1707 SCENIC DR SNO CO PUD Geotech Report 2022-10-25

Settlement Estimates Provided ail loose soil is removed and the subgrade is prepared as recommended in this report, we estimate the total settlement of shallow foundations for the control building will be less than 1-inch. The settlements will occur rapidly, essentially as loads are applied. Differential settlements are estimated to be less than 1/rinch over a 25-foot length. Foundation Design We recommend widths of at least 18 and 24 inches, respectively, for continuous wall and isolated column footings supporting the proposed control building. The design frost depth for the Puget Sound area is 12 inches;therefore, we recommend that the footings be founded at least 18 inches below lowest adjacent finished grade. Lateral Resistance Lateral loads can be resisted by passive resistance on the sides of the foundations and by friction on the base of the footings. Passive resistance should be evaluated using an equivalent fluid density of 350 pcf (triangular distribution) where foundations are poured neat against native soil or are surrounded by structural fill compacted to at least 95 percent of the MDD, as recommended. Resistance to passive pressure should be calculated below a depth of 1 foot where the adjacent area is unpaved. Frictional resistance can be evaluated using 0.45 for the coefficient of base friction against base of the footings. The above values incorporate a factor of safety of about 1.5. If soils adjacent to footings are disturbed during construction, the disturbed soils must be recompacted, otherwise the lateral passive resistance value must be reduced. Foundation Drains We recommend that perimeter footing drains be instalied around the control building. The perimeter drains should be installed at the base of the exterior footings. The perimeter drains should be provided with cleanouts and should consist of at least 4-inch-diameter perforated pipe placed on a 3-inch bed of, and surrounded by, 6 inches of drainage material enclosed in a non-woven geotextile fabric such as Mirafi 140N (or approved equivalent) to prevent fine soil from migrating into the drain material. We recommend that the drainpipe consist of either heavy-wall solid pipe (SDR-35 PVC, or equal) or rigid corrugated smooth interior polyethylene pipe (ADS N-12, or equal). We recommend against using flexible tubing for footing drainpipes. The drainage material should consist of pea gravel or "Gravel Backfill for Drains" per WSDOT Standard Specifications Section 9-03.12(4). The perimeter drains should be sloped to drain by gravity, if practicable,to a suitable discharge point, preferably a storm drain or to the adjacent wetland area. We recommend that the cleanouts be covered, and be placed in flush mounted utility boxes. Water collected in roof downspout lines must not be connected to the foundation drain lines. Construction Considerations Immediately prior to placing concrete, all debris and loose soils that accumulates in the foundation excavations during forming and steel placement must be removed. Debris or loose soils not removed from the foundation excavations will result in increased settlement. GEOENGINEER� October24,2014 Page 13 F�ie ruo.aasz-oz�-o2