Seismic response of a water-covered frozen soil half-space: theoretical solutions, numerical verification and an unconventional surface amplification trend

The action mechanism of wave propagation in a water-covered frozen soil half-space is investigated under different seismic excitations based on theory of porous multi-phase medium theory. Unlike conventional saturated soils, this research poses a greater challenge due to the complex interactive effects among soil, pore fluids, ice, and overlying water. First, theoretical solutions for displacement amplification factor, amplitude and energy coefficients are successfully derived. Second, a straightforward comparison is made by reducing the model of three-phase frozen soil to two-phase saturated soil. This degradation yields consistent results, thereby validating accuracy of the findings. Notably, for the water-covered sites (offshore cases), it is discovered that surface displacement amplification factor increases with greater soil hardness (stiffness)—contrary to the widely held conventional perspectives (onshore cases). This remarkable yet unconventional phenomenon is further analyzed, rigorously clarified and proven using a newly derived formula. Lastly, effects of key parameters—such as incident angles, water saturation, porosity, cementation, and contact parameters—on wave propagation and seismic response are examined. Results reveal significant differences between the responses of frozen and saturated sites. This study refreshes the existing prevailing perspectives and can be referenced by anti-seismic engineering research on both onshore and offshore cold regions.