台阶法（带仰拱）一次开挖施工技术在软岩隧道中的应用

软岩隧道采用传统台阶法开挖时易出现初期支护封闭不及时、步距超标等问题，为解决上述问题，依托蒙华重载铁路部分隧道，提出台阶法（带仰拱）一次开挖施工技术，阐述三台阶（带仰拱）和二台阶（带仰拱）施工工艺流程，从结构力学与变形响应、施工便捷性与设备空间布置等方面综合分析，提出台阶高度和台阶长度的合理设置原则，结合段家坪隧道与中条山隧道现场施工情况，分析台阶法（带仰拱）一次开挖工法的工序组织、技术要点与应用效果，总结台阶法（带仰拱）一次开挖工法的施工技术特点，并提出该工法的推广应用前景。

Application of One time Excavation Method of Bench and Inverted Arch to Soft Rock Tunnel

The untimely primary support closure and overlarge of advancing distance are often encountered during soft rock tunnel excavation by bench method. As a result, one time bench excavation method (with inverted arch) is proposed for some tunnels on Menghua heavy haul railway; the construction flowcharts of three bench method (with inverted arch) and two bench method (with inverted arch) are introduced; the construction parameters such as bench height and bench length are put forward by comprehensively analyzing the structural mechanism, deformation response, construction convenience and arrangement of equipments; the construction organization, technical key points and applicable effect of the one time excavation method of bench and inverted arch in Duanjiaping Tunnel and Zhongtiaoshan Tunnel are presented. Finally, the construction characteristics of the above mentioned technology are summarized, and the technology is prospectively popularized.