Effects of site geometry and ground motion intensity measures on lateral spread displacements

Liquefaction-induced lateral spreading represents an important geohazard during earthquakes due to the significant displacements that are induced. These movements have the potential to cause significant damage to both the overlying infrastructure (e.g., buildings, bridges), as well as embedded infrastructure (e.g., pipelines). The objectives of this research are to use field observations and numerical simulations of lateral spreading to elucidate the important factors influencing lateral spread displacements. High resolution displacement data from the 2011 Christchurch earthquake are used with surface and subsurface data to evaluate the effectiveness of state-of-practice predictive models for lateral spread displacements and to identify topographic and geotechnical factors that have a significant influence on lateral spreading displacements. The results show that limitations in the existing lateral spread displacement predictive models are in need of improvements and that special care should be taken when evaluating lateral spreading displacements at sites with a topographic terrace and multiple free-faces. A set of 132 numerical models of free-face lateral spread sites are analyzed to evaluate 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. The results indicate that the main factor driving lateral spread displacements is the combined height of the free-face and liquefiable soil layer thickness. Sloping ground behind the free-face can increase the displacements by as much as 1 m in the zone 50-100 m from the free-face. The presence of a topographic terrace at a distance of up to 400 m from the free-face can result in more than 0.5 m of increased displacements between the free-face and terrace. The results of these analyses are also used to develop a framework for predicting the surface displacement profile behind the free-face of a lateral spread site. Another set of 456 finite element simulations are performed to investigate the effects of earthquake intensity measures (IM) on the triggering of liquefaction and on lateral spreading displacements. The IMs that are best able to distinguish between triggering and non-triggering of liquefaction are cumulative absolute velocity with a minimum acceleration threshold of 50 cm/s² (CAV₅₀), normalized dissipated energy [equation], and Arias intensity (I [subscript a]). The IM with the most potential for predicting lateral spreading displacements is cumulative absolute velocity (CAV, defined without an acceleration threshold). Considering only the part of the motion after which liquefaction is triggered (IM [subscript post]) as the predictor of lateral spread displacements results in only a marginal improvement in predictive capacity. The largest increase to predictive capacity after selecting the appropriate IM comes from including information about the geometry of the site.