THREE-DIMENSIONAL NUMERICAL SIMULATION OF FULLY COUPLED GROUNDWATER FLOW AND LAND DEFORMATION IN UNSATURATED ALLUVIUM-BEDROCK AQUIFER SYSTEMS DUE TO GROUNDWATER PUMPING

A hydrogeomechanical numerical model is presented to evaluate three-dimensional groundwater flow and land deformation in unsaturated alluvium-bedrock aquifer systems due to groundwater pumping. This multidimensional numerical model is developed on the basis of the fully coupled poroelastic governing equations for saturated-unsaturated groundwater flow in deforming porous and fractured geologic media and the Galerkin finite element method. A series of two-layer aquifer systems, which are composed of an alluvium underlain by a bedrock, is then simulated using the hydrogeomechanical numerical model. In the numerical simulations, four different cases of bedrocks are considered for the purpose of comparison: a bedrock with a single joint, a bedrock with one joint set, a bedrock with two joint sets, and a bedrock with three joint sets. The numerical simulation results show that the orientation and density of joints in the bedrocks have significant effects on the spatial distributions and temporal changes of hydraulic head and displacement vector in the alluvium-bedrock aquifer systems. Such effects of the joints in the bedrocks are caused by their relatively high hydraulic conductivity and deformability compared with those of the matrices in the bedrocks. Therefore it may be concluded that the bedrocks and joints in the bedrocks cannot always be ignored if they observed in actual aquifer systems, and thus they must be properly considered when more rigorous and reasonable predictions of the long-term groundwater level change and land deformation induced by groundwater withdrawal are to be obtained.