Reinforcement strategies of construction in shallow-hurried tunnel entrance using pipe-roofing method in valley

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.