Comparisons are made of the predictions of the finite and distinct element methods for the case of a long, open excavation in jointed rock. Two types of rock mass have been considered: one containing only vertical joints, the other containing only horizontal joints.
On fait des comparaisons des previsions des methodes des elements finis et des elements distincts pour le cas d"une longue excavation ouverte dans des roches à discontinuities. On a considere deux types de masse rocheuse: l"un qui ne contient que des diseontinites verticales, l"autre ne comprenant que des discontinites horizontales.
Die Ergebnisse von Finiten Element- und Distinct Element Berechnungen werden fuer den Falleiner langen vertikalen Böschung in geklueftetem Gebirge mit einander verglichen. Zwei Gebirgstypen wurden betrachtet: In einem Fall wurden nur vertikale Kluefte - und im anderen nur horizontale Kluefte angenommen.
The analysis of the mechanical behaviour of jointed rock. masses is a difficult problem. Natural rock masses consist of blocks of intact material separated by discontinuities, i.e. joints, bedding planes, etc. For the purpose of analysis it is often assumed that these discontinuities (or "joints") are planar features. The mechanical behaviour of the rock mass is thus a complicated function of the response to loading of the intact blocks and of the joint planes. The spacing and location of the joint planes is also important in determining the response of the overall mass.
Several different numerical techniques have been proposed for the solution of boundary value problems in jointed rock masses. For example, the finite element, boundary element and distinct element methods have been used for a variety of problems, including the analysis of the effects of surface loading, underground excavations and open excavations and slope stability in jointed rock masses. Each method of analysis has its strengths and weaknesses. To date, there has been little discussion in the literature of the relative merits of the various approaches.
The aim of this paper is to compare the performance of the finite element and distinct element methods when they are applied to the analysis of a surface excavation in jointed rock. To illustrate this comparison, predictions are considered for the case of a basement excavation in regularly jointed rock. Although the cases considered are hypothetical, values of the key parameters describing the geometry of the problem and the mechanical behaviour of the rock mass are typical of the conditions encountered in the central business district of Sydney, Australia.
In recent times deep excavations have become a feature of urban construction and reconstruction. The excavation of deep basements in the city environment may have a number of important influences on existing structures and services. The results of the analysis reported in this paper should be of use in the preliminary design of excavations of this type as well as in deciding which numerical techniques are suitable for this class of problem.
The problem considered here is an open, rectangular excavation which is much longer than its width.