The rules were clear: do not make the excavation any bigger than the shoring system and never allow the excavation walls to be unsupported at any time.
These were the tough requirements set down by the North Carolina Department of Transportation (NCDOT) when Charlotte Mecklenburg Utilities let a $3.4-million project to install a 36-in. water main in the Andover-McAlway Rd. area of Charlotte. The new potable water line tapped into an existing 54 in. water main pipeline running directly under busy Providence Road.
Only one contractor, B.R.S. Contracting Inc. of Richfield, NC, had a solution for the shoring conundrum. B.R.S. partnered with local equipment distributor Stafford and Efficiency Production Inc., which manufactures trench shielding and shoring equipment.
“The DOT requires only ’active shoring’ devices, which means that the trench could not be open at any time during the excavation, so traditional trench boxes were not an option,” said Roger Kimrey, B.R.S. project superintendent. “We called Efficiency months ago and they have been working with us all along to design, develop and present a shoring system to the DOT that was an active shoring system that would work great for this project.”
DOT Requirements Met
In order to make the tap on the existing 54 in. water main, B.R.S. needed to dig down 18 ft. in the middle of the busy four-lane road to the pipe, and then bring in the new 36 in. pipe through a 60 in. bore casing that had been bored 40 ft. from a cross street. The new water main connects to other fresh-water pipes in the area and supplies two water towers.
The excavation needed to be as tight as possible, without any over-cutting. B.R.S. used an Efficiency Production custom-engineered Shore-Trak sheeting guide frame system to shore the 12-by-16-by-20-ft. deep four-sided pit.
“The system was not only the best shoring option, it was the only shoring option approved by the DOT,” Kimrey said
Efficiency’s Shore-Trak is a pre-fabricated, custom-engineered, cross-utility shoring system that integrates with Efficiency Production’s universal slide rail system. Efficiency slide rail is a component shoring system comprised of steel panels (similar to trench shield sidewalls) and vertical steel posts. Shore-Trak guide frames can be used instead of slide rail panels where existing cross-utilities are present.
B.R.S. first needed to cut out the road’s surface to the exact required measurements of the system, 12-by-16-ft. Then after digging out approximately 30 in. of dirt in the hole, B.R.S. laid in two 12-ft. and two 16-ft. Shore-Trak sheeting guide frames square and flush in the open cut. With a 24 in. auger, pilot holes were bored out 6 ft. deep for the universal slide rail system corner posts, which have two integrated continuous grooved rails.
The outside rails on the posts are slotted to slide over specially-designed t-tracks on the end of the guide frames that secured the entire system in a four-sided configuration. Specially-designed internal walers with special tracks on the end were then secured in the “open face” inside rail of the slide rail posts.
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