RESEARCH OF UNLOADING RATES OF CONFINING PRESSURE UNDER PORE WATER PRESSURE CYCLES ON MECHANICAL PROPERTIES OF SANDSTONE

Considering the actual excavation conditions of the water-level fluctuation zone in the Three Gorges reservoir area, the effects of different pore water pressure cycles and unloading rates of confining pressure on the mechanical properties of sandstone were studied by the indoor triaxial unloading experiment. The results were as follows:1) the effect of the pore water pressure cycles and unloading rates of confining pressure on peak intensity of deviator stress and deformation modulus of sandstone was significant. The more the cycles, the smaller the peak intensity and deformation modulus; the faster the unloading rates, the larger the peak intensity and deformation modulus; 2) when destroyed, axial and circumferential rates of strain variations or peak confining pressure all increased with the increase of pore water pressure cycles and decreased with the increase of unloading rates of confining pressure, however, the impact on the circumferential was more obvious than the axial; 3)the rupture angles of the sandstone under 0.3 MPa pore water pressure were not relevant to the unloading rates of pore water pressure.