ABSTRACT:

Numerical methods often play a pivotal role in predicting the behaviour of engineering structures found in/on the rock mass. However, there is no precise method available for modelling rock masses as they contain natural discontinuities and joints. Thus, a practical equivalent continuum approach is used in which properties are assigned to the rock mass in such a way as to represent the contributions of the intact rock and joints towards its overall response. This paper presents the outcome of static and dynamic study carried out on the underground Nathpa Jhakri hydro power cavern in India using FLAC2D software using this approach. The advantage of this approach is that it estimates the properties of jointed rock mass from the properties of intact rock and a joint factor (Jf), which is the integration of the properties of joints to take care of the effects of frequency, orientation, and strength of joint. The results are compared for three different material models i.e. elastic, mohr-coulomb and ubiquitous joint models under various stages of excavation. For static analysis, the predicted and observed behavior of the cavern is compared. It is shown that the predictions are satisfactory in an appropriate sense. For dynamic analysis study revealed that a ubiquitous joint model is more appropriate for dynamic analysis of underground structures in rock.

1 INTRODUCTION

Rock masses often contain natural discontinuities and joints which makes the task of their modelling quite challenging. This has led to a scarcity of technical literature detailing precise ways for modelling rock masses, and hence this paper is aimed at contributing to this area. In the present study, the joint factor model presented by Ramamurthy (1993) is incorporated in a commercial finite difference code (FLAC), which is widely used for modelling rock masses.

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