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<br />- - .. ...TABliE 1 . -- -,.., <br />- ~ - INDEX ANDSTRENGTH~..PROPERTIES OF:SOILS FOR PONDS -~ ~- - <br />_ - -'ATTERBERG -PARTICLE S1Z <br />E `EFFECTIVE- - __ :EFFECTIVE <br />SAA~II'.LE ~ _ LIMITS _ <br />,=: DATA =~` _ <br />;FRICTION ANGLE COHESION- <br />- .- . -_ -_ (LL - PA `(% passing Na 200) ~- <br />_ - <br /> _ c (ps - _- . <br />East Flume Borrow 29 - 11 50 29.7 72 <br />East Flume Ke wa 32 - 16 56 33.4 14.4 <br />West Horse Foundation 32 - 15 69 - <br />2. Slope Stability <br />The slope stability for the West Horse Embankment Dam was analyzed with the two- <br />dimensional slope stability program SLOPE/W ®(Version 2.41). The SLOPE/W model utilizes <br />the Bishop's Method to determine the factor of safety for a circular failure surface that is found <br />during a search routine for the critical surface. To address concerns regarding the stability of the <br />embankment dam after the pond was filled and the water level in the dam had reached a steady <br />state, the slope was analyzed with the water level at the spillway (5 feet above the tce of the <br />embankment). The water level through the dam under these conditions was estimated using <br />Casagrande's Tangent Method (see attached calculation sheet), which, with the available <br />information, can be used to conservatively estimate the height at which the line of steady-state <br />seepage exits the toe of the dam. Utilizing the above mentioned soils data and the estimated line <br />of seepage though the dam; the stability of the embankment was calculated with the groundwater <br />• level downstream from the embankment at the ground surface. The proposed embankment design <br />incorporating upstream slopes of 2H:1 V, downsVeam slopes of 3H:1V and a height from the <br />upstream toe to the crest of the dam of 8 feet was analyzed. <br />Soil strength parameters estimated from the information contained in the geotechnical testing <br />are shown in Table 2. <br />3. Results <br />To address the embankment stability, the failure surface was modeled in the material <br />underlying the embankment. Through modeling it was determined that the embankment has a <br />factor of safety 1.80 for the downsVeam slope. <br />The SLOPE/W stability analysis is attached. <br /> <br />