Extrusion prediction of tunnel face reinforced with fiberglass bolts considering interface debonding

Fiberglass bolts are extensively used to control the extrusion of tunnel face and enhance tunnel stability. A novel computational approach based on the finite difference method is proposed to predict the extrusion of tunnel face reinforced with fiberglass bolts. Given the 3D stress state of the tunnel face, the spherical symmetric model is utilized. The strain-softening constitutive model effectively captures the characteristics of post-peak progressive failure in rock. To more realistically describe the interaction between the bolts and the rock mass, the model incorporates the relative shear deformation and the occurrence of interface debonding when the shear stress exceeds the ultimate shear strength. A robust iterative procedure is introduced to address the interaction. The effectiveness and high efficiency of the proposed method are validated through comparison with numerical simulations. Compared with previous studies, the proposed method emphasizes the importance of the rock softening characteristics and the debonding at the bolt-rock interface. Additionally, it employs a robust iterative computational procedure instead of predefined force patterns to obtain a more realistic representation of bolt stress conditions. The method has been applied to two real engineering projects, and the analysis results show satisfactory accuracy. Parameter analysis is conducted to evaluate the effects of the geological strength index, in situ stress, bolt density, and overlap length on the responses of the bolts and rock mass. The proposed approach provides an efficient and accurate predictive tool for the preliminary design of tunnels reinforced with fiberglass bolts.