The application of discontinuum idealizations to the analysis of dam foundations is addressed. The options for the representation of the rock mass discontinuities are discussed, from the perspective of assessing failure modes involving the rock mass. An example of concrete gravity dam analysis is presented, considering various patterns of rock mass jointing. Issues involved in modeling rock bridges in non-persistent joint sets are examined. The study of arch dam foundations with discrete element block models is discussed, reviewing methods and choices available for building efficient models. Several practical cases exemplify the information these analyses provide about the structural and rock mass behavior.

1. Introduction

The progress in numerical techniques, continuously translated into advanced software, has made available very elaborate tools for rock engineering analysis. These developments have opened wider possibilities for the representation of the rock mass, its structure and constitutive behavior.As the range of options expands, careful examination and evaluation is demanded for their pertinent application to each type of problem.

The study of concrete dam foundations typically resorts to different types of models depending on the purpose of the analysis. For example, for the prediction of deformations under normal operating conditions, equivalent continuum models are often sufficient. Assessment of collapse modes involving the rock mass have been traditionally approached by considering sliding on discrete failure planes, either the concrete-rock interface of gravity dams, or rock discontinuities that may create unstable wedges in the abutments of arch dams. Discrete element (DE) models allowa straightforward analysis of these mechanisms, invoking the conceptual model underlying the classical methods, such as Londe's.

DE techniques are, however, increasingly employed to create more complex representations of the rock mass blocky structure, for various purposes and at different scales of analysis. The main issues involved in the generation and application of such models to dam foundation analysis are discussed in the following sections, making use of a fewillustrative examples, viewed from the perspective of safety assessment.

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