Mitigation of Liquefaction Damage to Shallow-Founded Structures with In-Ground Structural Walls

Abstract

Stiff in-ground structural or diaphragm walls have previously been used as a liquefaction countermeasure for existing building structures. The available design methodologies for typical mitigation techniques are based on free-field conditions, disregarding seismic interactions among soil layers, mitigation, foundation, and superstructure. In this paper, we use three-dimensional (3D) fully-coupled nonlinear finite-element analyses, validated with centrifuge test results, to evaluate how the properties of structural walls (SWs) in layered liquefiable soils affect the seismic performance of a potentially inelastic structure on mat foundations. The SWs were shown to reduce foundation’s permanent settlement in most cases (although not to acceptable levels), at the expense of its peak transient and residual tilt. However, SWs amplified the foundation’s settlement in cases involving a thick, dense draining crust (Hcrust≥4 m) or a uniform and thick medium to dense sand layer. Increasing the wall’s penetration into the lower dense sand layer and its flexural stiffness were shown to be effective in reducing foundation settlement by reducing shear-type deformations within the critical layer. Simultaneously, increasing the foundation-to-SW distance amplified settlement by increasing the potential for accumulation of shear strains. For the cases considered, foundation tilt was relatively insensitive to changes in wall geometry and flexural stiffness. Overall, Hcrust was the most influential parameter for mitigation effectiveness in terms of permanent settlement and tilt, followed by the relative density of the critical layer. The limited numerical sensitivity study presented in this paper shows that SWs may not always benefit the overall performance of the soil-foundation-structure system, and their design requires consideration of system and ground motion characteristics with great care.