The Cheapside Street sanitary sewer project in London, Ontario, is reputed to have the longest microtunneling push in North America. In the final push, 83 pipe were jacked a distance of approximately 253.15 metres. On February 24, 1996, the Soltau RBS 400 broke through the exit shaft at 8:00 a.m., completing an installation by microtunneling that had taken almost a year to complete in tough environmental conditions.

Concrete pipe awaiting installation.

Like any difficult project, there were lessons learned that will make the next microtunneling job easier:

a) It is critical that more test or bore holes be taken for microtunneling projects than are taken for open cut methods. Holes should always be deeper than the invert of the pipe. Without accurate information, it is very difficult for the contractor to determine what microtunneling boring head should be used.

b) A quality pipe product must be supplied to the contractor. An attitude of "it's concrete, and this is good enough," is not acceptable. It is critical to have a smooth outside diameter on the pipe. This helps to reduce the friction as the pipe is pushed through the ground. Pipe squareness is also critical for keeping the pipe on line during the push. Concrete strengths and reinforcing are equally important as the pipe must not destruct during pushing.

c) Proper bentonite lubrication around the pipe while the pipe is being pushed is very important. It will help to reduce friction and jacking pressures.

d) Construction of a suitable launch shaft is very important. Various shaft types can be constructed. Circular poured concrete in short lifts, and removing the ground under it to lower it to the required depth is one way. Another is concrete segments stacked in a vertical position, and yet another is sheet piles driven into place with horizontal bracing.

More than anything, this project was a testimonial to how people can work together to overcome challenges that first seem overwhelming. Dedication to the successful completion of the project, and the will to try out new approaches to problems by employing new technology separated success from failure. Men worked together to solve problems, without pointing fingers and condemning actions.

This article has been abridged.