SELECTED SLOPE STABILITY PROBLEMS, PROPOSED S.R. 6219 CONSTRUCTION, SOMERSET COUNTY, PENNSYLVANIA

S.R. 6219 is proposed as a four lane alternative to the existing S.R. 0219 from near Meyersdale to near Somerset in Somerset County, Pennsylvania. A.G.E.S., Inc. was subcontracted to design the foundations for several structures along the alignment. In addition, A.G.E.S. was given the task of re-designing several proposed embankments, including geotechnical treatments at or below roadway and structures. The construction will occur through sedimentary rocks of late Pennsylvanian age with sandstones, siltstones, shales and coals and claystones being the predominant existing bedrock. Soil origins include strip and deep mine spoil, colluvium, alluvium and residual.

The embankments will be constructed over existing alluvial, colluvial and mine spoil soils as much as 80 ± feet thick, with an allowable factor of safety of 1.5 for slope stability. The majority of the embankments will be constructed with varying sizes of rock “toes” using Best Available Rock (BAR). The colluvial soils will be partially or removed altogether in some cases to reduce settlement and improve stability. The mine spoils will be removed within 5 feet of pavement and backfilled with suitable material. Soil or rock with acid potential due to pyrite will be encapsulated within proposed embankments. The rock toes will be restricted in the vicinity of proposed structures to allow a “pile window” for construction of the abutment and pier foundations. In order to ensure no fill encroachment occurs along an existing stream (Swamp Creek), a reinforced soil slope (RSS) up to 179 feet in height is proposed. The slopes were designed using GSTABLE with the Modified Bishop method of analysis.