917 112TH ST SE Geotech Report 2022-10-25

Habitat for Humanity of Snoomish County ES-5168 April 26, 2017 Page 12 Utility Support and Trench Backfill In our opinion, on-site soils will generally be suitable for support of utilities. Remedial measures may be necessary in some areas in order to provide support for utilities, such as overexcavation and replacement with structural fill and/or placement of geotextile fabric. Groundwater seepage may be encountered within utility excavations, and caving of trench walls may occur where groundwater is encountered. Depending on the time of year and conditions encountered, dewatering, as well as temporary trench shoring, may be necessary during utility excavation and installation: On-site soils may be suitable for use as structural backfill throughout utility trench excavations provided the soil is at (or slightly above) the optimum moisture content at the time of placement and compaction. Moisture conditioning of the soils may be necessary at some locations prior to use as structural fill. Each section of the utility lines must be adequately supported in the 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. 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 proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications detailed in the Site Preparation and Earthwork section of this report. In addition, the upper one foot of pavement subgrade should be compacted to the relative compaction of at least 95 percent. It is possible that 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 thicker crushed rock or structural fill sections prior to pavement. Cement treating;.the base can be considered to improve conditions. For lightly loaded pavement areas subjected primarily to passenger vehicles, the following preliminary pavement sections may be considered: • Two inches of asphalt concrete (AC) placed over four inches of crushed rock base (CRB), or; • Two inches of AC placed over three inches of asphalt treated base (ATB). ESNW can provide pavement section design recommendations for truck traffic areas and right- of-way improvements, upon request. Additionally, City of Everett road standards may supersede the recommendations provided in this report. Earth Solutions NW,LLC