This research program addresses the instability of natural and man-made slopes founded on colluvium. (Colluvium consists of a mixture of residual and transported soils.) When this material is part of a slope, the mixture is continually in a near-failure state because of constant downslope movement caused by gravity. Since colluvium is a very common surficial deposit, this failure mode has important implications for the creation, operation, and/or expansion of the large number of natural and man-made slopes that are founded on this material.
Examples of such instability include the March 1996 slope failure of a 135-acre landfill in Ohio -- the largest slope failure ever in a municipal solid waste landfill -- and the upstream slope failure of the San Luis Dam in September 1981.
Based on these and other recent case histories, it appears that a drained residual shear strength can be mobilized in cohesive colluvial materials underlying natural and man-made slopes, with the adverse effect that a much flatter slope is required to design against failure. This results in a smaller area for development in natural slopes and reduced airspace or capacity in landfills, either by limiting the expansion or requiring the expensive excavation of colluvium from the expansion area and/or from under the existing waste.
The project includes a study of field case histories and a combination of analytical and experimental techniques. A goal of this project is to develop design recommendations for the construction/expansion of natural and man-made slopes founded on colluvium.
