- Geotechnical
Market
- Development
Location
- Branson, Missouri
Overview
Record precipitation in Southwest Missouri in April 2008 prompted the U.S. Army Corps of Engineers (USACE) to open all of Table Rock Dam’s floodgates to prevent overtopping the dam. The subsequent flow into Lake Taneycomo below the dam was the highest on record since the dam’s construction in 1958 and resulted in significant scour along the banks of the lake. The slope below one condominium building at the Suites at Fall Creek fell away, leaving the building hanging without support over a drop of roughly 30 feet to the water.
GeoEngineers performed a geotechnical investigation and installed inclinometers to monitor the eroded slope. With geotechnical data in hand, the project team considered possible solutions to save and protect the condominium buildings. A traditional solution for such conditions is to place a riprap (stone or gravel that protects against erosion) barrier along the eroded slope. The USACE rejected this approach because the riprap would need to extend too far into Lake Taneycomo to be effective, potentially changing the river hydraulics and disturbing the important fish habitat at the site.
The GeoEngineers team then designed an innovative retaining structure that used conventional soil nails combined with vertical elements in a bottom-up sequence rather than traditional top-to-bottom excavation. When completed, the retaining wall also blended with the surrounding environment to avoid spoiling this important tourist and fishing destination.
GeoEngineers’ design also called for constructing a riprap toe at the bottom of the wall to provide scour protection. This approach, otherwise known as a launchable stone toe, made it possible to build the wall with almost no excavation below the lake surface and had the added benefit of providing a platform for construction operations, reducing the impact on the local ecological system. GeoEngineers observed construction to provide engineering recommendations as needed.
Approach
- GeoEngineers conducted a geotechnical investigation and installed inclinometers to continue monitoring the erosion that threatened one building precariously perched on a slope that had already washed away.
- With geotechnical data in hand, GeoEngineers considered possible solutions to save and protect the Suites at Fall Creek condominium buildings.
- GeoEngineers used finite element modeling to predict wall performance while optimizing the design.
- The resulting innovative retaining structure used conventional soil nails combined with vertical elements in a bottom-up sequence rather than traditional top-to-bottom excavation.
- Design called for a launchable riprap toe at the bottom of the wall to prevent undercutting of the wall and scour of the riprap.
- GeoEngineers also observed construction to provide engineering recommendations as needed.
Awards
ACEC-Missouri Engineering Excellence Awards, Grand Award, Water Resources Category, 2010
Results
- The hybrid soil nail and vertical element retaining wall design eliminated the need for two rows of soil nails, saving the Suites at Fall Creek more than $100,000.
- GeoEngineers’ design incorporated a launchable stone toe that allowed the contractor to avoid excavation below the Lake’s water level, reducing the environmental impact on the Blue Ribbon fishing area throughout construction.
- The completed retaining wall’s exterior shotcrete was stained and carved to resemble native dolomitic bedrock in the region, meeting USACE’s requirements for the final structure to blend with the surrounding environment.
- GeoEngineers’ design protected this popular tourist destination for the future without harming the appearance or ecology of the area.
Accolades
Chris Carson, Project Engineer
Carson-Mitchell, Inc. (general contractor)
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