This dissertation details work conducted by researchers from the University of Texas at Austin aimed toward the development and implementation of a new in-situ liquefaction testing technique. This technique is an active method that may be used to directly evaluate the liquefaction resistance of soils in place. The test is based on the premise of dynamically loading a native soil deposit in a manner similar to an earthquake while simultaneously measuring its response with embedded instrumentation. Dynamic loading is performed via a large, truckmounted hydraulic shaker (vibroseis) that is used to excite the ground surface and generate stress waves of varying amplitudes within an instrumented portion of the soil mass. The embedded sensors consist of instrumentation to measure the coupled response of soil particle motion and pore water pressure generation.
The validity of this new test method has been demonstrated by conducting field experiments at the Wildlife Liquefaction Array (WLA) in Imperial Valley, California. The extensive site characterization, the documented occurrence of earthquake-induced soil liquefaction at the site twice in the 1980's, and the likelihood for re-liquefaction of the site during subsequent earthquakes make the WLA an ideal location for verifying the proposed in-situ dynamic liquefaction test method.
In-situ liquefaction tests were carried out at three separate locations at the WLA. The tests were successful at measuring: (1) excess pore water pressure generation, and (2) nonlinear shear modulus behavior in the native silty-sand deposits as a function of induced cyclic shear strain and number of loading cycles. These results are compared to pore pressure generation curves and nonlinear shear modulus curves previously developed for WLA soils from laboratory testing methods. Variations in the dynamic soil response across the site are also discussed and the importance of evaluating liquefaction from direct in-situ measurements is emphasized. These accomplishments represent a large step forward in the ability to accurately evaluate the susceptibility of a soil deposit to earthquake-induced liquefaction.
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