Simulation of excavations in jointed rock masses using a practical equivalent continuum approach

A simple practical equivalent continuum numerical model previously presented by Sitharam et al. (Int. J. Rock Mech. Min. Sci. 38 (2001) 437) for simulating the behaviour of jointed rock mass has been incorporated in the commercial finite difference programme fast Lagrangian analysis of continua (FLAC). This model estimates the properties of jointed rock mass from the properties of intact rock and a joint factor (J(f)), which is the integration of the properties of joints to take care of the effects of frequency, orientation and strength of joint. A FISH function has been written in FLAC specially for modelling jointed rocks. This paper verifies the validity of this model for three different field case studies, namely two large power station caverns, one in Japan and the other in Himalayas and Kiirunavara mine in Sweden. Sequential excavation was simulated in the analysis by assigning null model available in FLAC to the excavated rock mass in each stage. The settlement and failure observations reported from field studies for these different cases were compared with the predicted observations from the numerical analysis in this study. The results of numerical modelling applied to these different cases are systematically analysed to investigate the efficiency of the numerical model in estimating the deformations and stress distribution around the excavations. Results indicated that the model is capable of predicting the settlements and failure observations made in field fairly well. Results from this study confirmed the effectiveness of the practical equivalent continuum approach and the joint factor model used together for solving various problems involving excavations in jointed rocks. (C) 2002 Elsevier Science Ltd. All rights reserved.