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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.

This paper studies the effect of structure-soil-structure interaction (SSSI) on the seismic response of neighboring structures with shallow foundations on liquefiable sand. The problem is studied through coupled hydromechanical analyses.Nonlinear soil response is modeled with PM4Sand, calibrated on the basis of soil element tests of Hostun sand. The numerical methodology has been compared against six centrifuge model tests, showcasing its ability to predict the settlements. Three idealized structures of width B are considered, of different aspect ratio and foundation bearing pressure q, founded on two liquefiable layer depths, D L /B = 1 and 2. Initially, the response of a single building is studied, offering insights on the developing failure mechanisms. While the settlement increases with q in the case of a deep (D L /B = 2) layer, this is not the case for the shallow (D L /B = 1) layer, where the increased soil confinement leads to the development of a stiffer soil column, which offers increased support to the structure. Pairs of identical structures are subsequently analysed, revealing the effect of SSSI on settlement (w) and rotation (ϑ). While its effect on w is beneficial, its effect on ϑ is detrimental, leading to a dramatic increase compared to the single structure. The detrimental effect of SSSI on θ is shown to be a function of the gap (s/B) between the buildings and the depth of the liquefiable layer (D L /B). In the case of the shallow layer, the two structures rotate away from each other. This is not the case of the deeper layer, where they may either rotate away or towards each other, depending on s/B.

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