3003 W CASINO RD BLDG 45-06 Geotech Report 2025-03-03

Geotechnical Engineering Report lierracon Proposed Flight Line Steam Line Project Boeing Everett Facility • Everett, Washington January 17, 2012 • Terracon Project No.: 81115085 We recommend that excavations greater than 4 feet in vertical height be adequately sloped or braced to prevent injury to workers from sloughing and spalling. All excavations should be sloped or shored in the interest of safety following local, and federal regulations, including current OSHA excavation and trench safety standards. 4.2.4 Temporary Shoring We recommend that temporary shoring systems be used where excavations will be located adjacent to property lines, roadways, or utilities, and might result in ground loss and damage to these facilities. A trench box is one type of support system which might be used. The zone between the trench box and the excavation face should be backfilled as necessary to limit ground movements. The lateral soil pressures acting on temporary excavation support systems will depend on the ground surface configuration adjacent to the trench, and the amount of lateral movement which can occur as the excavation is made. For support systems that are free to yield at the top at least one-thousandth of the height of the excavation, soil pressures will be less than if movements are limited by such factors as wall stiffness or bracing. We recommend that yielding systems be designed using equivalent fluid densities of 35 and 85 pounds per cubic foot (pcf) for horizontal ground surfaces and ground surfaces inclined at 1.5H:1V above the horizontal, respectively. For braced non-yielding systems, we recommend I that the shoring be designed for a uniform lateral pressure of 25H in pounds per square foot (psf), where H is the depth of the planned excavation in feet below a level ground surface. Similarly, for a ground surface inclined at 1.5H:1V, we recommend that braced non-yielding shoring be designed for a uniform lateral pressure of 55H. The above recommended lateral soil pressures are based on a fully drained condition and do not include the effects of hydrostatic water pressures. In addition, the above values do not include the effects of surcharges (e.g., equipment loads, storage loads, traffic loads, or other surface loading). Hydrostatic water pressures and surcharge effects should be considered as appropriate. 4.2.5 Construction Dewatering Slight groundwater seepage was observed in borings B-3 and B-4 at depths of approximately 3 and 51/4 feet below the surface, respectively. The groundwater seepage observed in the borings is interpreted to represent water perched within existing fill soils located above lower permeability glacial till soils. Given the relatively low permeability of the site glacial till soils, perched groundwater may develop above the till or within sandy zones within the till during periods of extended wet weather. We understand that pothole explorations completed by the contractor encountered moderate groundwater seepage near existing utility trenches. Perched groundwater within utility trench backfill should be anticipated. I Responsive • Resourceful • Reliable 6