这种结构看起来像的拱，下部更平稳，被叫做突拱。

This structure looks like the arch, the lower more stable, is called sudden arch.

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要使突拱变为更直的拱，它需要石头的内部构造适合光滑。

To suddenly arch into a more straight arch, it needs to fit the internal structure of the stone smooth.

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结果表明：突水位置发生在仰拱或墙脚位置时，对衬砌结构的受力影响显著；

The results show that mechanical behavior of lining structure change evidently when suddenly effluent water happen at inverted arch or foot of wall.

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