Effect of time on the stress–strain behaviour of a single rock joint

The time-dependent behaviour of discontinuities is important in many geotechnical applications. To investigate the stress–strain behaviour of jointed specimens tested at various rates of strain and at constant deformation in various stress conditions, three cases were examined: (a) increasing compressive load at different constant strain rates, (b) increasing compressive load at changing strain rates, (c) stress variations with a constant amount of displacement along the complete stress–strain curves for 5 min (stress relaxation). Triaxial tests were carried out on samples of the Penrith and Stainton Sandstones using a 5 MN servo-controlled stiff testing machine and confining pressures in the range of 0–30 MPa. Both intact and jointed specimens with saw cut and split joints were tested. The joints were produced with orientations of 30, 45 and 60° to the direction of the principal stress. Three different strain rates were applied.