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Huddlcunn -Berry <br />In general, as for driven piles, screw piles/helical piers should be designed to <br />penetrate the fill and soft clay soils and bear into the dense gravel soils. In addition, to <br />eliminate reductions in capacity from group effects, the piles/piers should be spaced a <br />distance equal to three times the diameter of the largest helix. It is anticipated that the <br />screw piles/helical piers will reach refusal within 5 to 10 feet of the top of the gravel and <br />cobble layer. Therefore, pile lengths of up to approximately 32 feet may be possible. <br />Screw piles/helical piers should have a minimum length of 5.0 feet. <br />Based upon our experience with other projects utilizing screw piles or helical <br />piers, allowable axial capacities of between approximately 20 and 60 tons are anticipated <br />for piles /piers with a minimum shaft diameter of 3- inches. However, the actual allowable <br />capacity should be determined based upon the results of pile load testing conducted on <br />the project site. <br />With regard to the pile cap, the bottom of pile cap elevation should be a minimum <br />of 36- inches below the finished grade for frost protection. In addition, it is recommended <br />that a minimum of 1 foot of soil cover be maintained above the tops of the pile caps <br />4.2 Non - Structural Floor Slabs and Exterior Flatwork <br />In general, it is recommended that non - structural slabs -on -grade be constructed <br />above a minimum of 12- inches of structural fill with subgrade preparation and fill <br />placement in accordance with applicable portions of the Foundations section of this <br />report. <br />4.3 Water Soluble Sulfates <br />As discussed previously, the concentration of water soluble sulfates at the New <br />Elk Mine and Jansen Yard* sites were as high as 0.003% and 0.004 %, respectively. These <br />concentrations represent a negligible degree of potential sulfate attack on concrete <br />exposed to these materials. However, due to the presence of fill materials at both sites, <br />Type I -II sulfate resistant cement is recommended for construction at these sites. <br />4.4 Lateral Earth Pressures <br />Stemwalls, grade beams, and/or retaining walls should be designed to resist lateral <br />earth pressures. For backfill consisting of the native soils or imported granular, non -free <br />draining, non - expansive material, we recommend that the walls be designed for an <br />equivalent fluid unit weight of 50 pcf in areas where no surcharge loads are present. <br />Lateral earth pressures should be increased as necessary to reflect any surcharge loading <br />behind the walls. <br />4.5 Seismic Site Classification <br />Based upon the results of the subsurface investigation, it is recommended that the <br />• New Elk Mine and Jansen Yard sites be classified as Seismic Site Class D for a stiff soil <br />profile. However, Seismic Site Class C may be possible depending on the results of site <br />specific shear wave velocity geophysical surveys. <br />WA2008 ALL PROIECTS'.00456 -River City CO.W1f=(S tnc'ASS6 -000a Nm EW200 - Ge&W456 -om R082410.&c 9 <br />