7505 SEAWAY BLVD Geotech Report 2022-10-25

November 11, 2016 HWA Project No. 2014-117-21 4.8 GENERAL EARTHWORK 4.8.1 Temporary Excavation Maintenance of safe working conditions, including temporary excavation stability, is the responsibility of the contractor. In accordance with Part N of WAC (Washington Administrative Code) 296-155, temporary shoring will be required wherever the excavation is deeper than 4 feet. Per these requirements,the existing fill soils are classified as Type C soils. Temporary unsupported excavations within these soils may be sloped no steeper than 1'/2H:1 V(horizontal: vertical). The existing weathered glacial till soils are classified as Type B soils. Temporary unsupported excavations within these soils may be sloped no steeper than 1H:1V(horizontal: vertical). The existing non-weathered glacial till soils are classified as Type A soils. Temporary unsupported excavations within these soils may be sloped no steeper than 3/4H:1 V (horizontal: vertical). 4.8.2 Dewatering Perched groundwater was encountered in several of our borings at the project location; particularly on the western portion of the property. Prospective contractors should be prepared to encounter and manage water intrusion from perched water zones above the till and water-bearing sand lenses within the till layer. We expect localized pump and sump systems will likely be the most effective dewatering method. 4.8.3 Structural and Non-Structural Fill The native weathered and non-weathered glacial till soils will be suitable for use as fill in non-structural areas if earthwork is completed in the dry summer months of July through September;provided they are properly moisture conditioned and free of deleterious materials. Organic material was encountered in the samples obtained from the fill material. Any concentrated pockets of organics encountered within the fill material should be removed prior to placement as non-structural fill. Additionally,these soil have high fines content and will be highly moisture sensitive when exposed to wet weather. We expect that these soils will be at, or slightly over, optimum moisture content upon excavation and will require some drying prior to placement and compaction. If any earthwork is to take place or extend into the wet weather months of October through June, the onsite native soils will not be suitable for use as non- structural fill, and clean, freely draining gravel, such as Gravel Borrow(Section 9-03.14(1) of the WSDOT Standard Specifications) should be imported for non-structural fill. Fill in all structural areas and under pavement base course should consist of imported material consisting of clean, freely draining gravel, such as Gravel Borrow(Section 9-03.14(1) of the WSDOT Standard Specifications) 2014-117 Final Geotechnical Report 13 HWA GEOSCIENCES INC.