Experimental simulation investigation on fracture behavior and bolt anchoring mechanism in a circular tunnel under support in layered rock mass.

This paper aims to explore the fracture behavior and bolt anchoring mechanism in circular tunnel under support in layered rock mass. Seven support methods, horizontal and vertical bedding planes are set up, and cubic rock-like material samples with a prefabricated circular hole and bedding planes are tested under uniaxial compression. During the compression, the failure of the hole sidewall is monitored by a camera. The fracture behavior in tunnels under support in layered rock mass is reproduced. After uniaxial compression failure, the fracture behavior of specimens is analyzed via CT scanning, and the bolt anchoring mechanism is analyzed. The results demonstrate that the system bolt and steel floral pipe provide higher improvement. The shotcrete and steel arch can provide supporting pressure for the tunnel, which effectively prevents the surrounding rock from spalling. The strength increment for the vertical bedding specimen is larger than that for the horizontal bedding specimen. CT observations combined with theoretical analysis indicate that the anchor bolt generates anchoring effect by improving the stress state and the mechanical properties of the surrounding rock in the anchorage zone where the fractures are compacted, arrested, and deflected, which could increase the bearing capacity of the surrounding rock.