Abstract:Land subsidence is mainly caused by excessive exploration of groundwater resource, which has been a common and serious geological hazard. Land subsidence has the characteristics of the long-term development of soil deformation, in which one of the main reasons for the phenomenon is the rheology of clay in aquitard and sand in aquifer. Therefore, based on the generalized Kelvin viscoelastic model used to simulate the rheological properties of aquitard and aquifer, combined with Terzaghi’s one-dimensional consolidation theory and continuity condition, the equation governing rheological consolidation and definite solution condition of long-term deformation of the aquitard–aquifer foundation owing to groundwater level variation are obtained. Using Laplace transform, based on traditional matrix transfer method and boundary transform technique, the calculation formulas of the pore water pressure and settlement of the two-layer system in Laplace space are derived, respectively. In order to obtain the solutions in time domain, the Stehfest method is used to calculate numerical inverse transformation and the computation program has been developed. Compared with the existing analytical solutions of single-layer soil, the experimental results and numerical simulation results of two-layer system, the two methods and computation program are verified. In contrast to the traditional matrix method, the boundary transformation technique can transform the involved mixed-type boundary conditions into more tractable uniform boundary conditions; in the meanwhile, it has higher computational accuracy and efficiency. Finally, based on the boundary transformation technique and average consolidation degree defined by the total settlement, more numerical examples have been conducted to investigate the influences of viscosity of skeleton, soil layer permeability and water head falling rate on the long-term deformation of two-layer soil. The results show that the influences of permeability coefficient and drawdown rate on consolidation progress are mainly reflected in the early and middle stage, and the consolidation progress develops more slowly with the decrease of the permeability and drawdown rate. However, the viscosity coefficient exhibits a significant effect on the later stage of soil deformation, and the time needed to complete the deformation is longer with the increase of viscosity under the same groundwater drawdown.