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compacted in accordance with the criteria discussed above. A detail of a typical compaction criteria for <br /> trench backfill is shown in Figure 5. <br /> Temporary Excavations <br /> We recommend temporary excavations constructed in the existing fill be inclined no steeper than 11/2H:1V. <br /> Lesser inclined slopes may be necessary if seepage is present on the face of the cut slopes or if localized <br /> sloughing occurs. In addition, vibrations from construction equipment can cause sloughing of temporary <br /> slopes and thus slopes may have to be flattened if sloughing is observed. For temporary slopes at the site, <br /> we recommend that: <br /> ■ no traffic, construction equipment,stockpiles or construction supplies be allowed at the top of the cut <br /> slopes within a distance of at least 10 feet from the top of the slope. <br /> ■ exposed soil along the slope be protected from surface erosion using waterproof tarps or plastic <br /> sheeting. <br /> ■ construction activities be scheduled so that the length of time the temporary cut is left open is reduced <br /> to a practical minimum. <br /> ■ erosion control measures be implemented as appropriate such that runoff from the site is minimal. <br /> ■ surface water be diverted away from the open excavation and slopes. <br /> ■ the general condition of the slopes be observed periodically by a geotechnical engineer to confirm <br /> adequate stability. <br /> Sedimentation and Erosion Control <br /> In our opinion,the erosion potential of the on-site soils is low to moderate.Construction activities including <br /> stripping and grading will expose soils to the erosional effects of wind and water.The amount and potential <br /> impacts of erosion are partly related to the time of year that construction actually occurs. Wet weather <br /> construction will increase the amount and extent of erosion and potential sedimentation. <br /> Erosion and sedimentation control measures may be implemented by using a combination of interceptor <br /> swales,straw bale barriers,silt fences and straw mulch for temporary erosion protection of exposed soils. <br /> All disturbed areas should be finish graded and seeded as soon as practicable to reduce the risk of erosion. <br /> Erosion and sedimentation control measures should be installed and maintained in accordance with the <br /> requirements of Snohomish County. <br /> Recommended Additional Geotechnical Services <br /> Recommendations are provided where we consider additional geotechnical services to be appropriate. <br /> These additional services are summarized below: <br /> ■ GeoEngineers should be retained to review the project plans and specifications when complete to <br /> confirm that our design recommendations have been implemented as intended. <br /> ■ During construction, GeoEngineers should evaluate subgrade preparation for foundations and floor <br /> slabs, pavement subgrades,evaluate the compaction of structural fill and provide a summary letter of <br /> our construction observation services.The purposes of GeoEngineers construction phase services are <br /> GEOENGINEERS August3,2018 Page16 <br /> File No.0643-015-00 <br />