Study on the failure mechanism of rock mass around a mined-out area above a highway tunnel – Similarity model test and numerical analysis

Abstract

Tunnel construction beneath a mined-out area may inevitably break the existing balance of the surrounding rock mass, which would result in the collapse of the inner cavity of the mined-out area and even the deformation of the tunnel structure. Based on the engineering background of the Yudushan tunnel of the major expressway guarantee project for the 2022 Beijing Olympic Winter Games, both the similarity model test and numerical simulations were conducted to investigate the failure mechanism of the rock mass around the mined-out area above the highway tunnel. In the model test, we studied the progressive failure process of the surrounding rock during tunnel excavation and loading. The information obtained by using a variety of monitoring methods indicated that the displacement changes at different positions in the mined-out area were generally concave, and the stress variations detected by the stress sensors were different for each position in the tunnel. At the same time, by comparing the results with those of the numerical simulation, the validity and accuracy of the results in the model test were verified. Furthermore, the effects of the relative parameters of the mined-out area on the failure mechanism were discussed in terms of the length, location and distance to the tunnel in the numerical simulations. The test and simulations revealed the failure law of the surrounding rock and tunnel deformation characteristics during the excavation beneath a mined-out area, which had beneficial significance for guiding similar engineering construction.