Research on construction technique and stability analysis of outlet in shallow tunnel under unsymmetrical pressure

Longtan tunnel, a key part of HU-Rong Expressway engineering including many geological problems such as shallow cover, unsymmetrical pressure, water rush, mud rush and rock burst, is a representative of long and broad expressway tunnel under complex geological conditions. It is very difficult for engineer to build tunnels with shallow cover and unsymmetrical loading. The design and construction of Longtan Tunnel are described from safety point of excavation and support. FLAC3D is used to simulate the excavation and supporting process of the exit section of Longtan Tunnel under the condition of shallow cover and uneven pressure. Some conclusions are drawn through analyzing the characters of stress and displacement fields and plastic zone of surrounding rock after excavation. It will be useful for the project construction.