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Allestad <br /> June 18, 1990 <br /> Spread Footing Foundations <br /> Conventional spread footings founded on undisturbed dense to <br /> very dense or hard natural glacial soils should provide good <br /> support for the proposed structure. All footings for the <br /> residence should be at least 18 inches wide and founded at <br /> least 18 inches beiow the lowest adjacent final qrade. <br /> Square feotirigs should be at least 24 inches wide. <br /> Footings may be designed based on an allowable vertical <br /> bearing pre;�sure of 2000 psf. <br /> Footings shoulc be deepened as required to penetrate the <br /> existing fill and medium dense soils to bear on the <br /> recommended dense glacial soils. To provide a level bearing <br /> surface, footin�,�s should be stepoed in areas where the <br /> b=aring soil surface slopes. An averaqe step ratio no <br /> steeper than 1.5:1 (horizontal:vertical) should be used to <br /> reduce overlapping of foundation stresses. Where fill soils <br /> are thick, foundation loads may be trans£erred from the <br /> recommended minimum foundation depths to the bearing soils <br /> by a monolith of lean concrete having a minimum compressive <br /> strength of 1000 psi. The width of the lean concsete <br /> monolith should bE at least as wide as the f�oting. <br /> Settlement of spread footing foundati.ons constructed as <br /> recommended is expected to be �aithin tolerable limits for <br /> this structure. For example, the estimated settlement of a <br /> continuous wall footings carrying loads up to 2 klf are <br /> expected to be less than 1/2 inch. Maximum differential <br /> settlement within the proposed structure is expected to be <br /> less than 1/4 inch. Settlements are expected to occur <br /> prirazirily during construction. <br /> F'or lateral design, resistance to lateral loads can be <br /> assnmed to be provided by friction acting at the base of <br /> fc�:ndations and by passive earth pressure. A coefficient of <br /> fr�ction cf 0.45 may be assumed with the dead load forces in <br /> contact with onsite soi.'.s or structural fill. An allowa�le <br /> static passive earth pressure of 250 psf per foot of depth <br /> may be used for the. sides of for�tings poured against <br /> undisturbed natural soils or properly compacted structural <br /> fill. <br /> The bearing values indicated above are for the total dead <br /> load plus frequently applied live loads, If normal code <br /> requirements are applied for design, the vertical bearing <br /> values m:,�� be increased by 50� for short durations of <br /> loading which will include the effects of wind or seismic <br /> forces. Allowable lateral passive pressures may be <br /> increased by 33� for wind and seismic forces. <br /> Paae No. 5 <br /> Project No. 90-122-01 <br />