Seismic site response, liquefaction-induced lateral spreading and impact of seasonal frost on pile foundations in cold regions

Abstract

Permafrost sites are experiencing significant changes due to anthropogenic activities and climate change, leading to substantial variations in soil dynamic properties and increased seismic risks. The associated geohazards, including differential settlement, slope instability, and liquefaction of degraded, unconsolidated materials in seismically active warm permafrost regions, pose substantial threats to the built infrastructure. This study aims to assess the seismic site response of warm permafrost sites and analyze the impact of seasonal frost on liquefaction-induced lateral spreading and pile foundation behavior in cold regions. Northway Airport, Alaska, was used as the study site to characterize permafrost conditions, while the Slana River site and the newly constructed bridge along the Tok Cut-Off were selected as the prototype for investigating liquefaction-induced lateral spread and its impact on pile foundations. Geophysical testing methods, including Multichannel Analysis of Surface Waves (MASW), Horizontal-to-Vertical Spectra Ratio (HVSR) method of ambient noise, and Electrical Resistivity Tomography (ERT), were used to map the shear wave velocity profiles. A one-dimensional equivalent linear analysis assesses site response across multiple seismic hazard levels, accounting for frozen and thawed conditions. Meanwhile, a three-dimensional finite element modeling approach, i.e., OpenSees, simulates ground liquefaction and the interactions between pile foundations and liquefiable soils under varying conditions of seasonal frost depth and soil properties. The results from this study show that, in degraded permafrost areas, changes in shear wave velocity (Vs) due to thawing significantly influence ground motion characteristics during seismic events. Seasonal frost depth and soil permeability emerged as critical factors in affecting liquefaction-induced lateral ground spreading, with lower soil permeability and greater frost thickness increasing liquefaction susceptibility and resulting in a larger amount of ground lateral spread. Furthermore, this study demonstrates that seasonal frost can substantially reduce ground lateral spreading. However, it can also increase internal forces such as shear force and bending moment in bridge pile foundations and form additional plastic hinges, complicating the seismic design of deep foundations. These findings highlight the need to understand comprehensively permafrost degradation-induced changes in soil dynamic properties in cold regions. This study proposes a framework for assessing permafrost degradation's impact on the seismic site response. It offers new insights for engineers and policymakers to develop effective strategies for constructing and retrofitting resilient infrastructure and mitigating the hazards in seismically active cold regions.