9908 18TH AVE W 2024-12-03 - Laserfiche WebLink

Pacific Ridge — DRH, LLC ES-7852.01 March 15, 2022 Page 13 Utility Support and Trench Backfill The native soil observed at the test pit locations are generally suitable for utility. Use of the native soil as structural backfill in the utility trench excavations will depend on the in-situ moisture content at the time of placement and compaction. If native soil is placed below the optimum moisture content, settlement will likely occur once wet weather impacts the trenches. As such, backfill soils should be properly moisture conditioned, as necessary, to ensure acceptability of the soil moisture content at the time of placement and compaction. Native soil will be difficult or impossible to use as utility trench backfill during extended wet weather conditions. In this respect, moisture conditioning or treatment of the soils may be necessary at some locations prior to use as structural fill. The existing fill soil may not be suitable for utility trench backfill and the use of imported soil should be anticipated; ESNW should evaluate suitability of existing fill during construction. Utility trench backfill should be placed and compacted to the specifications of structural fill provided in this report or to the applicable requirements of the presiding jurisdiction. 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 or yielding subgrade conditions will require remedial measures, such as overexcavation and/or placement of thick crushed rock or structural fill sections, prior to pavement. We anticipate new pavement sections will be subjected primarily to passenger vehicle traffic. 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). Heavier traffic areas generally require thicker pavement sections depending on site usage, pavement life expectancy, and site traffic. For preliminary design purposes, the following pavement sections for occasional truck traffic and access roadways may be considered: • Three inches of HMA placed over six inches of CRB, or; • Three inches of HMA placed over four and one-half inches of ATB. A representative of ESNW should be requested to observe subgrade conditions prior to placement of CRB or ATB. As necessary, supplemental recommendations for achieving subgrade stability and drainage can be provided. If on-site roads will be constructed with an inverted crown, additional drainage measures may be recommended to assist in maintaining road subgrade and pavement stability. Earth Solutions NW, LLC