2721 WETMORE AVE MARQUEE APARTMENTS Geotech Report 2023-06-22

Subsurface Exploration, Geologic Hazard, and 2721 Wetmore Preliminary Geotechnical Engineering Report Everett, Washington Preliminary Design Recommendations drain system should be provided as discussed under the "Drainage Considerations" section of this report. The on-site soils contain a high percentage of fine-grained material that makes them moisture-sensitive and subject to disturbance when wet. 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 of rock or CDF to provide a working surface during foundation construction. We recommend a 6-inch layer of crushed rock or CDF for this purpose. Given its typical content of significant amounts of fines, the crushed rock should not be utilized as capillary break material. 10.1 Lateral Resistance Lateral loads on the foundation caused by seismic or transient loading conditions may be resisted by a combination of passive soil pressure against the side of the foundation and shear friction resistance along the base. An allowable base friction value of 0.40 and an allowable passive earth pressure of 350 pounds per cubic foot (pcf), expressed as an equivalent fluid unit weight, may be used for that portion of the foundation embedded below 2 feet. The above values only apply to a vertical foundation element cast "neat" against the undisturbed, very stiff to hard natural sediments. For fill placed around a mat or other foundation elements, a passive earth pressure value of 250 pcf is recommended. For this value to apply, the fill must be placed as structural fill and compacted to at least 95 percent of ASTM D-1557. Passive resistance within 2 feet of the ground surface should be ignored. The passive values presented are used assuming an equivalent triangular fluid pressure distribution beginning at the surface. The triangular pressure distribution is truncated above 2 feet. 11.0 FLOOR SUPPORT A slab-on-grade floor may be used directly over the very dense natural sediments or over structural fill placed over the natural sediments. We anticipate that the lowest level of the building will support car traffic. Slab design can assume a soil subgrade modulus of 150 pci for slabs cast over the very stiff to hard natural sediments or a limited thickness of properly compacted structural fill placed over these materials. The floor should be cast atop a minimum of 6 inches of washed pea gravel or clean, washed crushed rock to act as a capillary break. It should also be protected from dampness by an impervious, 15-mil (minimum thickness) plastic sheeting placed atop the capillary break specifically designed for use as a moisture barrier. The capillary break and moisture barrier are May 28,2019 ASSOCIATED EARTH SCIENCES,INC. FSM/1d-190168E001-2-Projects\20190168\KE\WP Page 11