ABSTRACT

This paper presents the results of parametric numerical analyses carried out on elements of jointed rocks. The analyses are carried out using the commercial explicit finite difference code FLAC, with special user defined FISH functions to simulate the exact behavior of the jointed rock mass.The FISH function uses joint parameters as input to calculate the joint factor (J f) and the joint factor along with properties of intact rock is used to represent the overall behavior of the jointed rock mass using confining stress dependent hyperbolic constitutive model. Triaxial test cases of different jointed rocks are taken up and the experimental stress-strain behavior is compared with the results of numerical analyses. The results of analyses are compared for different strength and failure criteria to choose the best criterion for the analysis of jointed rock mass behavior. Then the parametric analyses of the rock elements are carried out varying different joint parameters to understand the effect of each of these parameters on the overall behavior of rock mass. The results clearly demonstrated the efficiency of the numerical model and also the study has brought out the significance of each joint parameter on the mechanical behavior of jointed rock masses.

1 INTRODUCTION

Due to the increasing need of structures built in and or on rock masses for various engineering applications like tunneling, mining, rock slopes etc. it is of vital importance to thoroughly understand the stress strain behavior of jointed rock masses. A systematic understanding and analyses of jointed rock masses pose complex problems to the geotechnical engineers because of the variations in the joint parameters like orientation of joints, strength and frequency of joint etc. The engineering behavior of jointed rock mass is highly influenced by its inherent discontinuities like joints, bedding planes, fractures and fissures etc. The strength of jointed rock is several times less than its intact strength. Fig. 1 clearly demonstrates this feature. The effect of various joint parameters on the overall stress-strain behavior of rock mass is of greatest interest for solving rock engineering problems. It is highly difficult to know the strength of jointed rock mass through field experimentation due to their complex behavior, high cost and practical difficulties involved. Some of the earlier researchers, Cai (1992), Zienkiewicz et al. (1977) have developed the equivalent continuum models to simulate the jointed rock mass. Some researchers have developed empirical relations to estimate the equivalent material properties of the jointed rock mass from the geometrical and mechanical properties of discontinuities. These equations can be incorporated in other constitutive models for effective simulation of jointed rock masses. e.g. Hoek and Brown (1980), Ramamurthy (1994). Most of these models are developed based on laboratory triaxial testing of small jointed rock samples. Hoek and Brown failure criterion is most widely used for the analyses of rock masses. However, this criterion requires estimation of many rock mass parameters, which is not feasible in some cases.

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