Modelling the thermal-hydro-mechanical behaviour of unsaturated soils with a high degree of saturation using an extended precise integration method

Unsaturated soils with a high degree of saturation (HDS) are commonly encountered in marine and lacustrine sediments. In these soils, the gas phase generally exists in the state of discrete bubbles, which is sensitive to stress and temperature changes and can dramatically change the soil's engineering properties. This paper explores the thermal-induced behaviour of HDS soils using an efficient extended precise integration method (XPIM). Biot poroelasticity theory, extended to include thermal effects and compressibility of gas-water mixture, is employed to analyze the soil behaviour under non-isothermal conditions. Based on the Laplace-Fourier transform and Taylor series expansion, such problems can be solved by XPIM. The robustness of XPIM was confirmed by comparing the present results with analytical solutions and test data. Extensive parametric studies are undertaken to examine both the effects of soil grain thermal expansion and anisotropic permeability on soil behaviour and temperature effects on the degree of saturation (S-r). The thermal-induced variations in S-r are more pronounced with lower initial values (e.g., 90% compared to 99%). These quantitative results demonstrate the benefits of the proposed method, which proves to be extremely efficient and several orders more precise than conventional numerical approaches, with its precision limited only by the computational effort used.