , the t rue Interval technique must be used, as opposed to the pseudo in te rva l technique. Rice (1984) used the t rue Interva l technique to obtain much of the data fo r h i s research. Using some of t h i s data , the manual waveform ana lys i s suggested by Hoar and Stokoe, 1984, was performed to obtain in s i t u damping r a t i o s . The Four ie r waveform a n a l y s i s suggested by Hoar and Stokoe, 1984, was not performed, because the computer f a c i l i t i e s to perform t h i s a n a l y s i s were unava i lab le . This sect ion w i l l b r i e f l y summarize the r e s u l t s of t h i s i n i t i a l look at obtaining damping r a t i o s from the seismic cone penetrometer. 8.3.1 Results o f Manual Waveform A n a l y s i s The decay of amplitudes of body waves as they propagate through the s o i l 1s a combination of geometrical and material dampings. The material component f o r body waves (a lso known as the v iscous damping component) i s given by the fo l lowing equat ion: and a l l other var iab les are def ined in F igure 8 . 3 . F igure 8.4 shows the r e s u l t s of t h i s data a n a l y s i s . In the sands above 15 meters, the damping r a t i o s ranged from 0.023 to 0.138, with an average value of 0 .08. In the c layey s i l t s below 15 meters, the damping r a t i o s ranged from 0.057 to 0.155, with an average value of 0.105. These damping r a t i o s are greater than those obtained by Hoar and Stokoe. A l s o , Seed and I d r i s s (1970) show s l i g h t l y higher damping r a t i o s in sand then in c l a y , whereas the opposite i s seen here. These dev iat ions from the expected values may be due to the way i n which the seismic cone penetrometer i n t e r a c t s with the s o i l . More research of t h i s technique i s needed before conc lus ive r e s u l t s can be obta ined. D = 1 n ( A l - R l / A 2 - R 2 ) where D = damping r a t i o Top Horizontal Geophone CD XI 3 I Rj - Straight-line travel path length from source to receiver a. Straight-line travel path length from source to receiver _L Z\ McDonalds Farm Hammer Shear Source Depth 10.6 meters (Data from disks - AR-82-24 thru 30) 10 20 30 40 50 60 Time (milliseconds) 70 80 Figure 8.3 Geophone Waveforms defining Quantities f o r Damping C a l c u l a t i o n Damping R a t i o 0 04-05 _L_ 1 15 _L_ . 2 10-r. •p a. a • 20-A 30 _L McDonalds Farm Hammer Shear Source Data from Rice,1984 disks AR-82-24 thru 30 Damping Ratio Calculated from Manual Waveform Analysis (Hoar and Stokoe, 1984) Figure 8.4 Damping Ratios from Manual Waveform Analysis versus 9. CONCLUSIONS 96 D i f f e r e n t types of sources and rece ivers used with the seismic cone penetrat ion t e s t were inves t iga ted for t h i s t h e s i s . The sources inves t iga ted were mechanical shear and compression wave sources c o n s i s t i n g of a hammer-and-weighted-plank source; a Buf fa lo gun source; a seismic cap source; and an embedded blade with seismic cap source. The rece ivers inves t iga ted were hor izonta l and v e r t i c a l geophones and accelerometers. The hammer shear source, prev ious ly invest igated by R ice , 1984, worked well and was used as a standard f o r comparison. The mechanical compression wave source was not used s u c c e s s f u l l y with the seismic cone penetrat ion t e s t , because the v e r t i c a l r e c e i v e r s , needed to detect t h i s source, d id not give a response representat ive of the s o i l response. Rather, the v e r t i c a l rece ivers probably responded to waves t r a v e l l i n g i n the cone and rods . Horizontal rece ivers used with the hammer P-wave source d id not produce amplitudes large enough to i n t e r p r e t a c c u r a t e l y . Add i t ion of several s igna l s may improve the in te rpre ta ion and should be researched f u r t h e r . The Buf fa lo gun source gave shear wave v e l o c i t i e s which compared r e l a t i v e l y well with the shear wave v e l o c i t i e s obtained using the hammer only at depths greater than 12 meters. At depths l ess than 12 meters the two sources d i f f e r e d by as much as 50 percent . However, the Buf fa lo gun was d i f f i c u l t to i n t e r p r e t because of the add i t ion of the P and SV-waves, e s p e c i a l l y a t shallow depths. The t r i g g e r i n g system used with the Buf fa lo gun was not cons i s tent enough to al low accurate compression wave v e l o c i t y p r o f i l e s to be determined. Thus, e i t h e r a more cons is tent t r i g g e r i n g c i r c u i t should be found for the Buf fa lo gun, or a t rue in terva l technique should be used, where the energy impulse i s detected simultaneously by two r e c e i v e r s , one meter apar t . The seismic cap sources, used o f f - s h o r e , were found to give reasonable shear wave v e l o c i t y determinat ions. In a d d i t i o n , reasonable compression wave v e l o c i t y determinations were found, i f the depth at which the seismic cap was f i r e d , remained constant . In te rpre ta t ion of the waves rece ived from the seismic caps was d i f f i c u l t , because of the add i t i on of compression, shear, and r e f l e c t e d waves. In terpreta t ion of the seismic cap source signal would be eas ie r i f the t rue in terva l technique, descr ibed fo r the Buf fa lo gun, was used. Use of t h i s technique would a lso e l iminate the necess i ty of c o n t r o l l i n g the f i r i n g depth of the seismic cap. The embedded blade source appears to g ive a more well defined SV-wave then the seismic cap alone. I t i s more d i f f i c u l t to use than the seismic cap alone, because the s o i l at mudline must be s o f t enough to allow the blade to be embedded, and because the blade must be l i f t e d from the mudline to attach a seismic cap a f t e r each t e s t . However, s ince the embedded blade source was used only once to obtain a seismic wave p r o f i l e , f u r the r i nves t i ga t i on of t h i s source should be c a r r i e d out before fu r the r conclusions can be made. Both geophones and accelerometers were found to give s i m i l a r shear wave v e l o c i t i e s f o r the hammer shear source. Less s i m i l a r i t y was seen fo r the Buf fa lo gun source. This cou ld be a r e s u l t of a var iab le phase s h i f t of the f i l t e r e d accelerometer. Since compression and shear waves from the Buf fa lo gun add together, the frequency of the s igna l may vary, and thus, the phase s h i f t due to the f i l t e r may a lso vary^ Although geophones were success fu l l y used with the explos ive o f f - s h o r e sources, the use of adequately f i l t e r e d accelerometers with o f f -shore explos ive sources should be Invest igated in the f u t u r e . Accelerometers may prove e a s i e r to i n t e r p r e t and more accurate . Since geophones are cheaper and e a s i e r to use, and give reasonable r e s u l t s with explos ive sources , they are probably the best rece iver to use. Accelerometers, because they are amp l i f i ed and can detect s ignals to a 98 greater depth, can be used fo r deep penetrat ion work with mechanical shear sources. However, a m p l i f i c a t i o n of the geophone signal may be cheaper, and thus geophones could a lso be used fo r deep penetrat ion work. As mentioned above, v e r t i c a l rece ivers can not be used in the seismic cone penetrometer, because they do not give a representat ive response of the s o i l . The use of compression and shear wave v e l o c i t i e s to determine Po isson 's r a t i o gave reasonable r e s u l t s i f the s t r a i n leve l and type of compression wave were taken in to account. The pre l iminary determination of the material damping r a t i o gave r e s u l t s which were higher than expected. These r e s u l t s probably i nd i ca te the accelerometer i s responding to the so i l - cone system, rather than to the s o i l a lone . Thus, fu r ther research should be undertaken to inves t iga te the response of the accelerometer to the cone a lone . Th is response could then be subtracted from the response to the combined cone-so i l system, and thus the s o i l response could poss ib ly be e x t r a c t e d . As bet ter computer f a c i l i t e s become a v a i l a b l e , greater ana lys i s of the data obtained from the seismic cone could be performed. For example, d i g i t a l f i l t e r i n g of the accelerometer responses could be c a r r i e d out . A l s o , a Four ie r waveform a n a l y s i s to obtain mater ia l damping (Hoar and Stokoe, 1984) from true Interval responses could be attempted. Both d i g i t a l f i l t e r i n g and Four ie r ana lys i s requ i re computer storage space and communication l i n e s between the recording o s c i l l o s c o p e and the computer, which are c u r r e n t l y unava i lab le , but which are being researched at U.B.C. REFERENCES 99 A l l e n , F . N . , R i char t , F . E . J r . , and Woods, R.D., 1980, " F l u i d Wave Propagation in Saturated and Nearly Saturated Sands",Journal of Geotechnical Engineering D i v i s i o n , ASCE, V o l . 106, No. GT3, March, pp.235-254. B a l l a r d , R.F. J r . and McLean, F . G . , 1975, "Seismic F i e l d Methods f o r In S i tu Modul i" , Proceedings of the Conference on In S i tu Measurement of S o i l P roper t i es , ASCE, V o l . 1, Ray le igh , N.C . , pp.121-150. Beeston, H.E. and M c E v i l l y , T . V . , 1977, "Shear Wave V e l o c i t i e s from Downhole Measurement", Earthquake Engineer ing and Structura l Dynamics, V o l . 5, No. 2, pp.181-190. Borm, G.W., 1977, "Methods from Exp lora t ion Seismology: R e f l e c t i o n , Refract ion and Borehole Prospect ing" , Proceedings of DMSR 77, Kar ls ruhe , 5-16 Sept. 1977, V o l . 3, pp.87-144. Campanella, R .G. , and Robertson, P .K . , 1981, "Appl ied Cone Research", Symposium on Cone Penetrat ion Test ing and Experience, Geotechnical Engineering D i v i s i o n , ASCE, O c t . , pp.343-362. Campanella, R.G. , Robertson, P .K . , and G i l l e s p i e , D., 1982, "Cone Penetrat ion Test ing in D e l t a i c S o i l s " , Canadian Geotechnical J o u r n a l , V o l . 20, Feb. Campanella, R.G. , Robertson, P .K . , G i l l e s p i e , D., Howie, J . , La ing , N . , and Gre ig , J . , 1985, "Pre l iminary Eva luat ion of Seismic Cone Penetrometer in Beaufort Sea", Report to Dept. of EMR, GSC. Unpublished. Geospace Corporat ion, " S p e c i f i c a t i o n s : Model GSC-14-13 Seismometer", Houston, Tx. H a r r i s , C M . and Crede, C . E . , E d i t o r s , 1961, Shock and V ib ra t i on Handbook, V o l . 1, "Basic Theory and Measurements", McGraw-Hill Book Company, New York, Chapter 12. Hoar, R . J . and Stokoe, K.H. I I , 1984, " F i e l d and Laboratory Measurements of Mater ia l Damping of S o i l in Shear", 8th World Conference on Earthquake Engineer ing, V o l . 3, pp.47-54. Hoar, R . J . and Stokoe, K.H. I I , 1978, "Generation and Measurement of Shear Waves In S i t u " , Dynamic Geotechnical Tes t ing , ASTM, STP 654, American Society f o r Test ing and M a t e r i a l s , pp.3-29. I sh ihara , K., 1967, "Propagation of Compressional Waves in a Saturated S o i l " , Proceedings of the Internat iona l Symposium on Wave Propagation and Dynamic Propert ies of Earth M a t e r i a l s , SMFD, ASCE, Albuquerque, New Mexico, pp.451-467. 100 Kahler , S. and Meissner, R., 1983, "Radiat ion and Receiver Patterns of Shear and Compressional Waves as a Function of Po isson 's Rat io" , Geophysical  Prospecting 31, pp.421-435. McLamore, V .R . , Anderson, D.G. , and Espana, C , 1978, "Crosshole Test ing Using Explos ive and Mechanical Energy Sources", Dynamic Geotechnical Tes t ing , ASTM STP 654, ASTM, pp.30-55. Mooney, H.M., 1980, Handbook of Engineering Geophysics, V o l . 1, Se ismic , Bison Instruments I n c . , "CTTapter 6. Mooney, H.M., 1974, "Seismic Shear Waves in Eng ineer ing" , Journal of Geotechnical Engineering D i v i s i o n , ASCE, V o l . 100, No. GT8, August, pp.905-923. N i co le t Instrument Corporat ion , 1982, "Operation Manual: Ser ies 4094 D ig i t a l Osc i l l oscopes" , Madison, Ws. P a t e l , N .S . , 1981, "Generation and Attenuat ion of Seismic Waves in Downhole Tes t ing" , M.Sc.E. Thes i s , Dept. of C i v i l Eng ineer ing , Un ivers i ty of Texas, Aus t in , Tx. P re t love , A . J . , 1965, "Some Current Methods i n V i b r a t i o n Measurement", V ibrat ions in C i v i l Engineer ing, ed i ted by B.O. Skipp, Butterworths & Co. L t d . , London, pp.95-110. P u l l a n , S . E . , and MacAulay, H.A. , 1984, "A New Source f o r Engineering Seismic Surveys", P repr in t , Geological Survey of Canada. R ice , A . , 1984, "The Seismic Cone Penetrometer", M.A.Sc. Thes i s , Dept. of C i v i l Engineer ing, Un ive rs i t y of B r i t i s h Columbia, Vancouver, B.C. R ichar t , F . E . J r . , H a l l , J .R . J r . , and Woods, R.D. , 1970, V ib ra t ions of S o i l s  and Foundations, P r e n t i c e - H a l l , I n c . , Englewood C l i f f s , N . J . Robertson, P.K. , Campanella, R.G. , G i l l e s p i e , D., and R ice , A . , 1984, "Seismic CPT to Measure In S i tu Shear Wave V e l o c i t y " , So i l Mechanics S e r i e s , No. 85, Dept. of C i v i l Eng ineer ing , Un ive rs i t y of B r i t i s h Columbia, Dec. Rockland Laborator ies , I n c . , 1969, " Ins t ruc t i on Manual: Model 1022F Dual Hi/Lo F i l t e r " , Tappan, N.Y. Schwarz, S.D. and Musser, J . M . , 1972, "Various Techniques fo r Making In S i tu Shear Wave V e l o c i t y Measurements - A Desc r ip t ion and Eva luat ion" , Proceeding of the Internat ional Conference on Microzonat ion f o r Safer Construct ion Research and A p p l i c a t i o n , V o l . 2, pp.593-608. Seed, H.B. and I d r i s s , I .M . , 1970, "So i l Moduli and Damping Factors for Dynamic Response Analyses" , Report to SWAJA, Earthquake Engineering Research Center, Un ivers i t y of C a l i f o r n i a , Berkeley, Report No. EERC 70-10, December, pp.1-40. Stokoe, K.H. II and Hoar, R . J . , 1978, "Var iab les a f f e c t i n g In S i tu Seismic Measurements", Proceedings of the Conference on Earthquake Engineering and So i l Dynamics, Pasadena, Geotechnical Engineer ing D i v i s i o n , ASCE, V o l . 2, pp.919-939. Stokoe, K.H. II and Hoar, R . J . , 1977, " F i e l d Measurement of Shear Wave Ve loc i ty by Crosshole and Downhole Seismic Methods", Proceedings of DMSR 77, Kar lsruhe, 5-16 Sept . 1977, V o l . 3, pp.115-137. T e l f o r d , W.M., Ge ldar t , L . P . , S h e r i f f , R .E . , and Keys, D.A. , 1977, App l ied  Geophysics, Cambridge Un ive rs i t y Press , Cambridge, England. Warrick, R .E . , 1974, "Seismic Invest igat ion of a San Frans ico Mud Bay S i t e " , B u l l e t i n of the Seismological Soc iety of America, V o l . 64, No. 2, A p r i l , pp.375-38"5T Whitman, R.V., 1965, "Ana lys i s of Foundation V i b r a t i o n s " , from V ib ra t i ons in C i v i l Engineer ing, ed i ted by B.O. Skipp, Butterworths & Co. L t d . , pp. 1597179": Wi lson, R.C. , Warrick, R .E . , and Bennett, M . J . , 1978, "Seismic V e l o c i t i e s of San Frans ico Bayshore Sediments", Proceedings ASCE Geotechnical Engineering D i v i s i o n Spec ia l ty Conference on Earthquake Engineering and So i l Dynamics, Pasadena, C a l i f o r n i a , pp.1007-1023. 102 APPENDIX A UBC IN S I T U TESTING S i t o L o c a t i o n ! MCDONALD'S FARM CPT Data . 05/14/85 NL MD JH Pago Noi 1 / 1 On S i t e Loci CPT-21 Cono Usedi UBC#B STD TIP Commontsi CMAX PORE PRESSURE SLEEVE FRICTION CONE BEARING FRICTION RATIO DIFFERENTIAL P . P . INTERPRETED U ta. o f «at«r) <ba-> Oc (bor) R f CO RATIO AU/Qc PROFILE Soft SILT Coarse SAND Fine SAND Soft clayey SILT Oopth I n c r s n a n t > . 0 2 5 m Max Depth i 20 .525 m O UBC I M S I T U 1 rES" r i M G S i to Loca t ions Schoo lhouse S i t e CPT Data i 03/22/85 14i 51 Page Noi 1 / 2 On S i to Loc i GSC#3 Cona Uaadi UBCiCB BT t h i n Commantsi 295cm l co*wator PORE PRESSURE SLEEVE FRICTION CONE BEARING FRICTION RATIO DIFFERENTIAL P . P . INTERPRETED Dopth Incramont t .025 m Max Oapth i 18.45 m L (V •P 01 E 0_ LU O UBC I M SI t o L o c o t l o n i Schoo lhouaa S i t s On S i to Loc i GSCIV3 15 PORE PRESSURE U (n. of *atar) 0 100 1 20-25 30-4 SLEEVE FRICTION (bar) 0 2.5 20-25-30-15 20 • 25 30 S I T U TESTING CPT Oato i 03/22/85 14i51 Pago Noi 2 / 2 Const Usadi UBC#6 BT t h i n Commontai 295cm Ic«+«atsr CONE BEARING FRICTION RATIO DIFFERENTIAL P.P. 0c (bar) Rf «> RATIO AU/Oc 250 0 5 -.2 0 .8 i5-tr- J—1—'—1—I 15 maximum bearing of 387 bar 25 20 25 30 Dopth Incronant i . 025 m Max Dopth i 18.45 m 15-INTERPRETED PROFILE Generalized stopped on frozen 20- ground 25 30-SAND t h i n g r a v e l l y l a y p r (3 I S . ' O U B C I M S I X U T E S " r i MG S i t e L o c a t l o n i SWIMMING POINT CPT Dato i 03/27/85 PKR DC Pago Not 1 / 1 On S i t e Loc i GSC #8 ON SHORE Cong Usadi UBC8 STDSBEHINO Conmontei ICE DPTH-1.5m PORE PRESSURE SLEEVE FRICTION CONE BEARING FRICTION RATIO DIFFERENTIAL P.P. INTERPRETED Depth Increment • i 025 m Max Depth i 14.3 • O W L 01 •P 0) J QL LU a UBC IN S I T U T ESTING S i to L o c a t i o n ! R i c h a r d s Is.-Tutt On S i t e Loci ' GSC#9 CPT Oata i 03/28/85 12i 51 Cone Usodi UBC#6 S t d T i p BT Pago Noi 1 / 1 Commantai 190 cm l ca/0 H20 PORE PRESSURE SLEEVE FRICTION U (*. of voter) (bar) 0 100 _0 . . . . 2.5 CONE BEARING 0c (bar) FRICTION RATIO Rf (X) 'frozen at surface r e f u s a l 10 15 Oapth Increment i . 025 m DIFFERENTIAL P.P. RATIO iU/Oc -.2 0 .B 0 Max Depth i 13. 7 m INTERPRETED PROFILE generalized ir> 15-sandy SILT SAND to s i l t y SAND clayey SILT to s i l t y CLAY Dense SAND Clayey SILT to s i l t y CLAY O UBC IN S I T U T ESTING S i t e L o c a t i o n ! Tuk Harbour S i t s CPT Dato i 03/30/8S 12i 10 Pago Noi 1 / 1 On S i t o Loc i GSC#12 Cono Uaedi UBC#6 S t d T i p BT Commentei 660cm Ica+wator PORE PRESSURE SLEEVE FRICTION CONE BEARING FRICTION RATIO DIFFERENTIAL P.P. INTERPRETED Dopth Increment i . 0 2 5 m Max Depth i 14.775 m 

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