The failure characteristics and control of large deformation in deep fractured hard rock roadways based on cracking evaluation: a case study

Large deformation often occurs after excavation in deep mine roadway which located in the complex engineering geological environment of high in situ stress and fractured rock mass. Taking deep buried roadway of Jinchuan Nickel Mine crossing fractured hard rock as engineering background, in situ comprehensive monitoring and analysis of large deformation were carried out. Based on the identification of engineering geological characteristics of fractured rock mass with high in situ stress, a method to characterize the cracking process in the surrounding rock mass was put forward, and the support control measures should be taken pertinently based on the evolution process of large deformation. The results show that the cracking evaluation method by using borehole digital television can characterize evolution of failure in fractured hard rock mass and support system. The indexes in this method include the length of the broken zone, the depth, and degree of the cracking. The application in roadway repair and new tunneling projects show that the proposed measures of support system can significantly restrain the development of internal cracking of surrounding rock, effectively control large deformation. Through this method to control large deformation, the safety during construction period can be improved, the repair times can be reduced, and the traffic interruption can be avoided. Thus, the operation cost of roadway can be reduced, and the production benefit can be increased.