11831 AIRPORT RD WHOLE SITE FILE Geotech Report 2022-10-25

3. Structural fill placed below foundations should be compacted to 95 percent of the MDD (ASTM D 1557). 4. Structural fill placed as crushed rock base course below pavements should be compacted to 95 percent of the MDD (ASTM D 1557). We recommend that a representative of GeoEngineers be present during proof-rolling and/or probing of the exposed subgrade and pavement subgrade soils,and during placement of structural fill.GeoEngineers will evaluate the adequacy of the subgrade soils and identify areas needing further work, perform in-place moisture-density tests in the fill to evaluate whether the work is being done in accordance with the compaction specifications, and advise on any modifications to procedure that may be appropriate for the prevailing conditions. Weather Considerations The on-site soils generally contain a high percentage of fines (silt and clay) and are moisture-sensitive. When the moisture content of these soils is more than a few percent above the optimum moisture content, these soils become muddy and unstable, operation of equipment on these soils will be difficult, and it will be difficult or impossible to meet the required compaction criteria.Additionally,disturbance of near-surface soils should be expected if earthwork is completed during periods of wet weather.The contractor will need to take precautions to protect the subgrade during periods of wet weather. The wet weather season in western Washington generally begins in October and continues through May; however, periods of wet weather may occur during any month of the year.The optimum earthwork period for these types of soils is typically June through September. If wet weather earthwork is unavoidable, we recommend that: • the ground surface in and around the work area should be sloped so that surface water is directed away from the work area. The ground surface should be graded such that areas of ponded water do not develop. The contractor should take measures to prevent surface water from collecting in excavations and trenches. Measures should be implemented to remove surface water from the work area; • erosion control techniques should be implemented to prevent sediment from leaving the site; • earthwork activities should not take place during periods of heavy precipitation; • slopes with exposed soils should be covered with plastic sheeting; • the contractor should take necessary measures to prevent on-site soils and soils to be used as fill from becoming wet or unstable.These measures may include the use of plastic sheeting,sumps with pumps, and grading. The site soils should not be left uncompacted and exposed to moisture. Sealing the surficial soils by rolling with a smooth-drum roller prior to periods of precipitation will help reduce the extent that these soils become wet or unstable; and • construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practical. GEOENGINEERSii April 14,2017 Page 23 File No.2095-032-00