In order to guarantee the construction safety and high efficiency of bench method in soft rock,the geometric parameters of bench method used in Zhongtiaoshan Tunnel is optimized and analyzed.And then,the numerical simulation method and site monitoring method are adopted;and the safety of primary support structure,stability of tunnel face and construction convenience are taken as references for optimization work.The analytical resuhs show that:1) The stress on tunnel primary support structure is rational and the construction machinery operation is convenient when adopting bench method for soft rock tunnel and the top heading length is controlled within range of 4-5 m.2) The tunnel construction efficiency and the tunnel face stability can be guaranteed when the top heading height is 0.6H (H refers to height of tunnel cross-section);the top heading height should be in the range of 0.6H-0.7H when the tunnel is in bad surrounding rock (i.e.shallow bury or water inrush from Grade Ⅴ surrounding rock).%为提高台阶法在软岩条件下施工时的安全性,充分发挥其施工高效的固有优势,以中条山隧道为工程依托对该法施工时几何参数的选取进行优化分析.分析采取数值模拟结合现场监测数据的方法,以初期支护结构安全性、掌子面稳定性以及施工便利性作为优化选择的依据.根据研究成果可知:在软岩条件下隧道采用台阶法施工时,上台阶长度控制在4～5m时隧道初期支护结构受力合理,施工机械操作便利;上台阶高度取值为0.6H(H为隧道高度)时能较好地兼顾隧道的施工效率以及掌子面的稳定性,但是在围岩条件较差如Ⅴ级围岩掌子面出水或浅埋情况下,其取值应适当提高但也不宜超过0.7H.
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