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

CENTRAL UTILITY PLANT PARKING LOT Everett,Washington Organic soils, where present,can be stockpiled and used later for landscaping purposes or may be spread over disturbed areas following completion of grading. If spread out, the organic strippings should be in a layer less that 1-foot-thick, should not be placed on slopes greater than 3H:1V(horizontal to vertical), and should be track-rolled to a uniformly compacted condition. Materials that cannot be used for landscaping or protection of disturbed areas should be removed from the project site. Fill and former topsoil layers are present at the site and may represent unsuitable soils for support of new pavement areas. These soils have supported a parking lot surfaced with crushed rock for several years. The unsuitability of these materials and the need for removal and replacement will depend on planned site grades,weather conditions during construction,and the consistency of the fill and former topsoil deposits exposed at the planned subgrade elevation. A conservative approach would be to remove these materials and replace them with properly compacted structural fill. Alternatively,these soils can be evaluated during subgrade preparation and localized removal and replacement can be completed, as necessary. The latter approach can potentially reduce project costs; however, will require more flexible measurement and payment contractual provisions. Subgrade Preparation Prior to placing new fills, pavement or hardscape base course materials,subgrade areas should be proof rolled to locate any soft or pumping soils. Proof-rolling can be completed using a piece of heavy tire-mounted equipment such as a loaded dump truck. During wet weather, the exposed subgrade areas should be probed to determine the extent of soft soils. If soft or pumping soils are observed,they should be removed and replaced with structural fill. Structural Fill All fill supporting pavement areas or in utility trenches should meet the criteria for structural fill presented below. The suitability of soil for use as structural fill depends on its gradation and moisture content. MATERIALS Fill placed to support pavements/hardscape and as utility trench backfill will need to be specified as structural fill as described below: • Structural fill placed to construct parking areas and to backfill utility trenches should consist of common borrow as described in Section 9-03.14(3) of the 2012 WSDOT Standard Specifications. If structural fill is placed during wet weather, it should consist of gravel borrow as described in Section 9-03.14(1) of the 2012 WSDOT Standard Specifications, with the additional restriction that the fines content be limited to no more than 5 percent. • Structural fill placed as crushed surfacing base course below pavements should conform to Section 9-03.9(3)of the 2012 WSDOT Standard Specifications. REUSE OF ON-SITE SOILS The existing crushed gravel surfacing covering a majority of the project site may be reused as structural fill for areas of over-excavation or as a subbase for the parking lot. The crushed gravel GEOENGINEERS October 17,2012 Page 5 File No.10738-010-00