LARGE DIAMETER PIPE BURSTING FOR UPGRADING THE MILLSTONE SANITARY TRUNK SEWER

This paper presents an overview of the Millstone Sanitary Trunk Sewer project undertaken in Nanaimo, British Columbia. Due to increased population growth, the sewer exceeded its original design capacity and was also experiencing inflow and infiltration problems. After extensive review of various options for upgrading, such as pumping and parallel sewers, pipe bursting was chosen by the City. Pipe bursting was chosen as it offered the least amount of environmental impact and was expected to be the least cost.The Millstone Sanitary Trunk Sewer required the upsizing of approximately 3900 m of 350 mm diameter asbestos cement pipe to 650 mm diameter HDPE. This upsize is considered “experimental” for current pipe bursting technology, therefore the project was undertaken in a two stage process. A demonstration section was undertaken to confirm if the available pipe bursting technology would result in a successful completion of the project. If the demonstration section was not successful the City did not want to commit the itself and the contractor to the remaining portion of the contract.Contractors and pipe bursting equipment manufacturers were prequalified for the project. The work was awarded to Terraco Excavating Ltd of Calgary, Alberta for CAN3.9million using the TRS static pipe bursting equipment. Although there were a few minor problems on the demonstration section, they were not of sufficient concern to cause termination of the contract by the City or the Contractor. Work was proceeding smoothly on the remaining work until a deeper section of the sewer was encountered where the asbestos cement pipe wall was thicker. The City, working cooperatively with contractor, reviewed installation data that was being collected and developed revised construction methods which permitted the successful completion of the work.The contract was ultimately completed ahead of schedule and under budget. The project has been recognized by the International Society for Trenchless Technology and Trenchless Technology Magazine as trenchless project of the year.