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Illinois Contractor Overcomes Unusual Ground Conditions

Fischer Excavating, based in Freeport, Ill., is in the process of installing not one but two behemoth pump stations for the city of Clinton, Iowa.

Thu June 19, 2014 - Midwest Edition
James McRay

Fischer Excavating, based in Freeport, Ill., is in the process of installing not one but two behemoth pump stations for the city of Clinton, Iowa, right along the banks of the Mississippi River along with a new gravity sewer, and forcemain.

The cast-in-place sanitary pump station is 21 by 27 ft. (6.4 by 8.2 m); and the larger stormwater pump station measures 40 by 48 ft. (12 by 14.6 m). Both pump stations extend about 23 and 25 ft. (7 and 7.6 m) below final grade and are located west of existing pump stations. The final surrounding grade is 588 ft. (179 m).

Installing the two structures alongside each other at that depth posed many challenges, particularly in shoring the excavation for the safety of all personnel working in the pit. However for this project, the size of the excavations was only one problem. The ground conditions were an even much tougher challenge as the soil is stiff clay to 16 ft. (4.9 m) deep, but then hits solid rock.

Given all these variables, shoring options were limited; coming down to sheeting, beam and plate, or a slide rail system. For Fischer, the choice was easy.

“We prefer to use an Efficiency [Production manufactured] Slide Rail System if we can,” said company co-owner Joe Fischer. “I usually have a few ideas on what might work for shoring, but the first thing I do is call the team in Efficiency’s special operations shoring division,” said Fischer.

“[Special ops’] Rod Austin came out to the site and we threw around some ideas on how to shore the big pits,” continued Fischer. “Then within a short time, they sent us a clean proposal with CAD drawing of two slide rail systems that would work for both pump stations. And then it was just a matter of finalizing a plan.”.

With the drastic change in soil from clay to solid rock, an untraditional design for the slide rail system was required. However that was no problem for Austin. “I had installed a slide rail system just south of the location about a year ago, so I had a good idea what might work in the ground conditions,” he said.

The solution that the engineering team at Efficiency devised was two custom-designed ClearSpan slide rail systems to shore around the excavations for the pump station installations; The slide rail would be installed only to 16 ft. (4.9 m), or the approximate depth of the clay until it hit the rock. Then for the final 16 ft. (4.9 m), the rock would be quarried out to final grade.

“To size the system, we first we had to calculate the sloping of the rock to determine how far back we needed to set the slide rail,” said Austin. “Then we designed the system to be six feet larger than Fischer’s cut in the rock, so the slide rail sits on a three foot ledge of rock all the way around.”

The result was a 46 by 50 by 16 ft. (14 by 15 by 4.9 m) ClearSpan slide rail system that shores the sanitary pump station installation; and a 61 by 74 by16 ft. (18.6 by 22.6 by 4.9 m) ClearSpan system — the largest slide rail system ever designed and installed — shoring the stormwater pump station cast-in-place installation. Efficiency’s slide rail system allowed Fischer to excavate and shore the two giant pits less than 10 ft. (3 m) from each other.

“We thought that we would end up deeper in the clay but it was a little shallower,” said Bryan Austin, Fischer’s project superintendent. “We had to plan out exactly how the system would sit on the rock ledge and how deep we’d need to drill in the rock to get to grade,” Austin said. “Rod and [special ops’] Tim [Hurst] were immensely helpful in getting all that figured out, and helping us install the systems which really worked out great,” Austin added.

The slide rail equipment was rented from Efficiency Shoring & Supply’s Chicago branch office, whose branch manager, Mark Mitchell, also assisted with installing the ClearSpan systems plus another slide rail system that shored the construction of an outlet structure into the Mississippi River.

“Hands down, we have the best rapport with Fischer than any other contractor,” said Mitchell. “I think we did seven or eight slide rail jobs with Fischer last year that they are so good using slide rail, that they really don’t need us there,” he said. “So when we are on their job site helping install, the job is fun and easy and just an enjoyable professional experience,” Mitchell said.

Joe Fischer added, “Mark and all the special ops guys have a lot of experience installing slide rail so when they were working with our crew, it was like they had worked together for years.”

Efficiency Production’s slide rail is a component shoring system comprised of steel panels (similar to trench shield sidewalls) and vertical steel posts. The shoring system 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.

The 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 more than 40 ft. (12 m).

Fischer’s heavy equipment on the project included a JD 450 excavator to dig in the slide rail system. They also rented a JD 450 excavator with a hammer to remove the rock. Other heavy equipment Fischer had on site included a Cat IT 38G wheel loader, and Komatsu 400 excavator for compacting backfill.

Fischer Excavating, incorporated in 1995, is a complex contracting firm responsible for heavy and highway transportation projects, municipal and county infrastructure improvements, and commercial, industrial and residential developments. The firm is pre-qualified for transportation (and related infrastructure) development with the Illinois Department of Transportation, Illinois Capital Development Board and the U.S. Army Corp of Engineers.

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