Project Profile: Connecting the Locks

May 1, 2011
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As the old adage goes, “One good idea begets another,” an apropos slogan for Bacco Construction Co., based in Iron Mountain, MI, which has recently undertaken two very important excavation projects in Sault Ste. Marie, MI.

The first project was a $9,500,000 storm sewer separation upgrade in downtown Sault Ste. Marie, just east of the town’s historic Soo Locks. Excavation challenges abounded on the project, not the least of which was that of finding an appropriate and cost-effective shoring system.

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Bacco’s solution was the use of a slide rail shoring system from Efficiency Production Inc.-a leading manufacturer of trench shielding and shoring equipment. “The system has been great for us, and we’re typically getting in 80 to 100 linear feet of 8-foot-long pipe per day,” says Chris Wentland, Bacco’s project superintendent on the storm-sewer separation project.

…Second Great Idea
And the begotten second great idea? Having successfully mastered the ins and outs of Efficiency’s Slide Rail, Bacco was the successful low bidder on another high-profile project in Sault Ste. Marie for the Army Corp. of Engineers. Bacco was commissioned to excavate a deep trench…directly between the two canals of the Soo Locks.

The Soo Locks of the St. Mary’s River raise and lower large cargo freighters and other ships 21 feet between the higher water level of Lake Superior and the lower level of Lake Huron. The largest ships are as long as 1,000 feet. The locks have two canal chambers with large doors on each end that raise and lower the water level. Between the two operating canals is an island, at the east end of which the locks’ operations building is located. Bacco’s excavation project was on the west end of the island.

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Along the island side of the two canals are tunnels about 22 feet deep the run along the length of the canals. Bacco’s job was to excavate and install a connecting tunnel running perpendicular to the existing tunnels. This required excavating down 22 feet, exposing the outside walls of the two tunnels, sawing through each tunnel wall for access, and then pouring-in-place a new access tunnel. The total length of the trench was 96 feet. Slide rail was again used for shoring.

Unlocking Challenges
Efficiency’s universal slide rail is a component shoring system comprising 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 feet by 50 feet (with Efficiency’s ClearSpan System); or in a linear configuration using the company’s Multi-Bay system to install lengths of pipe over 40 feet.

Slide rail is installed simultaneously as the trench or pit is excavated by sliding the panels into integrated rails on the posts-either double or triple rails, depending on needed depth-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.

For the locks project, Bacco used slide rail in a five-bay configuration with Efficiency’s Multi-Bay system.

In the course of excavating the trench, Bacco encountered a critical cross-utility just below ground that had to be exposed and supported. This created an interesting challenge: Not only did Bacco have to excavate underneath the utility, but it had to shore around it as well.

A Tight Fit
Compounding the excavation and shoring challenges, the tunnels’ exposed outside walls slanted down into the trench. Bacco overcame these particular challenges by using Shore-Trak sheeting guide frames instead of slide rail panels to stand up KD sheeting. The bottom of the sheets shored tightly around the sloping face of the tunnel walls and the supported the crossing utility. Efficiency’s Shore-Trak integrates seamlessly into the slide rail system, the only prefabricated slide rail system to do so.

“Despite all the challenges, the slide rail system worked very well,” says Steve Rigoni, project superintendent of the locks project. “The trench is very safe, which is important because it is going to be open for a while.”

The ground condition Bacco encountered can only be described as “extremely hard,” consisting of shale and heavy clay. To excavate the trench and install the slide rail system, Bacco used a Caterpillar 345B excavator plus a Caterpillar 938H frontloader. All heavy equipment for the excavation, including excavators and slide rail components, went through the locks on a barge in order to get to the work site on the island.