Abstract:

In recent years, with China's social and economic development, more and more cities began to plan and build metros. Meanwhile, the metro construction encountered the sandy pebble soil in some cities, especially the running tunnels of Chengdu Metro line 1 and 2 are almost both need to cross the sandy cobble soil. According to the design, Chengdu metro No.1 and No.2 lines will be constructed by mudding-type earth pressure balance shield. And during shield tunnelling, the face stability control that will be a key operation to ensure the construction can be carried through smoothly. Nowadays, the study of supporting earth pressure is mainly focused on sandy and clay soil; but the study involving the face movement and collapse of cobble-soil is seldom. So based on the heavily discrete characteristics of cobble-soil, the paper analyzes the shield tunnel face deformation and failure while the support pressure is lower than the limit pressure which constructed by using earth pressure balance method and the deformation and failure of excavated face by discrete element method. The results show that: (1) supporting earth pressure of tunnel face is lower than earth pressure at rest; (2) after the face loses stability, the slider ahead of the tunnel face is a surface body. The results will give reference to determine the face control pressure of shield tunnelling.

Key words: cobble-soil, shield tunnel, face stability, discrete element method