Kenny Construction Co.

When it comes to complex underground utility projects, an experienced contractor realizes soil conditions will make or break a successful delivery. Kenny Construction sent a project team to Columbus, Ohio, that understands what it takes to deliver the Olentangy-Scioto Intercepting Sewer Augmentation Relief Sewer (OARS) project in a joint venture with Obayashi.

“The ground is the boss,” says Bob Rautenberg, project manager for Kenny Construction. “The biggest challenge of this project is mining the ground.”

In October 2010, Kenny/Obayashi was awarded the first phase of the OARS project, which involves the construction of a 22-foot-diameter deep tunnel wastewater conduit that will relieve the existing Olentangy Scioto Interceptor Sewer. This tunnel will be approximately 4.5 miles long and will be built into the bedrock at a depth of 170 feet. Special drop structures will be constructed to direct flow from shallow sewers to the deep tunnel, according to Kenny Construction.

Inlets with de-aeration chambers will dissipate energy and minimize air entry into the tunnel, the company says, and a pump system will dewater the tunnel after high-water events and direct water to the Jackson Pike Waste Water Treatment Plant. This phase also includes a 52-foot-diameter pump station shaft, a 42-foot-diameter screen shaft and a 48-foot-diameter shaft with an internal surge chamber and hydraulic drop pipe.

“The OARS tunnel is sized to provide adequate conveyance for all storms in a typical year,” Kenny Construction says. “Its 54 million-gallon capacity will significantly reduce overflows in the downtown Columbus area.”

Kenny/Obayashi earned the contract with a low bid of $264.5 million. The construction team broke ground in fall 2010, and completion is expected in June 2015.

Specially Made

As managing partner of the joint venture, Kenny Construction worked closely with Nicholson Construction Co. Nicholson performed pre-excavation grouting and constructed overburden support of excavation at the 52-foot and 42-foot diameter shafts. Nicholson will perform the same construction services at the 48-foot-diameter shaft beginning in 2012.

The tunnel will be mined through Karstic limestone. This type of material can prove challenging for mining.  In fact, Kenny had a mining machine custom manufactured to handle the conditions.

According to Rautenberg, this machine can mine in either open mode or slurry mode. At this point in the job, the construction team has started excavating the shafts for the tunnel.

The second phase of the project is expected to cost $90 million, according to the city of Columbus. Construction is expected to start this fall, and this phase should be completed by the end of 2014.

Finding the Funding

The city of Columbus obtained $264.5 million from the Ohio Water Pollution Control Loan Fund at a 3.25 percent interest rate over a 20-year loan. The city says it has requested similar funding for the second phase, as well.

“Financing this project through the Ohio EPA’s below-market interest rate loan program will save millions of dollars in interest payments over the life of the loan, compared to financing through higher interest rate bonds,” the city says. “The savings will be passed on to the city’s sewer utility rate payers, thereby minimizing the slight increase expected in sewer rates over the next several years due to the cost of this project.”

Digging In

Founded in 1927, Kenny Construction has headquarters in Northbrook, Ill. The company has constructed  subways, tunnels, airports, stadiums, buildings, hotels, power plants, mass transit, bridges, highways and other types of infrastructure throughout the world.

Kenny Construction was also the first general contractor to be awarded the National Safety Council’s Green Cross for Safety Award and has received numerous Association of General Contractors Build America Awards for unique contributions to the construction industry.

Through its tunnel group, Kenny says it has maintained its position as a leader in rapid tunneling technology for more than 25 years.

“Kenny was the first contractor in the world to mine hard rock with a 30-foot-diameter tunnel-boring machine,” it says. “Kenny then set its sights on high production efforts with the first continuous horizontal and vertical muck-removal systems.”

Led by Patrick Kenny and Ted Budd, the vice president of the tunnel group, the company has participated in more than $1 billion in tunnel projects in the last decade.

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