Project: Deep Rock Tunnel Shaft - Indianapolis, IN
Customer: Citizens Energy Group - Indianapolis, IN
Contractor: S-K JV: J.F. Shea Construction - Walnut, CA; Kiewit Corp - Omaha, NE
Finisher: Bencor Corporation - Dallas, TX
Project obstacles and solutions: The Deep Rock Tunnel Connection is a series of underground tunnels designed to solve the combined sewer overflow (CSO) problems the city of Indianapolis has experienced during heavy rain events. CSO is channeled to the tunnels where it flows to one of two treatment plants. As part of this project, Bencor was hired to construct shafts to the tunnel 250 feet below the surface.

Bencor specializes in slurry wall drilling and grouting solutions. Their drill heads pulverize earth, rocks and other aggregates. These are mixed with water to make a slurry that is pumped into a processing tank. These voids are then poured with a self-consolidating concrete that forms the walls of the shaft. These walls were poured 400 yards at a time. Since the drilled out void was full of water, the concrete had to be poured below the water level via a tremie pipe. As concrete exits the pipe, it displaces the water until the entire pit is full of concrete. Tremie placement is tricky because if the pipe is pulled above the waterline, the process has to be reset and started again. Bencor poured these at a very fast pace - 28.5 yards every 90 seconds. This required three mixer trucks to be pouring at the same time and at the same speed. After the three trucks were emptied, Bencor pulled a section of the tremie pipe out of the pit and proceeded with the next pour. The entire process required the IMI operational staff to be in high gear - from dispatch to plant personnel to drivers to quality control. These pours happened during the coldest weather of the season - even in single digit temperatures - all without any interruption in delivery.

There were a total of seven shafts built for the tunnel. IMI supplied a total of 20,000 yards of concrete for the shaft walls. For more information on pouring specialty concrete, including continuous pours for underground foundations, caissons and shafts, contact the sales representative for the concrete plant nearest your location. Click here.

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