In support of tunneling operations, Bencor installed slurry wall access and exit shafts, and a comprehensive ground improvement program along the tunnel alignment.

The Project

The new Kaneohe / Kailua Sewer tunnel is a 3-mile long, 12-foot diameter, gravity conveyance tunnel designed to increase the reliability and capacity of the community’s sewer system.

The Solution

Bencor installed reinforced concrete slurry walls for two shafts (ID up to 84 feet and depth 105 feet) and designed and implemented an extensive ground improvement program involving the installation of over 5,800 jet grouting columns treating over 54,000 cubic yards for water tight bottom plugs and structural support and cutoff grouting along the tunnel alignment, diversion structures, and pipelines. Jet grouting was accomplished utilizing both single-axis and multi-axis drill rigs. Anticipated soil conditions included highly variable sequences of fill, alluvium, clays, sands and gravels, and silts. Challenges included a high groundwater table.

In addition, Bencor employed real time monitoring of all pertinent parameters utilizing advanced on-board computers, sensors, wireless remote transmission, viewing data in real time so as to mitigate any potential problems as the work was being installed.

Project Facts


City and County of Honolulu

Main Contractor(s)

Southland / Mole JV

Keller Business Unit(s)



Department of Design and Construction, Waste Water Division, City and County of Honolulu