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ARCADIS <br />This analysis is for a straight slope from the toe of the slope to the structure or point <br />which is conservative for the concrete ditch and slurry wall since the slope would <br />have to slough to that angle from the proposed cut slope of 2:1. As shown, the factors <br />of safety are all well above 1.0 indicating the slopes will be stable. For the proposed <br />excavation limit a factor of safety of 1.35 is considered appropriate for the temporary <br />slope condition. The factors of safety for the concrete ditch and slurry wall are above <br />1.5 which is considered an acceptable threshold value for long-term structures. <br />These factors of safety would be less if the pit is dewatered, an adverse phreatic <br />surface is allowed to develop or if significant wave action erodes the 2:1 slope. It is <br />recommended that the pit slope be monitored and maintained at 2:1. <br />To evaluate a more adverse condition of a fully saturated slope with the pit fully <br />dewatered. The circular failure charts from Rock Slopes: Design, Excavation, <br />Stabilization, Publication No. FHWA-TS-89-045, Pages 9.5-9.13, September, 1989 <br />were used. Results from this analysis are the following: <br /> Calculated Factor of Safety for <br />Slope Evaluated Slope Angle Saturated Circular Slope <br /> Failure, ~ = 34° <br />Slope at Excavation Limit approx. 19° 1.00 <br />Slope Toe to Conc. Ditch 15°t~~ 1.34 <br />Slope Toe to Slurry Wall 7.125°~Z~ 2.233 <br />~~~15° angle is calculated from 15 feet slope height and 55 feet horizontal measurement from <br />toe to ditch edge <br />~2~7.125° angle is calculated from 15 feet slope height and 120 feet horizontal measwement <br />from toe to slung wall <br />This analysis is also for a straight slope from the toe of the slope to the structure or <br />point which is conservative for the concrete ditch and slurry wall since the slope <br />would have to slough to that angle from the proposed cut slope of 2:1. Although the <br />factors of safety are lower than the infmite slope evaluation, the analysis shows that <br />Mr. Steve O'Brien <br />14 May 2008 <br />Page: <br />c:ww~tiw+m°~wr~w~de~nsa~~ys,<oe.a=.ma 2/3 <br />