Engineering Evaluation of Permanent Ground Deformations Due to Seismically Induced Liquefaction
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This study concerns the engineering evaluation of permanent lateral ground deformation associated with liquefaction and lateral spreading during earthquakes. Newmark's rigid sliding block model is used, based on the assumption that generally, the deformation occurs during shaking in the downhill direction of the ground surface slope. The study involves laboratory tests, analytical work, and comparisons with case histories and field observations. It culminates with a simplified method to predict lateral deformation using regional attenuation relations for peak ground acceleration and velocity. The laboratory work includes two series of tests. In the first series, drained and undrained cyclic triaxial experiments at different frequencies on clean, medium dense Ottawa sand were used to test a basic assumption of Newmark's method. It is concluded that the method can be applied to dry sand but not to saturated medium dense or dense sand, due to their dilative character and to the shape of their dense stress-strain curves, which do not exhibit the strength plateau required by the method. In the second test series, undrained monotonic and cyclic triaxial/torsional experiments were conducted on very loose, layered, fluvially deposited silty sand SF-7 obtained from the hydraulic fill in the Lower San Fernando Dam. It was found that the stress-strain behavior is contractive in all the tests which covered a range of consolidation pressures. The rigid block model is also used to establish values for the yield acceleration of a fully submerged slope of silty sand where the ratio of undrained shear strength and effective vertical overburden pressure remains constant. In conjunction with this ratio and with available accelerograms, the sliding block model is successfully used to predict lateral displacement in the western United States, including the 1987 Wildlife site case history.