For this purpose the mechanism of forming a rock tunnel roof arch and reinforcement will be illustrated with the underground powerhouse in the Three Gorges Project.

为此，以三峡工程地下厂房拱顶设计为例，研究洞顶岩石拱结构形成及加固机理。

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Because the first caving of work face haven't been finished, the tunnel roof and hole can not be used and gas often goes beyond the limit, so some measures must be taken.

由于工作面初次放顶没有完成，顶板巷道、顶板钻孔等不能发挥作用，常发生瓦斯超限现象，必须采取针对性措施。

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Though the load analysis on the tunnel roof wall-rock in the fault footwall tunnel, this paper solves the problem of the tunnel support of tunneling through the great fault;

通过对断层下盘巷道顶板围岩的受力分析，解决了煤巷掘进过大断层的巷道支护问题；

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"The mountains and the roof of the tunnel and everything shook, " Villaroel says.

CNN: Chilean miners waited for death

The Rig 421 oil drill, so-called Plan C, is currently at 265 meters and en route to the roof of the tunnel at Level 150 (150 meters above sea level).

CNN: STORY HIGHLIGHTS

Sections of a drill which broke through the roof of a rail tunnel came from a construction site above the ground, accident investigators have found.

BBC: Construction drill came from site above rail tunnel