The weakening effect of hydrostatic pressure on rock mass of different lithology

The weakening effect of hydrostatic pressure (P-w) on rock mass is an important topic in the field of underground construction. In this article, a new technique is introduced to simulate the mechanical conditions and geological processes of rock mass formation using the MTS815 Rock Mechanics Test System. With this technique, intact rock specimens of marble, sandslate, greenschist, and lamprophyre acquired from rock masses are transformed into rock mass replica specimens with structural planes whose major mechanical characteristics resemble the target rock masses. These replica specimens are subjected to hydro-mechanical interacted tri-axial compression tests to reveal the weakening effect of the hydrostatic pressure on the rock mass. The experimental results show that hydrostatic pressures of 1-4 MPa have a significant effect on the mechanical properties of the rock masses. The internal cohesion c decreased dramatically when the hydrostatic pressure increased; however, the increased pressure had less effect on the internal friction coefficient mu. The deformation modulus decreased when the hydrostatic pressure increased under low confining pressure, but barely changed when the confining pressure rose above 20 MPa. These results have provided an important basis for engineering construction planning and have created a new effective way for laboratory studies of rock mass mechanical properties.