管幂进洞工法在山谷地形浅覆隧道中的应用与补强对策

REINFORCEMENT STRATEGIES OF CONSTRUCTION IN SHALLOW-HURIED TUNNEL ENTRANCE USING PIPE-ROOFING METHOD IN VALLEY

近年来,随着环境保护观念的提升,减少地表开挖的理念已逐渐落实在隧道设计及施工上。在隧道洞口浅覆段采用的明挖法已逐渐被暗挖法所取代,即使在地质、地形条件上不尽理想的区段,考虑到整体路线及水资源保护等因素,也是如此。以台湾北部一正施工中的双线双车道公路隧道为例,探讨管幂工法在浅覆盖采用暗挖法所面临的困难及其对策。由于该案例处于山凹处,洞口浅覆盖厚度约100m。开挖过程中,因为遭遇到地质变异,多雨的气候与谷部入洞的地形,使得降雨所汇集的地表水,不断入渗至隧道内,开挖面自立性极差。故施工进洞时,原设计采用的管幂工法几乎难以进行。经采取拱盖培厚及双层管幂等补强对策后,勉强施工,其处理经验与心得,可为以后类似工程提供参考。

The growth of environmental protection awareness in Taiwan has made it necessary for tunnel engineers to consider altering the natural surroundings as little as possible when undertaking tunnel design and construction in practice.Tunnel projects in Taiwan have progressively evolved into using the method of direct excavation to replace the traditional method of cut and cover excavation when dealing with tunnel entrances.Even when both the geological and topographical conditions are unfavorable,the method of direct excavation is still adopted because it leads to the lowest environmental impact.The applicability of various methods of direct excavation for tunnel entrances is discussed.These methods include the fore-poling method,the pipe roofing method,the plate shield method,and ground improvement method.The site of a twin road tunnel under construction in northern Taiwan is given as an example.Engineering difficulties and landslide failures at the site are encountered during construction;and remediation technologies are adopted and evaluated after each failure.The observations and suggestions provide dependable references for future tunnel projects facing similar problems in Taiwan.