LANDFORM DESTRUCTION - LEETSDALE, PENNSYLVANIA

In 2005, a landslide partially blocked Beaver Road, a busy thoroughfare in the Borough of Leetsdale, near Pittsburgh, Pennsylvania. The geomorphic aspect of the area ensures that landslides will continue to occur as part of the natural processes of landform destruction. The road was constructed by cutting a bench into a steep hill that rises to a narrow crest ~300 ft above the Ohio River. Massive slumps mark the eastern part of the upper slope, while a discontinuity-bound rock face punctuated by small holes, of unknown origin, but possibly related to prehistoric slides, marks the western part. The lower slope is covered with colluvium exhibiting ground water seeps. A broad river terrace lies below Beaver Road, and a remnant of another terrace lies ~150 ft upslope. A bench of uncertain origin, partially obscured by colluvium, lies ~30 ft above the road. The terraces indicate multiple episodes of down cutting by the Ohio River and prominent stress-relief fractures, parallel to the Ohio River, occur in the cut at road level. The intersection of these fractures with those related to folding, break the strata into blocks of varying sizes, which tend to be pulled outward and downward away from the slope by gravity. The slide involved movement of discontinuity-bound sandstone blocks and overlying colluvium of the bench, which serves as a natural drop-zone for debris falling from above. Geotechnical borings revealed that the hill is capped by highly weathered sandstone and underlain by the notorious Pittsburgh “red beds”. Evidence of prior slumping and slide planes were observed in borings near the top of the bench.

The slide is the latest of many, the clean-up costs of which have created a financial burden for Leetsdale Borough; therefore a solution to minimize clean-up costs associated with future landslides was needed. Repair options included retaining wall construction, rock-fall walls/nets/screens, and pinning rock forms; however, these alternatives are expensive, and have questionable cost-effectiveness. The selected repair included removal of the bench to construct a wider drop zone at the base of the slope to capture falling debris. The final slope configuration was developed using empirical relationships between slope and engineering characteristics of the prominent lithologies.