Effects of pre-existing cracks and temperature on failure mode of granite from Eastern China

Abstract In order to study the effects of high temperature and pre-existing cracks on the failure mode of rock, granitic rocks from Eastern China with three pre-fabricated cracks parallel to each other oriented at 30° and 45° and subjected to different temperatures are tested. Changes in the strength and failure modes of the rock are studied extensively. Various factors that affect the failure modes and their transitions are analyzed by measuring the mineral composition, chrominance, mass, thermal conductivity and P-wave velocity of the material. The results show that pre-existing cracks result in changes in the failure mode of plate-shaped granite samples from intermediate splitting to Y-shaped shear fractures. Under the combined action of pre-existing parallel cracks and high temperature (≥300 °C), the failure mode changes from a Y-shape to a stair-step shape. The angles of the crack selected for testing (30° and 45°) have no significant effect on the failure mode of the samples. The change in the failure mode of the rock caused by parallel cracks and high temperature is mainly due to stress concentration around the cracks (especially at the tip of the cracks). Moreover, high temperature causes thermal damage on the rock which changes the brittleness and plasticity of the material. Damage to this rock due to an increase in temperature is mainly caused by the evaporation of water inside the rock and the growth in crack (especially at temperatures above 400 °C, when the rate of the volume expansion of the quartz increases rapidly), which can be measured by the changes in the thermal conductivity, P-wave velocity, and rates of mass loss and quartz expansion with temperature.