2320 CALIFORNIA ST Geotech Report 2025-07-25

Administration Building Office Expansion Everett,Washington 111 failure be removed and the subgrade repaired. If ATB is used and is serviceable when final pavements are constructed,the crushed surfacing base course can be eliminated, and the design portland cement concrete ' or asphalt concrete pavement thickness can be placed directly over the ATB. Earthwork ' Based on the subsurface soil conditions encountered in the test pits, we anticipate the soils at the site may be excavated using conventional heavy duty construction equipment. The materials we encountered include fill and very dense glacial till. Glacial till in the area commonly contain cobbles and boulders that may be encountered during excavation. Accordingly,the contractor should be prepared to deal with boulders. ' The on-site glacial soils underlying the fill contain significant fines (material passing the U.S. standard No.200 sieve) and will be highly moisture-sensitive and susceptible to disturbance, especially when wet. Ideally, earthwork should be undertaken during extended periods of dry weather (June through September) when the surficial soils will be less susceptible to disturbance and provide better support for construction equipment. Dry weather construction will help reduce earthwork costs and increase the potential for reusing the glacial soils as structural fill. ' The onsite dense glacial till soils has moisture contents approximately 2 to 3 percent over optimum. Therefore,the soils may need to be dried to achieve the specified compaction criteria. Clearing and Site Preparation Construction of the proposed addition will require removal of the sidewalks, landscaping,and hardscape,and ' other appurtenant structures. Based on our exploration and site observations,we estimate that the top soil is about 3 to 4 inches thick. All existing utilities should be removed from foundation footprints and rerouted if needed. Areas to be developed or graded should be cleared of surface and subsurface deleterious matter including any debris,shrubs,trees and associated stumps and roots. Graded areas should be stripped of organic soils. Consideration should be given to separating the underlying sand fill soils if encountered during constructions and reusing the on-site sandy fill as structural fill where possible. The organic soils can be stockpiled and used later for landscaping purposes or may be spread over disturbed areas following completion of grading. If spread out, the organic strippings should be in a layer less than 1 foot thick, should not be placed on slopes greater than 3H:1V, and should be track-rolled to a uniformly compacted condition. Materials that cannot be used for landscaping or protection of disturbed areas should be removed from the project site. Subgrade Preparation Prior to placing new fills, pavement base course materials,or on-grade floor slabs,subgrade areas should be evaluated to locate any soft or pumping soils. Prior to proof rolling, all unsuitable soils should be removed from below building and pavement areas. Proof rolling can be completed using a piece of heavy tire-mounted ' equipment such as a loaded dump truck. During wet weather,the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed, they should be removed and replaced with structural fill. 1 GEOENGINEERS October30,2009 Page 7 File No.0482-031-02