Gravelly Soil Liquefaction Mark D. Evans, Ph.D., P.E. Associate Professor United States Military Academy Department of Civil and Mechanical Engineering Mahan Hall West Point, NY 10996 ABSTRACT Gravelly soils are sometimes present in tailings dams and these soils are potentially liquefiable. In this presentation, experiences in assessing the liquefaction potential of gravelly soil in dams using both laboratory and in situ techniques are discussed. These techniques are: large scale cyclic triaxial testing with correction for membrane compliance; and large scale Becker Hammer penetration testing. The results from a laboratory investigation into cone penetration testing to assess gravelly soil behavior is also presented. The results from several investigations will be summarized and compared to approaches and results obtained for investigations targeting sandy soil. Shear modulus and damping properties for gravelly soils are also presented. INTRODUCTION Evaluating dynamic properties and liquefaction behavior of gravelly soils has become a high priority in the geotechnical engineering community. Due to high hydraulic conductivity, gravels and gravelly soils were once thought to be unliquefiable. Gravel blankets and drains are often used as remedial measures to improve liquefaction resistance by rapidly dissipating high pore pressures generated during earthquake loading. However, several liquefaction-induced failures in gravel and gravelly soil prompted a critical reevaluation of the behavior of gravelly soils subjected to dynamic loading. In recent years, the liquefaction behavior of gravelly soil has been investigated in the laboratory by many investigators (see Reference list). Also, field evidence has shown that most liquefied gravelly soils are comprised of both sand and gravel. EMBANKMENT DAMS Embankment dams consisting of gravelly soil or founded upon gravelly soil where gravel liquefaction has been considered include: •Aswan High Dam, Egypt •Folsom and Mormon Island Dam, CA •Ririe and Mackay Dams, Idaho •Oroville and Seven Oaks Dams, CA •Shimen and Baihe Dams, China •Terzaghi and Seymour Dams, British Columbia •Daisy Lake Dam, British Columbia •Scott’s Flat and Santa Felicia Dams, CA •Vern Freeman Diversion Structure, CA •Devil Canyon Second Afterbay, CA Grain size distributions for these soils range from rockfill to sandy gravel or gravelly sand. Aswan High Dam Analyzed for Liquefaction Potential Triaxial Specimen of Aswan High Dam Sluiced Rockfill Triaxial Specimen of Aswan High Dam Rockfill (gravel) Triaxial Specimen of Aswan High Dam Rockfill (gravel) Triaxial Specimen of Gravel Triaxial Specimen of Gravel 1.00 1.00 (a) (b) o o i i t 0.80 t 0.80 a a 0.60 0.60 re R re R u u s s 0.40 0.40 res res re P 0.20 re P 0.20 o GC=0%, Dr=40% o GC=20%, Dr=40% P P 0.00 0.00 03691215 03691215 Number of Stress Cycles Number of Stress Cycles 1.00 1.00 (c) (d) o o i 0.80 i 0.80 t t a a 0.60 0.60 re R re R u u s s 0.40 0.40 res res re P 0.20 re P 0.20 o GC=40%, Dr=40% o GC=60%, Dr=40% P P 0.00 0.00 03691215 03691215 Number of Stress Cycles Number of Stress Cycles Pore Pressure Response for Sand and Gravel Mixtures 100 100 ) ) a a GC=40% P P GC=0% k 50 k 50 GC=60% ( GC=20% ( s s s s e e r r t t 0 0 S S or or at -50 at -50 vi vi (a) First Stress Cycle (b) First Stress Cycle e e D D -100 -100 -2 -1 0 1 2 -2 -1 0 1 2 Axial Strain (% ) Axial Strain (% ) 100 100 ) ) a a GC=40% P GC=0% P k 50 k 50 GC=60% ( GC=20% ( s s s s e e r r t 0 t 0 S S or or at -50 at -50 vi (c) Fifth Stress Cycle vi (d) Fifth Stress Cycle e e D D -100 -100 -2 -1 0 1 2 -2 -1 0 1 2 Axial Strain (% ) Axial Strain (% ) Stress – Strain Response for Sand and Gravel Mixtures 0.6 1.00 e l Confining Pressure=100 kPa b (b) o u (a) i n Matrix Relative Density=40% t i 0.80 a a r Do 0.4 Corrected for Membrane Compliance % St 0.60 GC=40% re R 5 u g s ude n t i i s 0.40 res u pl 0.2 m re P A 0.20 o R Ca GC=0% P GC=40% GC=0% CS 0 0.00 1 10 100 1000 03691215 Number of Stress Cycles Number of Stress Cycles 5 100 ) a ) GC=40% 0 P k % 50 ( ( GC=0% s s in e a r r t t -5 0 S l S or ia x -10 GC=40% at -50 A Fifth Stress Cycle vi (c) GC=0% e (d) D -15 -100 03691215 -2 -1 0 1 2 Number of Stress Cycles Axial Strain (%) CSR, PP, and S-S Response for Sand and Gravel Mixtures 0.5 1.20 e l (a) Confinging Pressure =100 kPa b (b) o u i 1.00 n Corrected for Membrane t i 0.4 a a r Do Compliance 0.80 % St 0.3 re R 5 u s g 0.60 ude n t i i res s 0.2 u pl 0.40 Dr=65%, GC=0% m D =65%, GC=0% r re P A 0.1 o 0.20 P R Ca Dr=40%, GC=40% Dr=40%, GC=40% CS 0 0.00 1 10 100 1000 0 3 6 9 12 15 Number of Stress Cycles Number of Stress Cycles 5 100 (d) (c) ) a ) P 0 k 50 % ( ( s Dr=65%, GC=0% s in e a r r t t -5 0 S l S Dr=65%, GC=0% or Dr=40%, GC=40% ia x -10 at -50 A vi e Fifth Stress Cycle Dr=40%, GC=40% D -15 -100 03691215 -2 -1 0 1 2 Number of Stress Cycles Axial Strain (%) CSR, PP, and S-S Response for Sand and Gravel Mixtures 0.5 Confining Pressure=100 kPa Relative Density=40% 0.4 Corrected for Membrane Compliance g 5% 0.3 n i s plitude Strain GC=0% 0.2 GC=20% GC=40% CSR Cau GC=60% Double Am 0.1 0 1 10 100 1000 Number of Stress Cycles Cyclic Stress Ratio (CSR) for Sand and Gravel Mixtures 3.5 Sand-Gravel Composites 2.8-in. Diameter Specimens GC=100% 3 Two Membrane Relative Density = 40% 2.5 (GC=Gravel Content) 2 1.5 εvt 1 GC=0, 20, 40, and 60% Total Volumetric Strain (%) Total Volumetric ε 0.5 vt εv 0 0 20 40 60 80 100 120 Effective Confining Pressure (kPa) Volumetric Strain Caused by Membrane Compliance 0.8 Total Volumetric Strain Volumetric Strain Due to System Compliance 0.7 Volumetric Strain of Soil Skeleton Volumetric Strain Due to Membrane Rebound 0.6 Sand-Gravel Composite Gravel Content=20% 0.5 (%) 71 mm Diameter Specimen v ε Two Membranes, 0.3 mm Thick/Each Relative Density=40% 0.4 εvt 0.3 Volumetric Strain, εvs 0.2 0.1 εvm εve 0 0 50 100 150 200 250 Effective Confining Pressure, σ' (kPa) Volumetric Strain Caused by Membrane Compliance 0.40 ' 0.30 σ /2 d σ 0.20 CyclicStress Ratio Causing 5% Double Amplitude Strain, 0.10 Sand-Gravel Composite GC=100% Without Water Injection Dr=40% With Water Injection σ'=200 kPa 0.00 1 10 100 Number of Stress Cycles, N Effect of Membrane Compliance on CSR Causing Liquefaction 200000 Sand-Gravel Composites Confining Pressure = 100 kPa Relative Density = 40% 150000 GC=0% GC=20% GC=40% 100000 GC=60% Shear Modulus, G (kPa) Modulus, Shear 50000 0 0.001 0.01 0.1 1 Shear Strain, γ (%) Shear Modulus – Shear Strain for Gravelly Soils 1.0 Best-Fit Curve and Standard Deviation Bounds, This Study 0.8 0.6 This Study x Goto et al. (1994) ma Goto et al. (1992) G Hatanaka et al. (1988) G/ Hatanaka and Uchida (1995) 0.4 Hynes (1988) Iida et al. (1984) Kokusho et al. (1994) Konno et al. (1994) Seed et al. (1986) Shamoto et al. (1986) Shibuya et al. (1990) 0.2 Souto et al. (1994) Yasuda and Matsumoto (1994) Yasuda and Matsumoto (1993) 0.0 0.0001 0.001 0.01 0.1 1 Cyclic Shear Strain (%) Normallized Shear Modulus – Shear Strain for Gravelly Soils Becker Hammer Setup in Field (after Harder) Becker Hammer Setup in Field (after Harder) Becker Hammer Setup in Field (after Harder) Large Scale Chamber Test at ERDC Top Half (36 in.) Bottom Half (36 in.) Probe Location #1 Center 1.4” cone SPT #2 Intermediate 1.4” cone 1.4” cone #3 Intermediate 0.70” cone 0.70” cone #4 Intermediate 0.35” cone 0.35” cone #5 Intermediate 0.70” dummy cone 0.70” dummy cone 15’’ #6 Intermediate 1.4” cone 1.4” cone #7 Intermediate SPT SPT Large Scale Chamber Test at ERDC Placing Gravel Specimen in Large Scale Chamber Test at ERDC Placing Gravel Specimen in Large Scale Chamber Test at ERDC 1 tsf Stress vs. Ratio (semi-log scale) Data Corrected to: 12000.00 Dr50 Chamber/Tip Ratio 50 Data Plotted: 10000.00 Gravel Sand#1 8000.00 Sand#2 ) i s p 6000.00 ( s s e r 4000.00 St 2000.00 0.00 1.00 10.00 100.00 Ratio (Tip Diameter/Particle Diameter) Preliminary Results of Cone Tests in Large Scale Chamber 12000.00 3 TSF Stress vs.