Development of a micro-tunnel boring machine (MTBM) in pipe-roofing considering ground conditions

Pipe-roofing technology has been widely used to develop larger or more complicated underground spaces in urban cities in Japan. Rapid installation of roof pipes plays an important role in reducing underground construction cost and improving construction safety. Pipe-roofing has been attracting more attention to engineers and is one of the auxiliary construction and temporally support methods with less disturbing surrounding ground. However, ground conditions are very complicated and unknown and also a lot of underground utilities and facilities on the surface have been already constructed in the project sites. Cutting tool wear or failure due to hard rock layer or hard stones such as cobbles and boulders leads to tunneling work stoppage and in some cases, unforeseen obstacles make tunneling stop. This paper describes the recent pipe-roofing technology and the development of a micro-tunnel boring machine (MTBM), considering ground conditions. A newly developed MTBM shows many outstanding features in pipe-roofing under difficult ground conditions.