关键词: 大断面, 黄土隧道, 深浅埋, 破坏形式, 分界深度

Abstract:

New-built railway line from Zhengzhou to Xi’an is specially used to transport passenger. This line passes through many districts that mostly covered with loess and includes many double-line loess tunnels. These loess tunnels have a cross-section area of more than 160 m2 and a span of more than 15 m. That should be defined to be super large cross-section tunnel. Due to the special property of loess and the increase of tunnel’s span and area, how the wall rock pressure responds to the change in buried depth is unknown. At present, there has no unified opinion on the critical buried depth for large-span loess tunnel. To solve the problem, investigation was firstly done on 12 tunnels to find the relationship between ground surface cracks and buried depth. After analysis of the relationship, critical depth variety was given as follows: less than 11m defined to be super shallow burial; more than 60 m defined to be deep burial; and between 40 m and 60 m defined to be critical depth for shallow burial and deep burial. Shear slippage limit theory is used for check out the analytical conclusion; and a good agreement has been obtained. At the same time, 17 wall rock pressure-measurement cross-sections were intentionally arranged in deferent buried depths to collect a great deal of pressure data. Based on the data analysis, pressure-measurement results are in a good agreement with theoretical calculation; and it is proved that the given critical depth is correct.

Key words: large cross-section, loess tunnel, shallow burial, deep burial, breakage mode, critical depth