For tunnel sections with good surrounding rocks, the U-shaped rock-bolted section is selected as a final optimized section instead of the original circular reinforcement concrete lining section.

对隧洞围岩条件良好洞段，论证取消隧洞原圆形钢筋混凝土衬砌，选定马蹄形锚喷断面作为最终优化断面形式。

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It was caused by a private landowner clearing vegetation with a weed trimmer, which may have hit a rock and produced a spark that ignited the dry brush, U.S. Forest Service spokeswoman Linda Christman said.

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