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0 n- It< <br />HuddltsmBcrq 0 <br />With regard to deep foundations, driven pipe piles or H -piles are both appropriate. <br />As an alternative to driven piles, helical piers /screw piles may be utilized. Helical <br />piers/screw piles will provide similar support to driven piles; however, the helices <br />provide more uplift resistance than driven piles and this may be a design consideration at <br />this site. <br />Shallow Foundations <br />In general, the recommended shallow foundation alternatives include spread <br />footings, mat/raft, and monolithic (turndown) structural slab. As discussed previously, <br />mixed fill materials were present at the site. In addition, soft clay soils were present <br />below the fill. Therefore, it is recommended that shallow foundations be constructed <br />above a minimum of 48= inches of structural fill. <br />In general, due to the presence of coal and other deleterious materials, the existing <br />fill materials are not suitable for reuse as structural fill. Imported structural fill should <br />consist of a granular, non - expansive, non -free draining material such as pit run, crusher <br />fines, or CDOT Class 6 base course. However, if pit -run is used as structural fill, a <br />minimum of six inches of Class 6 base course or crusher fines should be placed on top of <br />the pit -run to prevent large point stresses on the bottoms of the foundations due to large <br />particles in the pit -run. <br />Prior to placement of structural fill, it is recommended that the bottoms of the <br />foundation excavations be scarified to a depth of 6 to 8- inches, moisture conditioned, and <br />re- compacted to a minimum of 95% of the standard Proctor maximum dry density, within <br />f2% of the optimum moisture content as determined in accordance with ASTM D698. <br />However, as discussed previously, soft clay soils were present at the site and soft <br />subgrade conditions are possible where the foundations are at depth. Where soft <br />conditions exist, subgrade stabilization utilizing pit -run and geotextile and/or geogrid <br />may be required. HBET should be contacted to provide specific recommendations for <br />subgrade stabilization based upon the actual subgrade conditions encountered during <br />construction. <br />Structural fill should extend laterally beyond the edges of the foundation a <br />distance equal to the thickness of structural fill. Structural fill should be moisture <br />conditioned, placed in maximum 8 -inch loose lifts, and compacted to a minimum of 95% <br />of the standard Proctor maximum dry density for fine grained soils or 90% of the <br />modified Proctor maximum dry density for coarse grained soils, within f2% of the <br />optimum moisture content as determined in accordance with ASTM D698 or D1557C, <br />respectively. Pit -run should be proofrolled to the Engineer's satisfaction. <br />For foundation building pads prepared as recommended with structural fill <br />consisting of imported granular materials, a maximum allowable bearing capacity of <br />2,000 psf may be used. In addition, a modulus of subgrade reaction of 250 pci may be <br />used for structural fill consisting of pit -run, crusher fines, or base course. It is <br />• recommended that the bottoms of exterior foundations be at least 36- inches below the <br />final grade for frost protection. <br />WA2008 ALL PROJEC7S`.00456 - Rher City Consultants Ine.0456 -OM New El ANA - Gro.00456 -OM R082410.doo 7 <br />