Numerical modelling of a structure with shallow strip foundation during earthquake-induced liquefaction

Abstract

Structures with shallow foundations are susceptible to excessive settlement and rotation in the event of earthquake-induced soil liquefaction. Numerical modelling of the problem remains challenging, due to persisting uncertainties regarding dynamic soil response and soil–structure interaction. In this paper, numerical simulations are employed to study the seismic response of a structure on a shallow mat foundation, resting on a liquefiable sand layer. A coupled hydromechanical analysis is performed employing the finite-differences code FLAC2D, modelling non-linear soil response with the constitutive model PM4Sand. A broad set of element tests on Hostun sand (widely used in centrifuge modelling) are performed and used for extensive model calibration. The calibrated model is then validated against centrifuge test results. The validation is not restricted to the recorded pore pressure, acceleration and settlement time histories, but extends to the deformation mechanisms extracted from centrifuge testing through image analysis, allowing for an in-depth assessment of the numerical simulation. Overall, the analysis is in good agreement with the centrifuge model test. The pore pressure build-up and the final foundation settlement and displacement fields are predicted with adequate accuracy. Although the accumulated displacements are well reproduced, the failure mechanism is not fully captured. This discrepancy is attributed to dissipation-related phenomena, which are not accurately reproduced in the numerical analysis.

Structure–soil–structure interaction (SSSI) of adjacent buildings with shallow foundations on liquefiable soil

“…The problem was studied through coupled hydromechanical analyses, employing the FD code FLAC2d, modelling nonlinear soil response with PM4sand. The model was calibrated against soil element tests of Hostun (HN31) sand with initial void ratio $$e\ = \ 0.838$$, conducted at the ETHZ geotechnical laboratory 18 . The numerical methodology has been compared against 6 centrifuge model tests of different liquefiable layer depths and foundation bearing pressures, where the ability to predict settlements was showcased.…”

“…Preset values, which are generally functions of an index property, can be used for the secondary parameters, which can also be calibrated against experimental data. To that end, the constitutive model was calibrated here based on the element tests of Hostun (HN31) sand described in detail in Kassas et al 18 ,. corresponding to a fully saturated layer of Hostun sand with void ratio$$\ e\ = \ 0.838$$.…”

“…Such models typically contain a large number of parameters, which have to be carefully calibrated against soil elements tests (e.g., Ref. [18]). Before extracting reliable results, validation against centrifuge model tests (or real scale shake table tests) is necessary (e.g., Ref.…”

“…The plane strain fully‐coupled numerical analyses are conducted employing the constitutive model PM4Sand, 11 as implemented in the finite difference (FD) code FLAC 8.1 33 . The constitutive model is calibrated on the basis of soil element tests, conducted at the ETH Zurich (ETHZ) geotechnical laboratory 18 . The numerical methodology employed herein has been compared against six centrifuge model tests of single structures on surface foundations with variable bearing pressures, resting on liquefiable layers of different depths 19 .…”

“…33 The constitutive model is calibrated on the basis of soil element tests, conducted at the ETH Zurich (ETHZ) geotechnical laboratory. 18 The numerical methodology employed herein has been compared against six centrifuge model tests of single structures on surface foundations with variable bearing pressures, resting on liquefiable layers of different depths. 19 The first key contribution of the present paper is the in-depth assessment of the effects of SSSI by direct comparison to isolated structures.…”