ABSTRACT

This paper highlights the applicability of a simple equivalent continuum model for modelling jointed rock mass. In this model, the jointed rock properties are represented by a set of empirical relationships that express the properties of the jointed medium as a function of the properties of intact rock and joint factor. The model is implemented in Fast Lagrangian Analysis of Continua (FLAC) using FISH functions. The verification of the model is based on simulation of triaxial compression tests by comparing the experimental and numerical test results. The applicability of the model to field problems is investigated by undertaking numerical modelling of some case studies on large scale excavations in jointed rocks. The study shows the efficiency of the approach in estimating ground movement and stress distribution around the excavations. The model predicted the deformation values well and study confirmed the usefulness of this simple approach for simulation of underground and surface structures in jointed rocks.

1 INTRODUCTION

Most rock masses encountered in civil and mining engineering projects contain pre-existing discontinuities (Figure 1). These discontinuities weaken the rock masses to an extent, which depends mostly on the size of engineering structure relation to discontinuity spacing. The strength and deformability of rock mass is also controlled by the characteristic of the joints that break up the mass, particularly their pattern and their orientation with respect to the in-situ stresses. In considering the effect of joints, the discrete approach emerged as an efficient tool and advocated since 1970s (Cundall, 1971). However, the numerical approach with modelling the joints explicitly has the limitation of computational complexity for modelling large-scale problems with extremely large number of joints. As an alternative to this, the equivalent continuum approach models the jointed rock masses as a continuum with the equivalent properties that represent implicitly the effects of the joints. Several numerical methods have been developed by various researchers to model jointed rock masses as equivalent continuum, using various techniques. Present approach attempts to use statistical relations, which are simple and obtained after analyzing large number of data from the literature on laboratory tests. The objective of the study was to provide a systematic frame work for conducting the equivalent continuum analysis of jointed rock masses, application to large-scale problem of rock excavations.

(Figure in full paper)

The model was implemented in the program Fast Lagrangian analysis of continua and was rigorously validated by simulating jointed rock specimens. Element tests were conducted for both uniaxial and triaxial cases and then compared with the respective experimental results. The results of the equivalent continuum modelling were also compared with explicit modelling results wherejointswereincorporatedinthemodelas interfaces. To represent highly discontinuous system, the laboratory investigationonblockjointedspecimensof gypsum plaster(BrownandTrollope,1970)was modelled numericallyusingequivalentcontinuum approach. To extend the applicability of the model to field applications,investigationweredoneby undertaking numericalmodellingofsomewell documented casestudies onundergroundcavernsand slopes.

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