Claystone slides, Interstate Route 79, Pittsburgh, Pennsylvania, USA

Landsliding is a significant geologic process and geotechnical consideration in the northern Appalachian Plateau of the eastern United States, especially in the vicinity of Pittsburgh, Pennsylvania (Fig. 1). Flat-lying interbedded strong and weak sedimentary rocks have been acted upon by erosion, stress relief, weathering, creep and sliding processes to produce masses of marginally stable colluvium on many of the steep hillsides common to the area. The precarious equilibrium of cc-lluvial masses is frequently upset by heavy precipitation and by construction activities, e.g., removal of toe support, loading the slope, changing surface and subsurface drainage (Gray et al. 1979, Hamel 1980).