The City of Oklahoma City is replacing an existing 66-in water pipeline that conveys raw water from Atoka Lake to the City’s water treatment plant. This pipeline currently crosses the Canadian River on elevated piers and is subject to flood hazards. To replace the aging pipeline and mitigate flood damage concerns, two parallel microtunnels will be constructed within the rock strata below alluvial floodplain deposits.
Access for the tunneling operations is from construction shafts located near the midpoint of the approximately 2,800 ft. (850m) long tunnels; opposing drives are launched from each shaft. This geometry dictated shafts of significant depth – in excess of 120 ft. The upper portion of each shaft will be excavated through loose sands with significant permeability, transitioning to conglomerate bedrock containing hard sandstone lenses. Due to this difficult geologic setting and proximity to the existing pipeline, a reinforced secant pile compression ring was specified by contract in the top 70 ft. of these construction shafts to provide a rigid, watertight support system. During final design, numerical modeling was utilized to demonstrate that the secant reinforcing could be eliminated, resulting in significant benefits to the project.
Charles Luxford, PE, SE, PEng, will present his peer-reviewed paper at the 46th Annual Conference on Deep Foundations, October 12 – 15, 2021 at the MGM Grand in Las Vegas, Nevada. Information and registration for the conference is available at the DFI Conference website.