Fall Creek Falls State Park Dam
S&ME provided a dam assessment and repair design for an approximate 78-feet tall earthen dam at Fall Creek Falls State Park. Services included a design report, design drawings, technical specifications, project manual, and an Engineer’s Opinion of Probable Construction Cost, construction administration, and construction quality assurance (CQA) services during dam construction.
The dam was originally constructed around 1968 and experienced progressive surface instability on the downstream slope due to a steep slope inclination of 2(Horizontal) to 1(Vertical).
The Fall Creek Falls Dam construction utilized zoned embankment construction with a central Impervious Core fill and exterior Common Fill material. The specification for compaction of the Impervious Core fill was 95 percent standard Proctor with the Common Fill specified at 90 percent relative compaction. The Common Fill experienced surface sloughing.
S&ME performed a topographic survey and bathymetric study for the dam area; geophysical survey of the dam’s downstream face, including electrical resistivity tomography (ERT), frequency domain electromagnetics (FDEM), and spontaneous potential (SP); natural resources jurisdictional study; ARAP 401/404 permitting; stormwater pollution prevention plan (SWPPP), and a CCTV camera evaluation of the interior condition of the existing service spillway 48-inch outlet culvert.
S&ME performed a subsurface exploration for the dam, including fifteen soil test borings and six piezometers. The soil test borings included SPT testing and sampling and undisturbed sampling. Laboratory testing included triaxial shear and soil index testing to estimate the engineering properties of the zoned embankment materials. We also performed hand auger borings and test pit excavations along the downstream slope to evaluate near-surface soil conditions.
We used the subsurface soil and water level data and laboratory test data from the exploration to perform slope stability analysis using Slope/W. The stability analysis included steady-seepage, time of construction, rapid drawdown, and seismic analysis.
Repair plans for the dam including excavation of the sloughed soil materials, modifications to the 48-inch diameter service spillway culvert outlet, and construction of a weighted filter overlay on the downstream slope. The embankment repairs were designed and permitted through the Tennessee Environmental Con Safe Dams program. The dam repairs were constructed between January 2024 and December 2024. S&M performed construction administration services, Construction Quality Assurance (CQA) services, and prepared a Construction Certification Report documenting the construction of the repairs.