1815 13TH ST SEATTLE CHILDRENS NORTH CLINIC 2019-07-08

CENTRAL UTILITY PLANT PARKING LOT Everett,Washington surfacing shall be removed in a manner where it can be segregated from the underlying fill or native soil without significant fines contamination. Most of the near-surface soils observed below the crushed gravel surfacing generally contain a high percentage of fines (silt/clay) and are highly moisture-sensitive. Portions of the fill and glacially consolidated soils that meet the requirements for common borrow may be suitable for use as common borrow during dry weather only, provided it can be properly moisture-conditioned prior to placement. The fill and glacially consolidated soils that meet the requirements for common borrow are expected to be suitable for structural fill in areas requiring compaction to at least 95 percent of maximum dry density (MDD) estimated in general accordance with American Society for Testing and Materials (ASTM) D 1557, provided the work is completed during the normally dry season (June through September) and that the soil can be properly moisture-conditioned. It may be necessary to import sand and gravel with a low fines content to achieve adequate compaction for support of pavement areas for wet weather construction. Imported structural fill consisting of sand and gravel(WSDOT gravel borrow)should be planned if construction occurs during wet weather. The use of existing fill and glacially consolidated soils that meet the requirements for common borrow as structural fill during wet weather should be planned only for areas requiring compaction to 90 percent of MDD or less, as long as the soils are properly protected from wet weather and not placed during periods of precipitation. The contractor should plan to cover and maintain all fill stockpiles with plastic sheeting if it will be used as structural fill. The reuse of on-site soils is highly dependent on the skill of the contractor and schedule, and we will work with the design team and contractor to maximize the reuse of on-site till soils during the wet and dry seasons. FILL PLACEMENT AND COMPACTION CRITERIA Structural fill should be mechanically compacted to a firm, non-yielding condition. Structural fill should be placed in loose lifts not exceeding 1 foot in thickness. Each lift should be conditioned to the proper moisture content and compacted to the specified density before placing subsequent lifts. Structural fill should be compacted to the following criteria: • Structural fill in new pavement and hardscape areas, including utility trench backfill,should be compacted to at least 90 percent of the MDD estimated in general accordance with ASTM D 1557,except that the upper 2 feet of fill below final subgrade should be compacted to at least 95 percent of the MDD. • Structural fill placed as crushed surfacing base course below pavements should be compacted to 95 percent of the MDD estimated in general accordance with ASTM D 1557. • 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 GeoEngineers be present during probing of the exposed subgrade soils in pavement areas, and during placement of structural fill. We will evaluate the adequacy of the subgrade soils and identify areas needing further work, perform in-place moisture-density tests in Page 6 October 17,2012 GeoEngineers,Inc. File No.10738-010-00