High-temperature tensile strength of rocks by hydraulic fracturing tests

Knowledge of the physical properties of rocks at high temperature is important for the design, construction and maintenance of nuclear waste disposal facilities in rock mass. This paper presents the results of a series of laboratory hydraulic fracturing (LHF) tests of rocks at various temperatures ranging from 30°C to 300°C. The experimental details, including the techniques used to apply high temperature in a stainless triaxial cell, are described. The mechanism of the fracture initiation and reopening is presented. The tensile strength of the rock was calculated based on the results of the LHF tests, and a comparison with that determined by the splitting tensile strength test (known as the Brazilian test) was made. The tensile strength of the rock decreased as the temperature of the rock went up and at the temperature of 300°C, the strength reduced to only about 25% of the room-temperature (30°C) strength. The increase in the permeability of the rock, as the temperature rose, is evidenced by the increase in the boundary porosity, although no direct measurement of the permeability was made. Issues concerning the LHF tests that merit further investigation are pointed out.