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Allestad <br /> June 18 , 1990 <br /> Zm•aorted granular fill should consist of clean, well-graded <br /> sand and gravel matecials free of organic debris and other <br /> deleterious material. We suygest the fol�owing gradtion <br /> guidelines: <br /> U.S. Standard Percent Passing <br /> Sieve Size by Dry Weight <br /> 3 inch 100 <br /> 3/4 inch 50 - 100 <br /> No. 4 25 - 65 <br /> No. 10 10 - 50 <br /> No. 40 0 - 20 <br /> No. 200 0 - 5 <br /> Permanent Slopes: All permanent graded slopes should be <br /> made no steeper than 2h:lv. Existing siopes within 20 feet <br /> of the proposed structr.ce should be bu+:.tresed with fill to <br /> flatten them to 2:1 (h:v) . All vegetation, de�ris and loose <br /> soils should be removed from the buttres fill axea prior to <br /> fill placement. All fill embankments should b;a key�d and <br /> benched into the existing soils. Embankment key width <br /> should be at least lo feet or half the sl��pe height <br /> whichever is greater. Key depth should penetrate at least 2 <br /> feet into the existing soils. All fill should be placed and <br /> coa�pacted in accordance with the recommendations presented <br /> under "structural fill" . <br /> Subgrade Preparation: Slabs-on-grade and pavements should be <br /> su_�ported on undisturbed natural soils or on properly <br /> compacted structural fill. Where existing fill is <br /> encountered subgrade preparation should include over- <br /> excavation of at least 12 inches and replacement with <br /> structural fill. It should be noted that where the proposed <br /> slabs cross the fill/natural contact line, there will be a <br /> high risk of oracking. Risk of cracking can be reduced by <br /> �elacing construction joint:; at the contact, placing 2-way <br /> reinforcement steel, and complete excavation and replacement <br /> of the existing fill with new structural fill. As an <br /> alternate to complete fill replacement, the natural soils <br /> could be over-excavated sufficiently and replaced with <br /> structural fill to provide a gradual and uniform increase in <br /> fill thickness across the subgrade. <br /> Site Drainage <br /> Adequate positive drainage should be provided away from the <br /> structure ta preverit water from ponding and to reduce <br /> percolation of water into the fill and backfill. Granular <br /> backfill should be cappe3 with paving or 12 inches of onsite <br /> silty soils. A desirable slope for surface drainage is 2g <br /> in landscaped areas and 1% in paved areas. Planters and <br /> landscaped areas adjacent to the building perimeter should <br /> be designed to minimize water infiltration into the subsoils <br /> behind the basement wa.ils. <br /> Page No. S <br /> Project No. 90-122-01 <br />