Experimental research of progressive damage of surrounding rock for soft fractured deep tunnel

The characteristics of rock progressive damage of deep tunnel are studied by using similarity model test. The similarity model is based on big section, soft fractured, deep railway tunnel. The barite, quartz sand and petroleum jelly are mixed in a fixed proportion as similar material. The self-developed test rig of plane strain model is adopted. In this device, the gas bag loading and lifting loading are used as loading system. The evolution of the strain field on rock surface during loading is monitored using the white light digital speckle correlation method (DSCM). The rock pressure change is monitored using pressure cells. The experimental results show that: (1) The shear V-shaped wedge form gradually deep from the tunnel arch sides and it has no damage in the crown of the arch but greater tensile deformation. Shear failure at the arch sides gradually expand to the crown of the arch and the shear arch crack forms over the crown of the arch. (2) Radial compression increases first and then decrease within a certain range of arch sides close to the tunnel wall, where is loosen zone. Tangential stress increased deep in the arch sides, and it is as the main resistance to pressure corresponding the pressure arch body; Radial compression decrease within certain range of the crown of the arch, where is loosen zone. The maximum principal stress direction changes far from the crown of the arch, and which is corresponding the pressure arch body. The surrounding rock show loosen zone-the pressure arch body-original stress zone after loading.