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16 soils that are expected to develop excess pore water pressures due to an increased load induced by construction. This case is also only applicable when undrained shear strengths are estimated to be less than drained shear strengths. Both upstream and downstream embankment slopes are evaluated under the end-of-construction loading condition. The most critical construction loading condition is typically at the end of construction; however, staged construction may require intermediate analyses. For this loading condition, embankment and foundation soils are analyzed using either drained or undrained shear strengths depending on the permeability and saturation of the soil. Fine-grained soils generally have low permeability such that little drainage occurs during construction. Therefore, when saturated, these soils are assigned undrained (total stress) shear strengths. Laboratory tests used to measure undrained shear strengths of fine-grained soils include the unconfined compression (UC) test, unconsolidated-undrained (UU) triaxial test, consolidated-undrained (CU’ or CU) triaxial test with or without pore pressure measurements, and direct simple shear (DSS) test. The shear strength envelope used should be consistent with the analysis method employed such that strengths are calculated based on confining pressure prior to construction. Soils that are free-draining have relatively high permeability and are assigned drained (effective stress) shear strengths with the phreatic surface defined by groundwater conditions. Laboratory tests used to measure drained shear strengths of free- draining soils include the consolidated-drained (CD) triaxial test, CU’ triaxial test, and direct shear (DS) test. Steady-State Drained Loading Condition The steady-state drained loading condition represents the long-term stability of the embankment dam under normal reservoir pool steady-state seepage conditions. Pore water pressures are assumed to have reached their steady-state condition with no excess pore water pressures remaining from construction or elevated reservoir pool levels. The phreatic surface and internal piezometric conditions correspond to long-term, normal operating conditions with the reservoir pool conservatively modeled at the maximum normal reservoir level, or service/principal spillway crest elevation. Typically, only the downstream embankment slope is evaluated under the steady-state drained loading condition. The upstream embankment slope is generally not analyzed because of stabilizing water pressure on the upstream face, providing a buttressing effect on the embankment. However, the factor of safety can be low if the upstream slope is very steep. In this case, analysis of the upstream embankment slope may be warranted. For this analysis, all embankment and foundation soils are assigned drained (effective stress) shear strengths. Laboratory tests used to measure drained shear strengths include the CD triaxial test, CU’ triaxial test, and DS test. Rapid Drawdown Loading Condition This condition represents a rapid lowering of the reservoir from the steady-state, normal pool to a significantly lower elevation, removing the buttressing effect of the reservoir. During rapid drawdown of a reservoir, the rate of unloading on the upstream slope is typically assumed to occur instantaneously, such that pore water pressures within the embankment do not have time to dissipate in fine-grained (cohesive) soils. This analysis assumes the embankment soils below the normal pool phreatic surface are saturated to steady-state conditions prior to drawdown and will remain saturated after drawdown. Given adequate drainage and time, pore water pressures will eventually dissipate in the fine-grained embankment soils. The rapid drawdown loading condition should be evaluated using a three-stage slope stability analysis as described by Duncan, Wright, and Brandon [2] for developing appropriate phreatic and shear strength parameters. The first stage of the analysis calculates the stress condition based on the existing steady-state seepage conditions of the embankment dam before drawdown. In the first stage, the phreatic surface and internal piezometric conditions correspond to long- term, normal operating conditions with the reservoir pool conservatively modeled at the maximum normal reservoir level, and all embankment and foundation soils are assigned drained (effective stress) shear strengths. The second stage of the analysis calculates the stress condition immediately after drawdown. In this stage,