11229 19TH AVE SE SILVER LAKE TOWNHOMES WHOLE SITE Geotech Report 2022-10-25

Geotechnical Report Proposed Development: 11229 - 19th Avenue SE, Everett, WA September 16, 2016 groundwater table, followed with structural fill such as WSDOT CSBC or Gravel Borrow. A layer of filter fabric should be placed on quarry spalls prior to placement of structural backfill. As an alternative to over-excavation and backfill, Building E may be supported by small diameter driven steel pipe piles (pin piles). Pin pile design recommendations are presented in Section 5.2.2 of this report. 5.2.1 Conventional Footings Exterior foundation elements should be placed at a minimum depth of 18 inches below final exterior grade. Interior spread foundations should be placed at a minimum depth of 12 inches below the top of concrete slabs. We recommend an allowable soil bearing pressure of 2,500 pounds per square foot (psf) be used to size the footings. The recommended allowable bearing pressure is for dead plus live loads. For allowable stress design, the recommended bearing pressure may be increased by one-third for transient loading, such as wind or seismic forces. Continuous and individual spread footings should have minimum widths of 18 and 24 inches, respectively. Footings designed and constructed in accordance with the above recommendations should experience total settlement of about one inch or less, and differential settlement of less than i/2 inch. Most of the anticipated settlement should occur during construction as dead loads are applied. Lateral Resistance: Lateral loads on the structure may be resisted by passive earth pressure developed against the embedded portion of the foundation system and by frictional resistance between the bottom of the foundation and the supporting subgrade soils. Footings bearing on the dense to very dense silty sand with gravel native soil or structural fill may be designed using a frictional coefficient of 0.35 to evaluate sliding resistance developed between the concrete and the subgrade soil. Passive soil resistance may be calculated using an equivalent fluid weight of 300 pcf, assuming foundations are backfilled with structural fill. The above values include a factor of safety of 1.5. Unless covered by pavements or slabs,the passive resistance in the upper 12 inches of soil should be neglected. Perimeter Footing Drains: Footing drains should be installed around the perimeter of the residence, at or just below the invert of the footings. Under no circumstances should roof downspout drain lines be connected to the footing drain systems. Roof downspouts must be separately tightlined to appropriate discharge locations. Cleanouts should be installed at strategic locations to allow for periodic maintenance of the footing drain and downspout tightline systems. 16-210 11229 19th Ave SE Rpt Page 6 PanGEO, Inc.