The effect of water on the time-dependent deformation and fracture of a granite

Abstract

The effect of water on the deformation, fracture and strength of Lac du Bonnet granite has been investigated through a variety of experimental techniques: standard short-term tests for compressive strength and fracture toughness, and longer-term, time dependent experiments that measure creep, static fatigue and slow crack velocity. When specimens of this granite are tested while in direct contact with water, such conventional measures of the short-term strength as the uniaxial compressive strength and the fracture toughness decrease by about 5% from the levels measured at room temperature and humidity. Because short-term tests require a few minutes to complete, part or all of this decrease in strength may only be due to time-dependent processes. When results of other, longer-term tests are extrapolated to zero elapsed time, the indication is that at very rapid loading rates (instantaneous or dynamic loading condition), the effect of water on strength may be negligible. In all time-dependent tests for creep strain, static fatigue and slow crack velocity, the effect of water is substantial. The creep strain and slow crack velocity increase and the long-term strength decreases when water is introduced into the previously dry testing environment. The size of the change, however, depends on the stress level (applied stress relative to the instantaneous strength). It is small at high stress levels becoming more substantial as the stress level is decreased. For example, at a stress level of 65%, the steady state creep rate of the lateral strain increased by 300% when water was allowed to flood the previously dry environmental chamber.