A study of the behaviour of jointed rock masses

This thesis dwells on three principal issues in rock mechanics: firstly, statistical analysis of laboratory strength data; secondly, failure criteria for rock mass and rockfill materials; and finally, constitutive relations for rock mass.; In the first segment, the Linear Regression Analysis, Simplex and LOWESS statistical techniques are used for fitting nonlinear failure envelopes to triaxial and shear test data for rock masses. The Simplex technique was found to be the most appropriate procedure for fitting strength data to nonlinear failure criteria, e.g. the Hoek-Brown criterion.; A discussion on existing failure criteria for rock masses is presented in the second part of this thesis with emphasis on the strength predictions from the Hoek-Brown criterion. The limitations of this criterion in the estimation of strength of rock masses in the range of low confining stresses is eliminated by the development of the Modified Hoek-Brown criterion. A numerical solution procedure is developed to generate the nonlinear Mohr envelope for this criterion. A methodology for estimating the parameters of this criterion from rock mass classification schemes is also presented. A set of non-dimensional, nonlinear shear and triaxial strength criteria are developed for estimating the strength of rockfill materials and the procedure for estimating these strength parameters from triaxial or shear test data is given.; The final aspect of this thesis deals with the development of constitutive relations for rock masses and their implementation into the finite element analysis program ABAQUS. These constitutive relations are developed on the basis of the incremental theory of plasticity with the Hoek-Brown surface adopted as the yield surface for the rock mass. This constitutive model is an elastic-perfectly plastic one involving six parameters and incorporates the associated as well as nonassociated flow rules.