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n U n Table 1. -Soil Properties IIsdta°'~P. ~~ ~ Sl](s Description Max dry density c Saturated Density c Cohesion s Direct Shear Friction an le Sil[stone Cla stone l28 ~ 140 300 45 Embankment C V I I S 128 200 . 1 ?r` 18 Z Alluvium 126 138 0 32 li EMBANKMENT DESIGN Based on the results of the geotechnical site investigation, it was decide that the embankment would be constructed of a mixture of the siltstone /clays[one bedrock and the sandy lean clay overburden -ocated on [he site. The embankment will not extend above the ground surface and will extend down into bedrock. A keyway trench will be used to insure proper cutoff between the embankment and foundation. DESIGN ANALYSIS AND CRITERIA The proposed reservoir embankment was analyzed using the XSTABLE v5.1 OSa computer program. XSTABLE was designed to analyze the slope stability of earth embankments subjected to several critical situations that may occur during the life of the embankment. For this project, four situations were identified as critical. Case 1 -Mining Conditions. The site will be mined with near vertical highwalls. There are several barbed wire fences adjacent to the mining site that have 30 foot setbacks. Case 2 -Mining Conditions. The Boyd Lake Outlet Ditch runs between Phase II and Phase III of the site. This ditch is seldom used and serves primarily for capturing agricultural return flows in the area and running them back to the river. Occasionally the reservoir will make releases back to the river for short time ,," periods. The critical condition would be having mining activities up to the limits in a dewatered condition. Case 3 -Full Reservoir. The reservoir is full for an extended period of time I `/ causing the embankment to become completely saturated and reach a steady state condition. Case 4 -Rapid Drawdown. The reservoir is evacuated in a short enough time period to leave the embankment saturated. Pore water pressures would be elevated until the embankment has a chance to drain down. Minor slope failures such as Bluffing are not considered critical and would be a part of routine ~ "~ maintenance. The critical condition would be a major slope failure that would compromise the integrity of the liner.