Studies On Tneory Of Coupled Consolidation For Soil Layer Induced By Groundwater Level Variation

Land subsidence has become one of the serious environmental and geological disasters, which could have influences in a large region within a long time and is usually non-recoverable. With the rapid economic development and acceleration of the urbanization process, the contradiction between the withdrawal of groundwater and land subsidence is more and more fierce in coastal areas and areas along rivers where soft clay prevails in the stratum. Therefore, it is necessary to have a deeply systematic study on the calculation theory of land subsidence induced by extensive exploitation of groundwater in the soft clay area.Most of the calculation methods for land subsidence are based on partial coupled model at present, which assume the soft soil layer deforms only in the vertical direction and ignore the coupled consolidation of soil layer. As for the few calculation method considering the coupled consolidation of soil layer, the governing equations are usually solved by numerical methods such as finite element method and finite difference method. It is noted that little has been done on the analytical theory for calculating land subsidence. Also, there are little study on the analytical theory for nonlinear and large strain consolidation induced by the withdrawal of groundwater at present. In this thesis, the coupled consolidation of soil layer induced by withdrawal of ground water was studied. Analytical and semi-analytical solutions were obtained for some practical pumping boundary conditions. The coupled consolidation behaviors of soil layer and the influences of soil properties on consolidation were analyzed in details. The main original work and innovative achievements are as follows:(1) When groundwater drawdown is extensively and uniformly distributed in the confined and unconfined aquifer, one dimensional consolidation theory can be employed to solve the consolidation of soil layer. Analytical expressions are derived for one dimensional consolidation of soil layer induced by general time-dependent groundwater drawdown. When groundwater table decreases linearly at first, then keep constant after a certain time, analytical solutions are derived for one dimensional linear consolidation, nonlinear consolidation, and large strain consolidation, respectively. The consolidation behaviors of soil layer were studied based on the derived solutions.(2) The consolidation of soil layer was solved based on Biot’s coupled consolidation theory when groundwater drawdown is not uniformly distributed in the aquifer. The general solutions for axisymmetrical consolidation of soil layer were obtained in transform domain using Laplace-Hankel transform. Analytical expressions were obtained for time-dependent groundwater drawdown boundary based on the general solutions. Analytical solutions were obtained when groundwater drawdown were uniformly distributed within a finite region and axisymmetrically distributed, respectively. The consolidation behaviors of soil layer and the influences of soil properties on consolidation were studied based on the derived solutions.(3) Using Laplace-Hankel transform, general solutions are derived for consolidation of soil layer induced by a vertical line pumping source. Based on the general solutions, the consolidation of soil layer system including confined and unconfined aquifer and soil layer was solved, analytical expressions were obtained in transform domain. The consolidation behaviors of confined and unconfined aquifer and soil layer and the influences of soil properties on consolidation were studied based on the derived solutions.(4) The consolidation of soil layer were studied using three dimensional consolidation theory when groundwater drawdown is non-axisymmetrical distributed in the aquifer. General solutions of the governing equations were derived using Fourier expansion and Laplace-Hankel transform. Analytical solutions for consolidation of soil layer were obtained for non-axisymmetrical groundwater drawdown boundary. The consolidation behaviors of soil layer were studied based on the derived solutions.(5) Considering the constitutive relation of soft clay obeys modified Cam Clay model and the compressibility and permeability is nonlinear with porosity, the consolidation of soil layer were studied using ABAQUS software. The influences of plasticity and nonlinear permeability and compressibility on consolidation behavior of soil layer were analyzed in details.