Investigating wave propagation response in layered unsaturated soil sites under thermo-hydro-mechanical coupling

Based on the theory of thermoelastic wave propagation, a dynamic analysis model of bedrocksaturated soil-layered unsaturated soil site under S-wave incidence is established in this paper. Using the transfer matrix method, combined with the boundary conditions, the recursive relationship of the amplitude vector between the media layers is established, and the influence of the thermal-hydromechanical multi-field coupling on the seismic response of the site is systematically studied. The findings indicate that the vertical displacement amplification coefficient of the site is, in general, greater than that of the horizontal direction, with a maximum ratio of up to 36.04, and the peak value mostly occurs at incident angles less than 3° (θ is ≤ 3°). The soil structure has a significant effect on the propagation of seismic waves: Case1 (homogeneous) displacement response is gentle; Case2 (upper soft and lower stiff) fluctuates markedly at incident angles of less than 3° (θ is ≤ 3°); and Case3 (upper stiff and lower soft) is relatively stable. The parameter sensitivity analysis shows that the change of groundwater level (Case2, +384.08 % ) has the most significant influence on the displacement response, followed by the phase delay time of heat flux (Case2, +344.49 % ) and the thickness of the first layer of unsaturated soil (Case2, +335.34 % ), while the influence of Kelvin medium temperature (Case2, +64.04 % ) and thermal conductivity (Case2, +14.11 % ) is relatively limited. It shows that the amplification effect of soil conditions and thermodynamic environment on seismic response is much higher than that of thermal conductivity. In engineering practice, systematic and coordinated measurement and comprehensive analysis of soil physical parameters should be carried out to effectively control the risk of structural damage under earthquake action.