Study on Construction Methods for Tunnels of Large Cross-Section Excavated in Weak Rocks

The double side drift method, CRD and CD method are widely adopted for super large cross-section excavation for tunnel in weak rock in China. Further, it is shown good adaptability because of the extensive application in highway, railway, especially in urban underground facilities. However, there are also some problems in work efficiency, structure safety and engineering management and so on. It is necessary to make optimization of construction methods under these conditions. In this paper these shortcomings for double side drift, CRD and CD methods are detailed. The work efficiency, load conversion mechanism and the influence on tunnel structure, and construction management are discussed. Then suggestions for tunnel excavation determination in such conditions are put forward. It is shown that if auxiliary measures are adopted first, partial excavation could be abandoned. Even full-face excavation may be feasible. The principle proposed in this paper has been used in practice, which is proved once more for tunnel excavation in soft and weak surrounding ground.