Fully coupled three-dimensional nonlinear numerical simulation of pumping-induced land movement

Excessive groundwater extraction can cause aquifer systems to move three-dimensionally. Based on the equilibrium of soil skeleton and continuity of groundwater flow, a fully coupled nonlinear three-dimensional mathematical model has been constructed, which incorporates the prevalent nonlinear mechanical and hydraulic properties of aquifer systems. The horizontal and vertical displacements with regard to nonlinear mechanical properties are obviously less than those results with linear stress-strain relationship, and the discrepancy between them increases with the elapsed time. Compared with the results with regard to the constant hydraulic properties, the horizontal and vertical displacement and the drawdown with nonlinear hydraulic conductivity increase. The discrepancy between the results with and without nonlinear hydraulic properties also increases with the elapsed time. For the ideal aquifer systems addressed in this study, horizontal displacement is predominant when groundwater is pumped from aquifer units. The horizontal strain is compressive within the zone contiguous to the pumping well, and it is tensile beyond that. However, the horizontal strain, especially the tensile strain, is negligible. Such small tensile strain cannot result in tensile stress because there is original compressive stress in soils. The nonlinear mechanical and hydraulic properties of aquifer systems have clear impacts on the numerical simulation of the displacement and the pore water pressure in hydrostratigraphic units, and their impacts increase with pumping time. They should be considered in land movement simulation due to long-term groundwater withdrawal.