Integral abutment bridges (IABs) provide a viable solution to address durability concerns associated with bearings and expansion joints. Yet, they present challenges in optimizing pile foundation design, particularly concerning horizontal stiffness. While previous studies have focused on the behaviour of various piles supporting IABs in non-liquefied soils under cyclic loading, research on their seismic performance in liquefied soils remains limited. This study addresses the gap by systematically comparing the performance of various pile foundations in liquefied soil, focusing on buckling mechanisms and hinge formation. Using the Pyliq1 material model and zero-length elements in OpenSees, soil liquefaction around the piles was simulated, with numerical results validated against experimental centrifuge tests. The findings indicate that IABs supported by reinforced concrete piles with a 0.8 m diameter (RCC8) experience greater displacement at the abutment top, while alternative piles, such as 0.5 m (RCC5), HP piles with weak and strong axis (HPS and HPW), steel pipes (HSST) and concrete-filled steel tubes (CFST), show pronounced rotational displacement at the abutment bottom. Maximum stress, strain and bending moments occurred at the pile tops and at the interface between liquefied and non-liquefied soil. Notably, CFST piles resisted buckling under seismic excitation, suggesting their superiority for supporting IABs in liquefied soil.

Ground liquefaction has been reported to occur for shallow earthquakes with a moment magnitude greater than 4.6. The first author of this study has collected many boiled soil samples from various liquefied since 1992. This study is concerned with the grain size distribution, physical and the shear strength properties, permeability/hydraulic conductivity of liquefied granular soils, relative density through laboratory tests and some interrelations are explored. It is shown that every granular geo-material may liquefy if the necessary conditions are satisfied. Large earthquakes may cause even the liquefaction of silty/clayey and/or gravelly soils. Empirical methods purely based on SPT values or its CPT /Vs varieties are not appropriate while the method proposed by Aydan-Kumsar is more appropriate as it can count the most fundamental parameters such as permeability and shear strength of various grounds. If the samples are subjected to pressure under confined state, it is possible to evaluate the characteristics of soils prone to liquefaction at any depth.

Fully liquefied soils behave like viscous fluids, and models developed within the framework of soil mechanics fail to catch their behaviour on the verge of liquefaction or after it. Several research works have shown that modelling the liquefied soil as a fluid is physically more convincing. Such an equivalent fluid can be characterised via an apparent viscosity (g) (sharply dropping when liquefaction is triggered) which can be modelled as a power law function of the shear strain rate (pseudo-plastic fluid), depending on two parameters: the fluid consistency coefficient (k) and the liquidity index (n). With this approach, it is possible to consider a simple correlation between the equivalent viscosity and pore pressure increments independent on the equivalent number of cycles, whose parameters can be calibrated from the results of stress-controlled laboratory tests. The paper investigates the effect of some relevant experimental factors (effective vertical stress, stress path, frequency and waveform of the applied cyclic load, soil fabric and pre-existing shear stress) on the apparent viscosity of soils during their transition from the solid to the liquefied state, and therefore also on the pore pressure increments generated by the stress path. To do that, the results of stress-controlled laboratory tests performed in a sophisticated simple shear apparatus, along with published data, have been interpreted in terms of the apparent viscosity. Simple correlations in terms of viscosity-based pore pressure generation and pseudo-plastic behaviour are proposed and confirmed from the results of 1D non-linear site response analysis for the (c) 2023 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.