Case History Summaries of Five Slope Failures: Missed Predictions and Lessons Learned: Fid-Bau Portal

Case History Summaries of Five Slope Failures: Missed Predictions and Lessons Learned

Gregory, Garry H.

Many slope failures could have been predicted well in advance by carefully observing warning signs and subtle site conditions. Summaries of five case histories of major slope failures and missed predictions are presented. The failed slopes consisted of: (1) slope failure of a levee around a major wastewater treatment plant during construction of a slurry wall. The significance of a thin organic-silt seam sloping adversely into the slurry wall and a very high water-head in the adjacent sludge landfill were not recognized during design; (2) Failure of a slope impacting a chemical storage structure at a water treatment plant. Obvious signs of an ancient landslide at the site and an adversely sloping weak seam were not detected during the original geotechnical exploration; (3) An extensive landslide in a large residential subdivision impacting more than 300 residents and damaging 27 homes. Historically known anomalies in the geologic formation, slickensides, and the potential for fully-softened and residual strengths were not recognized during design of significant fill and ground supported retaining walls; (4) A massive landslide on colluvial soils at a lakeside development. The very apparent presence of colluvial soils on which embankments were constructed and natural seepage paths that were blocked off by embankment fill were not considered during design of the development; and (5) A deep slope failure along a bentonite seam in the shale formation beneath a major roadway embankment adjacent to a lake. The 25-year history of this location included many preliminary signs of a deep slope failure, but these signs went unheeded until major movement was initiated following a period of heavy rainfall.