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Development of an In-Situ Test for Direct Evaluation of the Liquefaction Resistance of Soils K. H. Stokoe, II, E. M. Rathje and B.R. Cox University of.

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Presentation on theme: "Development of an In-Situ Test for Direct Evaluation of the Liquefaction Resistance of Soils K. H. Stokoe, II, E. M. Rathje and B.R. Cox University of."— Presentation transcript:

1 Development of an In-Situ Test for Direct Evaluation of the Liquefaction Resistance of Soils K. H. Stokoe, II, E. M. Rathje and B.R. Cox University of Texas at Austin W.-J. Chang National Chi-Nan University U.S.-Taiwan Workshop on Soil Liquefaction November 3-5, 2003

2 Goal: develop an in-situ testing procedure that can be used to evaluate directly the cyclic liquefaction resistance of soil in terms of u vs.  for different numbers of cycles Key Characteristics: involves a limited volume of material shakes soil like an earthquake

3 Elements of the In-Situ Liquefaction Test Dynamic loading source (similar to EQ shaking) Embedded instrumentation array (to monitor ground motion and measure pore pressure generation and dissipation) Analysis procedure(s) to permit shear strain time histories to be evaluated

4 Pore pressure generation curve Similar to Cyclic Strain Approach Used in Laboratory Testing (Dobry et al. 1982) tt

5 Schematic Layout of Field Setup in First-Generation Testing Backfill soil 3.3 m Footing Vibroseis Waterproof liner m 0.3 m 5 Liquefaction sensor Accelerometer Settlement plate

6 Dynamic Field Source uniform cyclic amplitude (  ) specified frequency (f) specified number of cycles (N) Well-Controlled Dynamic Loading: Dynamic Sources: First Generation-Vertical Vibroseis Second Generation – T-Rex and Liquidator

7 First-Generation Source: Vibroseis - Involves Rayleigh Waves Z Direction

8 Second-Generation Source: T-Rex - Involves Shear Wave Loading in X, Y or Z Directions

9 Frequency, Hz Force, kN Vertical Mode Horizontal Modes 12 Hz 5 Hz Theoretical Performance of T-Rex: Vertical and Horizontal Modes (60 kips) (30 kips)

10 Loading in X or Z Directions Second-Generation Source: Liquidator – Involves Shear Waves

11 Frequency, Hz Force, kN T-Rex-Vertical Liquidator 1.3 Hz Comparison of the Vertical Force Outputs of T-Rex and Liquidator (20 kips)

12 Embedded Instrumentation Array measure soil particle motion (2-D and 3-D geophones) measure pore pressure generation all measurements at same location “Liquefaction Sensor” Settlement Plates

13 Shoe 8.9 cm 2.5 cm 3.8 cm V. Geophone PPT H-Geophone Filter First-Generation Liquefaction Sensor

14 Instrumentation Van during Preliminary Field Trials Sercel 408XL System, up to 2000 channels VXI Technology System, 48-channel analyzer

15 Seismic testing Settlement-plate elevations Apply dynamic loading for a specific number of cycles Data analysis Rest for 30 minutes to 2 hours Final settlements Final S-wave velocities Retrieve sensors Saturation evaluation In-situ density measurement Staged testing Interactive testing Field Testing Procedure

16 Shear strain calculations 1.Processing of Geophone data 2.Strain calculation methods Pore Pressure Generation Curves Data Analysis Pore pressure processing 1.PPT data processing 2.Hydrodynamic and Residual pore pressure

17 Schematic Layout of Field Setup in First-Generation Testing Backfill soil 3.3 m Footing Vibroseis Waterproof liner m 0.3 m 5 Liquefaction sensor Accelerometer Settlement plate

18 QUARRY TEST SITE IN AUSTIN, TEXAS First-Generation Vibroseis First-Generation Instrumentation Van

19 Shear Strain (x10 -3 %) Time (sec) Test T1-3 at center of the array Pore Pressure Ratio, r u (%) Time (sec) (Band-pass filtered)  v = 6.4 kPa Test Series T1 – Small-Strain Level

20 Time (sec) Recorded r u Residual r u Test T1-6 at center of the array Test Series T1 – Large-Strain Level SDM method AW average Shear Strain (x10 -3 ) Pore Pressure Ratio, r u (%)

21 Mean shear strain amplitude (%) Note:  xz calculated by the SDM method Pore Pressure Ratio, r u (%) D r = 35% n=5 cycles n=10 cycles n=20 cycles Pore Pressure Generation Curves for Different Numbers of Loading Cycles tt n=2 cycles

22 Hollow Push Rod Liquefiable Layer Liquefaction Sensor Wire Rope and Electrical Cable Hydraulic Ram Installation of Embedded Sensors

23 Shallow Instrumented Zone Rayleigh Waves (Vertical Particle Motion) Loading with Rayleigh (R) Waves

24 Shallow Instrumented Zone Horizontally Polarized Shear (SH) Waves Loading with Shear (SH) Waves

25 Vertically Polarized Shear (SV) Waves Shallow Instrumented Zone Loading with Shear (SV) Waves

26 Instrumented Zone at Depth Vertically Polarized Shear (SV) Waves Loading with Shear Waves (SV) at Depth

27 Conclusions Development of the basic elements of a field liquefaction test have been initiated with first-generation equipment. Successful measurements of ground motion and pore pressure generation have been conducted. Second-generation dynamic sources, liquefaction sensors, and data acquisition equipment are nearly developed. The test will continue to evolve over the next few years, but there are already numerous applications.

28 Thank you National Science Foundation United States Geological Survey George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) Many graduate students at the University of Texas


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