In-situ observation on large deformation and failure of deep tunnel:Case study for the Jinchuan No. 2 Mine

In view of the large deformation behaviors in the deep tunnel of Jinchuan No. 2 Mine,this paper focuses on the tunnel failure modes induced by the large deformation,the multi-means on-situ testing and the safety management standard for tunnel’ s large deformation. Firstly,ten kinds of typical deformation and failure modes of the tunnel’ s arge deformation were summarized and the mechanism was clarified considering different support types of tunnels. Secondly,a complicated on-situ test,i. e. 3D dimensional laser scanning,borehole imaging observation and automatic multipoint extensometer,had been carried out to investigate the spatial asymmetry of deformation of deep tunnel,the non-uniformity deformation of the shallow and deep surrounding rock,and the jumping progressiveness of the rock’ s time-dependent deformation. The observation data indicated that the large deformation mechanism of the fragmented surrounding rock in Jinchuan No. 2 Mine is that the excavation induces the cracking of the shallow surrounding rock under high stress,and the cracking extension of the surrounding rock gradually develops to the deep,which deteriorates the bearing capacity of the surrounding rock and performances as continuous time-dependent large deformation,which is different from the traditional deformation and failure performance in shallow tunneling engineering. Finally,the safety management standard of large deformation of deep tunnel,which is based on the principle of functional failure and structural instability,was proposed. Based on the feedback analysis of the field application,the support methods of “double-layer spray anchor net+anchor injection” and “ spray anchor net+single reinforced concrete” were proposed for controlling the large deformation of deep tunnels in Jinchuan No． 2 Mine,based on the supporting principal of im- proving the stress environment and reconstructing the bearing ring for the surrounding,by utilizing composite effect be- tween the flexible and pressure effect of shorcrete,reinforcement function of rock bolt and bonding role of cement paste.