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. '� j,j� HUIIdICSl00•ECffy <br />iL Gy#r..;rjS RVC�tII <br />4.0 RECOMMENDATIONS <br />4.1 Foundations <br />Water Tanks <br />Based upon the nature of the proposed construction, HBET anticipates that <br />shallow foundations will be utilized for the new water tanks. Circular spread footing or <br />monolithic slab foundations are both appropriate alternatives. However, shallow bedrock <br />was present in the southern portion of the water tank pad and variable fill materials were <br />present in the northern portion of the water tank pad. <br />For water tanks in the southern portion of the pad area, foundations may be able <br />to be constructed directly on bedrock. For water tanks in the northern portion of the pad <br />area, it is recommended that the foundations be constructed above a minimum of 24- <br />inches of structural fill or structural fill extending to the native gravel soils, whichever is <br />less. In general, based upon the results of the subsurface investigation, it is <br />recommended that water tank foundations be set -back from the crest of the slopes a <br />minimum of 10 feet. <br />As discussed previously, the existing fill materials are moderately plastic and are <br />anticipated to be slightly expansive. However, if the proposed water tanks are not <br />sensitive to differential movements up to approximately 2 to 3- inches, the existing fill <br />• materials may be reused as structural fill, provided wood and other organic materials are <br />removed. Imported structural fill should consist of a granular, non - expansive, non -free <br />draining material such as pit run, crusher fines, or CDOT Class 6 base course. However, <br />if pit -run is used as structural fill, a minimum of six inches of Class 6 base course or <br />crusher fines should be placed on top of the pit -run to prevent large point stresses on the <br />bottoms of the foundations due to large 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 />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 ±2% of the optimum moisture <br />content as determined in accordance with ASTM D698 or D1557C, respectively. Pit -run <br />should be proofrolled to the Engineer's satisfaction. <br />For foundation building pad preparation as recommended, a maximum allowable <br />bearing capacity of 4,000 psf may be used for foundations on bedrock. A maximum <br />allowable bearing capacity of 1,500 psf may be used for foundations constructed on <br />structural fill above existing fill materials or native soils. In addition, a modulus of <br />• subgrade reaction of 150 pci may be used for structural fill consisting of the existing fill <br />materials and a modulus of 250 pci may be used for structural fill consisting of pit -run, <br />crusher fines, or base course. <br />W A2008 ALL PROIECTS`.00456 - Rim City Coasuhws 16e.0456 -0004 .N E&\200 - Geo`.MS"M R08240.dm 4 <br />