Abstract:

The concept of early close of excavation crosssection is introduced. It is pointed out that: 1) The early close of excavation crosssection has to be adopted in bad surrounding rocks. 2) The close time and distance of excavation crosssection reduce with the surrounding rock goes worse. 3) The close distance of excavation crosssection increases with partition of excavation crosssection increases. 4) The early close of excavation crosssection indicates the close of primary support. The classification of setting of early closed inverted arch of tunnels in Japan is introduced. The author believes that we have to learn how to improve the construction technologies so as to realize early close of excavation crosssection. The standards for early close of excavation crosssection in Japan have been perfected. The mode of the standards and concept of early close in Japan are introduced. The tunnels in Japan, adopting early close of excavation crosssection,are introduced. The early close modes of excavation crosssection are divided into 5 kinds. The rationality of adopting early close of excavation crosssection is summarized. The surrounding rock conditions in which early close of excavation crosssection has to be adopted are summarized. The structural parameters and construction technologies of tunnel using early close of excavation crosssection are introduced. The construction management methods of early close of excavation crosssection of Qiwei Tunnel in Japan, including management items, final displacement management standards, primary displacement speed management standards, early close modes and related modification, are introduced in detail. The construction technologies for largecrosssection tunnel in soft and weak surrounding rocks are summarized. The combination method of reinforcement of surrounding rock ahead of excavation face and early close of excavation crosssection, together with advance geological prediction hole drilling (under condition of water), are the basic methods for construction of bad surrounding rocks.

Key words: tunnel, mining method, soft and weak surrounding rock, early close of excavation crosssection