7100 HARDESON RD SITE DEVELOPMENT Geotech Report 2025-03-04

Geotechnical Engineering Report lierracon Merrill Creek Operations Base Expansion a Everett, Washington December 14, 2020 e. Terracon Project No. 81205012 GeoReport. EARTHWORK Earthwork is anticipated to include demolition of existing concrete pavement, minor filling and cutting to achieve the building floor subgrade elevation, excavation for footings and placement of backfill against footing sides, trenching and backfilling of sub-slab utilities and open-cut excavation and backfilling for construction of coach inspection pits. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations, floor slabs, and pavements. Existing Fill As noted in Geotechnical Characterization, both exploration borings encountered existing fill, as anticipated in Pre-Design Study letter dated June 8, 2020. The upper 10 to 12 feet of this fill is medium dense to very dense gravelly silty sand which appears to have been part of the re-working and re-compaction activities that preceded building construction in 1996/1997; this is the "Dense Fill" GeoModel layer. Below the upper 10 to 12 feet, the density of the non-re-worked fill is variable, ranging from loose to very dense gravelly silty sand; this is the "Variable Fill" Geomodel layer. Support of footings, floor slabs, and pavements, on or above existing fill soils, is discussed in this report. Site Preparation The perimeter of existing pavement to be demolished should be sawcut to its full depth prior to removal in order to reduce subgrade disturbance during slab removal, and to facilitate doweling where new pavement will join to existing pavement. Any soils disturbed during slab demolition or during removal or abandonment of utilities or other structures should be removed and re- compacted or replaced with structural fill. Following grading to the subgrade elevation, the entire subgrade should be proof-rolled with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck, water truck, or large steel-drum roller. The proof-rolling should be performed under the direction of the Geotechnical Engineer. Areas excessively deflecting under the proofroll should be delineated and subsequently addressed by the Contractor. Such areas should have soft soils removed and replaced with compacted structural fill. Excessively wet or dry material should either be removed or moisture conditioned and recompacted. Fill Material Types We recommend that only structural fill be used within the footprint of the building expansion and beneath all new pavements, except where an additional drainage capability is needed for footing drain, wall drains, sumps, and similar drainage structures. Structural fill should be used for trench Responsive ■ Resourceful s Reliable