Abstract:

As the concepts of environmental protection, conservation to water and soil and reducing the change of natural condition are prevailing, safe, energysaving, environmental protection tunnel construction techniques have gradually been carried out in tunnel design and construction. The shallow overburden tunnels used to be constructed by either cut & cover method or concrete slab protection roof and back fill method, which need massive excavation. Under the consideration of reducing excavation, advance support by pipe roof technique, instead of the traditional cut & cover method and concrete slab cover method, is most often used nowadays. This article discusses the construction of a twintube highway tunnel in northern Taiwan with hazardous factors for tunnel construction such as 100m long shallow overburden valley section with only dozens of centimeters to 2 meters soil covered in thickness, and coal debris and abandoned coal pits laid underneath it. Under the consideration of the energy saving, environmental protection and the conservation of water and soil factors, pipe roof method is adopted to pass shallow overburden section. In this case, because the geologic materials are made up of top soils, weathered rock and coal mine debris, the rainy climate causes the surface water affluxes in the valley year to year, which results in the enormous difficulties to the tunnel excavation. However, after several collapses and reinforcement processes, the tunnel can be passed. Therefore, this experience might be the reference of the following similar cases.

Key words: shallow overburden tunnel, collapse, pipe roof