1033 51ST PL SW Geotech Report 2022-10-28

7.2 SHALLOW FOUNDATIONS 7.2.1 _ General The proposed structures can be supported on conventional spread footings bearing on structural fill or undisturbed, dense glacial till. The following sections provide our recommendation for use in foundation-design and.construction. 7.2.2 Bearing Capacity We recommend that the proposed structures be supported on shallow foundations bearing on properly placed and compacted structural fill or dense glacial till. Footings should be sized based on an allowable bearing pressure of 2,500 psf. Footings founded on dense glacial till may be-sized based on-an allowable bearing pressure of 4,000 psf. These are net bearing pressures; the weight of the footing and overlying backfill can be ignored in calculating footing sizes. The recommended allowable bearing pressure applies to the total of dead plus long-term live loads and may be increased by one-half for short-term loads, such as those resulting from wind or seismic forces. Continuous wall and spread footings should be at least 18 inches wide. The bottom of exterior footings should be at least 18 inches below the lowest adjacent final grade. The bottom of interior footings should be placed at least 12 inches below the base of the floor slab. 7.2.3 Resistance to Sliding Lateral loads on footings can be resisted-by passive earth pressure on the sides of the foundation and by friction on the base of the footings. Passive earth pressure may be estimated using an equivalent fluid density of 350 pcf. Adjacent floor slabs, pavement, or the upper 12-inch depth of adjacent, unpaved areas should not be considered when calculating passive resistance. A coefficient of friction equal to 0.35 may be used when calculating resistance to sliding for footings in-direct.contact with the-glacial till.or structural fill. A safety-factor-of.1.5:has been applied to the recommended sliding friction and passive pressure. 7.2.4. Settlement For foundations designed in accordance with the recommendations provided above, total post- construction settlement should be less than 1 inch and differential settlement less than 'A inch. 7.3; :.FLOOR,SLABS Satisfactorysubgrade support for building floor slabs supporting up to 350 psf areal loading can be obtained on subgrade that is undisturbed glacial till or existing fill material that has been moisture conditioned and compacted to 95 percent of the maximum dry density, as determined by ASTM D1557. A minimum-6-inch-thick layer-of crushed surfacing base course,WSS 9-03.9(3)'-Crushed Surfacing, should be placed and compacted over the prepared subgrade to provide uniform support beneath the slab and as a capillary break. A subgrade modulus of 200 pci may be used to design the floor slab. G EODESIGN= 5 NWHome-1-01:101618