M ISC E LL A N EO U S PAPER S-76-6

THE EFFECTS OF CYCLIC TRIAXIAL TESTING TECHNIQUES ON THE LIQUEFACTION

BEHAVIOR OF MONTEREY NO. O SANDby

John P. Mulilis, Raymond C. Horz, Jr., Frank C. Townsend

Soils and Pavements Laboratory U. S. Army Engineer Waterways Experiment Station

P. O. Box 631, Vicksburg, Miss. 39180

April 1976

Final Report

Approved For Public Release; Distribution Unlimited

TA7.W34mS-76-61976

Prepared for Office, Chief of Engineers, U. S. Army Washington, D. C. 2 0 3 14

Under Project 4 A I6 II0 2 B 5 2 E , Task 04

ÜI

U B P ^ Y

DEC 2 0 76Bureau ci keo a

Denver, Colorado

D estroy th is report when no longer needed. Do not return it to the orig inator.

> / CS 0? N

BUREAU OF RECLAMATION DENVER LIBRARY

^cTtlSìiETflUnclassified

REPORT DOCUMENTATION PAGE READ INSTRUCTIONS BEFORE COMPLETING FORM^ .R E P O R T NU M BER 2. G O V T ACCESSION NO.

' Miseelianeous/Paper S-76-6 3. R E C IP IE N T ’ S C A TA LO G NU M BER

--------------------------------- / ------------------------------ -------------- “4. T IT L E (and S u btitle ) 'JfflÉ EFFECTS OF CYCLIC TRIAXIAL TESTING TECHNIQUES ON THE LIQUEFACTION BpiAVIOR OF MONTEREY NO. 0 SAND tS-i dé AAf>A i /)^

5. T Y P E O F R E P O R T & P E R IO D C O V E R E D

Final report6. P E R FO R M IN G ORG. R E P O R T NU M BER

A U T H O R *»John P. Mulilis Raymond C. Horz, Jr. Frank C . Townsend

8. C O N T R A C T OR G R A N T N U M B E R *»

JK P E R F O R M IN G O R G A N IZ A T IO N NA M E AND ADDRESSU. S. Army Engineer Waterways Experiment StationSoils and Pavements LaboratoryP. 0. Box 631, Vicksburg, Miss. 391^0

10. PROGRAM E L E M E N T , P R O J E C T , TASK AR EA & WORK U N IT NUM BERS

Project 1+A161102B52E, Task (A-

11. C O N T R O L L IN G O F F IC E NAM E AND ADDRESS

Office, Chief of Engineers, U. S. Army Washington, D. C. 2031 -

12/ R E P O R T D A T E

^April 1976,/13. NU M BER O F PA G ES

U o14. M O N ITO R IN G AG EN CY NAM E 6 A D D R E S S fif different from Controlling O ffice )

(

15. S E C U R IT Y CLASS, (o f this report)

Unclassified15«. DECLASSI FI C A TIO N /D O W N G RAD IN G

S C H E D U L E

16. D IS T R IB U T IO N S T A T E M E N T (o f th is Report)

Approved for public release; distribution unlimited.

17. D IS T R IB U T IO N S T A T E M E N T (o f the abstract entered in B lock 20, i f d ifferent from Report)

18. S U P P L E M E N T A R Y N O TE S

19. K E Y WORDS (Continue on reverse side i f necessary and id en tity by block number)

Cyclic triaxial compression tests Soil tests Liquefaction (Soils)Monterey No. 0 sand SandsSoil strength

2Qv A B S T R A C T (CantBoum am reverse a id * f f necessary and. id e n tify by block number)

The objectives of this investigation were to (a) participate in a coopera­tive cyclic triaxial testing program with seven other laboratories and (b)^de­termine the effect of various testing techniques and equipment, .i.e., specimen preparation and compaction, B value, density, loading wave form, and compaction equipment on the cyclic triaxial strength of a sand.A total of 28 saturated isotropically consolidated-undrained cyclic triaxial tests were conducted on 2.8-in.-diam by 7-in.-high specimen

DD ,5Sri. M73 EDITIO N O F » MOV 6 5 IS O B S O L E T E ____________ Unclassified_________ _s E C U R IT Y C L A S S IF IC A T IO N O F T H IS P A G E (When D ata Ent ered)

92051298

--------- Unclassified______________S E C U R IT Y C L A S S IF IC A T IO N O F TH IS PAGEfWTien D a ta Entered)

20. ABSTRACT (Continued).Monterey No. 0 sand. Specimens were compacted to 60 percent relative density (98.5 pcf) using three different compaction techniques (i.e. dry rodding, moist rodding, and moist tamping) with some instances of nndercompacting the lower layers. Some specimens were compacted to a relative density of about 66 percent while others were tested when the B value reached approximately 0.9 1. The effect of loading wave shape was evaluated by subjecting specimens to either a rectangular, near triangular, or sinusoidal loading wave form.

It was found that if careful attention was given to testing details, good agreement could be obtained by different testing laboratories. The test re­sults also demonstrated that the cyclic triaxial strength is greatly.influenced by the method of specimen compaction, density, and shape of loading wave. Specimens prepared moist, either rodded or tamped, were 38-58 percent stronger than comparable specimens compacted dry to the same relative density. A 12 percent increase in the relative density was sufficient to cause an increase in strength of approximately 22-30 percent. Furthermore, the severity of loading wave form on the cyclic triaxial strength was found to decrease in the following order: square, nearly triangular, and sine, with strength differencesof 13 to 30 percent being due to the loading wave shape. The test results also showed that for this sand, changing the diameter of the compaction foot, de­creasing the molding water content from 12.8 to 8.0 percent, or testing speci­mens with a B value of O .98 or O .91 had no significant effect on the cyclic triaxial strength of specimens.

UnclassifiedS E C U R IT Y C L A S S IF IC A T IO N O F TH IS PAGEOWien D a ta E n te red )

THE CONTENTS OF THIS REPORT ARE NOT TO BE USED FOR ADVERTISING, PUBLICATION, OR PROMOTIONAL PURPOSES. CITATION OF TRADE NAMES DOES NOT CONSTITUTE AN OFFICIAL EN­DORSEMENT OR APPROVAL OF THE USE OF SUCH

COMMERCIAL PRODUCTS.

1

PREFACE

This investigation was conducted as part of a study to determine the liquefaction response of soils under static and dynamic loads under Project UAl6ll02B52E, Task OU, Research in Military Engineering and Construction.

The laboratory tests were conducted by Messrs. R. C. Horz and G. D. Abel, with instrumentation assistance from Mr. B. T. Dent, under the technical direction and responsibility of Dr. F. C. Townsend. The work was conducted under the general supervision of Mr. C. L. McAnear, Chief, Soil Mechanics Division. Messrs. J. P. Sale and R. G. Ahlvin were Chief and Assistant Chief, respectively, of the Soils and Pavements Laboratory. This report was prepared by Drs. J. Paul Mulilis and F. C. Townsend. The report was reviewed by Mr. S. J. Johnson, Special Assistant, Soils and Pavements Laboratory. Technical monitor of this project was Mr. A. F. Muller of the Office, Chief of Engineers, U. S. Army.

COL G. H. Hilt, CE, was Director of WES during the conduct of the study and preparation of this report. Mr. F. R. Brown was Tech­nical Director.

2

CONTENTSPage

PREFACE...................................................... 2CONVERSION FACTORS, U. S. CUSTOMARY TO METRIC (Si) UNITS

OF MEASUREMENT............................................ UPART I: INTRODUCTION........... ............................ 5

Objective and Scope .................................... 5Previous Investigations ................................ 6

PART II: MATERIAL, TESTING EQUIPMENT, AND PROCEDURES.......... 12Mate r i a l ................................................ 12Testing Equipment........................................ 12Testing Procedures IM­

PART III: TEST RESULTS AND ANALYSIS......................... 19Effects of Procedures and Equipment....................... 19Agreement with Other Laboratories ........................ 32

PART IV: CONCLUSIONS........................................ 36REFERENCES.................................................... 38

3

CONVERSION FACTORS, U. S. CUSTOMARY TO METRIC (Si) UNITS OF MEASUREMENT

The U. S. customary units of measurement used in this report can be converted to metric (Si) units as follows:

Multiplyinchesinches of mercury (60°f ) feetpounds (mass)pounds (force)pounds (force) per

square inchpounds (mass) per

cubic foot cycles per second

M .2 5 . 1+

3376.85 0.301+8

0.1+535921+ 1+ . 1+1+8222

689!+. 757

16 .0181+61.0

To Obtainmillimetrespascalsmetreskilogramsnewtons

pascals

kilograms per cubic metre Hertz

k

THE EFFECTS OF CYCLIC TRIAXIAL TESTING TECHNIQUES ON THE LIQUEFACTION BEHAVIOR OF MONTEREY HO. 0 SAND

PART I : INTRODUCTION

1. Since the pioneering work of Seed and Lee, the use of the cyclic triaxial test as an aid to investigating the liquefaction poten­tial of saturated sands under seismic loading conditions has "been widely accepted. Although the stress conditions in a cyclic triaxial test donot necessarily represent the stress conditions in an idealized soil

2element in the field, the test has been and is currently (1975) used3-lUby many commercial laboratories and research investigators. Despite

its wide use, however, there are certain variables in the test (i.e. method of preparation of reconstituted specimens, shape of the loading wave, etc.) whose effects are not fully understood.

Objective and Scope

2. With the above in mind, the objectives of the investigation described herein are:

a_. Participate in a co-operative testing program sponsoredby NRC-ASTM* for the purpose of comparing results of cyclic triaxial tests performed by different laboratories on the same sand using similar testing techniques and/or procedures.

b. Investigate the effect of varying certain testing equip­ment and/or procedures (e.g., specimen preparation, shape of the loading wave, etc.). Due to financial and time restraints, investigation of the effects of some tech­niques and/or procedures merely consists of performing two or three "check tests," and conclusions based on the results of these tests are tentative, subject to further substantiation.

* Nuclear Regulatory Commission-American Society of Testing Materials

5

Previous Investigations

Specimen preparation3. The effects of specimen preparation method on the static

15-17stress-strain behavior of sands has been studied in detail by Oda.Oda performed static drained triaxial tests on specimens of four sands of different angularity, compacted to the same density using two differ­ent methods of preparation. In one method, ’’tapping,” dry sand was placed into a mold with a spoon, then densified by tapping the side of the mold with d rubber tipped tamper. In the other method, ’’plunging,” dry sand was placed into a mold with a spoon, then densified by plunging a tamper vertically into the sand. Results of the triaxial tests indi­cated that specimens formed by the tapping method produced the higher static strength, tangent modulus, and dilatancy; the increase in strength was approximately 30 percent.lg

U. Mahmood studied the compressibility characteristics of specimens of Monterey No. 0 sand prepared by two methods; ’’pluviation,” in which dry sand was rained through air into a ring compressionmeter (i.e. a one-dimensional oedometer), and ’’vibration,” in which dry sand was placed into a ring compressionmeter, and vertical vibrations were applied on top of the sand layers by means of a vibrating plate (frequency = 2000 cps,* amplitude =1/2 mm) equal in diameter to that of the specimen. Results from compressibility tests on dense specimens indicated that the specimens formed by pluviation were more compressible and exhibited higher lateral stresses than specimens compacted by vibration.

5. In 1972, one of the authors (Mulilis) performed several drained cyclic simple shear tests on dry specimens of Monterey No. 0 sand, using a modified Geonor simple shear device to determine the settlement characteristics and the variation of the shear modulus and damping ratio of the sand with respect to the strain amplitude,

A Table of Factors for converting U. S. Customary units of measure­ment to metric (Si) units is presented on page 3.

6

vertical stress, and number of cycles. Although the majority of the specimens were prepared by pluvial compaction (i.e. raining sand), a limited series of tests were performed on specimens prepared by vibra­tory compaction; the vibrator used to compact the specimens was a BVI Vibro-Graver. The effects of the method of sample preparation on the settlement characteristics of the sand are shown in Figure 1. It can be seen that specimens compacted by vibration exhibited less settlement during the initial cycles than specimens compacted by pluviation.

6. From a knowledge of the variation of shear modulus with shearstrain amplitude and vertical stress, and the one-dimensional reboundmodulus of the specimens, the settlement curves (Figure l) were convertedto "liquefaction curves" using a theory developed by Martin, Finn and

20Seed which quantitatively relates the volume reductions occurring during drained cyclic tests to the progressive increase in pore water pressure during undrained cyclic tests. These results are presented in Figure 2, which shows the computed relationship between the cyclic stress ratio and the number of cycles to cause initial liquefaction. Initial liquefaction as defined here and throughout this investigation implies the induced pore pressure equaling the initial effective confining pres­sure for the first time.

7. As shown in Figure 2, the resulting curves are generallysimilar to experimentally determined curves, although the computed cyclicstress ratios at which the pore pressure becomes equal to the confiningpressure are somewhat lower than those determined experimentally by

2 21others. 9 Furthermore, it may be noted that although the specimens prepared by different methods were compacted to the same density and tested under the same initial confining stress, differences of up to 50 percent in the dynamic strength are indicated.

8. Stress controlled cyclic triaxial tests were performed by22Ladd on saturated specimens of three different sands prepared by two

different methods: (a) "dry vibration," whereby vibrations were inducedinto the specimens in a vertical direction by means of a vibrograve tool connected to a 1.5 in. diameter compaction foot, and (b) "wet tamping," whereby a 1.0 in.-diameter rod was used to compact specimens which were

19

7

1* E f fe c t of v ib ra to ry com paction on the se tt lem en t c h a r a c t e r i s t i c s of M on terey No. O sand in s im p le sh e a r t e s t s (after Pyke, 1973)!9

CY

CLI

C S

TRE

SS

R

AT

IO,

t/C

^

0 .25

0.20

0.15

0.10

0.05

0

D r = 60%= 1600 PSF

1l \i ^

V\ V IB R A T E D

P L U V IA T E D

3 10 30NUMBER OF CYCLES TO IN IT IA L LIQUEFACTION

F i g . 2. C o m p a r i s o n of r e s u l t s of s im u la t e d l iq u e fa c t io n t e s t s fo r s a m p l e s ofM o n te r e y No. O san d p r e p a r e d by d i f fe r e n t c o m p a c t io n p r o c e d u r e s ( a f te r M u l i l i s , C h an , and S e e d , 1975)®

prepared at a water content of 9 percent. Test results indicated that specimens prepared by the two compaction methods, to the same density, could have differences in liquefaction potentials of up to 100 percent, with the specimens prepared by the wet tamping method being stronger in all tests. g

9. Mulilis, Chan, and Seed used 11 different compaction methods to form cylindrical specimens (7 in. high by 2.8 in. in diameter) of Monterey No. 0 sand at the same density (relative density = 50 percent). Once formed, the specimens were saturated, consolidated isotropically, and tested under undrained stress controlled cyclic triaxial conditions. Test results indicated that the dynamic strength of saturated sands, remolded to the same density by different compaction procedures, was significantly different. Variations in the dynamic strength of Monterey No. 0 sand were found to be in the order of 100 percent; however, tests on other sands indicated that the magnitude of the effect of the method of preparation used may be a function of the type of sand.Wave form shape

10. In performing undrained cyclic triaxial tests on uniformlyggraded silt and a uniformly graded, medium sand, Lee and Fitton foundthat specimens tested using a triangular loading shape yielded somewhathigher strengths than specimens tested using a Mnear rectangular” loadingshape. The difference in dynamic strength was about 5 percent for thesilt and about 10 percent for the sand. Similar results were observed

23 2kby Seed and Chan and Thiers in performing cyclic loading tests on an undisturbed sensitive clay. They each found that triangular loading shapes gave strengths which varied from 5 percent to 20 percent greater than the strengths obtained by rectangular loading.

11. In performing undrained cyclic triaxial tests on Monterey25No. 0 sand, Silver et al. observed that specimens which were tested

using a sine wave form exhibited cyclic strengths which were approxi­mately 15 percent greater than specimens which were tested using a rectangular wave form. However, they further observed that if the rise time in the rectangular wave form was degraded such that the wave shape did not have a nearly instantaneous change of velocity in either the

10

loading or unloading portion of the cycle, then the strength of specimens which were tested using the degraded wave form was approximately the same as that of specimens which were tested using the sine wave form.

11

PART II: MATERIAL, TESTING EQUIPMENT, AND PROCEDURES

Material

12. A 100-lb bag of Monterey No. 0 sand was received by the Waterways Experiment Station (WES) from the Richmond Field Station, University of California, Berkeley, California, and a gradation test was performed on the material. As shown by the grain size distribution in Figure 3, the material is a uniform medium sand (SP), mostly passing the No. 30 standard sieve but retained on the No. 100 sieve, with a coefficient of uniformity of about 1.5 and a mean particle diameter of about 0.36 mm. The specific gravity of the sand is 2.65, and the maxi­mum and minimum densities as determined in accordance with ASTM specifi­cation D 20^9 were 105*7 pcf (e . = 0 .5 6) and 89*3 pcf (e = 0 .8 5)^ m m maxrespectively.

Testing Equipment13* In this investigation, the cyclic axial loads were applied

by two different pneumatic loading units.a_. One of these units consists of regulators and solenoid

valves to provide alternating air pulses to a double-acting load cylinder so that a load is cyclically applied from the load cylinder through the connecting piston to the specimen. This unit has the capability of applying cyclic loads in a rectangular wave form, a triangular wave form, or forms varying between rectangular and triangular.

b_. The other unit is a sinusoidal loading system designed by Chan and Mulilis,^ The main components of the system are a sine wave generator, a volume booster relay, and a double-acting air piston. Initially, the pressures on both sides of the double-acting air piston are iden­tical. At the start of the test, when deformations are extremely small, the sine wave generator applies a cyclic air pressure to one side of piston while the pressure on the other side of the piston remains at a static value.As the test proceeds, the induced pore water pressure increases and eventually equals the initial effective confining pressure, which produces peak-to-peak axial strains in the order of approximately 5 percent. It is at this point that the volume booster relay boosts the quantity of air flow required to keep the output pressure matching the signal pressure from the sine wave generator.

12

U. S. STANDARD SIEVE NUMBERS

F i g . 3. G r a in s i z e d i s t r ib u t io n fo r M o n te re y N o. O sa n d

13

PER

CEN

T CO

ARS

ER B

Y W

EIG

HT

This air boost enables the load on the specimen to remain constant during large strains which generally is not the case in most other loading systems.

lU. All tests were performed at a loading rate of one Hz, and for any one test irrespective of the loading system used, four variables were monitored continuously during each test: axial load, axial deforma­tion, pore pressure, and chamber pressure. The variables were monitored with electronic sensors and recorded using a high-speed continuous line recorder. The equipment was carefully calibrated prior to testing. All tests were isotropically consolidated and conducted undrained.

Testing Procedures

Specimen preparation15. The majority of the specimens were tested at a relative density

of 60 +2 percent (98.1+7 +0.3 pcf) using three different methods of prepa­ration as described below. In addition, several tests were performed on specimens which were compacted by variations of a particular method (as described in a subsequent section) such as under compacting the lower layers and using different molding water contents. All specimens were compacted in seven 1-in. layers inside a rubber membrane (thickness =0.012 in.) which was mounted on the base of the triaxial cell and sup­ported by a split forming mold. Vacuum was applied to the mold to hold the membrane taut against the side of the mold.

a. Dry rodding. The desired weight of dry soil for the first layer was slowly poured into the mold, and a 3/8-in.-diam rod was forced through the layer in a circular pattern until the layer decreased in thickness to the desired height. Subsequently, the height of each layer was deter­mined to the nearest 0.01 in. by placing a straight edge across the top of the mold, and measuring the distance from the top of the layer to the top of the mold with a scale. The procedure was then repeated for each succeed­ing layer producing a specimen approximately J in. high by 2.8 in. in diameter.

b_. Moist rodding. The desired weight of dry soil for the first layer was placed in a beaker, and enough de-aired

water was added to produce a moisture content of 12.8 per­cent. The soil and water were then thoroughly mixed and poured into the mold, and compacted in the identical manner previously described. The compacted layer was then scari­fied to a depth of about 1/10 in. and the procedure was repeated for each succeeding layer producing a specimen approximately 7 in. high by 2.8 in. in diameter.

c_. Moist tamping. This method of preparation is identical to that previously described, except that the size of the tamping foot is different for this method. In this case, each layer of moist sand (w = 12.8$) was compacted using a tamping rod with a tamping foot equal to one-half the speci­men diameter. Figure U shows a sketch of the tamping de­vice. The tamping rod consists of a steel rod 12 in. long "by 3A in. in diameter with a steel tamping foot attached to one end. The tamping foot is l/k in. thick by l/b in. in diameter. The steel rod can slide through a bushing which is encased in a disk; a locking collar is used as a "stop" to control the height of drop, and hence, the final height of the compacted layer. The locking collar was positioned on the steel rod to produce the desired height for the first layer, clamped tight, and the tamping rod was placed inside the mold with the disk resting on top of the mold. The compaction procedure consisted of repeatedly raising and lowering the steel rod through the bushing while the disk was moved in a circular fashion around the mold. Tamping was continued until the locking collar hit the top of the bushing, the tamping rod assembly was then removed from the mold, and the compacted surface of the layer scarified to a depth of about 1/10 in. The locking collar was then positioned on the steel rod to produce the desired height for the next layer, and the compaction pro­cedure was repeated for each succeeding layer, producing a specimen approximately 7 in. high by 2.8 in. in diameter.

l6. After the specimen had been compacted by any one method and sealed by placing the top cap and securing the membrane with an O-ring,10 in. of vacuum A .9 psi) were applied to the specimen through the top cap. Subsequently, the forming jacket was removed, and the specimen was supported by the vacuum while the height and diameter of the specimen were measured. A straight edge was placed on the top cap of the speci­men, and a scale was used to measure the height of the specimen to the nearest 0.01 in. The diameter of the specimen was originally measured with calipers to the nearest 0.001 in.; two mutual perpendicular read­ings being taken at three equally spaced locations (approximately the

15

F ig . 4 . T a m p in g r o d

16

quarter points) along the height of the specimen. A thin steel circum­ferential tape,* which is wrapped around the specimen and calibrated to read the diameter directly, was used in the latter stages of the investigation. With a little practice and extreme care, it was found that the diameter computed from the average measurements obtained by the calipers agreed reasonably well with that obtained by the use of the circumferential tape. However, since the circumferential tape measures the average diameter at any one location on the specimen, whereas the calipers measure a "two-point11 diameter, the use of the circumferential tape will result in a more accurate measurement of the diameter and is recommended.Saturation

IT. The process of saturation consisted of two phases: seepagesaturation and back-pressure saturation. After determining the dimen­sions of the specimen, the triaxial chamber was assembled and a chamber pressure of 2 psi was applied to the specimen which was encased in a chamber fluid of de-aired water. The vacuum on the specimen was then increased to 20 (9 psi) in. A line containing de-aired distilled water was opened to the bottom of the specimen, and water was allowed to seep into the soil very slowly, displacing the air in the specimen. When water had completely filled the specimen voids and about 100 cc had been allowed to seep through the soil, the valve in the water line was closed and the vacuum on the specimen was increased to about 27 in. (13.3 psi) while the chamber pressure was reduced to zero. Air bubbles could then be observed coming through the line from the top of the specimen; the vacuum was maintained until air was no longer observed coming from the specimen. At this time, the vacuum line was closed and the vacuum was slowly reduced by allowing additional water to enter the specimen while the chamber pressure was increased to 5 psi to support the specimen.When the vacuum had completely dissipated, back-pressure saturation, consisting of simultaneously increasing the chamber pressure and the back pressure, was used to further saturate the specimen. Typically,* Commercially available from Pi Tape, P. 0. Box 398» Lemon Grove,

Calif. 920^5

IT

complete saturation of the soil was obtained with a back pressure of about 60 to 100 psi.

18. The degree of saturation for this testing is expressed in terms of Skempton!s B-parameter. The B-parameter is the ratio of the induced change in pore pressure Au to a change in chamber pressureAct in an undrained state, i.e., c

B = AuAct (i)

The value was determined by closing the drainage line, increasing the chamber pressure by 10 psi, and observing the increase in pore water pressure. Except for the tests which were performed for the purpose of investigating the effect of the B-value on the results, a B-value of 0.97 or greater was typically obtained. During saturation, any change in height of the specimen was measured with a dial indicator read to the nearest .01 mm.Consolidation

19. After saturation had been achieved, the specimen was consol­idated under the effective confining pressure at which it would be tested. Consolidation was accomplished by increasing the chamber pressure while allowing drainage such that the final difference between the chamber pressure and the back pressure was the desired effective confining pressure. All tests in this investigation were performed at an effective confining pressure of 1^.5 psi. Once the specimen was fully consolidated under the effective confining pressure, the drainage valves were closed and the cyclic load was applied until the specimen deformed to a peak-to-peak axial strain of 10 percent.

18

PART III: TEST RESULTS AND ANALYSIS

20. The results of all tests are summarized in Table 1. Fig­ures 5 through 12 are plots of the test results expressed in terms of the cyclic stress ratio (R) versus the number of cycles of loading required to cause initial liquefaction. The cyclic stress ratio (R) is defined as:

whereR =

+ o — cd2 a 1 o

+_ a ^ = cyclic deviator stress (psi)

(2)

aQ f = initial effective confining pressure (psi)The results shown in Figures 5 through 12 are discussed below. While the discussions and comparisons are made on the basis of the number of cycles required to cause initial liquefaction (at which time the peak- to-peak axial strain was typically 5 percent or less), similar observa­tions apply for different failure criteria (e.g., a particular peak-to- peak axial strain).

Effects of Procedures and Equipment

Effects of methods of preparation21. The results of tests performed on specimens prepared by dry

rodding are presented in Figure 5 ? while the results of tests performed on specimens prepared by moist rodding are presented in Figure 6. Both series of tests were performed using a square loading wave. As shown in Figure 6, based on the results of two tests, the effect of reducing the molding water content from 12.8 percent to 8.0 percent had virtually no effect on the cyclic strength of the material. A comparison of dry rodding and moist rodding (see Figure 7) compaction methods, however, clearly shows that the specimens prepared by moist rodding were signif­icantly stronger than those prepared by dry rodding; the increase in the cyclic stress ratio required to cause initial liquefaction is

19

T a b le 1S u m m a ry of T e s t R e s u lts

roo

T e s t*W ave F o r m

S am p leP r e p a r a t i o n

M ethodw%

U n d e r-C o m p a c tio n

Ydp c f

Dr% B

+<T ^ — cd2< r'o N .**l n 5** N ** 10 R e m a rk s

1 R ee t D ry R odding 0 No 96. 57 60. 6 0 .9 8 0. 200 109 112 125 • B ad t e s t2 R ee t D ry R odd in g 0 No 98. 25 5 8 .7 0 .9 8 0. 192 8 8 - -

3 R ee t D ry R odd in g 0 No 98. 84 62. 2 0 .9 8 0. 203 4 54 R ee t D ry R odd in g 0 No 98. 31 59. 1 0 .9 8 0. 185 26 265 R ee t M o is t R odd ing 12. 8 No 9 7 .9 8 57. 1 0 .9 8 0. 395 3 2 36 R ee t M o is t R odd in g 12. 8 No 97. 89 56. 5 0 .9 8 0. 379 3 2 37 R ee t M o is t R odd ing 1 2 .8 No 97. 28 5 2 .9 0. 98 0. 317 2 1 2 D is too low r8 R ee t M o is t R odding 12. 8 No 9 8 .4 3 59. 8 0 .9 8 0. 321 10 10 119 R e e t M o is t R odd ing 12. 8 No 9 9 .2 7 6 4 .7 0 .9 8 0. 296 7 7 8

10 R ee t M o is t R odd ing 12. 8 No 98. 36 59. 4 0 .9 8 0. 267 20 20 2111 R ee t M o is t T a m p in g 1 2 .8 No 98. 80 6 2 .0 0. 98 0 .4 0 9 4 5 612 R e e t M o is t T a m p in g 12. 8 No 9 8 .8 8 62. 4 0 .9 8 0 .4 0 3 2 3 - -13 R ee t M o is t T a m p in g 12. 8 Y es 9 8 .4 0 59. 6 0 .9 1 0 .4 0 4 3 414 R ee t M o is t T a m p in g 1 2 .8 Y es 98. 36 59. 4 0 . 92 0 .4 0 5 4 5 615 T r ia n g le M o is t T a m p in g 12. 8 No 98. 62 6 0 .9 0. 98 0. 381 7 8 916 T r ia n g le M o is t T a m p in g 12. 8 No 98. 46 60. 0 0 .9 8 0 .4 0 2 4 5 617 R ee t M o is t T a m p in g 8. 0 No 98. 60 60. 8 0 .9 8 0 .4 0 7 3 4 418 R ee t M o is t T a m p in g 8 .0 No 9 8 .7 1 61. 4 0 .9 8 0 .4 0 7 3 4 419 R ee t M o is t T a m p in g 12. 8 No 9 9 .7 5 67. 5 0. 97 0 .4 0 7 8 10 1220 R ee t M o is t T a m p in g 12. 8 No 99. 48 6 6 .0 0 .9 7 0. 306 59 61 6321 R ee t M o is t T a m p in g 12. 8 No 9 9 .4 2 65. 6 0 .9 7 0 .4 7 3 5 7 922 R ee t M o is t T a m p in g 12. 8 No 9 8 .7 2 61. 5 0 .9 8 0 .4 0 4 5 6 723 R ee t M o is t T a m p in g 12. 8 Y es 98. 41 59. 7 0 .9 7 0 .4 0 0 4 5 624 Sine M o is t T a m p in g 12. 8 Y es 98. 47 60. 0 0 .9 8 0. 373 11 11 1325 Sine M o is t T am p in g 12. 8 Y es 98. 36 5 9 .4 0 .9 1 0. 392 9 11 1426 R ee t M o is t T a m p in g 12. 8 Y es 98. 36 5 9 .4 0 .9 3 0. 386 6 7 827 Sine M o is t T a m p in g 1 2 .8 Y es 9 8 .6 6 61. 1 0 .9 7 0. 312 33 35 3728 Sine M o is t T a m p in g 12. 8 Y es 9 8 .7 4 6 1 .6 0. 98 0 .4 5 9 7 7 9* A ll t e s t s w e re p e r f o r m e d on i s o t r o p ic a l ly c o n so lid a te d s a m p le s a t an in i t ia l e f fe c tiv e co n fin in g p r e s s u r e of 14. 5 p s i .

** N. = n u m b e r of cy c les to in i t ia l l iq u e fa c tio n ; = n u m b e r of c y c le s to 5 p e r c e n t a x ia l s t r a i n - p e a k to p e a k ; an d N jq = n u m b e r of c y c le s to 10 p e r c e n t a x ia l s t r a in - p e a k to p e a k .

Cyc

lic

Stre

ss

Rat

io,

± 0

*. /

20*

0 .5

N ot4: N u m b ers co rre sp o n d tosp e c im e n s l is te d in T ab le 1

3 0 .4

33

0 .3

Y = 9 8 .4 7 p c f ave(D = 60. 0 %)

0 .2

2

0.1

0 ______________________1 3 dum ber of Cycles 30 100

F ig . 5. C y c le s o f lo ad in g to in it ia l liq u e fac tio n fo r sp e c im e n s p re p a r e d by d ryrodding and re c ta n g u la r w ave loaded

300

Cyc

lic

Str

ess

Rat

io,

± 0*

, /

20"

0 .5

o 0 .4

3•J

0 .3

0.2

N ote: N um bers sp ec im e i

V

corresp on d to s lis te d in T able 1

17 18

w = 8%

# w = 12.

(y = 98. 65 p cf, I ave5% (Y = 9 8 . 39pcf, ave

= 61. 2%) rD = 59. 5%) r

N6

. 5

1► 8

9

0.1

d u m b e r of Cycles ^ 100 300

F ig . 6. C y c les of loading to in it ia l liq u efaction for sp e c im en s p rep ared by m o is trodding (rectan gu lar w ave)

Cyc

lic

Stre

ss

Rat

io,

± O

', /

2CT

0 .5

5 0 .4

33

0 .3

0.2

0.1

N ote: Numbe l is te d

\

r s c o rre sp o n d to spe n T ab le 1

5

c im en s

---------------------- ^

6'

1----------------------------Nv

( » 8

9

_______ 3 2

^ ^ ■ ^ 1 0

m o is t roddi ig (w = 12. 8%)

----------------------4 dry rodding

dum ber of Cycles 100 300

F ig . 7. E ffe c t of sp e c im e n p re p ara tio n m ethod on num ber of lo ad in g c y c le s toc a u se in it ia l liq u e fac tio n (re c ta n g u la r w ave)

approximately 58 percent at 10 cycles and 38 percent at 30 cycles.Similar results were observed by Mulilis, Chan and Seed in performing undrained cyclic triaxial tests on specimens of Monterey No. 0 sand re­molded to a relative density of 50 percent and tested at an initial effective confining pressure of 8 psi. They found that specimens prepared by moist rodding were approximately 20 percent stronger than those prepared by dry rodding when compared at the cyclic stress ratio required to cause initial liquefaction in 10 cycles. The difference in the magnitude of the increase in strength (58 percent versus 20 per­cent) could be due to the fact that their specimens were compacted to a lower relative density (50 percent versus 60 percent), and prepared in a slightly different manner (after initially rodding each layer with a 3/8-in. rod to the approximate desired height, a cylindrical surcharge, 2.8 in. in diameter, was used to achieve a level surface and decrease the thickness of the-layer to the final desired height).Effects of size of tamping foot

22. Figure 8 presents the results of tests conducted to evaluate the effects of tamping foot size, i.e., moist rodding versus moist tamp­ing. Based on the results of two tests performed on specimens compacted using a larger diameter tamping foot, it may be seen that the size of the tamping foot had virtually no effect on the strength of the soil. Since no effect of tamping foot size was observed, and since the moist rodding and moist tamping compaction procedures were otherwise identical, it was decided to use the moist tamping method of compaction to prepare the remaining test specimens. This decision was based on the fact that the fiioist tamping equipment provides closer control over the density of each layer. g

23. Mulilis, Chan and Seed0 also investigated the effects of tamp­ing foot size on the cyclic triaxial strength of Monterey No. 0 sand molded to a relative density of 50 percent. They found that specimens prepared by moist tamping were approximately 10 percent stronger than specimens prepared by moist rodding. The small difference between the results of their investigation and the one described herein could be

2h

Cyclic

Stre

ss Ra

tio,

± 0*,

/ 2OF

0.5

3 0 .4

33

0 .3

0.2

N ote: N um ber sp ec im e

1 2 4 \ 5

3 c o r re sp o n d to ns l i s te d in T ab le 1

A 11

• 3 /8 " di A 1 .4 " di

im foo t (y = 98. 3( aveim foo t (y = 98. 8" ave

' p c f , D = 5 9 . 5%) r: p c f, D = 62. 2%) r

-----------------* ----- ^<(

i »8# 9

0.1

3 % u i o i 30 100 300Number of CyclesF ig . 8. E ffe c t of tam p in g foot on lo ad ing c y c le s to in it ia l liq u e fa c tio n ( re c ta n g u la r w ave)

due to scatter or to the fact that their specimens were compacted to alower relative density (50 percent versus 60 percent) and prepared in aslightly different manner (the moist tamping methods of compaction wereidentical, and the differences in the moist rodding method of compactionwere described in paragraph 21).Effects of variable compaction and lower B-value

2k. When compacting a specimen in layers, each succeeding layerdensifies the material in the layers below it. This fact was recognizedby Chen in 19 +8; hence, three tests were performed on specimens whichwere prepared using a procedure of variable compaction suggested by

25Silver et al. The concept of variable compaction consists of prepar­ing each layer at an initially looser density than the final desired value by a certain percentage. An optimum value of percent under­compaction is chosen for the first layer and each succeeding layer is prepared denser, or at a lower percent undercompaction, the result hope­fully being a uniform specimen with respect to density. Typically, the optimum value of percent undercompaction ranges between zero to about 20 percent, with the higher value being associated with very loose specimens. For the three specimens tested at 60 percent relative densi­ty, a value of 10 percent undercompaction was chosen.

25. In order to investigate the effect of the B-value on the strength of the soil, the three specimens were tested at B-values of only 0.91» 0.92, and 0.93, as opposed to the typical B-value of 0.97 or greater. Figure 9, comparing the effects of undercompaction and B-value, shows that specimens which were undercompacted and tested at a lower B-value were approximately 10 percent stronger. Thus, it may be con­cluded that using a procedure of variable compaction and testing at a lower B-value may result in somewhat higher strengths.

26. To throw some light on the subject, the degree of saturationwas calculated for various B-values using the following relationship

27suggested by Black and Lee.

S.1

1 - Z (l-B) 1 - Z Q (3)

26

Cycli

c Str

ess R

atio,

± (f ,

/ 20"

0 .5

3 0 .4

33

0.3

0.2

N ote: N u m b ers spec im ens

13 VV ,

:o rre sp o n d to l is te d in T ab le 1

. 14

•

▲

No v a r ia b le com pa(Y = 98. 39 p c f, aveV a ria b le com pactic (YJ l u = 9S. 37 p c f,

:tion , g = 0. 98D = 59. 5%) r

n , p = 0 .9 1 - 0 .9 3 D = 59.4% )d v d x 1 1,1,1

9

0.1

d u m b e r of Cycles ^ 100 300

F ig . 9. E ffe c t of u n d e r co m p ac tio n and 0 v a lu e on n u m b e r of lo ad in g c y c le s toin i t ia l liq u e fa c tio n ( re c ta n g u la r w ave)

where

Q = Bn. (% 1 °d

Z YD

AaY = C (— -) d n.1

D = 1 - (P.lP.-i— )+ BAa '

andB = Skempton's parameter

= initial degree of saturation= pressure corresponding to (typically 60 psi for the lowerB-values, and 60 to 100 psi for the higher B-values)

n. = initial porosity (for a relative density of 60 percent,1 n = 0.1+05)

C. = compressibility of the soil structure (for n. = 0.1+05,_ 1+ m 2 1

Cd is approximately equal to 10 — )= compressibility of water

Aa3 = change in chamber pressure

The results of these calculations indicated that for the conditions used in this investigation, a measured B-value of 0.91 to 0.98 implied a degree of saturation of 99-9 percent. Thus it may be concluded that the increase in strength of the three specimens was probably due to the fact that the specimens were formed using a procedure of variable compaction, rather than to the fact that they were tested at a lower B-value.Effects of wave form

27. The effects of loading wave form on the cyclic triaxial strength were investigated by conducting tests on specimens prepared by moist tamping using the procedure of variable compaction and using a

28

sine wave load form. In addition, two tests were performed on specimens compacted by moist tamping with no variable compaction using a nearly triangular loading wave. The results of the tests using a sine loading wave are shown in Figure 10, and a comparison of the results of tests using a sine loading wave (on specimens prepared using the variable compaction procedure), nearly triangular loading wave (on specimens prepared without using the variable compaction procedure) and rectan­gular loading wave (on specimens prepared without using the variable compaction procedure) is presented in Figure 11. Although only two tests were performed using the nearly triangular loading wave, and there is some scatter in the data, the following observations could be made regarding the effect of loading wave form on the strength of the soil (see Fig. 11):

eu Specimens which were tested using a nearly triangularloading wave were approximately 13 percent stronger than specimens tested using a rectangular loading wave.Similar results were observed by Lee and Fitton, Seed and Chan and Thiers (see paragraph 10).

b_. Specimens which were tested using a sine loading wave were approximately 15 percent stronger than specimens tested using a nearly triangular loading wave and approximately 30 percent stronger than specimens tested using a rectan­gular loading wave; part of the difference in strength is probably due to the procedure of undercompaction (see paragraph 26). Similar results were obtained by Silver et al. (see paragraph 11). It can be noted that the shape of the rectangular loading wave used in this investigation was in between the shapes of the degraded rectangular loading wave and the severe rectangular load­ing wave used by Silver et. al.

Effects of density28. While it is generally agreed that the liquefaction potential

of a soil decreases with increasing density (other factors being equal), the degree to which a small change in density affects the liquefaction potential of a particular soil is not so well known. Since it is nearly impossible to consistently prepare specimens to an exact density, a tolerance of +2 percent relative density (j 0.33 pcf) was arbitrarily chosen in this investigation. However, to investigate the effect of a small change in density on the strength of the soil, three specimens

29

Cyc

lic

Stre

ss

Rat

io,

± 0*

, /

20*

0 .5

3 0 .4

3J

0 .3

0.2/

N

/

00 Y = 98. 56 p c f, I av e> = 60. 6% r

25 V 24

27

N ote: N u m b ers sp e c im e i

c o rre sp o n d to s l is te d in T ab le 1

0.1

dum ber of Cycles ^ 100 300

F ig . 10. N um ber of load in g c y c le s re q u ire d to c a u se in it ia l liq u e fac tio n on m o isttam ped sp e c im e n s (sin e w ave load ing)

Cyclic

Stre

ss Ra

tio,

± 0",

/ 20“'

0.5

3 0. 4

33

0.3

0.2

\ 5

. 2 8

1 5 ' V

V T r ia n g le , no v<(Y = 98. 54 j ave

• R e c ta n g u la r , n c o m p ac tio n

ir ia b le co m p ac tio ncf, D = 60. 4%) r3 v a r ia b le

N6 4N . \ 25 2 4 \ .

i \

Ty = 9«. 39 i aveA S ine , v a r ia b le

27 (V = 98. 56 J c 1 ave

cf, D = 59. éÿo) rcom p ac tioncf, D = 60. 6%) r

910

1 Sine" ^ v— T ria n g le'- T R e c ta n g u la r

N ote: N u m b ers sp e c im e r

c o rre sp o n d to s l i s te d in T ab le 1

0.1

dum ber of Cycles ^ 100 300

F ig . 11. E ffec t of lo ad in g w ave fo rm on c y c le s to in i t ia l liq u e fa c tio n fo r m o is t-tam p ed sp e c im e n s

were compacted to a somewhat higher density; the average relative density of these specimens was 66.U percent (99*5 pcf). The results of tests performed on these specimens are presented in Figure 12, to­gether with the results of similar tests performed on five specimens whose average relative density was 59*5 percent (98*39 pcf). It may be observed in Figure 12 that the slightly denser specimens were signifi­cantly stronger; the increase in the cyclic stress ratio required to cause initial liquefaction is approximately 30 percent at 10 cycles and 22 percent at 30 cycles. Thus it can be concluded that for Monterey No. 0 sand, an increase in relative density of about 12 percent (1.2 pcf) can cause an increase in strength of approximately 22 percent to 30 percent.

Agreement with Other Laboratories

29. The test results of the cooperative testing program with seven other laboratories are summarized in Table 2 and presented in Figure 13. Test specimens were required to be prepared by the moist tamping procedure to a density of 98.5 pcf (relative density = 60 per­cent), saturated to a B-value greater than 0.90, and consolidated under an effective confining pressure of 1 kg/cm (lU.5 psi). These results show that a reasonable correlation in dynamic strength exists between the various laboratories. However, these results presented are not the initial results reported by all of the laboratories and retesting by several laboratories was required to produce this agreement. The ini­tial lack of agreement was due to deviation from the prescribed proce­dure concerning testing details. Most noticeable of these details were (a) loading wave form, (b) small differences in specimen density, and (c) specimen preparation technique.

32

Cyc

lic

Stre

ss

Rat

io,

± O

' , /

20"

'0 .5

3 0.4

33

0.3

0.2

A. y = 99. 55 pcf m ave• Y = 9 8 .3 9 p c f ( w av e

D = 66.4% ) rD = 59. 5%) r

16

K .

8

s . = 66.4%r

> _____ 20

9

~D = 5 9 . 5% r

N ote: Num ber specirru

s co rre sp o n d to n s l is te d in T ab le 1

0.1

dum ber of Cycles 30 100 300

F ig . 12. E ffe c t of d en sity on the num ber of sq u a re w ave lo ad in g c y c le s to c a u se in it ia l liq u e fac tio n fo r m o ist- ta m p e d sp e c im e n s (re c ta n g u la r w ave)

T a b le 2S u m m a ry of T e s t R e s u l t s O b ta in e d f r o m .

C y c lic T r i a x ia l S tre n g th T e s ts on M o n te re y No. 0 S and ( a f te r S i lv e r , M. L . e t a l . , 1975)'

L a b o r a to ry T e s t S p e c im e n B D ryD e n s ity r aA v e r . N .*l V N * 10

N o. N o. P r e p a r a t i o n D ia m e te r V alue p c f1 2 T a m p in g 2 .7 9 0. 94 98. 6 0. 35 13 14 16

3 w ith C O - 2 .7 9 0. 95 9 8 .7 0. 35 12 13 154 2 2 .7 9 0. 95 9 8 .4 0 .2 8 35 36 386 2 .7 8 0. 93 98 . 3 0 . 28 44 45 477 2 .7 9 0. 99 9 8 .7 0. 30 25 26 288 2. 79 0 .9 7 9 8 .7 0 .4 4 8 9 11

A v e r . 98. 62 28 T a m p in g 2. 79 0. 98 9 8 .7 0 .4 6 7 8 10

24 w et 2 .7 9 0. 98 98 . 5 0 . 37 11 12 1427 2 .7 9 0 .9 7 98 . 7 0. 31 33 35 3825 2. 79 0. 91 9 8 .4 0. 39 9 11 14

A v e r . 98 . 63 1 T a m p in g 2 .4 2 0 .9 7 99 . 5 0. 36 6 7 8

2 w et 2 .4 2 0. 91 99. 1 0 . 33 10 10 113 2 .4 2 0. 93 99 . 1 0 . 31 26 27 294 2. 42 0. 94 9 9 .2 0. 30 42 42 43

A v e r . 99. 24 1 T a m p in g 2 .8 2 1 .0 97. 6 0. 30 36 37 - -

2 w e t 2. 82 1 . 0 97. 1 0 . 35 10 10 - -

3 2. 82 1 .0 97. 7 0. 33 11 11 - -

4 2 .8 2 1 . 0 97 . 3 0. 29 17 185 2 .8 2 1 . 0 9 7 .6 0 .2 9 34 376 2. 82 1 .0 9 7 .6 0 .2 5 59 60 - -

A v e r . 97. 55 5 T a m p in g 2 .4 0 .9 9 9 8 .4 0. 38 9 9 10

8 w et 2 .4 0. 96 9 8 .4 0. 32 24 24 269 2 .4 0. 90 98 . 5 0. 46 5 5 8

10 2 .4 0. 95 98 . 3 0 .2 5 88 90 91A v e r . 9 8 .4

6 1 T a m p in g 2. 8 0. 98 9 8 .9 0. 46 8 8 102 w et 2 .8 0. 96 9 9 .0 0. 35 17 16 183 2. 8 0. 98 99 . 1 0 .2 6 42 42 444 2. 8 0. 95 9 9 .0 0 .4 0 15 13 155 2 .8 0. 98 98 . 6 0. 30 31 31 346 2. 8 0. 98 98 . 5 0. 32 20 20 22

A v e r . 98 . 87 1 T a m p in g 2 .9 0. 98 99 . 3 0 . 26 33 36 40

2 w et 2 .9 0 .9 8 9 9 .6 0. 36 10 11 163 2 .9 0. 98 99. 3 0. 46 7 7 104 2 .9 0. 98 99. 3 0. 31 18 22 27

A v e r . 99. 38 18 T a m p in g 2. 0 0. 96 9 9 .2 0. 29 43 46 - -

19 2 .0 0. 98 99. 2 0. 32 16 1920 2 .0 1 .0 9 9 .2 0. 41 6 8 1321 2. 0 1 .0 9 9 .2 0. 36 11 14 19

A v e r . 99. 2

* N. = n u m b e r of c y c le s to in i t i a l l iq u e fa c t io n ; = n u m b e r of c y c le s to 5 p e r c e n t a x ia ls t r a i n - p e a k to p e a k ; and = n u m b e r of c y c le s to 10 p e r c e n t a x ia l s t r a i n - p e a k to p e a k .

3^

STR

ES

S

RA

TIO

LO

0.8

b"<

ii°lbOJ

lioc

0.6

0.4

0.2

1 1 1 1 1 1 I I ------------------ 1— 1 1 1 1 1 1 1 ------------------1----------- 1 1 1 ! 1 I I

MONT WET TAI

DR

1------------------ 1---------- 1.... 1 1 1 1 11

EREY SAND NO. 0 WIPING COMPACTION = 60 PERCENT

LEGEND

S Y MR D I 1 A R O R A T O R Y

_____________________ 7

INITIAL LIQUEFACTION

m

□ i

A 2 0 3 • 4

0 ,

(

-------- 0 -

O 5 — ■ 6A 7V 8

___________ 1_______1 1 I I 1 I I ___________ 1______ 1 1 1 I I 1 1 ___________ 1_______ 1____ L . 1 1 1 1 1 ___________ i______ i ........................

10 100 1,000 NUMBER OF CYCLES TO IN IT IA L LIQUEFACTION

10,000

F i g . 13. S u m m a r y c u r v e show ing s t r e s s r a t io v e r s u s n u m b e r of c y c l e s to in i t ia l l iq u e fa c t io n fo r a l l t e s t r e s u l t s ( a f t e r S i l v e r , et a l . 1975)^5

PART IV: CONCLUSIONS

30. In performing undrained cyclic triaxial tests on Monterey No. 0 sand, the following conclusions regarding the effects of testing techniques and/or procedures on the liquefaction potential of the soil may he drawn:

a_. The cyclic strength of specimens prepared moist wasapproximately 38 percent to 58 percent greater than that of comparable specimens prepared dry.

b_. Specimens which were tested using a sinusoidal loadingwave form exhibited higher strengths than specimens tested using either a nearly triangular or square loading wave form, while specimens tested using a nearly triangular loading wave form exhibited higher strengths than speci­mens tested using a square wave form.

c_. An increase in the relative density of a specimen of ap­proximately 12 percent (1.2 pcf) may cause 22 percent to 30 percent increase in the strength of the specimen.

d_. Changing the diameter of the compaction foot from 0.375 in. to l.H in., or the molding water content from 12.8 percent to 8.0 percent or testing specimens after a B-value of either 0.98 or 0.91 has been obtained, appeared to have no significant effect on the strength of the specimens.

e. Specimens prepared using a procedure of undercompaction were approximately 10 percent stronger than comparable specimens formed without using a procedure of variable compaction.

f_. Good agreement in cyclic triaxial strength values may be obtained by various laboratories if careful attention is given to testing details.

31. As was mentioned in the beginning of this report, the in­vestigation of the effect of some of the variables merely consisted of performing two or three "check tests," and the conclusions based on the results of these tests are tentative, subject to further substantiation.It is, therefore, recommended that additional tests be performed in order to further substantiate the above tentative conclusions. Further­more, in order to develop a better understanding of the phenomena of liquefaction, and the liquefaction potential of in situ soils as opposed

36

to that measured in the laboratory, it is also recommended that research be conducted in the following areas:

¡a. Testing of different types of soil to see if the variables investigated herein are soil dependent.

b_. Testing of specimens with frictionless end platens to see if the stress concentrations existing near frictional end platens have an effect on the strength of the soil.

c_. Comparison of the strengths of specimens tested with a uniform loading wave as opposed to an irregular loading wave, which actually occurs in the field.

<1. Investigation into the very small strains which can be observed prior to occurrence of initial liquefaction.

e_. Investigation into the effect of anisotropically consoli­dating specimens, allowing them to rebound, and then reconsolidating them isotropically (i.e., testing remolded specimens under similar but simplified stress conditions which occur when an "undisturbed sample" is removed from the ground and tested isotropically).

f\ Investigating the correlation (if any) between the static and cyclic strengths of soils.

g. Investigating the effect of long-term consolidation on the static and dynamic strength of sands.

37

REFERENCES

1 . Seed, H. B., and Lee, K. L., "Liquefaction of Saturated Sands During Cyclic Loading," Journal, Soil Mechanics and Foundations Division, American Society of Civil Engineers, Vol 92, No. SM6, Nov 1966,pp 105-131» •

2. Seed, H. B., and Peacock, W. H., "Test Procedures for Measuring Soil Liquefaction Characteristics," Journal, Soil Mechanics and Foundations Division, American Society of Civil Engineers, Vol 97* No. SM8, Aug 1971, PP 1099-1119.

3. Castro, G., Liquefaction of Sands, Harvard Soil Mechanics Series,No. 8l, Jan 1969.

k . Ishihara, K., and Yasuda, S., "Sand Liquefaction Due to Irregular Excitation," Soil and Foundations, Japanese Society Soil Mechanics and Foundation Engineering, Vol 12, No. U, Dec 1972, pp 65-77-

5. Lee, K. L., and Alhaisa, A., "Earthquake Induced Settlements in Saturated Sands," Journal, Geotechnical Engineering Division,American Society of Civil Engineers, Vol 100, No. GTl, Apr 197l»> pp 387-1» 06.

6. Lee, K. L., and Fitton, J. A., "Factors Affecting the Cyclic Loading Strength of Soil," Vibration Effects of Earthquakes on Soils and Foundations, American Society for Testing and Materials, Special Technical Publication 1+50, 1969» PP 71-95*

7. Lee, K. L., and Focht, J. A., "Liquefaction Potential of Ekofisk Tank in North Sea," Journal, Geotechnical Engineering Division, American Society of Civil Engineers, Vol 100, No. GT1, Jan 1975» PP 1-18.

8. Mulilis, J. P., Chan, C. K., and Seed, H. B., "The Effects of Method of Sample Preparation on the Cyclic Stress-Strain Behavior of Sands," Report No. EERC-75-18, University of California, Berkeley, July 1975.

9. Rocker, K. Jr., The Liquefaction Behavior of Sands Subjected to Cyclic Loading, Massachusetts Institute of Technology Soils PublicationNo. 221, June 1968.

10. Shibata, T. , "Liquefaction of Saturated Sands During Cyclic Loading," Proceedings, Third Japan Earthquake Engineering Symposium, Tokyo,Nov 1970, pp 167-I7I».

11. Tanimoto, K., and Suga, Y., "On the Dynamic Strength of Saturated Sand," Proceedings, Third Japan Earthquake Engineering Symposium, Tokyo, Nov 1970, pp 191-198.

38

12.

13.

lU.

15.

1 6 .

IT.

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39

2 3 . Seed, H. B. and Chan, C. K., "Pulsating Loading Tests on Samples of Clay and Silt from Anchorage, Alaska," Report on Anchorage Area Soil Studies to U. S. Army Engineer District, Anchorage, Alaska, Aug 19Gb.

2b. Thiers, G. R., "The Behavior of Saturated Clay Under Seismic Loading Conditions," PhD Dissertation, University of California, Berkeley, Calif., 1965.

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1*0

In accordance with ER 70-2-3, paragraph 6c(l)(b), dated 15 February 1973> a facsimile catalog card in Library of Congress format is reproduced below.

Mulilis, John PaulThe effects of cyclic triaxial testing techniques on

the liquefaction behavior of Monterey No. 0 sand, by John P. Mulilis, Raymond C. Horz, Jr., ^andj Frank C. Townsend. Vicksburg, U. S. Army Engineer Waterways Experiment Station, 1976.

40 p. illus. 27 cm. (U. S. Waterways Experiment Station. Miscellaneous paper S-76-6)Prepared for Office, Chief of Engineers, U. S. Army,

Washington, D. C., under Project 4A161102B52E, Task 04.References: p. 38-40.

1. Cyclic triaxial compression tests. 2. Liquefaction (Soils). 3. Monterey No. 0 sand. 4. Sands. 5. Soil strength. 6. Soil tests. I. Horz, Raymond C., joint author. II. Townsend, Frank Charles, joint author.III. U. S. Army. Corps of Engineers. (Series: U. S. Waterways Experiment Station, Vicksburg, Miss. Miscellaneous paper S-76-6)TA7.W34m no.S-76-6