The Develpoment And Application For Numerical Simulation Of Groundwater Fall By MODFLOW Based On TGM

Faults affect the migration and distribution of groundwater. With the effect of the faults, groundwater presents the characteristics of discontinuity, and the numerical simulation of the groundwater becomes more complex. It is important for the conforming of the groundwater distribution and the selection of the water source and mining plan to analysis the structural conditions and simulate the effects of faults on distribution of groundwater.The problem of groundwater fall can be categorized as seepage problem with free surface. If we want to get the outflow in the upper reaches of the faults, we should determine the position of the seepage face firstly. Because of the uncertainty of the position, the numerical method does not work, what we can do is using the iteration to get the numerical solutions.In this dissertation, we analyzed the principle, methods, structure and program process of the MODFLOW and Trefftz boundary element method. We also discussed the possibility of the calculating of the groundwater fall by TGM. HFB package is the traditional method to solve the groundwater fall problem. But when using this method, the selection of parameters is arbitrary and not compatible with the character of discontinuous. The new package(FUT) of MODFLOW is developed by using the Trefftz Galerkin boundary element method and can solve these problems easily.Through the computer experiments, the validity of FUT package in solving the groundwater fall problem was testified. Firstly, in the calculation of heat conduction and the groundwater seepage between the graff, results of the Trefftz Galerkin boundary element method(TGM) were compared with the analytical solution and physical experiment, which verified the accuracy of the TGM. Secondly, the TGM was used to resolve the groundwater fall problem in the condition of constant head. The result is compared with the Dupuit equation, which analyzed the applicability of the Dupuit equation. Finally, an example of groundwater fall in the steady flow was calculated by the MODFLOW with the FUT package. Results showed that the new method was more accurate and steady than the MODFLOW without the FUT package, and pumping in the downstream of the fault had no effect to the upper water level. In conclusion, the new package(FUT) needs less computer time as well as its satisfactory accuracy and convergence. It provides a new way to solve the groundwater fall problem and broadens the range of the application of the MODFLOW.