Deformation behavior analysis of tunnels opened in various rock mass grades conditions in China

Abstract

The [BQ] method is a rock mass classification method to evaluate the quality of the rock mass and determine the construction parameters. This method is more empirical and cannot provide predictions for the deformation of tunnels after excavation. To predict the surrounding rock deformation of deep-buried tunnels by using the [BQ] method in China, first, data of 52 tunnels were collected and analyzed to determine the relationship between the grades of the surrounding rock, excavation method, burial depth, tunnel span, and surrounding rock deformation. Second, the equivalence of different surrounding rock grades to the range of geological strength index (GSI) scores were determined using methods, such as fitting GSI to another classification system RMR and RMR to BQ, and considering the correction factors of BQ values. This approach provides the basis for theoretical calculations based on the Hoek–Brown strength criterion. On the basis of the Hoek–Brown strength criterion, a theoretical approach to the deformation of surrounding rock under three failure models, namely, elastic–brittle–plastic, strain-softening, and elastic-perfectly-plastic, is presented when considering the installation time of primary support and the volumetric force of bolts. Finally, the theoretical approach is analyzed and compared with the measured data to verify its feasibility. Moreover, the effects of burial depth, grades of surrounding rock, support parameters, support time, and deformation allowance of the surrounding rock are analyzed. Analysis results can provide some guidance for the prediction of surrounding rock deformation of deep-buried tunnels in China.