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' Geotecllnical Engi�leering I,etter Alhussaini Slope Stabilization and Retaining Walls Everett, Washington NGA File No. 867612 December 10, 2012 Page 9 material prior to placement. Tlie exposed sub�rade should be compacted to a non-yielding � condition. The sloping area above the wall locations should be bencl�ed ro allow placement of the walls and any wall backfill placenlent. Temporary and Permanent Slopes Tempoi-ary cut slope stability is a function of inany factors, including t�he type and consistency of soils, depth of the cut, surcl�argc loads adjacent to the excavation, lengtll of tiine a cut remai�ls open, and the presence of surface water or groundwater. It is exceedingly difiicult under these variable conditions to estimate a stable, temporary, cut slope angle. Therefore, it should be the responsibilit�y of the coutractor to maintaiil safe slope configuratioiis sulce they are continuously at the job site, able to observe tlie soil and groundwater conditions ei7countered and able to monitor the �Zature and condition of tlie cut slopes. The following infonnation is provided solely for tlle Uenefit of the owner and otl�er design consultants and should ilot be consti-ued to imply tl�at Nelson Geotechnical Associates, Ine. assumes responsibility for job site safety. Job site safety is the sole responsibility of the project contractor. For planning purposes, we recoinmeud tliat temporary cuts in tlle on-site and undocunlentcd till soils be no steeper thai� 2 Horizontal to 1 Vertical (2I-I:1 V). If significailt growldwatet- seepage, wet soil conditions or surCace water 11ow were encountered, we would expect tl�at 1lattcr iiicli�lations would be necessary. We reconunend that cut slopes be protccted fi�oii� erosion. Tlle slope protection ineasures may inclticle covei-ing cut slopes with plastic sheeting and diverting surface runoff away fi-om the top of cut slopes. We do not recoiml7end vertical slopes for cuts deeper than four feet, if worker access is necessaiy. We reconuilend that cut slope heights and inclinatious confom� to appropriate OSHA/WISI�A regulations. Permanent cut and structural fill slopes should be no steeper than 2H: l V. However, flatter inclinations may be rec�uired in areas where loose soils are encountered. Pennanei�t slopes should NELSON GEOTECHNICAL ASSOCIATES, INC.