A need for increased wastewater treatment facilities in a growing community 20 mi. southeast of Wausau, WI, involved the construction of a lift station in a 40-ft. (12.2 m) deep, 28-ft. (8.5 m) wide, 45-ft. (13.7 m) long excavation.
Digging the big pit was a challenge, primarily because of the unstable, sandy soil at a site adjacent to existing structures.
To stabilize the excavation, A-1 Excavating of Bloomer, WI, opted for the Pro-Tec Slide Rail System as an alternative to steel sheeting. According to John Powell, Pro-Tec’s on-the-job specialist, the slide rail system offered several significant advantages.
For example, according to Powell, vibrations involved in driving steel sheeting would have disturbed foundations and underpinnings of adjacent structures at the site and the Pro-Tec slide rail system consists of a dig-and-push sequence that keeps vibrations down to a minimum. He also said walers are used on the inside of steel sheeting, taking up a lot of room and the Pro-Tec system eliminates these members so a lot of clear span space is gained.
In addition, the amount of material to be excavated is far less using the slide rail system and if sheeting were used, the pit would have had to be oversized to accommodate inside walers, said Powell.
Digging was handled by a Caterpillar 375 hydraulic excavator with a 7 cu. yd. (5.3 cu m) bucket. The Cat machine was also used to place and extract the slide rail components, which consisted of four corner posts, six spreader posts, 30 steel panels and six triple roller beams.
“This was a triple track system, with spreader posts and corner posts all consisting of three tracks,” said Brian Radovich of Wisconsin Shoring & Supply, Pro-Tec’s distributor for the area. “Panels ride on the inside, middle, and outside tracks so that each panel can go by one another. This way, you’re driving down or pulling up one panel at a time.
“Panels can be stacked, but given the size and depth of the pit on this job, the triple track system was used so panels can move independently of each other whether you are driving them down or pulling them up. In removal, they pulled the pieces up two feet at a time, backfilling and compacting, then pulling again. The whole system is installed from the top down and removed from the bottom up,” Radovich added.
Spring Lake Concrete, Chippewa Falls, WI, handled the cast-in-place concrete structure for the lift station. Central Wisconsin Engineers & Architects, Weston, provided the engineering.
(This article was provided by Fensholt Advertising, a firm working for Pro-Tec.)