3500 TERMINAL AVE Geotech Report 2022-10-25

Port of Everett—South Terminal Wharf& Electrical Upgrades—Phase 2 127 • We anticipate that soft or loose conditions may be encountered when excavations reach planned foundation elevations and may require overexcavation.The need for overexcavation should be determined in the field during construction by a Hart Crowser representative.Overexcavation could extend up to 3 feet below the design subgrade elevation. For the condition in which the subgrade is above groundwater elevation and the native subgrade has been deemed suitable by a Hart Crowser representative,a minimum of 12 inches of crushed rock base should be placed elevation and compacted to 95%relative density up to the required foundation bearing surface elevation. For the condition in which the subgrade is below groundwater elevation or the native subgrade has been deemed unsuitable by a Hart Crowser representative,we recommend installing a geosynthetic which provides base reinforcement,subgrade stabilization,drainage,and acts as a separation fabric that is equal-to-or-better than Mirafi® RS280iover the overexcavated subgrade,followed by at least 12 inches of free-draining crushed rock. Quarry spalls should be compacted by thoroughly tamping with the heel of an excavator bucket or using a similar procedure.The geotextile should then be wrapped over the top of the spalls.A minimum of 6 inches of crushed surfacing base course(CSBC)or 1.25-inch-minus gravel should then be placed to backfill up to the required foundation bearing surface(subgrade) elevation.The geosynthetic over the spalls will separate the spalls from the smaller crushed rock above. • An increase in the allowable soil bearing pressure of up to one-third for loads of short duration,such as seismic forces,should be allowed. • To consider frost penetration, place the base of all footings at least 18 inches below the lowest adjacent finished grade. • Found structure foundations outside of an imaginary 1H:1V plane (where H is horizontal and V is vertical)projected upward from the bottom edge of any adjacent footings or utility trenches. If structure foundations are founded within the imaginary 1H:1V projection, loads may be transferred through the soil to the lower footing of interest, potentially exceeding the bearing capacity.When structure foundations cannot be founded outside of the 1H:1V projection,consult with Hart Crowser to assess potential foundation design implications. • Use a modulus of subgrade reaction based on a 1-foot-by-1-foot square plate [k(1xl)] of 100 pounds per cubic inch (pci) in cases in which the water table is within 1.5B of the foundation,where B is the footing width. For cases in which the water table is deeper than 1.5B below the foundation, use a k(zxl) of 100 pci. Use the equations in section Marine Operations Building Foundations to correct for different foundation sizes and shapes. Lateral Pressure on Permanent Subgrade Walls We understand that the new electrical vaults will require excavation depths of up to 10 to 12 feet below ground surface. For the existing dredged fill above the water table we recommend calculating active and at-rest lateral earth pressures using an equivalent fluid unit weight for the soil equal to 35 and 55 pcf, respectively. Use an allowable passive equivalent fluid unit weight for this material of 240 pcf,which V 19232-01 HARTCROWSER December 6,2017