Couple Effect of Joint Pore Pressure and Joint Orientations on Rock Strength Based on Numerical Modeling

The joint pore pressure inside rock mass significantly affects groundwater bursting. To investigate the couple effect of joint pore pressure and joint orientations on rock strength, this study utilized the three-dimensional numerical modeling code of 3DEC to carry out the experiments of uniaxial and triaixal compression tests. Seven three-dimensional models with parallel oriented joints of 0°, 15°, 30°, 45°, 60°, 75°, 90° inclination angle were developed. The input parameters of rock, joints and fluid properties were calibrated based on the results of previous studies. The established models were tested in the uniaxial and triaxial compression tests under uncoupled mechanical state and coupled hydro-mechanical state with various joint pore pressures (0.5, 1.0, 2.0, 3.0 MPa). The results show that the strength varied with different joint orientations producing the classic “U”-shaped curve. However, when the joint pore pressure was involved, the strength changed to a “W”-shaped curve. Additionally, the effect of the joint pore pressure on rock strength depends on orientations. The strength was decreasing with the increase of joint pore pressure when the orientations are 0°, 15°, 30°, 75° and 90°; the strength was increasing with the increase of joint pore pressure when the orientation is 60°; the strength was increasing first and then decreasing when the orientation is 45°. The results indicate that the joint orientation plays more important role than joint pore pressure on the strength change, thus needs to be considered for studying groundwater bursting.