Utah’s Central Weber Sewer Improvement District recently awarded an important underground utility project to Whitaker Construction Company of Brigham City, Utah. 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 ft. (1,370 m) of 108 in. (274 cm) RCT pipe with an outside diameter (O.D.) of 11 ft. (3.3 m), with an average depth of 18 to 20 ft. (5.5 to 6 m) deep. The pipe is designed with extra thick walls as to be “anti-floatation” in the very high water table in the relatively agricultural, rural area.
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 ft. (2.4 to 3 m) tall trench shields do not provide enough pipe clearance to install a mammoth 11 ft. (3.3 m) O.D. reinforced concrete pipe.
Whitaker needed a custom shoring solution for this deep and wide pipeline.
National Trench Safety, Efficiency Production
Whitaker’s first call for shoring assistance was to Tom Hartman of National Trench Safety in Freemont, Calif. 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 of Efficiency Production Inc. — a 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 to Mike (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 just the 10 foot box.”
“Whitaker ordered the shields around December 1st (2008), and wanted them on the job site before Christmas,” Hartman continued. “So Efficiency really turned the order around fast, and was able to get the shields and arch onsite, 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 are Efficiency Production HT-6 10 by 28 ft. (3 by 8.5 m) and 4 by 28 ft. (1.2 by 8.5 m) boxes with 16 ft. (4.9 m) spreaders on the front end, and hi-clearance arch on the back end.
The job required laying approximately 550 joints of the 8 ft. (2.4 m) long pipe. Each stick of pipe weighs approximately 45,000 lbs. (13,700 kg), so a Cat 385 excavator is used to take the joints of pipe right off the truck and into the trench. Whitaker is getting eight to 10 pieces of pipe installed a day. They also are 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 is located in Brigham City, Utah, 60 mi. north of Salt Lake City. It has been in the underground utility business for 56 years and is still a family owned company.
Efficiency Production Inc., “America’s Trench Box Builder,” provides a wide selection of standard and custom trench shielding and shoring systems. Efficiency’s products are designed specifically for safe and cost effective installation of utility systems and infrastructure improvements. All products are P.E. certified to meet OSHA and MIOSHA standards.
(James McRay is the Marketing & Media Manager of Efficiency Production, Inc. He can be reached at 800-552-8800; email@example.com)