T. G. Sitharam* and G. Madhavi Latha **
*Associate Professor **Research
Associate
Department of Civil
Engineering, Indian Institute of Science, Bangalore, India.
Tel:+91-80-3602261
Fax:+91-80-3600404
email: sitharam@civil.iisc.ernet.in
A simple statistical relation to obtain the elastic modulus of jointed rocks and thereby predicting their stress-strain response in triaxial compression is presented in this paper. This equation has been arrived from the multi variant regression analysis of large amount of experimental data reported in literature. In this equation, the jointed rock is represented as a continuum material with equivalent elastic modulus (Ej) obtained from the properties of the intact rock and joint factor (Jf). Joint factor is the integration of the properties of joints to take care of the effects of frequency, orientation and strength of joint. The equation presented in this paper is simple compared to similar equation developed by earlier researchers. The effect of confining pressure is also incorporated in the equation thus facilitating the use of a single equation to use for any confining pressure. This equation is incorporated in a commercial finite difference program Fast Lagrangian Analysis of Continua (FLAC) to carry out the equivalent continuum analysis of jointed rock samples tested in triaxial compression. The constitutive behaviour of the rock is represented by a confining stress dependant hyperbolic relation with Mohr-Coulomb failure criterion. The numerical model has been validated against experimental results from wide range of intact and jointed rock samples with different joint fabric and joint orientation and for a wide range of confining pressures (1 MPa to 155 MPa). Results showed that the stress-strain curves obtained from numerical analysis are matching closely with the experimental stress-strain curves for various intact and jointed rock samples exhibiting linear to highly nonlinear stress-strain behaviour. This study confirmed that the numerical model developed in the present study can efficiently simulate the effects of number of joints, strength of joint, orientation of joint, type of rock and confining pressure.
Keywords: Rocks, intact, jointed, triaxial, stress-strain, equivalent continuum, numerical model