Numerical model for simulating 3D regional land subsidence

Horizontal deformation resulted from excessive groundwater exploitation has received attention in recent years because of earth fissures and technological development of deformation monitoring, such as GPS and InSAR. However, traditional uncoupling 1D model of land subsidence cannot simulate horizontal deformation. Though Biot model is able to simulate horizontal deformation, using this model is not appropriate for numerically solving the problem of regional land subsidence because the size of discrete model and time step is limited due to long computation time and ill-conditioned linear system matrix. To overcome inherent weaknesses above, uncoupling 3D mathematical model of land subsidence is developed by combining the benefits of uncoupling 1D model and Biot model. Uncoupling 3D mathematical model consists of groundwater flow and deformation equation. Both equations are coupled with parameters (i.e., Young modulus, Poisson ratio and specific water storage). Groundwater flow equation initially computes 3D flow field (equivalent fluid pore pressures) and then the deformation equation calculates 3D deformation based on the known flow field. The derivation of uncoupling 3D mathematical model shows that Biot model can be simplified to uncoupling 3D model based on the assumption that the total normal stress does not change in the process of groundwater flow; uncoupling 3D model can be simplified to uncoupling 1D model based on the assumption that the radial displacements vanish. Meanwhile, numerical experiment shows that uncoupling 3D model can provide deformation results similar to Biot model with much less running time compared with Biot model. Therefore, uncoupling 3D model can be considered as an alternative model to Biot model and an improved model for uncoupling 1D land subsidence model to simulate 3D regional land subsidence.