“…Seepage flow with a free surface is usually analyzed on the basis of a fixed finite element mesh as originally proposed by Neuman (NEUMAN, 1973), because in contrast to adaptive mesh methods, unfavourable distortions of finite elements are avoided. On the basis of the fixed mesh method, different numeric techniques have been proposed, such as the variable permeability method (BATHE et al, 1979), the residual flow method (DESAI & LI, 1983), the initial flow method (ZHANG et al, 1988), the virtual flux method (VFM) (ZHU & SU, 1991; ZHU, 1997), the variational inequality method (JANSEN et al, 1988), the refined Gauss point method (WANG & HUANG, 1997), the variational inequality method (ZHENG et al, 2005b) and related methods (SHU et al, 2007;ALT, 1980;WANG, 1998;ZHENG et al, 2005a;BORJA & KISHNANI, 1991;GABRIELLA et al, 2016;AZUSA et al, 2018). However, for determining the free surface with higher accuracy, most of the aforementioned numerical methods require a very fine discretization, especially in the vicinity of the free surface, which is computationally expensive for 3D problems in engineering practice.…”