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.
Our society depends very much on infrastructures such as roads, railroads, gas, electric power, water, sewer system, communication line, and so on. Sewage coverage has already reached 78% in Japan, and the market for constructing the sewage system is saturated especially in urban areas (Matsui et al., 2015). A new trend in this field is urban renewal, utilizing more underground spaces. Required underground spaces are becoming much larger or much more complicated shape. However, underground in urban areas is already congested with many utilities as well as many buildings on the surface. In order to keep ground stability during construction of underground spaces, pipe-roofing technology has been used at the project sites these days. Ground conditions and used construction system play an important role in reducing the construction cost and improving safety.
Unfortunately fully understanding the ground conditions is very difficult or impossible in spite of pre-geological survey. Difficult ground conditions, machine troubles, or unexpected obstructions in the ground sometimes stop the tunneling operation.
This paper describes the recent pipe-roofing technology and the development of a micro-tunnel boring machine (MTBM) used in pipe-roofing considering ground conditions.
Fig. 1 shows an example of pipe-roofing works that before constructing an underpass beneath the existing freeway, a lot of pipes are installed to control surface settlement or ground failure during the underpass construction afterward. After pipe installation, the installed pipes are filled with concrete in order to reinforce the strength of the pipe roof structure. Now, it is recognized that pipe-roofing is one of auxiliary construction and temporally support methods without severe ground settlement or collapsing surrounding ground. Currently, underground spaces such as tunnels, subway stations, pedestrian underpasses etc., in urban areas are larger and more complicated shape and constructed near existing facilities and structures both in the underground and on the ground surface. Therefore, pipe-roofing has been attracting close attention of engineers as a supplementary construction method.
