1010 N BROADWAY EVCC 2018-01-01 MF Import

PROPOSED LIBERTY HALL,EVERETT COMMUNITY COLLEGE Everett,Washington n Construction traffic should be restricted to specific areas of the site, preferably areas that are surfaced with the existing asphalt or working pad materials not susceptible to wet weather disturbance. • Construction activities should be scheduled so that the length of time that soils are left exposed to moisture is reduced to the extent practical. Routing of equipment on the native subgrade soils during the wet weather months will be difficult and the subgrade will likely become highly disturbed and rutted. In addition, a significant amount of mud can be produced by routing equipment directly on the silts and clays in wet weather. Therefore, to protect the subgrade soils and to provide an adequate working surface for the contractor's equipment and labor, we recommend that the contractor protect exposed subgrade soils with sand and gravel,crushed gravel, recycled asphalt grindings,or ATB. Permanent Cut and Fill Slopes We recommend that permanent cut or fill slopes be constructed at inclinations of 3H:1V or flatter, and be blended into existing slopes with smooth transitions. To achieve uniform compaction, we recommend that fill slopes be slightly overbuilt and cut back to expose well-compacted fill. To reduce erosion, newly constructed slopes should be planted or hydroseeded shortly after completion of grading. Until the vegetation is established, some sloughing and ravelling of the slopes should be expected. This may necessitate localized repairs and reseeding. Temporary covering, such as clear heavy plastic sheeting, jute fabric,or erosion control blankets (such as American Excelsior Curlex 1 or North American Green S15O) could be used to protect the slopes during periods of rainfall. Utility Trenches Trench excavation, pipe bedding, and trench backfilling should be completed using the general procedures described in the 2010 WSDOT Standard Specifications or other suitable procedures specified by the project civil engineer. The silts and clays, glacial deposits, and fill soils encountered at the site are generally of low corrosivity based on our experience in the Puget Sound area. Utility trench backfill should consist of structural fill and should be placed in lifts of 8 inches or less (loose thickness) such that adequate compaction can be achieved throughout the lift. Sand backfill, containing less than 5 percent fines, may be compacted in loose lifts not exceeding 12 inches when placed below five feet of the finished ground surface. Each lift must be compacted prior to placing the subsequent lift. Prior to compaction, the backfill should be moisture conditioned to within 3 percent of the optimum moisture content, if necessary. The backfill should be compacted in accordance with the criteria discussed above. Figure 6 illustrates recommended trench compaction criteria under pavement and non-structural areas. Sedimentation and Erosion Control In our opinion,the erosion potential of the on-site soils is low to moderate. Construction activities including stripping and grading will expose soils to the erosion effects of wind and water. The amount and potential impacts of erosion are partly related to the time of year that construction GEOENGINEERLO June 10,2010 I Page 9 File No:5636-010.00