Development of an in situ dynamic liquefaction test

An in situ dynamic liquefaction test has been developed at the University of Texas at Austin. The distinct characteristics of this testing procedure are the simultaneous in situ measurement of ground response and pore water pressures. The in situ liquefaction test directly measures pore pressure generation in the field and avoids many of the laboratory testing limitations related to sample disturbance, boundary conditions, and small sample size.; The essential components of in situ dynamic liquefaction test are a dynamic loading source and an embedded instrumentation array for simultaneously monitoring the ground response and pore pressure generation. The dynamic loading system consists of a vibroseis truck that applies dynamic loads to the ground surface and generates waves propagating through the instrumented test area. An instrumentation system and associated data reduction procedures were developed to monitor the coupled behavior between the soil skeleton and the pore water pressure. The measured response to dynamic loading was used to evaluate the pore pressure generation characteristics of the soil in terms of the induced shear strains and excess pore pressures.; The developed in situ dynamic liquefaction test was used to dynamically load reconstituted test specimens located near the ground surface. For the first time, pore pressure generation curves that describe the relationships between excess pore pressure, shear strain amplitude, and number of cycles were measured in situ. These curves are similar to those previously measured in the laboratory. The developed testing technique represents a new testing alternative for the study of liquefaction and potentially will have a significant impact in the field of geotechnical earthquake engineering. The test results indicate that the proposed testing technique can capture the coupled response of the induced shear strain and the excess pore pressure generation during and after dynamic loading.