STUDY ON MECHANICAL PROPERTIES OF WATER-SATURATED SURROUNDING ROCK DURING UNDERGROUND TUNNEL EXCAVATION

In order to explore the influence of unloading rate corresponding to different excavation methods on saturated surrounding rock, conventional triaxial compression test and unloading confining pressure test with constant axial displacement (rate of 0.1~5 MPa/s) were carried out on saturated sandstone. The results show that the circumferential deformation is the main reason for the failure in the unloading confining pressure test. With the increase of unloading confining pressure rate, the confining pressure and axial principal stress of the failure point increase and are located outside the conventional triaxial compression envelope. The variation of circumferential energy, total energy and dissipation energy shows a V-shaped change. The failure mode of the specimen changes from conjugate shear failure to tensile strain + conjugate shear mixed failure. The dilatancy angle of the specimen decreases first and then increases with the increase of plastic shear strain.