Case assisted in completion of the OARS tunnel project, which helped Columbus reduce the environmental impacts caused by Combined Sewer Overflows (CSOs).

The project

The OSIS Augmentation and Relief Sewer (OARS) tunnel project was designed to collect and consolidate combined overflows from the Olentangy Scioto Interceptor Sewer (OSIS) and convey the combined flows to the Jackson Pike and Southerly wastewater treatment plants for biological treatment. The project consisted of two phases and was developed to provide adequate capacity for all storms in a single year.

The solution

Case Foundation was awarded the work for phase two of the OARS project. Phase two consisted of two additional 30 foot inner diameter access shafts (Shafts 4 and 5) and a 10 foot inner diameter drop shaft (Shaft 3). Installation of the secant piles was accomplished using two BG 40 rigs equipped with 1180 millimeter tools to install piles to a depth of up to 65 feet keyed into bedrock shale. Concrete was placed using a tremie pipe and reinforcement was installed in every other pile and was designed as wide flange soldier piles.

Project Facts


City of Columbus

Main Contractor(s)

Trumbull Corporation

Keller Business Unit(s)

Case Foundation


City of Columbus