Numerical investigation study on tensile-shear failure behavior of rock bolts in inclined strata mining tunnels

In response to the problem of severe deformation and failure of the surrounding rock of the mining tunnels in inclined strata, a tensile-shear failure numerical model of rock bolts was adopted to analyze the rock bolts failure behavior and the surrounding rock mechanical response, and explore the influence of different factors on rock bolts failure. The results indicate that: (1) As angle between the rock bolt and the interface decreases, the shear force of increases, and the rock bolt is easier to fracture. The maximum displacement is 250.2 mm of fractured position. A new evaluation index of shear axis ratio was proposed. The larger the shear axis ratio, the rock bolt is easier to fracture. The shear axis ratio at the interface has increased by 95 % compared to the non interface. (2) The plastic zone and the surrounding rock deformation exhibit the same inclination trend as the strata. In final state, the maximum deformation is 297.7 mm at the bottom and top position perpendicular to the rock bolts at the interface. At the moment of rock bolts fracture, the interface displacement of surrounding rock immediately increased by about 10 mm. And the stress in the surrounding rock decreased about 1 MPa. The weakening effect of surrounding rock stress shifts with the change of rock bolt fracture position. The stress at the arch waist decreases by 44 %, the stress at the arch crown decreases by 25 %. When the fracture of the rock bolts at the arch crown and arch waist ends, the stress at the side wall begin to decrease by 40 %. (3) As the inclination angle increases, the deformation of the surrounding rock and the number of rock bolt failures increase. The range of the plastic zone in the surrounding rock gradually increases, and the degree of rock bolts asymmetric fracture more aggravated. As the diameter of the rock bolt increases, the fractured number of the rock bolts and range of plastic zone decreases.