Experimental investigations on the mechanical properties of rocks containing a single discontinuity

Abstract

An extensive experimental programme was undertaken to investigate the strength and deformational characteristics of six rock types containing a single joint under various loading and straining conditions. A monitoring system was set up using a microcomputer controlled logger and the required computer programs for data logging and processing were also developed. For the purpose of achieving reliable findings the effects of system constraints on the experimental results in triaxial testing of jointed specimens were investigated. On the basis of a satisfactory end-specimen condition the results of triaxial compressive tests performed on the specimens of three rock types, containing artificial joints at different orientations, are presented, and the effects of joint inclination, confining pressure (0-70 MPa) and joint surface roughness on the mechanical behaviour of jointed specimens were investigated. A method to calculated volumetric strain in the rock specimens has been developed and the volumetric strain, lateral strain and instantaneous Poisson's ratio for both intact and jointed specimens are calculated. Time-dependency of jointed rocks for the three cases of different constant strain rates, changing strain rates and stress relaxation at various points on the complete stress-strain curve has examined. The failure criteria applicable to jointed media are reviewed and the necessary parameters for an appropriate failure criterion have been defined. The stick-slip characteristics of jointed rocks are investigated and two types of stick-slip phenomena are introduced in conjunction with the type of rock and type of testing system.