Conestoga-Rovers & Associates (CRA), of Canandaigua, NY, recently installed six new precast concrete manholes at an existing shopping center in Allen Park, MI. Due to the deep grade that the manholes were installed in 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 CRA's project was impacted by environmental concerns. All of the dirt removed from the approximately 2-square-mile area was collected in containers, covered and hauled away; it was classified as hazardous material because of the landfill. All told, 15 containers, 20 cubic yards each, 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 feet deep, while two others' foundations were set at a grade of 25 feet 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.
The three traditional shoring methods for four-sided pits — tight-sheeting, welded walers or four-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. Plus, CRA wanted to be able to reutilize the shoring system for all six excavations.
Project Manager Larry Leach, a 42-year veteran of CRA's Kalamazoo, MI, office, 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 specifications 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 spots, and in all types of soil conditions," Ross said. "And a set of Slide Rail components — panels and posts — can be used over and over again on the same project."
Efficiency's Universal Slide Rail is a component shoring system comprised of steel panels (similar to trench shield side walls) 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 feet by 50 feet with Efficiency's ClearSpan™ System; or in a linear multi-bay configuration to install pipe that is over 40 feet in length.
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 when you move to the open-face inside rail, it's like starting all over again. There is a lot more flexibility."
CRA rented a four-sided system from Efficiency, utilizing a set of 12-foot by 12-foot panels and 24-foot corner posts to install the four manholes with the shallower 12-foot to 13-foot grade. On the deeper 25-foot-deep manhole installations, CRA swapped in 28-foot corner posts and also a set of 16-foot panels on two sides of the four-sided system.
"We soon discovered one of the advantages of Slide Rail: It can be installed easily on a sharp, sloping hill by adding a panel on the high side and leaving out a panel on the low side," Leach said.
The manholes were precast sections with a 60-inch 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."
CRA used a Cat 330 and a Cat 321 excavator, as well as a Komatsu 200 LC with a 50-foot long boom. Additional equipment included a Cat 950G front-end loader.
CRA provides engineering, environmental consulting, construction, and information technology solutions for a variety of contractors. CRA has over 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.
|James McRay is the director of Marketing and Media at Efficiency Production, Inc.|