3620 BROADWAY VERIZON 2019-01-11

T � Geotechnical Engineering Evaluation NGA File No.983917 Stadium Flowers Addition March 10,2017 Everett,Washington Page 8 Foundation Support Conventional shallow spread foundations should be placed on undisturbed medium dense or better native glacial soils or be supported on structural fill extending to those soils. We encountered medium dense soils at approximately 1.6 to 2.4 feet below the existing ground surface with the excavation, corresponding to depths of approximately 2.4 to 6.4 feet below the projected surface of the asphalt or concrete existing throughout the site. Where undocumented fill or loose soils are still exposed at the planned footing elevation, the subgrade should be over-excavated to expose suitable bearing soil. The over-excavation may be filled with structural fill, or the footing may be extended down to the native bearing soils. If footings are supported on structural fill,the fill zone shouldextend outside the edges of the footing a distance equal to one-half of the thickness of the structural fill below the footing. Footings, including interior footings, should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Foundations should be designed in accordance with the current IBC. Footing widths should be based on the anticipated loads and the allowable soil bearing pressure. Water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations constructed as outlined above, we recommend an allowable design bearing pressure of not more than 2000 pounds per square foot(psf) be used for the design of foundations supported on the medium dense or better native soils, or structural fill extending to the competent native soils. A representative of NGA should evaluate the foundation bearing soil. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than one-inch total and 1/2-inch differential between adjacent footings or across a distance of about 30 feet based on our experience with similar projects. Lateral loads may be resisted by friction on the base of the footing and passive resistance against the subsurface portions of the foundation. A coefficient of friction of 0.30 may be used to calculate the base friction and should be applied to the vertical dead load only. Passive resistance may be calculated as a triangular equivalent fluid pressure distribution. An equivalentfluid density of 150 pounds per cubic foot (pef)should be used for passive resistance design for a level ground surface adjacent to the footing. This level surface should extend a distance equal to at least three times the footing depth. These recommended values incorporate safety factors of 1.5 and 2.0 applied to the estimated ultimate values for frictional and passive resistance, respectively. To achieve this value of passive resistance, the foundations should be NELSON GEOTECHNICAL ASSOCIATES, INC.