The Central Weber (Utah) Sewer Improvement District recently awarded an important underground utility project to Whitaker Construction Company of Brigham City, UT. Whitaker is in the process of installing a new treated water discharge line from the treatment plant to the Weber River.
Whitaker is installing 4,500 linear feet of 108-inch RCT pipe with an outside diameter of 11 feet, at an average depth of 18 20 feet. The pipe is designed with extra thick walls to prevent it from floating in the very high water table of the relatively agricultural area of Utah.
There are always numerous challenges when a contractor installs large diameter pipe. A pipeline like a treated water outfall is typically installed using trench shields to protect workers from trench cave ins. But, standard 8 or 10-foot tall trench shields do not provide enough pipe clearance to install a mammoth 11-foot reinforced concrete pipe.
Whitaker needed a custom shoring solution for this deep and wide pipeline.
Whitaker personnel contacted Tom Hartman at National Trench Safety, Freemont, CA. Hartman had worked with Whitaker on a previous project when he was based in Salt Lake City.
“Pipe clearance really was the biggest problem to overcome,” Hartman said about the project. “Whitaker’s first idea really was the best option; to use a spreader arch on a tall trench box.”
Hartman called Mike West, vice president of engineering at Efficiency Production Inc. – a leading manufacturer of trench shielding and shoring equipment headquartered in Michigan – to discuss custom engineering a pin in place spreader arch and trench shield that would provide the necessary pipe clearance for Whitaker’s project.
“Time was critical on this project, and I knew that Efficiency Production had experience with custom engineered trench shields and arches,” said Hartman. “I talked West and together we came up with the idea of a pin in place spreader arch that would pin to a 10-foot tall shield, and a second, 4-foot tall stacked box which would give us 140 inches of clearance rather than 112 inches we’d have with the 10 foot box.
“Whitaker ordered the shields around Dec. 1 (2008), and wanted them on the jobsite before Christmas,” Hartman continued. “So Efficiency really turned the order around fast, and was able to get the shields and arch on site, on time.”
Added West: “A pin in place spreader arch is nothing new. What made this arch unique is that we designed it to pin over the collars of both trench shields, essentially locking the two shields together which made it easier to pull the box through the trench. But the arch could also be used with just one trench shield.”
The stacked trench shields were Efficiency Production’s HT 6 10 by 28 and 4 by 28-foot boxes with 16-foot spreaders on the front end, and high clearance arch on the back end.
The job requires laying approximately 550 joints of the 8-foot long pipe. Each stick of pipe weighs approximately 45,000 pounds, so a Caterpillar 385 excavator is used to move pipe joints from the truck directly into the trench. Whitaker is getting eight to 10 pieces of pipe installed a day. They are also installing three cast in place structures, including two ground pipe-to-box culvert transition structures.
The project started Dec. 26, 2008 and is scheduled to be completed in August 2009.
Whitaker Construction Company has been in the underground utility business for 56 years and are still a family-owned company.
FOR MORE INFORMATION:
Whitaker Construction Company, (435) 723-2921, www.whitcon.com
Efficiency Productions, Inc., (800) 552-8800, www.epi-shields.com