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- to <br /> <br />to bedrock, we believe straight-shaft piers drilled Into bedrock are the <br />most desirable foundation to minimize potential differential movement. <br />if differential movement can be tolerated, shallow spread footings on <br />the upper clays are a satisfactory alternative. Differential movement <br />up to about 1} inches might occur. <br />Stockpile Reclaim: For the proposed cut depth of 17} feet below final <br />surface elevation 6402.0 feet, the base of the excavation will be founded <br />approximately 7 to 10 feet Into claystone bedrock. Fig. II shows a <br />generalized cross-section through this site. Spread or mat type founda- <br />tions bearing directly on thn claystone bedrock are satisfactory and <br />should be designed In accordance with recommendations presented below. <br />Excavatlan through the shallow depth of clay soil should remain <br />• <br />C~ <br />temporarily stable on a near-vertical cut. However, approximately 3 to <br />4 feet of water bearing clayey sand and gravel uhderlies the clay Bolls <br />and may cause undermining. Therefore, sloping of excavation walls to~ <br />approximate 1:1 (horizontal to vertical) slopes throughout the upper <br />soil together with an external drainage system should be considered. If <br />erosion Is min(mal, a collection channel within the pit could be used. <br />Constderatlon for hydrostatic uplift or a permanent drain system is <br />mended. Lateral pressures for design of walls are presented below. <br />Train Loadout: The train loadout will be a leg-supported hopper spanning <br />the railroad spur. At the proposed final surface elevation of 6397.5 feet, <br />approximately 3 feet or less of soil overburden will occur. Ftg. 12 <br />shows a generalized cross-section. ; ' <br />Straight-shaft piers as a foundation system offer an advantage by <br />providing a single plot to support each leg and concentrating the structure <br /> <br />