2202 100TH ST SW Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazard,and Stephens Everett Property Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations 11.0 FOUNDATIONS Spread footings may be used for building support when they are founded on approved structural fill placed as described above, or on undisturbed natural soils that are prepared as recommended in this report. Based on our observations, suitable foundation bearing soils are expected to be near the surface. One should refer to Figure 2, and to exploration logs in the Appendix for the observed depth to bearing soils at the exploration pit locations. If foundations will be underlain by a combination of medium dense to dense native sediments and new structural fill, we recommend that an allowable bearing pressure of 3,000 pounds per square foot (psf) be used for design purposes, including both dead and live loads. If foundations are underlain by dense lodgement till sediments alone, or dense lodgement till and CDF as described in the "Site Preparation" section of this report, an allowable foundation soil bearing pressure of 5,000 psf should be used for design. An increase of one-third may be used for short-term wind or seismic loading. It should be noted that the area bounded by lines extending downward at 1H:1V from any footing must not intersect another footing or filled area. In addition, a 1.5H:1V line extending down from any footing must not daylight because sloughing or raveling may eventually undermine the footing. Thus, footings should not be placed near the edge of steps or cuts in the bearing soils. Perimeter footings should be buried at least 18 inches into the surrounding soil for frost protection. However, all footings must penetrate to the prescribed bearing stratum, and no footing should be founded in or above organic or loose soils. Anticipated settlement of footings founded as recommended should be less than 1 inch with differential settlement one-half of the anticipated total settlement. Most of this movement should occur during initial dead load applications. However, disturbed soil not removed from footing or mat excavations prior to concrete placement could result in increased settlements. All footing areas should be observed by AESI prior to placing concrete to verify that the design bearing capacity of the soils has been attained and that construction conforms to the recommendations contained in this report. Such observation may be required by the City of Everett. A perimeter foundation drain system should be provided as discussed under the "Drainage Considerations" section of this report. The contractor must use care during site preparation and excavation operations so that the underlying soils are not softened. If disturbance occurs, the softened soils should be removed and foundations extended down to competent natural soil. Once the base of the excavation is reached, consideration should be given to "armoring" the exposed subgrade with a thin layer March 29,2019 ASSOCIATED EARTH SCIENCES,INC. TG/ms-180567E001-2-Pro%ects\201805671KEtWP Page 15