Abstract：In this paper，a brittle damage-failure mechanism for rock structures subject to earthquake loading is adopted for analysis of dynamic responses of damaged concrete gravity dams and rock foundation. The concept of the modified net effective stress which involves the coupling affects among damage，pore pressure and porosity evolution in cracked rock mass and concrete is introduced into the modified Mohr-Coulomb failure criterion in order to express the brittle dynamic damage growth and propagation phenomenon. The developed brittle dynamic damage model is based on the localization of damaged failure in brittle materials. Therefore，the brittle dynamic damage process is considered as the process of local fractures in material without plastic deformations. The dissipations of energy during the dynamic process consist of dissipations of the local damage development，the local changes of seepage flow velocity and the local evolution of porosity within the networks of crack-damaged porosity only; no energy is dissipated with the everlasting deformation. The numerical results of the brittle dynamic damage analysis for the concrete dam and the rock foundation show that the significant damage growth starts in the upstream side at the corner between the dam and rock foundation where a high stress concentration area exists. Damage growth is found to be more susceptible in the softer rock foundation than that in the intact rock foundation.
