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Pre-Chlorinated Bursting: Cost Effectiveness On A Large Scale
Because construction is taking place in mature neighborhoods, trenchless methods of construction are being used to limit surface damage and disruption of traffic and routine activities, said John Bidigare, vice president of Bidigare Contractors. Most, he said, is by pipe bursting, with some segments installed by horizontal directional drilling (HDD).
The pipe bursting process uses a bursting tool which is inserted into the pipe being replaced. The tool is pulled through the old pipe, shattering or splitting it. An expander behind the head displaces fragments or pieces of pipe as new pipe is pulled in behind it. Two types of bursting tools are available: a pneumatic bursting head uses percussive action to crack pipe; static heads are equipped with blades that cut or split the pipe.
Key benefits of the method are reduced excavation requirements allowing new pipe to be installed in urban areas where restoration would be costly and disruptive and the ability to increase the size of new pipe. Bidigare said that in Brownstown, approximately 115 bursts will be made with average lengths of 375 feet. Average depth of the host pipe is six to 7 feet at the invert. In residential areas, service connections were reinstated immediately after each burst was completed. Because of the relatively short lengths of the bursts, water customers were without water for only a few hours the day of construction.
“Pipe bursting was chosen for the Brownstown project to increase the size of the existing main in the location of the old main for several reasons,” explained Bidigare. “One is to minimize the surface disruption caused by excavation and the restoration it requires. The Township is an advocate of trenchless technology, and Wayne County has adopted a new policy that abandoned pipe be removed from the ground and not abandoned in place which would have caused increases in the project cost and the schedule to complete the work.”
Bidigare said most construction is in Wayne County Road right-of-way which has grass/landscaped surfaces with some paved areas. Subsurface conditions are in fill material of previous trenches above the existing water main. The old pipe was assessed from record drawings, previous repair experience and other factors. Locations of pipes are confirmed by opening and inspecting gatewells.
A burst plan was developed and reviewed with the project engineer and client. The plan identified the length of each burst, the number of gatewells, hydrants and services along the burst paths, and any other water main connections required.