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SiA M. 6 fl. (2) <br />o s/l (da XhSJ (t1q-dt <br />Slope stability of the proposed Priola Pit by Albert Frei and Son's Inc was evaluated <br />using a simple analysis to determine the factors of safety associated with the adjacent <br />concrete ditch and slurry wall located on City of Thorton property to the north and west <br />of the site. The slopes were evaluated using an infinite slope analysis and saturated. <br />conditions since the pit will not be dewatered (e.g. the existing water table will not create <br />an adverse phreatic surface condition). The material in the pit wall will be in-place <br />gravel and is assumed to be cohesionless and have a friction angle (0 ) of 34 degrees. <br />For an infinite slope the factor of safety is: <br />FS = Tan (4)), where 0 is the slope angle. Calculated values are shown below. <br />Tan (0) <br /> <br />Slope Evaluated Calculated <br />Slope Angle Factor of Safety for <br />Infinite Slope, m = <br />34 <br />Pro sed Sloe 2:1 26.6° 1.35 <br />Slo Toe to Conc. Ditch 15.3°(') 2.47 <br />Slope Toe to Slur Wall 5.40 <br />15.3° angle is calculated from 15 feet slope height and 55 feet horizontal from toe to ditch edge <br /><2? 7.1 ° angle is calculated from 15 feet slope height and 120 feet horizontal from toe to slurry wall <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 have to <br />slough to that angle from the proposed cut slope of 2:1. As shown, the factors of safety <br />are all well above 1.0 indicating the slopes will be stable. For the proposed excavation <br />limit a factor of safety of 1.35 is considered appropriate for the temporary slope <br />condition. The factors of safety for the concrete ditch and slurry wall are above 1.5 <br />which is considered an acceptable threshold value for long-term structures. These factors <br />of safety would be less if the pit is dewatered, an adverse phreatic surface is allowed to <br />develop or if significant wave action erodes the 2:1 slope. It is recommended that the pit <br />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 were <br />used. Results from this analysis are the following: <br /> <br />Slope Evaluated Calculated <br />Slope Angle Factor of Safety for <br />Saturated Circular Slope <br />Failure, 0 = 34° <br />Slope at Excavation Limit a rox. 19° 1.00 <br />Slope Toe to Conc. Ditch 1.35 <br />Slope Toe to Slur Wall 7.10(2) 2.25 <br />(1) 15.3° angle is calculated from 15 feet slope height and 55 feet horizontal from toe to ditch edge <br />(Z) 7.1 0 angle is calculated from 15 feet slope height and 120 feet horizontal from toe to slurry wall <br />