Seismic Evaluations
Advanced engineering assessments to evaluate seismic stability of CCR disposed facilities
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The Challenge
- Needed a way to consistently monitor high risk facilities
- EPA regulations on CCR disposal (2015)
- Closure/remediation may be required
The Tennessee Valley Authority is the largest public power utility in the United States, operating ten coal-fired power plants. In 2015, the United States Environmental Protection Agency (EPA) put into effect national regulations and requirements for the safe disposal of coal combustion residuals (CCR).
The requirement included that a qualified engineer demonstrate that each CCR impoundment and landfill have adequate structural stability for both static and seismic loads. If determined that the impoundments do not meet the minimum factors of safety required by EPA, TVA will need to either close or remediate these facilities at a considerable cost.
The Solution
Geocomp developed and performed enhanced seismic assessments of TVA’s CCR facilities. Using best practices aimed at eliminating inherent over-conservatism in conventional methods, Geocomp demonstrated that their critical CCR disposal facilities meet the EPA requirements for seismic stability. The approach included realistic assessments of in-situ pore pressures based on field measurements with piezometer strings so that the correct effective stresses are used in analyses. This factor alone could improve seismic stability by 30% or more.
Next, the determination of appropriate earthquake induced shear stresses using a 2D nonlinear dynamic ground amplification analyses. Finally, the selection of pseudo-static coefficients corresponding to a displacement level within the tolerance of the analyzed facility.
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