Abstract:

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 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 supershallow tunnel. 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. This study discusses the applicability of various methods of direct excavation for supershallow tunnel. These methods include the forepoling method, the pipe roofing method, the plate shield method. The site of a twintube road tunnel under construction in northern Taiwan is given as an example. Engineering difficulties and landslide failures at the site were encountered during construction, and remediation technologies were adopted and evaluated after each failure. The observations and suggestions made in this study provide dependable references for future tunnel projects facing similar problems in Taiwan.

Key words: shallow tunnel, waste coal pit area, pipe roofing method, fore poling method, plate shield method