The Charlotte-Mecklinburg Utility recently let a $9.6 million bid to install 20,000 linear ft. (6,100 m) of high-capacity 48-in. (121 cm) steel spiral water main pipe, in 50-ft. (15 m) joint lengths.
Taking on the challenge of installing the behemoth sticks of pipe over that long run is Sanders Utility Construction Inc. of Charlotte, N.C.
“Before we started the project, we debated on whether to install 25-, 30- or 50-foot lengths of pipe,” said Freddie Young, project manager of Sanders Construction. “Because so much of this pipeline is going cross country, from a production aspect the most cost-effective option was installing 50-foot joints as much as possible.”
Shoring the installation of such long pipe is no easy task. To build one trench box to accommodate that length would require extremely high-capacity machines just to move the trench shield. So, Project Superintendent Steve Sanders contact local equipment dealer MSP Rents in Charlotte, for possible shoring options.
“I talked with Freddie about a couple of different shoring options, including building a 40- or 50-foot trench shield,” said Robbie Belk of MSP Rents. “Together, we called our trench shielding supplier, Safe-T-Shore, to get some more ideas on how to shore the pipeline.”
Mike West, Safe-T-Shore’s vice president of engineering, came up with a plan for a long in-line trench shielding system that incorporated two “trained” trench shields, with abutted high-clearance spreader arches.
Explained West: “We finalized a custom-designed system that combines a 34-foot and a 30-foot long trench box into one 64-foot modular unit. The boxes can quickly and easily be put in and pulled out of the trench as the pipe installation progresses, and it doesn’t require extraordinarily heavy equipment.”
Each trench shield is a custom-built Safe-T-Shield HDSD8 model with sidewalls measuring 9 in. (22.8 cm) thick and 10 ft. (3 m) high. Pin-in-place spreader arches with 60-in. (152 cm) cross beams are set at the adjoining ends of each box to allow greater clearance for the pipe joints. The outer ends of the two trench shields are equipped with 7-ft. (2.1 m) spreader pipes.
“We’ve actually built a couple of these ’Super-Arch’ boxes for other projects that have needed the extra length for long pipe installs,” West said. “In each situation, the contractor has been very happy with the trench shields, and they have worked very well.”
Sanders agreed.
“We’re real pleased with how the boxes are working,” he said. “We’re getting very good daily pipe production, and the shields are working exactly the way we expected them to work.”
Sanders recently ordered two more Safe-T-Shore trench shields to be primarily used for installing the pipe at greater depth, where stacking the trench shields is the optimal technique for shoring.
The average depth of the new water main is between 12 and 16 ft. (3.7 and 4.8 m) Approximately 60 percent of the pipeline runs across country, with 40 percent installed in the rights of way of existing roads. In places, Sanders uses only one trench box to install 25-ft. (7.6 m) joints of pipe.
This pipeline installation is part of the Charlotte Utilities’ Southwest Watermain Project, Phase B-1. When completed, the new transmission main will provide continued capacity to the city-wide water distribution system.
Undoubtedly, heavy machinery is necessary to manage the pipe installation and the two-shield combination, so Sanders is using a Komatsu PC750 and Komatsu PC400 excavators. The job started in January 2008 and will be completed in January 2009.
Founded in 1997, Sanders Utility Construction Co. Inc. employs more than 40 people and is capable of handling water, sewer or storm drain projects.
For more information, call MSP Rents at 866/898-7368 or Safe-T-Shore at 800/380-0103.
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