ABSTRACT:

In jointed rock masses deformability is associated with the mechanical properties of the intact rock and the rock joints. It is also known that the deformation modulus of jointed rock masses is anisotropic because of the presence of rock joints. This paper presents an analytical approach to the estimation of the deformation modulus of rock masses that contain any number of single joints or joint sets. The data needed for calculation are the elastic parameters of the intact rock, the orientations of the joints and the stiffness of the joints. The deformation modulus of the rock mass calculated in three-dimensional space can be plotted in a hemispherical diagram. From this diagram one can find the value of the deformation modulus in any given direction and even an estimate of the average overall modulus.

INTRODUCTION

The deformability of jointed rock masses is associated with the mechanical properties of the intact rock and the structure and the stiffness of the geological discontinuities, such as joints and faults, within the rock mass. The deformation modulus of the rock mass is not only required for engineering design, but also for numerical modelling. The deformation modulus is one of the obligatory input parameters in model simulations. Determination of the deformation modulus is always a problem in practice. The conventional means to determine the deformation modulus is to perform in-situ tests, for instance dilatometer tests, plateloading tests, flat-jack tests and block tests (Franklin and Dusseault, 1989; Yow Jr., 1993). Bieniawski (1978) and Serafim and Pereira (1983) proposed two empirical equations for the deformation modulus, which are established on the basis of the rock mass classification system RMR (Bieniawski, 1976), and Barton et al. (1980) proposed one empirical equation based on the classification system Q (Barton et al., 1974).

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