Laserfiche WebLink
Memo to Steve Renner <br />Fruits Highwall Stability <br />page 3 <br />An access road ascends from the foot of the cliff along an incised <br />cut to the top elevation of the portal bench. <br />Several episodes of portal face-up excavation and balanced portal <br />bench fill extension have resulted in an apparent continuous <br />highwall of approximately 160 feet in height above the portal. <br />Upon close examination, however, a "strand line" is apparent <br />approximately 60 feet above Che bench elevation. This line <br />represents the pre-excavation juncture between the competent <br />bedrock face and the accumulated talus. Examination of the <br />adjacent slopes suggest that the talus stood at approximately lh;1v <br />(45°) <br />Previous Stability Analyses <br />1979 Aaalyais (Beach) <br />The portal highwall and portal bench have each been the subject of <br />multiple stability analyses. In 1979 Andrew A. Porter of Geo <br />Testing Laboratories completed a simplistic analysis of the portal <br />bench using a Bishops Simplified Method of Slices developed by the <br />U.S. Bureau of Mines. <br />Direct Shear Parameters: <br />Bedrock Material: <br />--Fill Material: <br />Coal Waste: <br />(100 Rel Density) <br />Coal Waste: <br />(68~ Rel Density) <br />Results of Analysis: <br />Angle of Internal Friction (B) = 45.0° <br />Cohesion (C) = 4,000 psf <br />Density = 140 pcf <br />Angle of Internal Friction{B) 28.8° <br />Cohesion (C) = 1,740 psf <br />Density = 132 pcf <br />Angle of Internal Friction (B) = 33.6° <br />Cohesion (C) = BO psf <br />Angle of Internal Friction (B) = 21.8° <br />Cohesion (C) = 80 psf <br />Facial Slope Angle = 1.41h:1v (35.4°) <br />Static Factor of Safety = 1.65 <br />Pseudo Static Acceleration Factor = 0.102.g <br />Pseudo Static Factor of Safety = 1.43 <br />