Key Trends Regarding the Effects of Site Geometry on Lateral Spreading Displacements

Abstract

Nonlinear, effective stress finite-element analyses are used to model earthquake-induced displacements at lateral spread sites near a free face. The numerical analyses consist of 132 models with model geometries selected to isolate the influence of the height of the free face, the thickness of liquefiable layers, sloping ground behind the free face, and the presence of a topographic terrace on lateral spread displacement patterns. Each model is analyzed in the context of how the geometric factors influence the maximum horizontal displacement, the inland extent of displacements, and the shape of the displacement profile between the free face and the inland extent. For sites with flat ground behind the free face and with no terrace present, the dominant factor controlling the displacement pattern is the combined thickness of the free face and underlying liquefiable soil. Lateral spread displacements are significantly affected by the presence of sloping ground behind the free face, with the inland extent affected more significantly than the maximum displacement. The presence of a topographic terrace several hundred meters from a free face can increase appreciably the displacements in the area between the free face and terrace. A bilinear surface model is proposed as a framework for predicting displacement patterns at a free-face lateral spread site and used to model the displacements from the numerical simulations. The observations in this study are based only on a single input ground motion, but the framework can be extended with additional analyses utilizing a range of earthquake ground motions.