Liquefaction triggering and post-liquefaction deformation of Monterey 0/30 sand under unidirectional cyclic simple shear loading

Over the past decade, the focus of liquefaction engineering began to shift from analysis of the risk of initiation of soil liquefaction towards assessment of the consequences of liquefaction with respect to the seismic performance of engineered structures and facilities, which requires accurate and reliable tools for prediction of ground displacements and deformations over the small to moderate range (<1.5m).; Promising new predictive tools are evolving. These include both simplified, empirical tools as well as sophisticated analytical and constitutive models which can be incorporated in finite element and finite difference programs to solve boundary value problems. Unfortunately, the use of advanced constitutive soil models for liquefiable soils is hampered by a lack of high-quality laboratory testing data for use in the calibration and validation of existing models and the development of new ones. To address this urgent need, a program of uni-directional cyclic simple shear testing was performed on fully-saturated samples of Monterey No. 0/30 sand in the U.C. Berkeley bi-directional simple shear device. This testing program, combined with the companion bi-directional simple shear testing program, accomplished the goal of developing a high-quality laboratory liquefaction database for use in model development and calibration.; This study also quantitatively studied the effects of relative density and initial consolidation stress state on liquefaction triggering, as well as on post-liquefaction shear deformation and volumetric reconsolidation behaviors of Monterey No. 0/30 sand, with and without initial static “driving” shear stresses.; In addition to these experimental investigations, a suite of field performance case histories were analyzed to evaluate the performance of existing semi-empirical engineering tools for estimating liquefaction-induced ground deformations. A new semi-empirical procedure was proposed for predicting post-liquefaction volumetric reconsolidation ground settlements in essentially level ground (α ≈ 0 conditions). This new procedure was then modified for predicting liquefaction-induced ground settlement in sloping or near free-face ground (α ≠ 0 conditions). The new procedure was shown to perform well for the collected field performance case histories with small-to-moderate ground deformations. In addition, a tentative procedure is proposed for estimating liquefaction-induced lateral ground displacement potential.