This vital infrastructure is part of Japan’s “lifeline”, and the total length of lifelines in Japan is shown in Figure 1. Many of them were built during the high-growth period of the Japanese economy which started towards the end of the 1960s, and now these pipes need to be maintained, rehabilitated or renovated. This article looks at the current status and the challenges of lifelines in Japan by taking sewers as an example.

At the end of 1960s, the sewer supply rate was only around 6 per cent, however, sewers have become widespread since then and the number has multiplied by ten over the past 45 years, to a rate of 68.1 per cent. The total length of sewer pipes in Japan today is approximately 370,000 km.

More than 8,000 km of pipes were laid over 50 years ago, and most of these exist in urban areas. In Tokyo, the sewer supply rate has reached 100 per cent, and the total length of sewers is 15,600 km. However, 2,000 km of sewer pipes in Tokyo – about 13 per cent of the total network – have passed the age of 50. Sewers in the centre of Tokyo were almost complete by 1945, and construction in the surrounding areas occurred in later years. In some central areas of Tokyo, 80 per cent of sewers have passed their service lifetime.

As a result, restructuring the aged pipes has become an urgent matter in certain areas. The deteriorated pipes have been in use for a long time and have been severely damaged by the weight of vehicles on the road above. If the pipe breaks, it causes problems with cave-ins and odour. In 2005, 6,600 cases of cave-ins occurred throughout Japan and have become a serious problem. (Figure 3)

Therefore, there is an urgent need to take measures to repair these aged pipes. There are three main objectives for rehabilitating the pipes:

1. To take countermeasures against aged pipes. 2. To improve the lack of capacity. 3. To give consideration to the lifecycle of the asset.

Up until quite recently, renewing old pipes meant replacing pipes by using the open-cut method. However, this method involves construction noise and issues of traffic control that have considerable impact on the public. Therefore, a rehabilitation technique using Trenchless Technology is being used.

Figure 5 depicts the spiral-wound method. It rehabilitates the existing pipe by spirally winding the PVC profile to the inner-surface of the pipe, forming a new pipe within the existing pipe. The backfilling forms a strong bond with the existing pipe and the PVC profile. By this backfilling process, the two-layered pipe becomes a strong composite pipe that has more load-bearing ability than a new pipe. The case shown in the figure provides an example of rehabilitating an aged box culvert pipe (2.9 m X 2.0 m).

The CIPP (Cured-in-place pipe) method is shown in Figure 6. This method creates a new interior lining by pulling-in a resin-impregnated tube that transforms into solid state by thermosetting process. The first stage of this method starts with the introduction of a liner into the sewer pipe. Then, one end of the tube is clamped around the pipe and is expanded with compressed air to closely fit the existing pipe. By converting the compressed air into steam, the thermosetting resin is transformed to a solid state.

Utilising the trenchless technique minimises the need for traffic control, since it doesn’t require a large space to dig the road. The facility and the rig are also compact, ensuring that traffic is not obstructed.

In 2005, the sum total of construction using the rehabilitation method was 380 km, and the grand total of pipes renovated from 1996 to 2001 has reached 3,000 km. In Japan, many trenchless techniques other than those mentioned above are being developed, such as pipe-eating and pipe-bursting, and they are now being put into practice.