The purpose of the Dam Remediation and Outlet work project is to control seepage and internal erosion of the earthen portion of the dam. The project consists of a vertical concrete cutoff wall, chimney filter, void filler piles, downstream filter modification and steel liner within the principal spillway. AEI is under contract to provide construction materials field and laboratory testing and inspection in support of the project.
The vertical concrete cutoff wall consists of 5-foot diameter overlapping secant piles that are drilled and excavated to rock and backfilled with concrete. The purpose of the piles is to interrupt the flow of water entering the earthen portion of the dam.
The chimney filter consists of 5-foot diameter overlapping secant piles that are drilled and excavated to the existing horizontal filter and backfilled with fine chimney filter sand. The purpose is to intercept the flow of water that may seep past the vertical cutoff wall and allow a flow path to the existing horizontal filter minimizing any further internal erosion of the dam.
The void filler piles consist of secant piles that are drilled and excavated in areas of known voids within the earthen portion of the dam. These void filler piles are excavated to the horizontal filter and backfilled with fine chimney filter sand so that any water seepage that reaches this area is intercepted and directed down to the horizontal filter.
The existing principal spillway conduit exhibits numerous cracks with visible water seepage and steady flow streams thus reducing the ability to release lake water at the design release flow rates due to concerns of failure from over-pressurization. The existing cracks have been injected with an expanding agent to seal the flow of water. The steel liner consists of upstream and downstream transition areas with 12’-4” steel liners in between. Each section of steel liner is trolleyed in and positioned to match the original slope then welded and inspected. The annular space between the new steel structure and the existing conduit has been grouted with an expanding non-expedited grout. With the installation of the steel liner structure, releases can return to design rates without causing further damage.
The downstream slope of the earthen portion of the dam will be removed from the top of dam to the bottom of the existing conduit. The depth of cut into the earthen portion of the dam is approximately 10 to 15 feet. Upon completion of the excavation, the installation of the downstream filter can proceed. The filter which consists of layered fine and coarse filter sand will aid in the filtration of any seepage and water flow from within the earthen portion of the dam. Any flow of water that reaches this feature will be diverted down to the existing horizontal filter.
With all of the modifications/repairs in place, future internal erosion of the earthen portion of the dam will be minimized.
AEI will continue to provide construction materials field and laboratory testing and inspection through completion of the project which is anticipated in fall 2017.