While existing sewer systems in Japan have continued to function far beyond their design service life, the pipelines have deteriorated and need costly maintenance and repair. This has been a concern for Japanese sewage engineers for over 15 years, and has been a driving force for the development of alternative repairing techniques for underground infrastructure, such as lining systems or pipe bursting.

Recently, indirect costs have also been a focus when choosing between open cut and Trenchless Technology. Costs related to traffic disturbance, road or lane closing, timeframes for repairs, business interruptions and environmental intrusion have all become considerations in this decision. Expanding trenchless techniques

In 2004, the ExpanditTM bursting head was introduced to Japan by the United Kingdom-based company Perco Engineering Services. The EXP technology involves the insertion of the bursting head into the existing pipe to cause it to shatter. The new pipe is pushed in behind the bursting head, which is in turn pulled through the existing pipe, creating a cavity.

Pipe bursting under the rails

The EXP Technology solution has recently been used to replace a deteriorated sewage pipe under a railway.

The EXP Technology is the only truly hydraulic pipe bursting system in Japan. The burst heads correspond to the new pipe being installed. EXP-200V and EXP-250V are available for pipe replacement via a type-1 manhole, which has 900 mm diameter.

The EXP-250V model can be used for polyvinyl chloride pipe replacement, and the system allows for the installation of replacement pipes of up to 150 per cent of the diameter of the existing one. The system works with a hydraulically operated cone-shaped burst head, enabling it to be opened and closed. All heads are designed so that the user can work from an existing manhole or from a special chamber designed to install new pipes.

The project involved an existing foul sewer pipe, located under a rail line, which required upgrading. As the preferred method of construction was one that would permit an increase in the pipe’s capacity, an EXP method of construction was adopted. The drainage under the railway was replaced by the EXP system. Figure 2 shows a cross section of this stage of the project.

The original clay pipe measured 15.6 m in length, with an inner diameter of 460 mm, while the installed pipe inner diameter is 600 mm. At this site, the inner diameter of existing concrete pipes could be increased by about 150 mm, so that pipes measuring 450 mm in inner diameter would have been replaced with new pipes measuring 600 mm in inner diameter.

As the project was conducted under a rail line, the work had to be carried out with great caution. In the table below, P-1 and P-4 are the subsurface points, while P-2 and P-3 are the rail elevation points. According to estimations prior to pipe bursting, the rail level would rise about 1 mm. However, the rail elevation did not rise at all. The displacement of P-1 from the top of the pipe was 21 mm, and the displacement of P-4 was 2 mm. The table opposite shows the measured data. The pipe bursting work took approximately 12 hours, and was completed safely, without damage to the overhead railway. Conclusions

1. Pipe bursting is a proven method of replacing and upsizing underground utilities safely and economically. 2. The EXP system did not have any problem under a railroad. In fact, it proved to be ideally suited to such conditions. 3. As this method allows work from a manhole, there is minimal impact on residential areas. 4. The EXP system removes localised deviations such as dropped pipe or stepped joint, while also capable of replacing pipes.

The infrastructure constructed for Japan’s period of high growth after 1945 now needs restoring. This is a time of rehabilitation for Japan. There is growing awareness within the industry that trenchless pipe replacement methods may be developed as an alternative to pipeline renovation technology.

EXP technology was chosen as a cost-effective way of replacing deteriorating wastewater pipeline. If this practical study abates concerns held by utility owners about collateral damage from pipe bursting, the authors expect that there will be growing support for the use of pipe bursting as a rehabilitation technique in Japan.

This is an edited version of a paper entitled The Practical Study on the Pipe Bursting Technology by Expandit in Japan by T. Sato, H. Shimada, T. Sasaoka, K. Matsui, M. Hirai, R. Yamaoka presented at No-Dig 2009. Please refer to the paper for more detailed information, references and aknowledgements.