Mechanisms of Seismically Induced Settlement of Buildings with Shallow Foundations on Liquefiable Soil

TLDR

Seismically induced settlement of buildings on liquefiable soils has caused significant damage, yet engineers still rely on post‑liquefaction reconsolidation procedures, despite studies showing that shaking intensity, soil density and thickness, and building weight and width influence settlement. A series of centrifuge experiments with buildings atop layered soil deposits were performed to identify mechanisms involved in liquefaction‑induced settlement. Centrifuge tests show that settlement is not proportional to liquefiable layer thickness, occurs mainly during strong shaking, and is driven by building‑induced shear deformations, localized volumetric strains, excess pore pressures, drainage from transient gradients, and ratcheting into softened soil.

Abstract

Seismically induced settlement of buildings with shallow foundations on liquefiable soils has resulted in significant damage in recent earthquakes. Engineers still largely estimate seismic building settlement using procedures developed to calculate postliquefaction reconsolidation settlement in the free-field. A series of centrifuge experiments involving buildings situated atop a layered soil deposit have been performed to identify the mechanisms involved in liquefaction-induced building settlement. Previous studies of this problem have identified important factors including shaking intensity, the liquefiable soil's relative density and thickness, and the building's weight and width. Centrifuge test results indicate that building settlement is not proportional to the thickness of the liquefiable layer and that most of this settlement occurs during earthquake strong shaking. Building-induced shear deformations combined with localized volumetric strains during partially drained cyclic loading are the dominant mechanisms. The development of high excess pore pressures, localized drainage in response to the high transient hydraulic gradients, and earthquake-induced ratcheting of the buildings into the softened soil are important effects that should be captured in design procedures that estimate liquefaction-induced building settlement.