Mechanical characteristics analysis of fully anchored bolts considering different post-peak failure models of surrounding rock

Based on the neutral point theory,considering the dilatancy effect and different post-peak failure models of surrounding rock,the formulas of both axial normal stress and shear stress of fully anchored bolts are derived under the condition of stable equilibrium state and the influence of bolt axial force on the end and surrounding rock parameters (residual cohesion,dilatancy coefficient and strain softening coefficient) on axial normal stress,shear stress and neu- tral point is systematically analyzed. Research results prove that the axial normal stress along the bolt shows the varia- ble characteristics of first increase and then decrease from the inner endpoint to outer endpoint,and the stress curves in the elastic zone and the post-peak failure zone show obvious differences;the dilatancy stress along the bolt shows the variable characteristics of first increase and then decrease from inner endpoint to outer endpoint and the change fea- tures of shear stress at the interface between elastic and post-peak failure zone are closely related to the dilatancy coef- ficient and shear stiffness of surrounding rock;the normal stress and dilatancy stress decrease with the increasing residual cohesion and conversely increase with the enlarged dilatancy coefficient and strain softening coefficient;and mean- while with the enlarged bolt axial force on the end,the axial normal stress and the lateral shear stress increase while the inner shear stress decrease;the neutral point shows the variable characteristics of first increase and then decrease with the increasing residual coefficient,and when the residual cohesion is larger than a certain critical value,the neu- tral point is located in the elastic region,otherwise,the neutral point is in the post-peak failure region;in addition,the neutral point decreases as the dilatancy coefficient and strain softening coefficient. The results can provide a theoretical basis for the support design of the fully anchored bolt under the condition of different properties of surrounding rock.