1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC Geotech Report 2022-10-25

3. Structural fill placed as crushed rock base course below pavements should be compacted to 95 percent of the MDD estimated in general accordance with ASTM D 1557. 4. Structural fill for permanent slopes should be compacted to 90 percent of the MDD estimated in general accordance with ASTM D 1557. 5. Non-structural fill, such as fill placed in landscape areas, should be compacted to at least 85 percent of the MDD estimated in general accordance with ASTM D 1557. In areas intended for future development,a higher degree of compaction should be considered to reduce the settlement potential of the fill soils. We recommend that a representative from our firm be present during proof-rolling and/or probing of the exposed subgrade and pavement subgrade soils,and during placement of structural fill.Our representative 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 contain a high percentage of fines (silt) and are moisture-sensitive. When the moisture content of these soils is more than a few percent above the optimum moisture content,they become muddy and unstable. Operation of equipment in these conditions will be difficult, and the required compaction criteria will not be achieved.Additionally,disturbance of near-surface soils should be expected if earthwork is completed during periods of wet weather. During dry weather, the soils will: (1) be less susceptible to disturbance; (2)provide better support for construction equipment; and (3) be more likely to meet the required compaction criteria. 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. If wet weather earthwork is unavoidable,we recommend that the following steps be taken should the near-surface soil conditions begin to deteriorate: ■ 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 so 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. ■ Earthwork activities should not take place during periods of heavy precipitation. a 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 to which these soils become wet or unstable. ■ Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced with working pad materials not susceptible to wet weather disturbance. ■ Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practicable. GEOENGINEERS. April 22,2016 Page 11