O21 West Essex Highlands Geotech Slope Stability Model Memo 20250812pdf

Princeton Hydro, LLC Page | 5 Figure 4: Cross Section D with Bedrock Layer of GSI=20 Numerous slip surfaces extending deeper into the subsurface were uncovered for both cross sections. Factor of Safety Considerations Engineer Manual (EM) 1110-1-2908 Engineering and Design Rock Foundations, distributed by the U.S. Army Corps of Engineers November 1994, details design considerations for the evaluation of rock slope stability. In particular: The calculated factor of safety is primarily dependent upon the geometry of the potential failure path selected for analyses and the shear strength representative of the potential failure surface. In addition, other factors such as ground water conditions, potential for erosion, seismic loading, and possible blast-induced loosening of the rock mass must also be considered (Section 8-13, bold and underlined for emphasis). A design factor of safety is considered a minimum design or evaluation benchmark. Often, to account for uncertainties related to subsurface conditions, design parameters, risk tolerance, and other variables, a higher factor of safety is considered. EM 1110-1-2908 further states: For major rock slopes where the consequence of failure is severe, the minimum required calculated factor of safety is 2.0. For minor slopes, or temporary construction slopes where failure, should it occur, would not result in bodily harm or major loss of property, the minimum required factor of safety is 1.3 (Section 8-13).