Waste Disposal Facility Static and Seismic Slope Stability Evaluation, Illinois

SCS Engineers performed a static and seismic slope stability evaluation of a coal combustion waste disposal facility that was subject to vertical overfill beyond the design envelope for final waste.

SCS evaluated the worst-case profile across a horizontal cross-section representing approximately 1,700 feet of coal combustion waste in the first 20-acre disposal cell in the facility. The profile was selected to maximize driving forces and minimize resisting forces for a cover sequence and waste height of approximately 80 feet.

The site is located near the New Madrid Fault, which means it is located in a seismic impact zone. Based on the United States Geological Survey’s Seismic Hazard Curve for Peak Ground Acceleration (PGA) of the Coterminous 48 States (2002 data), the appropriate PGA was identified and utilized for the seismic stability assessment.

Seismic stability modeling was completed to calculate the factor of safety (FOS) for the worst-case cross-section noted above and an alternate option to utilize built-up terraces to decrease the critical sideslope. Based on the ultimate review of maximum acceleration and the yield acceleration, the stability analysis results indicated that the area is stable in the static condition, with minor deformation expected during seismic events.