8407 BROADWAY SECURE SPACE STORAGE Geotech Report 2025-04-24

ZipperGeo Broadway Everett Expansion Geoprofessional Consultants Project No. 2601.01 July 7, 2022 Slab Base To provide a capillary break and uniform slab bearing surface,we recommend on-grade slabs be underlain by a minimum 4-inch thick layer of compacted, crushed rock meeting the requirements of WSDOT Standard Specification Section 9-03.9(3), Crushed Surfacing Top Course, with the modification of a maximum of 7 percent passing the U.S. No. 200 sieve. Alternatively, a clean angular gravel such as No. 7 aggregate per WSDOT: 9-03.1(4)C could be used for this purpose. Alternative capillary break materials should be submitted to the geotechnical engineer for review and approval before use. Vapor Barrier From a geotechnical perspective, a vapor barrier is not necessary beneath the slab on grade floor unless moisture sensitive floor coverings and/or adhesives are used. If a vapor barrier is used, we recommend using a minimum 15-mil thick, puncture-resistant, proprietary product such as Stego Wrap, or an approved equivalent that is classified as a Class A vapor retarder in accordance with ASTM E 1745.Overlap lengths and the appropriate tape used to seal the laps should be in accordance the vapor retarder manufacturer's recommendations.When conditions warrant the use of a vapor retarder,the slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder/barrier. Backfilled Retaining Walls The proposed building may include backfilled foundation retaining walls. Our recommendations for retaining walls are provided below. Lateral Earth Pressures The lateral soil pressures acting on backfilled retaining walls will depend on the nature and density of the soil behind the wall, and the ability of the wall to yield in response to the earth loads. Yielding walls (i.e. walls that are free to translate or rotate)that are able to displace laterally at least 0.001H, where H is the height of the wall, may be designed for active earth pressures. Non-yielding walls (i.e. walls that are not free to translate or rotate)should be designed for at-rest earth pressures. Non-yielding walls include walls that are braced to another wall or structure, and wall corners. Assuming that walls are backfilled and drained as described in the following paragraphs, we recommend that yielding walls supporting horizontal backfill be designed using an equivalent fluid density of 35 pcf (active earth pressure). Non-yielding walls should be designed using an equivalent fluid density of 55 pcf (at-rest earth pressure). Surcharge pressures due to sloping backfill,adjacent footings,vehicles,construction equipment,etc. must be added to these lateral earth pressure values. For traffic loads, we recommend using a uniform rectangular pressure distribution of 70 psf. 15