1610 SE EVERETT MALL WAY Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazard, and Krebs Properly Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations conforms with the recommendations in this report. Foundation bearing verification may also be required by the governing municipality. 10.6 Foundation Drainage Perimeter footing drains should be provided, as discussed under the section on Drainage Considerations. 11.0 LATERAL WALL PRESSURES All backfill behind walls or around foundations should be placed following our recommendations for structural fill and as described in this section of the report. Horizontally backfilled walls, which are free to yield laterally at least 0.1 percent of their height, may be designed using an equivalent fluid equal to 35 pounds per cubic foot (pcf). Fully restrained, horizontally backfilled, rigid walls that cannot yield should be designed for an equivalent fluid of 50 pcf. Walls that retain sloping backfill at a maximum angle of 2H:1V should be designed for 55 pcf for yielding conditions and 75 pcf for restrained conditions. If parking areas are adjacent to walls, a surcharge equivalent to 2 feet of soil should be added to the wall height in determining lateral design forces. 11.1 Wall Backfill The lateral pressures presented above are based on the conditions of a uniform backfill consisting of either the on-site glacial sediments or imported sand and gravel compacted to 90 to 95 percent of ASTM:D 1557. A higher degree of compaction is not recommended, as this will increase the pressure acting on the walls. A lower compaction may result in unacceptable settlement behind the walls. Thus, the compaction level is critical and must be tested by our firm during placement. The recommended compaction of 90 to 95 percent of ASTM:D 1557 applies to any structural fill placed behind the wall within a distance equal to the wall height and up to the elevation of the top of the wall. Structural fill used to construct slopes behind retaining walls should be compacted to at least 95 percent of AS TM:D 1557 if the fill is placed above the elevation of the top of the wall. Surcharges from adjacent footings, heavy construction equipment, or sloping ground must be added to the above recommended lateral pressures. Footing drains should be provided for all retaining walls, as discussed under the section on Drainage Considerations. 11.2 Wall Drainage It is imperative that proper drainage be provided so that hydrostatic pressures do not develop against the walls. This would involve installation of a minimum, 1-foot-wide blanket drain for the full wall height using imported, washed gravel against the walls. February 13, 2007 ASSOCIATED EARTH SCIENCES,INC. TJP/ld-KE070023A1-Projects1200700231KE1WP Page 12