A Study on Liquefaction Evaluation Using Shear Wave Velocity for Gravelly Sand Deposits Ping-Sien Lin, National Chung-Hsing University Fu-Sheng Chen, China Engineering Consultants, Inc. Yin-Yu Jan, China Engineering Consultants, Inc. Chi-Wen Chang, National Chung-Hsing University Wen-Jong Chang, National Chi Nan University 國立中興大學 U.S.-Taiwan Liquefaction Workshop

Outline  Introduction  Literature Review  Testing Program  Results and Discussions  Conclusions  Future Works 國立中興大學

Research Initiation Soil liquefactions occurred in central Taiwan area after Chi-Chi Earthquake (Mw=7.6). Soil liquefactions occurred in central Taiwan area after Chi-Chi Earthquake (Mw=7.6). Liquefactions of gravelly soil observed in the Wufeng and Nantou Area Liquefactions of gravelly soil observed in the Wufeng and Nantou Area No proven methods for estimating the CRR of gravelly soil because of the existence of gravels No proven methods for estimating the CRR of gravelly soil because of the existence of gravels

Ground settlement caused by sand boiling (Taichung port) 國立中興大學

The Song-Gee Jewellery Store Inclined Severely and the Footing was Suck 國立中興大學

In situ testing methods: In situ testing methods: –Large Hammer Penetration Test (LPT) –In situ shear wave velocity measurement (V s ) Laboratory works: Laboratory works: –Large-scale cyclic triaxial tests (15 cm ×30 cm) to determine CRR –Cyclic triaxial tests with V s measurements Goal of research: Goal of research: Find appropriate techniques for liquefaction Find appropriate techniques for liquefaction potential assessing in gravelly soils potential assessing in gravelly soils Research Framework 國立中興大學

Literature Review Liquefaction evaluation framework Liquefaction evaluation framework – –Simplified procedure proposed by Seed (1997 NCEER Workshop) – –CSR=f (M, a max,  v, r d ) – –CRR from laboratory cyclic testing or in situ tests – –FS=CRR/CSR

CRR Evaluations for Gravelly Soils BPT-N b BPT-N b –Based on correction between SPT-N and BPT-N b (Harder and Seed 1986, Harder 1997) –Need further corrections Normalized shear wave velocity V s1 Normalized shear wave velocity V s1 –CRR and Vs are affected by same factors –Nondestructive, reliable –Procedure proposed by Andrus and Stokoe (2000) 國立中興大學

Correction Factors of BPT-N b30 Transferred energy Transferred energy ENTHRU : % of the measured maximum transferred energy with respect to the hammer effective energy ENTHRU : % of the measured maximum transferred energy with respect to the hammer effective energy Casing frictional force Casing frictional force –Computed by CAPWAP –Effect is minimum in shallow layer 國立中興大學

Correlation of Several Casing Total Frictional Force for BPT-N b30 and SPT-N 60 Fig.11 Correlation of Several Casing Total Frictional Force for BPT-N b30 and SPT-N 60 Rt=0 Rt=0.15MN Rt=0.2MN Rt=0.25MN Rt=0.47MN

國立中興大學 Testing Program  Trench excavation  Large hammer penetration test  In situ shear wave velocity measurement  Cyclic triaxial tests with shear wave velocity measurement

國立中興大學 Evidences of liquefaction at testing site (Fu-Tin Bridge)

國立中興大學 Current Condition of Testing Site (Fu-Tin Bridge)

國立中興大學 Current Condition of Testing Site

國立中興大學 Table1. Soil Profile in Trench Excavation GWT Clay layer Δ ═

Fig. 8 Simulation Curve by Equivalent Weight Substitution Method

國立中興大學 Large Hammer Penetration Test

國立中興大學 In situ shear wave velocity near the Wufeng research site were measured by C.P. Lin of the NCTU. In situ shear wave velocity near the Wufeng research site were measured by C.P. Lin of the NCTU. Using the Andrus and Stokoe shear wave velocity liquefaction assessment method showed that the safety factor of soil layer liquefaction resistance is less than Using the Andrus and Stokoe shear wave velocity liquefaction assessment method showed that the safety factor of soil layer liquefaction resistance is less than (BH-1,a max =0.79g,Z=2.97~13.03m,FS=0.09~0.52) (BH-2,a max =0.79g,Z=2.96~12.06m,FS=0.05~0.36) In Situ Shear Wave Velocity Measurement

Peak Horizontal Ground Acceleration Magnitude Of Earthquake CSR Induced by the Ground During the Earthquake Effective Overburden Pressure Shear Wave Velocity from the Research Site Fine Content FC(%) Fine Content Calculation FC(%) Overburden Pressure Correction Fine Content Correction Soil Layer Liquefaction Strength Liquefaction Resistance Safety Coefficient (Andrus and Stokoe,2000)

國立中興大學 Fig.14 The Profile of Shear Wave Velocity Near the Wufeng Research Site (Lin,et al., 2002)

Large-Scale Cyclic Triaxial Test Device 國立中興大學 Top plate Bottom plate Remolded Specimen Porous disc Accelerometer Impact source Triaxial Cell Accelerometer

國立中興大學 CSR N=15 = × (GC%) × (D r %) (R 2 = 0.968) (R 2 = 0.968) 15 By field Results of the Cyclic Triaxial Tests

Results of the Laboratory V s Measurement Effective confining pressure (kg/cm ) 2 ▓ Dr=20% GC=20% ▓ Dr=20% GC=40% ▓ Dr=20% GC=40% ▓ Dr=40% GC=40% ● Dr=20% GC=60% ● Dr=60% GC=40% 2

國立中興大學 FS Based on Cyclic Triaxial Tests Input parameters: Input parameters: –Equivalent number of cycles N 1 =15 (Mw=7.6) –CSR tri,cor =0.245 (N 1 =15 cycles) –a max =0.1~0.79 g a max CSR0.245 CRR FS

FS based on LPT Depth(m) 國立中興大學

Situ Table7. In Situ Shear Wave Velocities and FS Bore Hole #1Bore Hole #2 Depth (m) V s (m/sec) FS (0.79g) FS (0.5g) Depth (m) V s (m/sec) FS (0.79g) FS (0.5g)

國立中興大學 Conclusions 1.Based on the cyclic triaxial test : CSR field,GC=53,Dr=31% ≒ CSR tri,GC=40,Dr=40% CSR field,GC=53,Dr=31% ≒ CSR tri,GC=40,Dr=40% 2.By regression method : CSR Nl=15 = ×(GC%) ×(D r %) CSR Nl=15 = ×(GC%) ×(D r %) (R 2 = 0.968) (R 2 = 0.968)

國立中興大學 Conclusions 3. 3.Factors of safety from LPT-N b30 <1.0  match the field observation LPT2, a max =0.79g, Z=3.00~10.20m,FS=0.1~ Factors of safety from V s <1.0  match the field observation BH-1,a max =0.79g, Z=2.97~13.03m,FS=0.09~0.52

國立中興大學 Conclusions 5. 5.With proper corrections, both LPT and Vs methods are adequate for liquefaction evaluation of gravelly soils 6. 6.More research are needed in LPT especially in evaluating the transferred energy and casing friction

Future Works 1. 1.Fundamental research of dynamic behavior of gravelly soils   Analytical framework on particulate mechanics   Numerical analysis to verify the contribution in dynamic shear strain development from gravels 2. 2.Advanced laboratory experiments   Measure the variation of shear wave velocity during liquefaction process in cyclic triaxial test   Develop experimental technique to determine shear wave velocity of sands in gravelly soils

Future Works (cont.) 3. 3.Field testing   Establish CRR curve for gravelly soils by in situ dynamic liquefaction test   Explore other site characterization techniques in liquefaction evaluation for gravelly soils   Evaluate the effectiveness of remediation measures in gravelly soils 國立中興大學

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