In order to further understand the tunnel face stability and the progressive failure process of surrounding rock mass, a series of model tests were carried out to simulate tunnel excavation under different loading modes. The weak and broken rock mass of grade IVaccording to Chinese classification was chosen as the reference prototype. The test results show that, when tunnel is excavated, the rock mass at the upside of tunnel face destroys firstly, which is reflected by the reduction of both horizontal and vertical stress. The upper part of tunnel face has relatively large deformation initially, but with the increase of overlying load, the lower part deforms drastically until a slide failure surface is formed from the bottom to the top of tunnel face. The tunnel face finally collapses into dome shape when the overload is applied slowly, while it damages into chimney shape under the fast loading mode. In contrast, under the fast loading mode, the rock mass can bear even larger overlying load before the tunnel face collapses.
展开▼
