Experimental study on mechanical properties of excavated unloading rock mass under high osmotic pressure and cyclic loading and unloading environments

Exploring the evolution laws of mechanical properties of deeply excavated unloading rock mass under high osmotic pressure and cyclic loading and unloading environments is conducive to the realease of deformation and failure mechanism under combined loading. By distinguishing the excavation disturbance intensity from the magnitude of osmotic pressure, the triaxial loading and unloading tests are conducted, and unloading rock mass subjected to excavation disturbance under high osmotic pressure environments are conducted considering the combined action of specific pore pressure and cyclic loading. The results show that: (1) The magnitude of unloading directly affects the deformation laws and the failure strength of rock samples and the pore water pressure promotes their tensile and shear failure during the cyclic loading and unloading. (2) The increase of pore pressure intensifies the ductile deformation and strength attenuation of the unloading rock samples with the same magnitude during the cyclic loading and unloading process, and the axial, circumferential and volumetric deformation curves of the unloading rock samples fluctuate at the pore pressure of 2 MPa. (3) With the increase of pore pressure, the circumferential deformation of the rock samples at the unloading magnitude of 30% increases first and then decreases, while that at the unloading magnitude of 60% decreases first and then increases. (4) With the increase of unloading magnitude and pore pressure, the dip angle of the end fracture gradually increases when the rock sample is damaged, and the tensile and shear fracture surface generated along the axial direction of the rock sample becomes more prominent.