Stabilizing Deep Pit Sidewalls In Tight Quarters

Staff | September 28, 2010

Installing a 20-foot-square cast-in-place concrete foundation for a pump station at the bottom of a 24-foot-deep excavation in metropolitan Indianapolis presented more than a few problems for Bowen Engineering Corp. of Fishers, Ind.

CAT 330 and 345 hydraulic excavators team up during installation of the PRO-TEC Slide Rail System.

First and foremost was the location. The 30-foot-6-inch by 34-foot-6-inch-long and 24-foot-deep pit that was excavated to accommodate the poured concrete bed was sandwiched tightly between E. Westfield Avenue on the west side and a levee walling off the White River on the east with little operating room and no room at all to slope in any direction.

The pump station installation at what is known as the Broad Ripple section is a key element in the overall flood control plan for the area: The Indianapolis North Flood Damage Reduction Project, a joint venture between the U. S. Army Corps of Engineers and the city of Indianapolis, which will cost about $19 million shared 75 percent with federal funding and 25 percent by the city. The completed project will protect and remove approximately 2,400 properties from the 100-year floodplain.

Because of the depth and spoil placement, the contractor used a CAT 345 with its 42-foot-reach and 29-foot-depth capabilities to excavate the pit.

Working with MacAllister Machinery of Indianapolis, distributor for Slide Rail Supplier PRO-TEC Equipment, Charlotte, Mich., they looked at two different means of shoring up the sidewalls: tight sheeting and a PRO-TEC Slide Rail System.

Ti-back walers are installed outside panels and posts in the PRO-TEC system, creating true clear span area to work in.

Installation Time

From a material cost standpoint, careful calculations revealed that the two means were about equal. But when hours to install each were factored in, the Slide Rail System ended up taking about half the time it would take to drive steel sheeting.

Slide Rail Specialist Taylor Clark of MacAllister said the contractor was able to cut many hours and lots of dollars from the overall cost of installation as compared with tight sheeting.

Economical Consideration

"Working with Bowen, we opted for the PRO-TEC Slide Rail System as the most efficient and by far the best economical means of stabilizing the big pit," said Clark.

"Given the city street area we were working in, the Slide Rail System gave us the luxury of shoring up the walls without completely interrupting traffic and disturbing homes and businesses in the neighborhood."

Vibrations caused by driving tight sheeting into place are eliminated because the Slide Rail System uses a dig-and-push method of installation. Also, two 45-foot and two 35-foot tie-down walers were used on the outside of the panels and posts. In the PRO-TEC System, walers are installed on the outside of the panels and posts, allowing for a completely clear span in which to work

Triple Track

Components of the Slide Rail System installed consisted of four 26-foot corner posts, four 27-foot spreader posts, and 24 panels, all 4 inches or 6 inches thick and 8 feet by 16 feet in length. A triple track system was used, with each corner post and spreader post consisting of three tracks so that individual panels run on the inside, middle and outside tracks. This way, the CAT 330 easily handled only one panel at a time, whether pushing or extracting.

Once the pit walls were shored up and tied back to the walers, MacAllister supplied the contractor with PRO-TEC Railing Posts, a unique guardrail device that enhances the safety factor for jobsite personnel.

Flood events in the area have occurred in May 2002, July 2003, January 2005, and most recently in January 2007. The overall flood control project was begun in November 2001 and is scheduled for completion in fall 2010.