3500 TERMINAL AVE Geotech Report 2022-10-25

28 I Port of Everett—South Terminal Wharf& Electrical Upgrades—Phase 2 includes a factor of safety of 1.5.These values are based on a drained condition behind the walls so there is no buildup of hydrostatic pressure. In addition to the active soil pressures we recommend applying a horizontal traffic and material surcharge be applied.This surcharge may be calculated as 0.3 times the vertical surcharge load (e.g.,for a vertical surcharge of 250 psf the horizontal surcharge pressure on the wall is 75 psf). Below the water table,the active and at-rest pressure equivalent fluid weights are 17 and 26 pcf, respectively.Similarly,the equivalent fluid unit weight for passive resistance reduces to 110 pcf. Hydrostatic pressure should be applied to the wall when submerged. For seismic conditions, use a dynamic lateral uniform surcharge 14 times the height of the wall (14H) in pressure units of pounds-per-square-feet.This portion of the equivalent fluid unit weight should be applied as a rectangular distribution,while the static fluid weights presented above should be applied as triangular distributions. The use of active pressure is appropriate if the subgrade wall is allowed to yield a minimum of 0.001 times the height of the wall. For a non-yielding wall,at-rest conditions should be used.We expect that the vault walls will be non-yielding. General Dewatering Recommendations The design groundwater elevation of+12.5 ft MLLW provided on page 9 is based on the high observed annual tidal elevation.While it is unlikely that this elevation will be consistently observed during construction work,we anticipate that some dewatering measures will be required depending on the time of year,and recommend that the contractor anticipate tidal elevations and plan accordingly. Foundation Drainage For permanent drainage around the structure foundations,we recommend that a capillary break layer of at least 6 inches of free-draining material be placed below slabs-on-grade,vault foundations,and shallow footings.This 6-inch-thick layer should be composed of import material.We note that this is a minimum requirement for drainage. Refer to"Foundation Support for Civil Structures"for more structural subgrade recommendations. Backfilled Walls Walls with soil backfilled on one side will require drainage,or must be designed to withstand full hydrostatic pressure.We recommend the following: • Backfill with a minimum thickness of 18 inches of well-graded,free-draining sand (less than 3 percent fines based on the minus 3/4-inch fraction)or sand and gravel. • Install drains behind any backfilled subgrade walls. Drains with cleanouts should incorporate a minimum 4-inch-diameter perforated pipe surrounded by at least 6 inches of well-graded,free- draining sand(less than 3 percent fines based on minus 3/4-inch fraction),or sand and gravel.The drains should be sloped to carry the water to a sump or other suitable discharge. 19232-01 December 6,2017