Deep Tunnel System Geotechnical Subsurface Investigation, Phase 1A


Schedule

The Deep Tunnel System is currently in the preliminary planning stages. The City of Omaha will be drilling 15 exploratory geotechnical borings between fall 2018 and summer 2019.

Project Description

The Deep Tunnel is a major component in the CSO Program and will convey combined sanitary sewage and stormwater to the Missouri River Water Resource Recovery Facility (MRWRRF) for final treatment. The tunnel is currently envisioned to be approximately 17 feet in diameter, constructed in bed rock at a depth of up to 350 feet below the ground surface, and about 5 miles long, running parallel with the Missouri River. The tunnel will start about a mile north of the CHI Health Center Omaha (formerly CenturyLink Center) and end at the MRWRRF, just south of Highway 275 (South Omaha Bridge) along the Missouri River. Part of the preliminary planning stages for the DTS is to determine the alignment of the tunnel. Information collected from the geotechnical site investigation will be used in conjunction with other evaluation criteria when determining the preferred tunnel alignment. Horizontal tunnel alignments being considered are located between the Missouri River and 10th Street.

The geotechnical investigation consists of a drilling rig taking samples of both soil and bed rock at various locations along the proposed tunnel alignments. The size of boreholes vary between four to eight inches in diameter, depending on the equipment utilized by the Contractor. The drilling rig is mounted on a duel axle truck that can negotiate varying ground conditions. Activities associated with each boring location will take approximately ten days and include soil sampling and rock coring to a depth of 350 feet below ground surface, in-situ testing of rock permeability, and downhole geophysics to determine rock properties.

The geotechnical investigation is broken into several phases. Boring for Phase 1A is set to begin in late November 2018 and consists of 15 exploratory borings along the proposed tunnel alignments. Additional phases of the geotechnical site investigation will be determined once data collected from Phase 1A is analyzed.

Project References

Project Number: OPW 53379
LTCP Project Name: N/A

Additional Resources

Project Spotlight: Flood Impacts on CSO Program Efforts