Abstract: The fixed grid methods can be classified into initial flow method, variable seepage coefficient method, variational inequality method, node imaginary flow method, imaginary elements method and the water free surface adaptive grid method which was put forward recently. Each method has its advantages and disadvantages. To ultimately guide us to choose proper methods when processing the practical seepage problems in large scale, it is of great value to evaluate their applicability including flexibility, robustness, numerical stability, computational efficiency and reliability by comparing the accuracy, iterative steps, grid sensitivity, and initial free surface sensitivity of three different fixed grid methods. The results show that the water free surface adaptive grid method is of higher computing efficiency and accuracy than the other two methods in the same grid system. The initiative steps are less, and the accuracy of computing results is less sensitive to the initial free surface and grid density than the other two methods.

Key words: free surface of seepage flow ,    numerical simulation  ,   fixed grid methods  ,   method of water free surface adaptive grid