عنوان مقاله [English]
Dam foundations, as the most unknown media part of a dam-foundation-reservoir system, play important roles in system stability, due to the hydro-mechanical behavior of rock mass, especially after the first impounding. In this research, an equivalent continuum model with fully coupled stress-seepage behavior is developed for the rock foundation. First, the mathematical model and the governing equations of the coupled fields are introduced and then the finite element formulation is derived via Galerkins method. In order to describe the material nonlinearity, anisotropy, effective discontinuities, and alteration of permeability, due to either the closure or opening of rock mass joint systems, a multi-laminate material constitution rule is employed.The role of discontinuities could be paramount in rock mass behaviour. Therefore, effective and consistent modelling of these under normal and shear stresses is proposed. In most three-dimensional analysis programs, Mohr-Coulomb criterion is employed for rock mass modelling, and only a few two-dimensional analysis programs, such as UDEC, enjoy more realistic models of rock mass behaviour, such as that of Barton-Bandis. In this research, the Barton-Bandis constitutive law is developed and implemented for joint modelling in three-dimensional finite element analysis using an equivalent continuum approach. The solution algorithm is based on elasto-viscoplastic analysis with a non-associated flow rule, considering mobilized joint roughness, and explicit time integration.Hydraulic conductivity is based on cubic law, using more recent relationships between mechanical and hydraulic apertures for computing the hydraulic conductivity tensor.The performance of the developed model is examined by an existing hydromechanic test case. The methodology is applied to the case of a gravity dam with its surrounding rock. A sensitivity analysis of the foundation behavior is carried out, due to the variations of geometric parameters such as the number of joint sets, dip and dip direction angles, and scale effects, etc.It is concluded that in some cases, the inclusion of hydro-mechanical interaction effects could increase shear stress several-fold, and, thus, its negligence could lead to obviously non-conservative assessment of foundation behavior.