Experimental study on bolting effects of bolted joint rock masses considering strength of bolts

The strength of bolts is mainly affected by their diameter and materials (tensile strength). It is very important to improve the shear resistance of bolted joint rock masses. The shear tests on bolted joint are carried out. The influences of the strength of bolts on the shear deformation characteristics and bolting effects of bolted joint are studied. A model for calculating the shear resistance of bolted joint considering the strength of bolts is proposed, and the contribution of axial force and shear force of bolts to the shear resistance of joints under different strengths of bolts is analyzed. The results show that: (1) With the increase of the bolt diameter, the peak shear resistance of the bolted joint increases linearly. When the bolt diameter exceeds a certain critical value, it will play a bolting role. The greater the tensile strength of the bolts, the smaller the critical value. (2) With the increase of the diameter and tensile strength of the bolts, the plastic hinge of the bolts moves outward, the length of the deformation section increases, the capability of the bolts to resist deformation and failure is enhanced, and the shear resistance of the joints is enhanced. (3) The shear process of jointed joint can be divided into four stages: elastic, yielding, strengthening and residual stages. At the elastic and yielding stages, the bolts mainly play the role of pins. Their contribution is positively correlated with their tensile strength, and the relationship with the bolt diameter is affected by the thickness of the anchoring agent. At the strengthening stage, the bolts form a plastic hinge, and their contribution is provided by their shear resistance and axial force, which is positively correlated with the tensile strength and bolt diameter. At the residual stage, the fracture of the bolts does not provide shear resistance. (4) Based on the large deformation theory of the bolts, the anti-shear force model for bolted joint considering the strength of the bolts is proposed. The analysis shows that with the increase of the bolt diameter and tensile strength, the proportion of contribution of their axial force increases, and that of their contribution of shear force decreases.