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Interwest Construction Co.-Everett Contractor Yard Site Improvements,Everett,WA March 12,2021
<br /> Geotechnical Engineering Report P2184-T20
<br /> that an internal system of ditches,sump holes,and pumps will be adequate to temporarily
<br /> dewater excavations that do not extend deeply into the water table. The truck-scale pits and
<br /> sediment collection and stormwater pH sparing pit should be supported on 24 inchesof 2 p g pp to
<br /> 4-inch quarry spalls driven into the subgrade,or according to the manufacturer's directions.
<br /> We recommend that all structures be designed to accept static settlements and to
<br /> accommodate seismic settlements without catastrophic collapse.
<br /> The following sections present our specific geotechnical conclusions and recommendations
<br /> concerning site preparation,subsurface utilities,spread footings,slab-on-grade floors,truck-scale
<br /> and concrete wet pond,asphalt pavement,and structural fill. The Washington State Department of
<br /> Transportation(WSDOT)Standard Specifications and Standard Plans cited herein refer to WSDOT
<br /> publications M41-10,Standard Specifications for Road,Bridge,and Municipal Construction,and M21-01,
<br /> Standard Plans for Road, Bridge, and Municipal Construction, respectively.
<br /> 4_1 Site Preparation
<br /> ' Preparation of the project site should involve erosion control, temporary drainage, clearing,
<br /> stripping, excavations, dewatering, cutting, subgrade compaction, and filling.
<br /> Erosion Control: Before new construction begins,an appropriate erosion control system should be
<br /> installed. This system should collect and filter all surface water runoff through silt fencing. We
<br /> anticipate a system of berms and drainage ditches around construction areas will provide an
<br /> adequate collection system. Silt fencing fabric should meet the requirements of WSDOT Standard
<br /> Specification 9-33.2 Table 3. In addition, silt fencing should embed a minimum of 6 inches below
<br /> existing grade. An erosion control system requires occasional observation and maintenance.
<br /> Specifically,holes in the filter and areas where the filter has shifted above ground surface should be
<br /> replaced or repaired as soon as they are identified.
<br /> Temporary Drainage: We recommend intercepting and diverting any potential sources of surface
<br /> or near-surface water within the construction zones before stripping begins. Because the selection
<br /> of an appropriate drainage system will depend on the water quantity,season,weather conditions,
<br /> construction sequence, and contractor's methods, final decisions regarding drainage systems are
<br /> best made in the field at the time of construction. Based on our current understanding of the
<br /> construction plans, surface and subsurface conditions,we anticipate that curbs,berms, or ditches
<br /> placed around the work areas will adequately intercept surface water runoff.
<br /> Site Excavations: Based on our explorations, we expect that excavations will encounter medium
<br /> dense to dense gravelly fill soils in close proximity to existing grade, and loose/soft alluvial soils
<br /> with depth,both of which can be easily excavated using standard excavation equipment.
<br /> ' Dewatering: Our explorations encountered groundwater seepage at a depth of approximately 10 to
<br /> 11 feet below existing grade. The contractor should be prepared to deal with this condition. For
<br /> shallow excavations above the water table,should groundwater be encountered,we anticipate that
<br /> an internal system of ditches, sump holes, and pumps will be adequate to temporarily dewater
<br /> excavations. For deeper excavations below the water table,more extensive dewatering equipment,
<br /> Migizi Group, Inc. Page 7 of 16
<br /> N11G111 IIIiII
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