Mechanism of liquefaction mitigation by rectangular closed diaphragm walls in sloping liquefiable deposits

Abstract

Rectangular closed diaphragm walls (RCDW) has recently been used as a new type of liquefaction mitigation foundation; however, the mechanisms of liquefaction mitigation have scarcely been studied. This paper proposes a 3D nonlinear solid-fluid fully coupled effective stress numerical model in the OpenSees software to study the liquefaction mitigation mechanisms of RCDW. Data from centrifuge tests of an RCDW in a gently sloping liquefiable deposit are used to validate the predictive capabilities of the state-of-the-art numerical tool. The numerical model captures the soil and RCDW seismic responses well. The validated model was applied to investigate the effectiveness and mechanism of RCDW liquefaction mitigation under earthquake motions with different peak accelerations. The numerical results show that the RCDW can mitigate liquefaction in the soil core during small earthquakes and delay liquefaction triggering during moderate and major earthquakes. The RCDW mitigates soil liquefaction by (1) restraining shear strain in the soil core; (2) working as a cutoff wall against water migration from the near field toward the soil core, thereby enhancing the effect of liquefaction mitigation; and (3) resisting liquefaction-induced lateral spreading, which decreases the damage caused by large deformation. Moreover, (4) RCDW displacements are reduced by the support from the enclosed soil, which mitigates displacement of the superstructure. This understanding of the RCDW mechanism in liquefaction mitigation will help to improve the design of RCDW foundations in liquefiable ground.