A Study on Liquefaction Evaluation Using Shear Wave Velocity for Gravelly Sand Deposits

1. 國立中興大學 U.S.-Taiwan Liquefaction Workshop 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

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

3. 國立中興大學 Research Initiation • 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 • No proven methods for estimating the CRR of gravelly soil because of the existence of gravels

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

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

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

7. 國立中興大學 Literature Review • Liquefaction evaluation framework • Simplified procedure proposed by Seed (1997 NCEER Workshop) • CSR=f (M, amax, sv, rd) • CRR from laboratory cyclic testing or in situ tests • FS=CRR/CSR

8. 國立中興大學 CRR Evaluations for Gravelly Soils • BPT-Nb • Based on correction between SPT-N and BPT-Nb (Harder and Seed 1986, Harder 1997) • Need further corrections • Normalized shear wave velocity Vs1 • CRR and Vs are affected by same factors • Nondestructive, reliable • Procedure proposed by Andrus and Stokoe (2000)

9. 國立中興大學 Correction Factors of BPT-Nb30 • Transferred energy ENTHRU: % of the measured maximum transferred energy with respect to the hammer effective energy • Casing frictional force • Computed by CAPWAP • Effect is minimum in shallow layer

10. Rt=0.15MN Rt=0 Rt=0.2MN Rt=0.25MN Rt=0.47MN Fig.11Correlation of Several Casing Total Frictional Force for BPT-Nb30 and SPT-N60

11. 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

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

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

14. 國立中興大學 Current Condition of Testing Site

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

16. Fig. 8 Simulation Curve by Equivalent Weight Substitution Method

17. 國立中興大學 Large Hammer Penetration Test

18. 國立中興大學 In Situ Shear Wave Velocity Measurement • In situ shear wave velocity near the Wufeng research site were measuredby 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 1.00. (BH-1 ,amax=0.79g,Z=2.97~13.03m,FS=0.09~0.52) (BH-2 ,amax=0.79g,Z=2.96~12.06m,FS=0.05~0.36)

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

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

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

22. Results of the Cyclic Triaxial Tests 國立中興大學 By field 15 CSRN=15 = 0.0036 × (GC%) + 0.0050 × (Dr%) + 0.044 (R2 = 0.968)

23. Effective confining pressure (kg/cm ) Effective confining pressure (kg/cm ) Results of theLaboratory Vs Measurement 2 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%

24. 國立中興大學 FS Based on Cyclic Triaxial Tests • Input parameters: • Equivalent number of cycles N1=15 (Mw=7.6) • CSRtri,cor=0.245 (N1=15 cycles) • amax=0.1~0.79 g

25. 國立中興大學 FS based on LPT Depth(m)

26. Table7. In SituShear Wave Velocities and FS

27. 國立中興大學 Conclusions • Based on the cyclic triaxial test : CSRfield,GC=53,Dr=31%≒ CSRtri,GC=40,Dr=40% • By regression method : CSRNl=15 = 0.0036×(GC%) + 0.0050×(Dr%)+0.044 (R2 = 0.968)

28. 國立中興大學 Conclusions • Factors of safety from LPT-Nb30 <1.0 match the field observation LPT2,amax=0.79g, Z=3.00~10.20m,FS=0.1~0.67 • Factors of safety from Vs <1.0 match the field observation BH-1 ,amax=0.79g, Z=2.97~13.03m,FS=0.09~0.52

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

30. Future Works • 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 • 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

31. 國立中興大學 Future Works (cont.) • 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

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