A DISTINCT ELEMENT MODEL FOR DYNAMIC ANALYSIS OF JOINTED ROCK WITH APPLICATION TO DAM FOUNDATIONS AND FAULT MOTION

A two-dimensional numerical model for the analysis of jointed rock masses under dynamic loading is presented. The model is based on the distinct element method, which employs an explicit time integration algorithm, and allows the representation of the nonlinear behavior of the rock discontinuities and the rock matrix. Absorbing boundaries are implemented for dynamic analysis, and the model is validated against analytical solutions of elastodynamics involving media with discontinuities.; The model is applied to the earthquake analysis of concrete gravity dams on jointed rock foundations. A free-field calculation is developed in order to provide the dynamic lateral boundary conditions corresponding to an upward propagating wave. A finite-difference representation with an ubiquitous joint constitutive model is used in the free-field to simulate the jointed medium. Coupled mechanical-hydraulic analyses of the water flow through the rock fractures provide the initial conditions for the seismic analysis. The model allows an assessment of the effects of joint slip and separation on dam response and stability, and on the foundation permeability. For example, it is shown that significant permanent displacements may acumulate without noticeable effect on the response at the dam crest. Phenomena of strength degradation of rock joints due to cyclic loading are investigated in a simulation in which the repetition of a seismic excitation leads to severe damage.; The study of dynamic fault instabilities is a second application of the present model. The continuously-yielding joint constitutive model is used to simulate a fault with post-peak softening behavior, and the conditions for the onset of unstable slip are discussed. Simulations of rockburst processes triggered by underground excavations are presented, which demonstrate the influence of fault constitutive assumptions and other parameters, such as in-situ stresses.; A third class of problems addressed with the proposed model is that of fault motion induced by underground explosions. Plastic yielding of the rock material is accounted for, and the analyses show the dependence of slip on fault and rock mechanical properties. Fault interaction mechanisms are identified, such as the interlocking of intersecting discontinuities undergoing large shear displacements.