Degradation mechanism of intermittent jointed sandstone under water-rock interaction

Under the action of periodic rising and falling of reservoir water level, the damage and deterioration of the jointed rock mass in the hydro-fluctuation belt of a reservoir bank slope is likely to cause the reservoir bank slope to develop in an unstable direction. Based on this, the water-rock interaction tests on the intermittent joint sandstone are carried out. The degradation law and mechanism are comprehensively analyzed by combining the mechanical tests and the micro-structure detection. The results show that: (1) In the long-term process of water-rock interaction, the compressive strength and deformation modulus of intermittent jointed rock samples exhibit obvious tendency of deterioration, and there are obvious non-uniformity. Among them, the stage deterioration degree caused by the first three water-rock interaction periods is obviously larger, and the stage deterioration degree obviously decreases and tends to be stable after the five water-rock interaction periods. (2) Under the water-rock interaction, the mechanical parameters of different joint dip angles have different degradation degrees, and the overall distribution of stage deterioration degrees is U-shaped. When the joint dip angle is around 0° or 90°, the jointed rock sample changes from obvious tensile failure to shear one. The change characteristics of failure mode are obvious, and the corresponding mechanical parameters deteriorate greatly. When the joint dip angle is about 60°, the jointed rock sample maintains the shear failure of the joint plane as a whole, and the failure mode change characteristics are not obvious, and the corresponding mechanical parameters have a relatively small extent. These changes also make the anisotropic mechanical properties of jointed rock samples gradually weakened. (3) During the long-term operation of the reservoir bank slope, the occurrence of jointed rock mass in the hydro-fluctuation belt directly affects the deterioration trend and deformation and failure characteristics of the water-rock interaction. Therefore, in the long-term deformation stability analysis of the bank slope, attention should be paid to the deterioration of mechanical properties of rock mass in the hydro-fluctuation belt and the occurrence difference of jointed rock mass and transformation of its deformation and failure mode under water-rock interaction.