3003 W CASINO RD BLDG 40-58 Geotech Report 2022-10-25

3.0 CONCLUSIONS AND RECOMMENDATIONS Based upon evaluation of the data collected during this geotechnical investigation, it is our opinion that subsurface conditions at the project site are suitable for the proposed project, provided the recommendations contained herein are incorporated into the project design. The following sections present conclusions and recommendations regarding site preparation and earthwork, fill selection and reuse of onsite soils, wet weather earthwork, fill placement and compaction, temporary and permanent slopes, seismic design inputs, drilled shaft axial and lateral loading capacity and construction considerations, support of small or relatively lightly-load footings, concrete slabs-on-grade, flexible pavements, lateral earth pressures for retaining walls and tunnel walls, below-grade utility construction, and recommendations for geotechnical observation during construction. (Note that not all of these topics are discussed in detail in this interim draft report.) 3.1 SITE PREPARATION AND EARTHWORK Site preparation and earthwork will likely include demolition of existing buildings, asphalt pavement, the current 787 large parts rack, and other existing structures within the proposed structure footprint, abandonment of existing utilities, minor excavation related to subgrade preparation, and then placement of up to 16 feet of fill within the building pad footprint. Site preparation will also include earthwork, fill placement and compaction below the building slab-on-grade, the exterior apron, a modified Perimeter Road alignment, plus changes to the Everett campus road network. Site preparation and earthwork will also include removal and/or relocation of existing onsite utilities and modifications to portions of an existing pedestrian tunnel. It is our understanding that demolition, utility abandonment, and site grading/earthwork occur in phases,all of which will precede construction of the building foundations and the interior concrete slab on grade. Completion of earthwork construction in surrounding areas prior to floor slab construction will be critical,as discussed in Section 3.9. Topsoil, organic and man-made debris, and other deleterious material should be cleared and stripped from all areas to be occupied by the Building 40-58 pad fill footprint, building foundations, or retaining wall foundations. Any structures not removed entirely should be cut off at least 3 ft below the proposed floor slab, apron, or pavement subgrade. Any structure beneath retaining walls should be removed in its entirety. We understand that current demolition plans include removal of existing building slabs in the 40-83, 40-84, and 40-85 buildings. As an option, floor slabs could be rubblized (to remove "slab action" behavior during filling) and left in place. Similarly, existing asphalt could be rubblized in place and compacted to serve as a granular base layer. However, we understand that for environmental reasons,Boeing does not prefer this approach. 5/16/14 P:\1423\002\010\FileRm\R\Draft Bldg 40-58 Report\Bldg 40-58_draft rpt.docx INTERIM DRAFT 3-1