Effects of cyclic loading on pre-peak and post-peak behaviour of a brittle rock

The effects of cyclic loading on pre-peak and post-peak behaviour of a brittle rock, in Multiple-step Loading (ML) Triaxial Compression (TC) tests were evaluated using a stiff servo-controlled testing machine. The peak and residual strengths at different confining pressures (sigma(3)s) as obtained by a set of Single-step Loading (SL) TC tests can be determined rather accurately from the results of a relevant ML test using a single specimen. The stiffness until the maximum stress state at second and subsequent steps in the ML tests at the same sigma(3), is higher than the one during the primary loading. This is due to combined effect of two factors: (a) cyclic loading effect; (b) effect of pressure level on the stiffness and brittleness during primary loading. Due to factor (a) and pre-compression of specimen at high confining pressures in ML test decreasing sigma(3), failure after several loading steps is very brittle, which may result in under-estimating residual strength values.