Synchronized SBUs Bore Below Mississippi River: Multi-Tasking Auger Bores Move Muck For Force Main

July 2012, Vol. 67, No. 7
The 72-inch diameter Robbins Motorized SBU used in Clinton, IA, was the largest diameter machine of this type ever made.

Illinois contractor L.J. Keefe Co. is no stranger to utility crossing construction, but a recent force main project in Clinton, IA, was no easy task, requiring six crossings below major highways and a channel of the Mississippi River. The simultaneous construction required hard rock and mixed ground auger bores as well as TBM tunneling, all within a short construction schedule of just five months.

“We had an extremely tight time frame, but we were able to work with the general contractor, engineer and manufacturer to encompass multiple different soil conditions and tight tolerances,” said Larry Keefe Jr., general manager of L.J. Keefe Co. Three crossings were ultimately excavated using hard rock Small Boring Units (SBU-As) as well as a large diameter mixed ground, motorized SBU (SBU-M)), both manufactured by the Robbins Company.

The city of Clinton Contract B Force Main Project consists of a new treatment plant and wastewater lines serving the cities of Clinton, Camanche and Low Moor. Wastewater from all three communities does not meet current standards for effluent discharge, and the systems themselves are inadequate and often over capacity.

Project funding came from a $20 million allocation of the statewide construction project initiative known as I-JOBS. Clinton was one of three towns to receive the funds, which were set aside for water treatment improvements in towns of more than 10,000 people.

Clinton named HDR Engineering Inc. as the project designer and Illinois-based Merryman Excavation as the general contractor for 17,200 feet of new sewer pipe. The $9.5 million contract, which called for six crossings below roadways and rivers, was awarded to L.J. Keefe Co. Three, 200-foot long crossings in silt and sand below Union Pacific Railroad tracks utilized tunnel boring machines, while other crossings in hard rock required different methods. “We anticipated rock for two crossings under the river, so the clear choice was the Robbins SBU-A for these,” said Keefe. While the 250- and 270-foot long crossings were anticipated as rock bores, a third, 395-foot crossing below a major highway was not so clear cut.

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Robbins and L.J. Keefe crew members set the alignment of the SBU-M during its January 2012 launch.