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;;. <br /> �� <br /> DAVID L.NELSON AND ASSOCIATES, INC. <br /> �� Consulting Engincering Geology <br /> I <br /> F'' May 31 , 1991 <br /> � Project No. 4791 <br /> Page 8 <br /> � • <br /> I <br /> Structural Fills <br /> i • Permanent fill embankments are expected to stand at various slopes dependinq <br /> on the material and compaction affort used. For structural fill, that is fill <br /> i � comprised of clean imported or on site soils with a relative compaction in <br /> ! excess of 90; (ASTM D-1557), embankment slopes should be no steeper than <br /> 2H:1V, and properly protected from erosion. All fill placed downslope of the <br /> is <br /> i building site, if used, should be placed as structural fill. All fill areas <br /> should be observed and approved by the geotechnical consultant. Absolutely no <br /> � � filling should be <br /> � J performed upon the sloping portions of the site, including <br /> "temporary" foundation excavation spoils, without prior approval and <br /> �� observation by the geotechnical consultant. <br /> � <br /> '� Faundations <br /> `� In our opinion, the use of shallow spread footings Eounded on the native, <br /> undisturbed glacial till deposits should prove suitable for support of the <br /> ia <br /> ' r proposed duplex structure. For footinqs placed within the glacial till or <br /> outwash deposits as discussed below, an allowable bearing pressure of 3000 <br /> i+ pounds per square foot (psf) may be used. Within the slo in <br /> p' g portion of the <br /> site, a "stepped" type footings should be used, where excavation is performed <br /> � a into the dense glacial till for footing placement. We recommend that the <br /> (Q footings be placed a minimum of 2 feet into the dense glacial till within the <br /> sloping and downslope portions of the site, and a minimum of 6 inches into the <br /> � a dense glacial till or outwash deposits within the upslope portions of the <br /> site. The sugqested soil bearing capacities use a factor of safety of 2 and <br /> � is based on the following conditions: <br /> I* <br /> 1 . All footings should be founded into the native site soils <br /> � as described above. <br /> �� 2. All footing excavations should be prepared such that a <br /> � dense, nonyielding, uniform soil condition has been <br /> established prior to placement of footing concrete. <br /> tA <br /> 3, All footings should extend through any existing loose native <br /> I soil, non-structural fill or modified zones and be placed <br /> tfl to bear a minimum of 18 inches below finished adjacent qrade. <br /> , I i� <br />