New high-precision empirical methods for predicting the seepage discharges and free surface locations of earth dams validated by numerical analyses using the IFDM

The interpolation finite difference method (IFDM) can be used in the numerical analysis of steady-state seepage problems over arbitrary domains. In such analyses, by providing the coordinates of change points considering the polygonal domain and boundary conditions, a grid is automatically generated and a numerical solution is promptly obtained. Homogeneous, isotropic dams without tail drains have been investigated in a previous study. However, to consider dams with tail drains, we must alter the previous system slightly. This paper describes the altered system. In earlier times, when computation power was limited and before modern numerical calculation methods had been established, it was highly important for dam engineers to estimate the seepage discharge and the location of the free surface. Several empirical methods were proposed, and these have retained their functionality. For instance, the basic parabola method is an exemplary work that builds on classic empirical methods. In this work, the results obtained using A. Casagrande's method are compared with those obtained by IFDM, and it is confirmed that there are considerable deviations between them. The so-called “equivalent KZ flow method” is proposed and shown to significantly improve the calculation accuracy for the discharge and free surface location.