Dam Safety

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Dam Remediation Using High and Low Mobility Pressure Grouting

Logan Martin Dam, owned and operated by Alabama Power Company, is a hydroelectric generation site located on the Coosa River in Vincent, Alabama. Since construction in the late 1960’s, ongoing remedial pressure grouting projects have targeted significant seepage flow reduction beneath the embankment dam which is founded on karst, a limestone geology characterized by underground aquifers, caverns, and the potential for sinkholes, particularly as seepage flow erodes the underlying limestone and continually changes its distribution. Alden and Alabama Power have partnered to design and construct a large scale enclosed pressure grouting test chamber (3’ wide by 3’ tall by 30’ long) and an associated test protocol to evaluate and optimize grout mix design performance in geo-materials that simulate the fractured, cavernous geology at Logan Martin Dam.

This first-of-a-kind test approach uses a small production scale grout plant to prepare and inject the high mobility grout mixtures into the test chamber. The test chamber is designed with discharge ports along its length to allow water initially occupying the test chamber—and subsequently grout—to be displaced as newly batched grout is injected. Throughout the grout injection process, pressure and temperature measurements within the test chamber, as well as discharge flow rate and discharge flow specific gravity measurements out of the test chamber, are used to monitor and evaluate grout dispersion characteristics within the chamber.  

Grout injection criteria used to govern test advancement and later termination includes displaced grout quality (i.e., displaced grout specific gravity relative to that of the freshly batched grout) and the internal test chamber pressure. After grout injection, various performance metrics are evaluated to quantify mix effectiveness. The normalized grout take, for example, evaluates the overall mix efficiency by relating the injected grout volume to the volume available within the geo-material for grout to occupy.

Since conception, updates to the test facility and protocol have been made to facilitate low mobility grout testing, as well as grout performance testing in the presence of water cross flow. Results from this ongoing research program are being used to reduce grouting cost through grout mix design and bore hole spacing optimization, while also improving dam safety by increasing knowledge on how grout penetrates rock fractures without in-situ excavation.

Contact us if you would like to learn more.

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As part of project/dam surrender and removal efforts at the Saccarappa Hydroelectric Project (Saccarappa), Alden provided S. D. Warren Company d/b/a Sappi North America (Sappi) with the final design and fish passage analysis for nature-like fishways in the upper channels at Saccarappa Falls. The final design involves reshaping the existing bedrock channel into a form that is more conducive to fish passage while mimicking the morphology of a natural bedrock channel. Alden provided agency consultation while developing the design and will ultimately provide construction support. The proposed design complements a proposed double Denil fishway over the lower portion Saccarappa Falls designed in partnership with Acheron Engineering.

Alden conducted a site visit and reviewed existing geotechnical, hydrologic, site constraints, and other site data prior to developing the final design for the nature-like fishways. The final design was achieved by way of iteration between a 3D CAD representation of the proposed bathymetric surface and a 3D computational fluid dynamics (CFD) model. Expected small-scale roughness of the channel bed was incorporated into the CAD surface through a novel texturizing technique based on a high resolution laser scan of the existing bedrock surface. The CFD model was used to simulate proposed conditions at four discrete design flow rates. Hydraulic data output by the CFD model (e.g., depth and velocity) informed subsequent improvements of the proposed surface in CAD. Sappi and agency review and feedback was provided at 30%, 60%, 90%, and final drafts of the design. Fish passage effectiveness of the final design was analyzed by Alden biologists and engineers using USFWS’s SMath models developed for assessing velocity impediments by estimating fatigue, survivorship, and work. Alden also provided engineering consultation and inspections to support project construction.

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