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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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 (%)

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

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

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

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

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

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

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.

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