4801 HARBOR LN 2018-01-02 MF Import

Geotechnical Engineering f .ort ( J-1280 Johnson F esidence Addition 27 February 2002 Everett, Washington Page 7 experienced geotechnical professional prior to pouring foundation concrete or prior to mud slab placement. Lateral Resistance An allowable coefficient of base friction equal to 0.4 may be utilized when evaluating lateral resistance. A maximum allowable passive resistance of 100 pcf may be applied to foundations with at least 18 inches of embedment into the recommended bearing stratum, neglecting the upper 12 inches. The recommended maximum allowable passive resistance includes a factor of safety of at least 2, and includes a reduction considering potential removal of soils from the downhill side of the foundation in the event of a landslide. Foundation Drainaize We recommend equipping the residential addition with an interior perimeter footing drain. The drain should consist of a minimum 4-inch diameter rigid perforated pipe embedded in at least a 6-inch thick envelope of clean, free -draining granular material, such as WSDOT Gravel Backjill for Drains (Publication M41-10, 2000). Footing drains should be directed toward appropriate storm water drainage facilities at the toe of the slope that extends below the dwelling toward Belvedere Lane. Drains should not terminate on or above the steep slope. Roof drains should not be connected to the footing drains in such a fashion that water from the roof drains could enter the foundation drain. Backfilled Walls The foundation wall should be considered a retaining wall in the event that backfrll is placed against it. All backfrll placed behind the dwelling addition foundation walls and around foundation elements should be compacted to at least 90 percent of the modified Proctor maximum dry density (ASTM: D-1557). The following recommended earth pressures, presented as equivalent fluid weights, are based on the assumption of a uniform level granular backfrll with no buildup of hydrostatic pressure behind the wall. To minimize lateral earth pressures and prevent the buildup of hydrostatic pressures, the wall backfrll should consist of a free -draining granular material coupled with a perforated pipe drain placed at the base of the wall as described above. All backfrll within 24 inches of the wall should contain less than 5 percent fines, based on the portion passing the U.S. No 4 sieve, and have at least 30 percent retained on the U.S. No. 4 sieve. If the backfilled walls are structurally restrained from lateral movement at the top, we recommend that they be designed for an "at -rest" equivalent fluid weight of 50 pounds per cubic foot (pcf). If the tops of the walls are free to move laterally in an amount equal to at least 0.1 percent of the wall height during placement of backfrll soils, they may be designed for an "active" equivalent fluid weight of 35 pcf. Seismically induced dynamic lateral load increases on the foundation wall may be modeled as a rectangular pressure distribution additive to the values described above. The ultimate lateral earth pressure increase due to seismic loading is Zipper Zeman Associates, Inc. I18905 334 Avenue Wat, Suite 117 Lynnwood, Wuhinaton 98036 (425) 771 •3304 r