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

ZipperGeo Broadway Everett Expansion Geoprofessional Consultants Project No. 2601.01 July 7, 2022 Per IBC requirements, retaining walls supporting more than 6 feet of retained fill should be designed for additional dynamic seismic earth pressures. For walls supporting more than 6 feet of retaining fill, we recommend using a unform dynamic seismic earth pressure value of 10H psf. Resistance to Lateral Loads For recommended lateral resistance parameters, refer to the Building Foundation Recommendations section above. Drainage Adequate drainage measures must be installed to collect and direct subsurface water away from retaining walls. All backfilled walls should include a drainage aggregate zone extending two feet from the back of wall for the full height of the wall. The drainage aggregate should consist of material meeting the requirements of WSDOT 9-03.12(2) Gravel Backfill for Walls.A minimum 4-inch diameter, perforated PVC drain pipe should be provided at the base of backfilled walls to collect and direct subsurface water to an appropriate discharge point. We recommend placing a non-woven geotextile, such as Mirafi 140N, or equivalent, around the free draining backfill material. Wall drainage systems should be independent of other drainage systems such as roof drains. Drainage Considerations Surface Drainage Final site grades should be sloped to carry surface water away from buildings and other drainage-sensitive areas. Additionally, site grades should be designed such that concentrated runoff on softscape surfaces is avoided.Any surface runoff directed towards softscape slopes should be collected at the top of the slope and routed to the bottom of the slope and discharged in a manner that prevents erosion. CLOSURE The analysis and recommendations presented in this report are based, in part, on the explorations completed for this study.The number, location,and depth of the explorations were completed within the constraints of budget and site access so as to yield the information to formulate our recommendations. Project plans were in the preliminary stage at the time this report was prepared. We, therefore, recommend we be provided an opportunity to review the final plans and specifications when they become available in order to assess that the recommendations and design considerations presented in this report have been properly interpreted and implemented into the project design. The performance of earthwork, structural fill,foundations, and pavements depend greatly on proper site preparation and construction procedures. We recommend that Zipper Geo Associates, LLC be retained to provide geotechnical engineering services during the earthwork-related construction phases of the project. If variations in subsurface conditions are observed at that time, a qualified geotechnical engineer could provide additional geotechnical recommendations to the contractor and design team in a timely manner as the project construction progresses. 16