7010 COLBY AVE 2023-06-01 - Laserfiche WebLink

Mr. Paul Korenovsky ES-6067 June 20, 2018 Page 11 Utility Support and Trench Backfill In our opinion, native soils will generally be suitable for support of utilities. Organic-rich soils are not considered suitable for direct support of utilities and may require removal at utility grades if encountered. Remedial measures, such as overexcavation and replacement with structural fill and/or installation of geotextile fabric, may be necessary in some areas to provide support for utilities. Groundwater will likely be encountered within deeper utility excavations, and caving of trench walls may occur where groundwater is encountered. Temporary construction dewatering, as well as temporary trench shoring, may be necessary during utility excavation and installation as conditions warrant. In general, native soils are expected to be suitable for use as structural backfill throughout utility trench excavations, provided the soils are at (or slightly above) the optimum moisture content at the time of placement and compaction. Structural trench backfill should not be placed dry of the optimum moisture content. Each section of the site utility lines must be adequately supported in appropriate bedding material. Utility trench backfill should be placed and compacted to the specifications of structural fill as previously detailed in this report, or to the applicable specifications of the City of Everett or other responsible jurisdiction or agency. Preliminary Pavement Sections The performance of site pavements is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proof rolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications previously detailed in this report. Soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Areas containing unsuitable or yielding subgrade conditions will require remedial measures, such as overexcavation and/or placement of thicker crushed rock or structural fill sections, prior to pavement. Cement treatment of the subgrade soil can also be considered for stabilizing pavement subgrade areas if allowed by local jurisdictions. For lightly loaded pavement areas subjected primarily to passenger vehicles, the following preliminary pavement sections may be considered: • A minimum of two inches of hot mix asphalt (HMA) placed over four inches of crushed rock base (CRB), or; • A minimum of two inches of HMA placed over three inches of asphalt treated base (ATB). The HMA, ATB and C'RB materials should conform to WSDOT specifications. All soil base material should be compacted to a relative compaction of 95 percent, based on the laboratory maximum dry density as determined by ASTM D1557. Final pavement design recommendations, including recommendations for heavy traffic areas, access roads, and frontage improvement areas, can be provided once final traffic loading has been determined. Road standards utilized by the City of Everett may supersede the recommendations provided in this report. Earth Solutions NW,LLC