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HDPE Pipe Plays Major Role In City’s Sewer Expansion
Pipe routes were along the right of way of a busy divided street and through open space in a park. Soils contained a high concentration of clay. Because drought conditions during construction had lowered the lake water level, water did not enter the 7 foot deep trenches so by-pass pumping was not necessary.
To limit disruption of traffic, boring was used at street intersections. Even so, Erickson said, excavation this extensive does interfere with normal surface activities, and was complicated by "rubber neckers" attracted by the large equipment and activity.
Before being placed in the trench, joints of HDPE pipe were fused together in typical lengths ranging from 500 to 800 feet. Sections to be installed in high traffic areas were limited to 100 feet due to water, sewer and other utility easements crossing the median.
To handle HDPE pipe fusing, Gajeske personnel were on site for eight months, said Larry Lisowski, account executive/engineer. A McElroy 1648 MegaMc fusion machine was used for the large pipe, with multiple fusion units for smaller size pipe. To join two sections of pipe, the machine sheers ends of each piece of pipe and holds them together with two large clamps. The ends to be fused are subject to 500 degrees of heat applied while 1,000 pounds of pressure is applied to each segment of pipe. Pipe must cool before being moved. The complete process takes about one hour, then a crawler pulls the fused section of pipe to position for placement in the trench. To save time on pipe installation, many pipe sections were fused prior to moving to the project site.
Erickson said the benefit of using the pipe supplier as a subcontractor for fusing the pipe is that the company has certified personnel with experience and the equipment to fuse the large diameter HDPE pipe.
Lisowski said his firm is performing fusing services more frequently and is seeing water and sewer service providers specifying large diameter HDPE pipe more often than in the past.
One unexpected problem was getting pipe through the tunnels under road intersections. The solution was to drill holes two feet from the ends of the pipe to be pulled through the tunnels. Nylon strapping was threaded through the holes and attached to a rope which was connected to a vehicle at the other end of the tunnel, and pulled through.
Erickson said work began on the project more than a year ago to accommodate a housing development to be constructed along the route. The remaining section started at the Rowlett WWTP in October 2007 and will connect to the gravity section in September 2008.