More accurate theoretical prediction of mechanical behavior of viscoelastic–viscoplastic rock tunnels using combined supporting system

Abstract

The combined supporting system of rockbolts and linings is one of the most common methods for controlling the deformation of surrounding rock in tunnels. However, current theoretical analyses typically consider the deformation control effect of only one support type. Consequently, the bearing capacity of rockbolts or linings is not fully utilized as their combined effect is not considered. Thus, this study analyzes the mechanical responses of a “rockbolts + lining” combined supporting system for large deformation tunnels. For theoretical derivation, a viscoelastic–viscoplastic constitutive model is employed to describe the time-dependent behavior of surrounding rock. To satisfy the actual deformation development law, the effect of the stress path in the plastic zone of the surrounding rock is considered. An analytical solution is provided for predicting the tunnel behavior, where the installation time of the rockbolts and lining is considered sufficiently. Furthermore, the proposed analytical solution can be reduced to a viscoelastic solution and is well applied in a tunnel project. The superiority of the proposed solution is demonstrated by comparing it with previous solutions. Finally, a comprehensive parametric investigation is conducted, which considers the cohesion and internal friction angle of rock, the linear stiffness coefficient and installation time of rockbolts, and the stiffness and installation time of the lining. The results show that the cohesion and internal friction angle of the rock dominate the plastic deformation of the surrounding rock, thus further affecting tunnel deformation. The installation of rockbolts and lining can effectively restrict the deformation of the surrounding rock. Generally, better deformation control can be achieved by installing rockbolts (lining) earlier or by improving the stiffness of the rockbolts (lining). However, the stiffness of the rockbolts (lining) is limited to a certain range, in which significant deformation control can be achieved. After determining the installation time of the rockbolts and lining based on the actual construction level, the reasonable design parameters of the rockbolts and lining can be determined using the proposed solution such that their bearing capacities can be fully utilized in this combined supporting system.