Experimental Study on Performance of Bolted Joints Under Tensile–Shear Loads

Bolt support is an effective method to improve the shear resistance of jointed rock mass, and is widely used in the reinforcement of fractured rock mass in underground engineering. In this paper, the tensile-shear experiment of bolted jointed rock mass is carried out. The influence of the bolts number, inclination angle and spacing on the bolt-anchoring block strength is analyzed, and the mechanical behavior and failure mode are revealed. The results show that the stress–strain curve in the failure process of bolt-anchoring block under tension–shear can be divided into four stages: compaction stage, elastic stage, yield stage and plastic stage. The numbers, inclination angle and spacing of bolts have a significant effect on the shear strength of the bolt-anchoring block. The shear strength increases with the number of bolts, and under the same number of bolts, the shear strength is higher when they are arranged transversely perpendicular to the tangential force and arranged in multiple rows with large spacing. The anchoring inclination angle has the law of convex quadratic curve, and it is recommended to set the anchoring angle between 30° and 60°. On the basis of laboratory experiment research, the bolted strength characteristics of key blocks in large scale tunnel are simulated and analyzed with the key blocks of Laohushan tunnel. It provides an effective theoretical basis and bolt support scheme suggestions for engineering.