Safety First, Last, and Always

March 1, 2010

Safety, safety, safety. For the Dow Chemical Co.-the nation’s largest chemical company-safety is the first, last, and all-between consideration. Everything that goes on at its many worldwide facilities is looked at through the prism of safety…even the rainwater.

The Dow Chemical Co. is in the process of installing a new 25-foot-by-55-foot-by-30-foot lift station at its facility in Midland, MI, which will hold surface runoff water collected through an existing 54-inch storm-sewer line and will pump the water through a new 36-inch line to a recently built 10-million gallon aboveground water storage tank for future treatment.

To tap into the existing storm-sewer line, the new concrete structure is to be poured in place 35 feet deep in the ground. The working pit dimensions to accommodate the lift station needed to be over 60 feet long and 35 feet wide, and to stay open and properly shored for more than three months.

The low bidder for the project was Johnston Contracting, also located in Midland. Owner and operator Lee Johnston has many years of experience working with Dow, inside and outside its main facility. The biggest safety challenge to the project was that of properly shoring the large and deep working pit that would be open for a long period of time.

Dispelling the Sheet-Piling Myth
“There were two other contractors looking at this job, and they believed it would be a sheet-piling job,” Johnston says. “The folks on the project from Dow believed it would be sheet piling, and that was my initial thought. Or it was until I got a visit from Mike Ross at Efficiency [Production Inc.], who suggested a much more cost-effective alternative to sheeting.”

“I told Lee, “˜We can do this with slide rail,'” says Ross, Efficiency’s custom engineering and slide rail specialist. “We have a ClearSpan Slide Rail System that’s able to shore pits that big and do it better, faster, and cheaper than sheeting.” Indeed, with a custom-designed ClearSpan Slide Rail System from Efficiency in his proposal, Johnston’s bid was much lower than any other bidding contractor.

Dig-and-Push System Reduces Over-Excavation
Efficiency’s Universal Slide Rail is a component shoring system comprising steel panels (similar to trench shield sidewalls) and vertical steel posts. This highly versatile system can be used in a variety of configurations. In addition to the obstruction-free ClearSpan configuration, Efficiency’s Universal Slide Rail can be configured into small four-sided pits; or in a Multi-Bay configuration to install large tanks and structures; or 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-pushsystem. This allows the slide-rail system to be installed simultaneously as the pit or trench is excavated to grade.

A Cost-Effective Alternative
Sheeting is by nature a loud, long, and cumbersome way to secure a large excavation, and requires extra-specialized equipment in addition to an excavator. Johnston installed the entire Slide Rail System in 13 days, rather than the 30 days it would have taken to install an alternate shoring system like tight sheeting. “If we’d used sheeting, we’d have to have double walers and cross-braces,” said Johnston. “That would leave us with 12 penetrations to pour the concrete through, and would take an extra month to finish.”

As it was, Johnston had onsite installation assistance from Efficiency’s Slide Rail Systems manager, Greg Ross. “We really had no problems installing the system,” Johnston says. “A big advantage of using an Efficiency system is that, not having used slide rail before, Greg Ross was here a couple days to help us get started. That was a big help.”

Eliminating Cross-Members
Three Rivers Corp., also located in Midland and boasting Dow credentials, is the subcontractor installing the poured-in-place concrete tank. Brian Barber, project superintendent for Three Rivers, also has high praise for Efficiency’s ClearSpan System. “The open workspace is what I liked,” he says. “We’ll be able to form up the structure without having to deal with anything crossing the workspace.

“Other manufacturers’ slide-rail configurations need to be installed with cumbersome cross-members. Only Efficiency’s ClearSpan system is never encumbered by cross-members at any time.”

The new tank will sit on a 3-foot poured concrete footing. The 2-foot-thick walls will be formed 3 feet in from the edge of the footing on all sides. When completed, the new structure will be 30 feet tall and have a capacity to hold more than 100,000 gallons of stormwater.

To excavate the pit and install the slide-rail components, Johnston used the following equipment:

  • An 866E Koering excavator with a 3-yard bucket
  • A 330 Terex crane
  • A 108 Linkbelt crane with Lead and Drop Hammer to install opposite side posts and panels
  • A 7.8 Komatsu mini-excavator

Johnston Contracting was founded by Lee’s father, Dean Johnston, in 1965. Specializing in underground utility and chemical plant construction, Johnston Contracting is a member of the Michigan Infrastructure and Transportation Association (MITA).