Conestoga-Rovers & Associates (CRA) of Canandaigua, N.Y., recently installed six new pre-cast manholes at a shopping center in Dearborn, Mich. Due to the deep grade that the manholes were installed and the steep incline on a couple of the excavations, CRA needed a non-traditional shoring system.
The shopping center was built atop a retired landfill, and therefore the CRA’s project was impacted by environmental concerns. All the dirt removed from the approximately 2 sq. mi. (5.2 sq. m) area was collect in containers, covered and hauled away; classified as hazardous material because of the landfill. In total, 15 20-yd. (18.2 m) containers were filled and removed.
The new manholes were installed to access the original drainage pipe around the mall that was continually getting filled with silt and dirt. The drainage pipe was installed with a clean-out system, but the clean-outs had become ineffective.
The six manhole structures were installed at various depth grades around the shopping center. Four of the manholes were only 12 to 13 ft. (3.6 to 3.9 m) deep, while two others’ foundations were set at a grade of 25 ft. (7.6 m) deep. For each of the six holes, the challenge was the same: how to safely shore the excavation while expending as little money and effort as possible, while also working in some very tight and difficult spots.
Traditional Shoring Not an Option on Steep Slope
The three traditional shoring methods for 4-sided pits: tight-sheeting, welded walers, or 4-sided trench shields; were all dismissed at the outset of the bidding for the project. In several spots, the excavations needed to be dug on a tight slope or in spots inaccessible to a crane to drive sheeting. Addtionally, CRA wanted to be able to reutilize the shoring system for all six excavations.
Efficiency Production Helps Contractor Shore Excavations
Larry Leach, CRA’s project manager, started looking for a shoring solution by contacting Efficiency Production, Inc., a manufacturer of trench shielding and shoring.
Efficiency’s Slide Rail Systems Manager Greg Ross looked at the project’s specs and quickly knew that Efficiency’s Universal Slide Rail System would be perfect for the project.
“I knew that our Slide Rail was going to work, because it is designed and engineered to be installed in the tightest of spots, and in all types of soil conditions,” said Ross. “And a set of Slide Rail components — panels and posts — can be used over and over again on the same project.”
“Dig and Push” System Fits in Tight Spots, Steep Slopes
Efficiency’s Universal Slide Rail is a component shoring system comprised of steel panels (similar to trench shield sidewalls) and vertical steel posts. The versatile system can be used in a variety of configurations, such as small four-sided pits; large unobstructed working pits as big as 50 sq. ft. (4.6 sq m) with Efficiency’s ClearSpan System; or in a linear Multi-Bay configuration to install length of pipe more than 40 ft. (12 m).
Slide Rail is installed simultaneously as the trench or pit is excavated by sliding the panels into integrated rails on the posts — an outside slotted rail first, then an open-face rail on the inside — then pushing the panels and posts incrementally down to grade as the pit is dug; a process commonly referred to as a “dig and push” system. Efficiency Production is the only Slide Rail manufacturer to offer an open-face rail design on its Slide Rail posts.
“I like the [Slide Rail] System a lot, especially the open-face rail design,” said Leach, a second-time user of Slide Rail. “After installing 12 feet in the outside rail, it gets tight; but then moving to the open-face inside rail, it’s like starting all over again. There is a lot more flexibility.”
CRA rented from Efficiency a four-sided system, utilizing a set of 12 sq.-ft.-long (1.1 sq m) panels and 24 ft. (7.3 m) corner posts to install the four manholes with the shallower 12-to-13 ft. grade. On the deeper 25 ft. deep manhole installs, CRA swapped in 28 ft. (8.5 m) corner posts, and a set of 16 ft. (4.8 m) panels on two sides of the 4-sided system.
“We soon discovered one of the advantages of Slide Rail: it can be installed easily on a sharp slopping hill by adding a panel on the high side, and leaving out a panel on the low side,” said Leach.
The manholes were precast sections with a 60-in. (152 cm) inside-diameter.
“I’ve been surprised at how quickly and easily it is installed and removed,” concluded Leach. “I don’t think it would be as easy with another type of [shoring] system.”
Contractor Uses Specialized Excavator
CRA used a Cat 330 and a Cat 321 excavator, as well as a Komatsu 200 LC excavator with a 50-ft.-long (15.2 m) boom. Additional equipment included a CAT 950G front loader.
Conestoga-Rovers & Associates provides comprehensive engineering, environmental consulting, construction, and information technology solutions for a variety of contractors. With more than 30 years of experience in providing high quality and responsive services, CRA has grown to more than 90 offices and more than 2,700 people working on projects worldwide.
Efficiency Production Inc. 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 director of marketing and media for Efficiency Production Inc. For more information, call 800/552-8800 or e-mail [email protected]
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