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�i Huddles -Ber+y <br />• r:.it,.�'i:. tray t i c <br />Sewage Disposal Package Plant <br />HBET understands that the proposed sewage disposal package plant will be a <br />small structure above a slab foundation. In general, a slab foundation is appropriate <br />based upon the nature of the proposed construction and subsurface conditions. However, <br />mixed fill materials above slightly expansive native clay soils were encountered in the <br />subsurface. Therefore, in order to reduce the potential for excessive differential <br />movements, it is recommended that the foundation be constructed above a minimum of <br />24- 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. As discussed previously, the <br />native clay soils are anticipated to have a slight potential for expansion; however, the <br />magnitude of expansion is expected to be low. Therefore, with careful moisture control <br />and proper compaction, the native clay soils may be reused as structural fill. Imported <br />structural fill should consist of a granular, non - expansive, non -free draining material such <br />as pit run, crusher fines, or CDOT Class 6 base course. However, if pit -run is used as <br />structural fill, a minimum of six inches of Class 6 base course or crusher fines should be <br />placed on top of the pit -run to prevent large point stresses on the bottoms of the <br />foundations due to large particles in the pit -run. <br />Prior to placement of structural fill, it is recommended that the bottom of the <br />• foundation excavation 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 />Structural fill should extend laterally beyond the edges of the foundation a distance equal <br />to the thickness of structural fill. Structural fill should be moisture conditioned, placed in <br />maximum 8 -inch loose lifts, and compacted to a minimum of 95% of the standard Proctor <br />maximum dry density for fine grained materials or 90% of the modified Proctor <br />maximum dry density for coarse grained materials, within 12% of the optimum moisture <br />content as determined in accordance with ASTM D698 or D1557C, respectively. Pit -run <br />should be proofroIled to the Engineer's satisfaction. <br />For foundation building pad preparation as recommended with structural fill <br />consisting of the native clay soils or imported granular materials, a maximum allowable <br />bearing capacity of 1,500 psf may be used. In addition, a modulus of subgrade reaction <br />of 150 pci may be used for structural fill consisting of the native clay soils and a modulus <br />of 250 pci may be used for structural fill consisting of pit -run, crusher fines, or base <br />course. It is recommended that the bottoms of exterior foundations be at least 36- inches <br />below the final grade for frost protection. <br />Hoist Building <br />As discussed previously, the subsurface investigation indicated existing fill <br />materials above soft clay extending to dense gravel. It may be possible to utilize shallow <br />foundations above structural fill; however, depending on the bottom of foundation <br />• elevation, consolidation of the soft clay soils may result in excessive structural <br />settlements. <br />W X2008 ALL PROJECTS'OO456 -River City Consultants 1ne.0456 -0004 \ew ERVOO.OWOW56.0004 R082410.doe 6 <br />