Study on mechanical properties and energy evolution of Jinping deep buried marble

Compared with shallow rock mass, the occurrence environment of deep rock mass is more complex, which leads to the great difference between theri mechanical properties. The maximum buried depth of the tunnel in Jinping II hydropower station is more than 2 500 m, and the maximum ground stress of diversion tunnel is 70 MPa. It is of great theoretical value and practical significance to study the mechanical properties of hard rock under high stress conditions. Therefore, a series of static mechanical tests, including uniaxial and triaxial compression tests, were carried out systematically on Jinping marble from 2 400 m depth by MTS815 rock mechanics test system of Sichuan University. The test results show that the uniaxial compressive strength of Jinping marble is 180.43 MPa. With the increase of confining pressure, the marble shows the mechanical characteristics of “brittle-ductile-plastic” transformation, and 32.0 MPa is a demarcation point. At the same time, there are similar growth trends between the crack initiation stress, crack damage stress and crack peak stress, and the decreasing trend of the brittleness index is gradually flattened. Under low confining pressure, the elastic energy is dominant before the peak, while under high confining pressure, the dissipative energy increases more significantly, and the difference between pre-peak and post-peak elastic energy decreases, showing more obvious plastic characteristics. The research results provide a theoretical basis for accurately describing the mechanical behavior of deep rock and ensuring the stability of deep engineering.