The construction of increasing deep-buried underground projects, especially large mines, leads to more and more geological hazards. The surrounding rock of some 450∼800m deep iron mine deforms severely, with local support failures. Most of deformation failures occur at the cross between side wall and crown (or floor). In-site stress tests results of hollow inclusion triaxial strain gauge shows that these tunnels are affected greatly by modern tectonic stresses, with maximum principal stress of 13∼21MPa, and the field geostress generally features σV ≥σH >σh. Surrounding rock of large deformation is fissured rock. The FEM simulation of typical cross-section tunnel shows that the maximum stresses, about 40MPa, occur at crosses between side wall and crown (or floor), which fits the deformation failure positions by field survey. The research indicates that the large deformation of surrounding rock of tunnel is caused jointly by strong tectonic stress and gravity stress, with continuous large rheological deformation latterly. In addition, the common shotcrete-bolt support is hard to ensure the stability of the fissured surrounding rock under high stress. Through the analysis of deformation mechanics of surrounding rock and defects of prophase support system, this research finding is of great significance to the reinforcement and repair of surrounding rock of the mine.
With the development of engineering constructions such as transportation, water conservancy and hydroelectric power, energy, etc., human activity space is increasingly expanded to the deep part of the globe where numerous deep-buried underground engineering are involved. For example, the maximum depth of the diversion tunnel of Jinping II Hydropower Station is up to 2500 m, the mining depth of Tongling shizishan copper mine is up to 1100m and many coal mines will enter into the depth of 1000∼1500m (Zhou & Xie 2005).