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3 Photo 1. Severe longitudinal cracks in downstream slope Photo 2. Seepage exiting dam face Photo 3. Slope failure on downstream slope Triggers for More Quantitative Analyses Besides a change in conditions resulting from rainfall/flooding or other events, triggers requiring stability analysis be performed may include:  Designing a new dam.  Raising an existing dam.  Construction of a berm.  Potential reclassification of a dam to high hazard.  Deterioration of existing conditions, i.e. oversteepening of embankment slopes for any reason.  Reassurance that a latent, undetected issue has not developed – indicators of such an issue may include embankments with steep slopes (greater than 2H:1V), soft foundation conditions, high phreatic surface within the dam and/or foundation, seepage at the face or toe, depression/sinkhole formation or observed scarp or bulge.  Indications from field observations that instability may be developing – i.e. observed scarps, toe bulges, longitudinal cracking along crest or slope. Slope Stability Analysis Requirements The analyzed stability of a slope is expressed as a Factor of Safety (FS). FS values greater than 1 indicate the estimated driving forces are less than the resistance forces. However, due to inherent uncertainties in the behavior and characterization of earth materials, regulations and good practice require FSs greater than 1 for most loading conditions. Each regulatory agency has its own FS requirements; however, the following table provides some commonly adopted values: Loading Condition Min. Factor of Safety Steady State Drained 1.5 End of Construction 1.3 Rapid Drawdown 1.2 Post-Seismic 1.2 Pseudo-Static (where applicable) 1.0