The elastoplastic semi-analytic solution of a timely active support technique using NPR bolts for deeply-buried tunnels

Abstract

The timely active support technique using high-strength, high-toughness negative Poisson’s ratio (NPR) bolts as the key material (NPR-TAST) has a positive effect on disaster control in deeply buried tunnels. In this study, based on the finite difference method, a semi-analytical solution for NPR-TAST is proposed to investigate the effect of NPR bolts on ground reactions. The stress relief coefficient method is adopted to simulate the unloading process and the interaction process between the bolts and surrounding rock. Once the bolt deformation exceeds the set maximum value, the bolt would break. The proposed solution is validated by the previous semi-analytical and numerical solutions. The results show that, under large deformation conditions, conventional bolts tend to break. In contrast, NPR bolts can continuously deform with the surrounding rock, enhancing the bearing capacity of the surrounding rock. The key factors of NPR-TAST, including support timing, pre-stress magnitude, and constant resistance value of NPR bolts, are discussed. Early application of higher pre-stressed NPR bolts and increasing the constant resistance value of these bolts can more effectively control surrounding rock deformation and failure. The research results can provide guidance for the application of NPR-TAST in deeply buried tunnels.