Effect of high temperature damage on triaxial mechanical failure behavior of sandstone specimens containing a single fissure

The quantitative temperature (T)-dependent relationships between the strength properties and elastic modulus of both intact and fissured sandstone are presented. Based on the experimental results, it can be concluded that tensile strength (TS) and mode I fracture toughness (K-IC) decrease nonlinearly with increasing T. The elastic modulus (E) values of the intact and fissured sandstone specimens have different correlations with T and confining pressure (sigma(3)), whereas the Poisson's ratio does not depend on the temperature. As T increases, crack closure stress, crack initiation stress and crack damage threshold first increase and then decrease, however, these properties have linear correlations with sigma(3). The cohesion (C) of the intact specimen decreases nonlinearly with increasing T, whereas that of the fissured specimen first increases and then decreases. However, the internal friction angle (phi) of the intact and fissured specimens has nonlinear correlations with T. The permeability (k) of the intact sandstone decreases during the compaction-dominated stage and then increases at dilation-dominated stage under constant strain compression at sigma(3) = 30 MPa. Moreover, k decreases slightly as T increases to 250 degrees C but then increases with further increasing T. The crack types of intact and fissured specimens under different sigma(3) and temperature conditions are also discussed.