Mechanism of zonal disintegration in surrounding rock mass around deep rock engineering and its application

The mechanical behaviors of deep rock mass are different from those of shallow rock mass. Through cases of Jinping II Hydropower Station, the special phenomenon of zonal disintegration in the surrounding rock mass around the diversion tunnels, is analyzed. On the basis of fracture mechanics, a new strength criterion for deep rock mass is derived. The new nonlinear strength criterion that is relative to the rock mass rating classification can be applied to the study of the tensile failure of deep rock mass. Subsequently, zonal disintegration model is established, and the radius of fractured zone and none-fractured zone of deep surrounding rock mass around cylindrical tunnel are obtained, their exact positions and the evolution law of zonal disintegration of surrounding rock mass is determined. To validate the present model, comparison between calculation results and the experiment observation on facture and failure around underground openings is carried out. It is found that the numerical simulation result is in good agreement with the experimental one on failure modes around the hole. Through sensitivity analysis, the effects of stress condition, cohesion and the angle of internal friction on the phenomenon of zonal disintegration are determined. Finally, the present model is adopted in the analysis of the zonal disintegration in the surrounding rock mass around the diversion tunnels in Jinping II Hydropower Station. Meanwhile, the magnitude and distributions of fractured zones are determined by numerical simulation.