Abstract:The discontinuous deformation analysis(DDA) is a powerful numerical method for the analysis of discontinuous rock mass behaviours. And the three-dimensional discontinuous deformation analysis(3D DDA) is extended to allow the consideration of groundwater pressure. In geological modelling,various geo-information can be expressed as functions of spatial variables. On the basis of groundwater observation data,a three-dimensional piezometric surface using a relevant fitting function is constructed. And a general model of water pressure distribution on the surfaces of rock blocks is established. The water pressure submatrices are then derived by minimizing the total potential energy and are added to the global matrices. The extension to 3D DDA has been incorporated into a 3D DDA computer program,and numerical results from two test cases show the reasonability of the method.