Study On Failure Patterns Of Surrounding Rock In Deep Buried Hard Rock Tunnel

Along with the deep construction of hydraulic and hydro-power engineering, mining engineering and traffic engineering, engineering disasters such as rock burst in hard rock, large deformation in soft rock and so on occur more and more, which brings great threats to construction. In the excavation of deep buried hard rock tunnels, the geological conditions and stress fields become more complex, and the mechanical properties of rock masses are also different from those of shallow ones. Non-linear mechanical behaviors and complicated failure patterns in surroundding rock bring great challenges to underground excavation. It is essential to undertake researches on damage mechanism and stability of surrounding rock in deep buried hard rock tunnels.This research is supported by the Major State Basic Research Development Program of China (2011CB013500), the Foundation for Innovation Research Groups of the National Natural Science Foundation of China (51121005), the National Natural Science Foundation of International Cooperation Project (50820125405) and the National Natural Science Foundation of China (51079017,50909013,51004020). A numerical code called RFPA is applied to simulate failure process of intact and jointed rock mass in deep buried hard rock tunnel, and to explore the stress evolution relating unloading excavation, with considering the non-homogeneity of rock.The following conclusions are summarized by analyzing the failure patterns of surrounding rock in excavation of deep buried tunnels:1. Homogeneity index m can be inversed by simplifying the formulas of damage mechanics and Weibull formula, combining the experimental data of rock mass.2. In the stress adjustment of surrounding rock mass, the shape of "V" appears in the direction of minimum principal stress. When the upper section is supported, the failure crack starts at the location of waist position which forms the collapse cavity, and the floor comes out tensile failure in the bottom exaction.3. In the Excavation of fault rock mass, the transmission of the stress and energy are hindered by fault. And the damage degree of surrounding rock close to fault is more severe than other parts. Besides that, different angles of fault cause different failure patterns.4. The angle of layered rock mass decides the failure patterns of surrounding rock. When the angle is0°, the crack expands symmetrically. When the angle is45°, the crack is generated and expanded in the joint, and then becomes vertical to the crack. When the angle is90°, the failure can be considered to be vertical splits of rock.