The Not-So-Retaining Wall
Parking lots and access roads border the campus perimeter of a suburban apartment complex. A concrete retaining wall supports the parking lot along a stream channel. A culvert supports the adjacent roadway at the start of the wall, and a portion of the wall acts as a wingwall for the culvert. When Isett was retained, the wall was failing due to scouring of the soils beneath the wall foundation: we were asked to design a plan to stabilize the wall. In investigating the situation, the Isett team realized the scour undermining was caused by additional outflow pipes entering the stream at the culvert location, increasing the turbulent flow along the wall. The culvert also appeared to be undersized—filling completely during normal precipitation. While the short-term solution would involve deepening the footings and repairing the wall, the Isett team also recommended opening discussions with the township and the Pennsylvania Department of Transportation to increase the culvert size to reduce the turbulence of the flow along the wall, resulting in less scour. The Isett team included a professional geologist, who worked with the Department of Environmental Protection for the permitting and PNDI requirements, as well as surveyors to obtain the elevation and channel cross-section data needed to facilitate the design, and civil, forensic and geotechnical engineers.