101 E MARINE VIEW DR SEPA 018 - 011 Geotech Report 2025-04-15

Geotechnical Engineering Evaluation NGA File No.988017 East Marine View Drive Warehouse May 19,2017 Everett,Washington Page 7 The near surface soils are considered to be moisture-sensitive and can disturb easily when wet. We recommend that construction take place during the drier summer months if possible. However, if construction takes place during the wet season, additional expenses and delays should be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades, construction traffic areas, and paved areas prior to placing structural fill. The successful use of on-site soils as structural fill will be very difficult, but will depend on the moisture content of the soil at the time of construction. NGA should be retained to determine if any of the on-site soils could be used as structural fill material prior to construction. Foundations Conventional shallow spread foundations should be supported on compacted rock aggregate piers. Rock aggregate piers consist of augered or vibratory excavations holes which are then backfilled in successive lifts with crushed gravel which is rammed into place to create a dense column in which footings can bear on. The manner at which the material is packed into the hole also densifies the surrounding soils. We recommend that the piers consist of a minimum 16-inch diameter rock aggregate piers placed at 5 feet on center along the footing lines to provide proper support for the footings in the unsuitable soils. Isolated foundations should also be supported directly on a grid of compacted rock aggregate piers. Based on our explorations, the piers should be a minimum of 30 feet deep. The rock aggregate pier layout and overall design are generally performed by a rock aggregate pier company. Footings should extend at least 18 inches below the lowest adjacent finished ground surface for frost protection and bearing capacity considerations. Foundations should be designed in accordance with the 2015 IBC. Minimum foundation widths of 24 and 36 inches should be used for continuous and isolated footings, respectively. Footing widths should also be based on the anticipated loads and allowable soil bearing pressure. Standing water should not be allowed to accumulate in footing trenches. All loose or disturbed soil should be removed from the foundation excavation prior to placing concrete. For foundations supported on the aggregate piers as outlined above, we recommend an allowable design bearing pressure of not more than 3,000 pounds per square foot (psf) be used for the footing design for footings founded on compacted rock aggregate piers. The foundation bearing soil should be evaluated by a representative of NGA. We should be consulted if higher bearing pressures are needed. Current IBC guidelines should be used when considering increased allowable bearing pressure for short-term transitory wind or seismic loads. Potential foundation settlement using the recommended allowable bearing pressure is estimated to be less than one inch total and 1/2 inch differential between adjacent footings or across a distance of about 30 feet. NELSON GEOTECHNICAL ASSOCIATES, INC.