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, ' � ' � 1 � ' � � Geoteclulical Engineering Letter Alhussaini Slope Stabilization and Retaiuing Walls Everett, Washington NGA File No. 867612 Deceiilber ] 0, 2012 Page 10 be planted a�id the vegetative cover sl�ould be nlaintained until it is established. We should review plans and visit ille site to evaluate excav�tions for this project. Slope Improvements At a minimum, we rccomme�ld that slope improvements consist of removing all of the recently placed iill materials and improve thc resulting slope for permanent stability. Alter tl�e till has bee�1 removed Ii-ou� thc slope, surficial improven�ents or the terraced i-etaining walls cail be constructed as discussed in the Wall Design and Construction Recommendations subsection of this letter. Surficial slope i�nprovenlents �fter the fill has been removed should consist of coulpacting the exposed surface Co a non-yielding condition, placing suitable erosion control systenls on the prepared areas, and re-vegetating with deep-rooted drought-resistant plants. The actual improveinent methods for these areas will be higl�ly depended on the conditions eneountered during construction. We should work with your contractor to determine the best coul-se of action at tl�e tiiiie of coustruction. In general, we recominend that tl�e exposed soil after fi11 reinoval and compact�ion to a�ion- yiclding condition be covered with l�eavy duty jute netting. The jute netting should be stakcd at the top oi� tlle slope with 2- to 3-ioot long metal rcbar stakes that are either bent at the end or have a metal "T" welded to the end. "l�ile mat sllould be staked to the surface cvery iive Ceet. After tlie �natting is �laced, we recoi17il1endeci that deep-rooted vegetation be plaiited on the slope a�ld grass � seed be placed to re-establisl� vebetation growth. "I'he vegetation sliould be inaiiltaiiled until established. We recoiilmend a�nixtui-e of 25% each of the following vegetation: Snowber�y � (Syn�phoricarpos albus), Nootka rose (Rosa nutkana), Ocean Spray (Holodiscus discolor), and Orego�i-grape (Mai�l�onia nervosa). We should be retained to review and comillent on tlle slope � r ' �J � vegetation plan and observe the slope repairs. Wall Design a�id Construction Recommendations If a wall syste�u is elected to be placed on the slope after the uewly placed till has been ren�oved, the wall system sl�ould adhere to the design and coi7struction reconlmcndations presented in this letter and be impleineut�ed under tl�e supervision of NGA. NELSON GEOTECHNICAL ASSOCIATES, INC.