Abstract:
Slope movements in clay can compromise access roads and infrastructure where excavation or buttressing is impractical. This paper presents a case history of slope stabilization on the western downslope of the AEP Holloway Substation near Shadyside, Ohio, where ongoing monitoring documented shallow slips and platform sliding affecting FirstEnergy transmission facilities. Subsurface conditions consisted of low-strength clay over weathered shale with variable groundwater and hillside seeps. Site exploration of the slope was limited by access and dense vegetation; six borings were advanced near the crest only.
A steel plate pile system was selected to improve overall global stability with minimal earthwork. The design targeted an overall factor of safety of 1.5 in areas estimated at approximately 1.0 under existing conditions. The system comprises S- and C-shaped steel piles with attached rectangular plates, installed in a staggered grid and saw-tooth pattern to create horizontal barriers. Stabilization is achieved through pile bending resistance and passive resistance mobilized behind each plate, with soil arching between adjacent elements.
The design incorporated 3,305 plate pile elements in two work zones:Â Area A included 568 elements ranging from 6 to 19 ft, and Area E included 2,737 elements nominally 16 to 17 ft long. Construction occurred October-December 2025 under rain and snow conditions. Highly variable rock elevations produced frequent refusal, requiring extraction, retrimming, and reinstallation of many elements. Following installation, the slope was regraded and reseeded; the work finished on schedule and within budget.
Constructability lessons were governed by rock refusal. Shallow rock outcrops and variable rockhead drove field length adjustments and rework. Expanded subsurface exploration within the slide areas - additional borings and more widely spaced test pits - would better constrain rockhead variability, reduce constructability risk, and enable a more focused pile-length design. Improved definition of rockhead would also minimize steel waste from trimming and increase installation efficiency.