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I I I I I I I I I I I I I I I I I I I Geotechnical Engineering Investigation V. Embankment Analyses A. Slope Stability Analyses Method of Analyses The slope stability evaluation was perfonned using ST ABUG, a computer program developed as part of an investigation conducted by the Joint Highway Research Project, Engineering Experiment Station, Purdue University and modified by Geosoft. The program has the capacity to analyze slopes using simplified Bishop, Janbu, or Spencer's method of slices. All these methods are based upon plastic limit equilibrium analyses. Strain considerations are of no consequences, that is, the soil's strength parameters are independent of the stress-strain behavior and the shear strength of the soil is based on the Mohr-Coulomb failure criteria. The slope stability methods used in our analysis divide the soil mass, above an assumed slip surface, into vertical slices. This is to accommodate conditions where the soil properties and pore pressures vary with location throughout the slope. We have utilized Janbu's method of slices. In this method both moment and force equilibrium are satisfied. This method can be applied to both circular and non-circular failure surfaces. The computer program perfonns a automatic search to locate a critical failure surface corresponding to a minimum factor of safety. The user has to define the slope geometry, soil properties, and the coordinates for the initiation and termination points of the failure surfaces. Slope Geometry and Material Properties The slope geometry, for our slope stability analysis, was obtained from the "As Built" plans dated August 1932 and the Dam and Outlet Conduit Plan View by Hydro-Triad, undated. Subsurface conditions were interpreted from the exploratory borings drilled between August 4 and August 16, 1993. Material properties were assumed based on the subsurface soil conditions encountered during drilling, including the resistance to drilling and Standard Penetration Test, SPT "N" values, our experience with similar soil and rock conditions, and the average shear strength parameters of compacted soils in U.S. Bureau of Reclamation, Design Standards, Embankment Dams, No 13, Chapter 4. These parameters are summarized as follows: Continental Dam Page 11