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Pipe bursting continues to be a cost effective method for replacing aged cast iron, steel, ductile iron, and asbestos cement (AC) pipelines. The installation method has proven its cost effectiveness in urban, commercial, residential, and rural areas across the United States, particularly in the Rocky Mountain region. The Confederated Salish and Kootenai Tribes recently employed pipe bursting to replace 3,300 LF of AC pipe in the scenic Flathead region of northwest Montana.
|Pipeline Details and Project Summary|
|Project:||St. Ignatius AC Pipe Replacement|
|Owner/Engineer::||Confederated Salish and Kootenai Tribes|
|Contractor:||Cascade Pipeline Corporation|
|Install Method:||Pipe burst|
|Existing Pipe:||4” Asbestos Cement|
|Replacement Pipe:||6” DR18 Fusible C-900®|
|Pressure Test:||150 psi|
The Confederated Salish and Kootenai Tribes have a long and proud history in the area that today is comprised of Montana, Idaho, Wyoming, and British Columbia. The Flathead Reservation is located in the mountains of northwestern Montana. Similar to many other communities throughout the country, the tribes are faced with infrastructure challenges including the need to replace failing water pipelines. The highest recent priority for the tribes was replacing a 4-inch AC water pipeline installed a half century ago. Brett Birk, Project Engineer for Salish & Kootenai Housing Authority, was tasked with designing and managing the project using the most economical and minimally invasive means possible.
After evaluating both conventional “dig and replace” and pipe burst installation options, Birk decided on pipe bursting as the preferred solution. Pipe bursting allowed the surface to remain largely undisturbed while most of the existing AC pipe could be left in the ground. Only 10% to 15% of the AC pipe required special handling and disposal, versus 100% had dig-and-replace been utilized.
Bidding contractors had the option of installing 6-inch DR11 HDPE or 6-inch DR18 Fusible PVC® pipe for the replacement pipe. The low bid contractor, Cascade Pipeline, selected Fusible PVC® pipe based on its ease of reconnection. PVC pipe utilizes standard, off-the-shelf ductile iron fittings versus the specialized fused-on flanged fittings and electro-fusion service saddles required to reconnect HDPE pipe. John McNatt, owner of Cascade Pipeline, said, “Fusible PVC® pipe is more adaptable, workable, and serviceable for the end-user than HDPE pipe.”
Cascade, an Underground Solutions licensed fusion contractor since 2009, completed all pipe fusion on the project. Cascade also used the “pre-chlorination” method of pipe bursting. Fused pipe strings were chlorinated and pressure tested to 150 psi on the surface prior to pull-in. While some contractors who use pre-chlorination do not employ a temporary water supply system, Cascade did not want any end users off-line, even for a few hours. As a result, Cascade installed an above-ground temporary water system that kept water flowing throughout construction. Following installation, the pipe was pressurized again prior to final approval and acceptance.
Project engineer, Brett Birk, commented, “The project was located in a culturally sensitive area to the tribes, so minimizing open-cut excavation was very important. Pipe bursting also reduced the impact of construction on residents in the project area. The crew was well trained in working with Fusible PVC® pipe and the project went smoothly. We got exactly the project we expected.”