Analytical Study Of One-dimensional Land Subsidence Considering Changes In Groundwater Levels

Ground subsidence severely constrains the sustainable development of the economy and society,and is a common type of slow-onset geological disaster,with a significant cause being the decline of the groundwater level.In the analysis of ground subsidence,the correct characterization of boundary conditions is one of the keys to accurate evaluation and prediction of subsidence.For the sake of computational convenience,previous studies have treated the top of the aquifer system as a fixed head boundary condition,leading to existing analytical solutions being unable to reflect changes in the groundwater level during the ground subsidence process.Therefore,this paper regards the top of the aquifer system as a non-constant head boundary condition and studies the one-dimensional consolidation problem of layered soil caused by the depressurization of the aquifer,considering the response of the groundwater level.The main work is as follows:(1)A single-layer mathematical model based on the Neuman unconfined-flow boundary condition and Terzaghi’s one-dimensional consolidation theory was proposed.This model can achieve a semi-analytical solution for the head drop and settlement in the Laplace domain.MATLAB calculation programs have been written,and the solution in the time domain can be obtained by numerical inversion.The new model considers the response of the water table,and the solution can intuitively describe the groundwater level drop during the ground settlement process.Based on this,the effects of consolidation coefficient,elastic modulus,and aquifer thickness on the response of the water table and ground settlement were studied.(2)A multi-layer mathematical model based on Neuman’s unconfined-flow boundary condition and Terzaghi’s one-dimensional consolidation theory was proposed,combined with the boundary transformation method,to achieve the solution of water table decline and settlement in the Laplace domain for the multi-layer model.By comparing the degenerate solution with the existing solution,the validity of the proposed mathematical model was verified,and it was found that previous mathematical models may have underestimated ground settlement.On this basis,the effects of specific yield,compressibility of pore water,permeability coefficient,and viscosity of soil skeleton on water table response and ground settlement were studied.(3)The applicability of the above model was improved.For the water table response in the case of a thick unconfined aquifer,the difference between the results calculated by the iterative method and the linearization method was compared.Considering different groundwater level change patterns,the effects of the amplitude and rate of groundwater level decline on water table response and ground settlement were analyzed.