2320 RAILWAY AVE Geotech Report 2023-02-01

I Interwest Construction Co.-Everett Contractor Yard Site Improvements, Everett, WA March 12,2021 IGeotechnical Engineering Report P2184-T20 during a large-scale seismic event,which could lead to post-construction settlement. However,we I expect that this effect will be attenuated by the overlying fill deposits previously placed across the site. Based on this, we recommend that the scale house structure be designed to accommodate differential settlements of 2 inches over 50 feet without catastrophic collapse. I 4.0 CONCLUSIONS AND RECOMMENDATIONS Improvement plans involve the construction of a new scale house and concrete scale pits towards I the southeast corner of the project area,and the implementation of final site grading to facilitate the functionality of the proposed drainage plan. As currently proposed,runoff waters will be collected I along the perimeter of the site and treated before ultimately being discharged to the new stormwater system along Railway Avenue,immediately west of the project area. The introduction of stormwater filtration vaults and a sediment collection and stormwater wet pond are incorporated I into the proposed drainage plan. Heavy duty pavements will be introduced along the perimeter of nnewtruck scales. off er site and adjacent to the We o er these recommendations: I • Feasibility: Based on our field explorations, research, and analyses, the proposed improvements appear feasible from a geotechnical standpoint. I • Foundation Options: Foundation elements should be constructed on medium dense or denser undisturbed native soils, or on structural fill bearing p ads that extend down to medium dense or denser native soils. We anticipate that adequate bearing soils will be I encountered at relatively shallow depths (less than 2 feet) across much of the proposed building area, with existing fill soils being in a suitable condition for foundation support. We do not foresee the need for any localized over-excavations. Recommendations for Ispread footings are provided in Section 4.3. • Floor Options: Floor sections should bear on medium dense or denser native soils or on I properly compacted structural fill that extends down to medium dense or denser native soils. We anticipate that adequate bearing soils will be encountered at relatively shallow depths(less than 2 feet)at the proposed building area,and we do not foresee the need for a Igranular fill subbase. Recommendations for slab-on-grade floors are included in Section 4.4. Fill underlying floor slabs should be compacted to 95 percent (ASTM:D-1557). • Excavation Considerations: General trench excavation,pipe bedding,and trench backfilling should be completed using the general procedures described in WSDOT Standard Specifications, Section 7-17, or other suitable procedures specified by the project civil Iengineer. As indicated on the exploration logs, the site soils are typically in a loose to medium dense condition. It should be expected that occasional organics and pieces of I timber could be present based on the depositional history and might be difficult to excavate where encountered. The contractor should be prepared to deal with these conditions. • Truck-Scale Pits and Concrete Wet Pond: The precast truck-scale pits and sediment Icollection and concrete stormwater wet pond will encounter poorly consolidated alluvial sands and peat underlying the upper yard fill. This material will cave and run during excavation,so temporary shoring will likely be required. Groundwater levels are expected Ito be near the bottom of the excavations,and seepage should be anticipated. We anticipate I Migizi Group, Inc. Page 6 of 16 MIGILI 401 ,.,, (I