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Geotechnical Engineez-ing Eti�aluation Packer Property Retauung Walis and Steep Slope E��aluation Everett, t�ashingtan NGA File No. 8701 I3 March I I, 2013 Page 12 fact�r of sa%ty of 2.0. The upper four feet of pile embedment shauld be neglected when calculating the passive resistance due to the presence of loose maierial on the slope. iiebacks Generai: Ttiese systems could include drilled, grouted tiebacks, or mechanically installed ancliors such as Manta Ray or Helical anchors. We recommend that one of the anchors be tested ta a minimum of 200 percent of the design laads to confirm design values. We recommend that measurements be made bv the contractor zn the field at the time of tieback installation to verify that tiebacks do not encnunter any existing structures or underground utilities. No-Load Zone: The aizchor portion of all tiebacks must be lacated a sufficient distanee behind the walt face to de�Telop resistance ��zthin a stable soil �nass. We recammend the anchorage be obtained behind an assumed na-load zone. The na-laad zone is deftned by a line extending horizontally from the base oi the wall back towards the residence a distance of �ve feet. The line should then extend up from tlie base elevation at an angle from the horizontal of 60 degrees. We expect that some undocun�ented fill may exist beyond the no-load zone. We therefore recc�mmend that t13e anchors be a minimum of 20 feet long. We recoinmend that we monitor sc�il conditions during anchor installation in order to evaluate adequate penetration into competent soils. Soil Design Values: The tiebacks will iikely terminate in glacial soils below the walls. For use in design of the anchors, we estimate an allowable �-out to soil ad�iesion of 1,500 pounds per square foot (ps fl. Load carrying capacities on the arder of 10 kips or inore could be achieved usin�; �- to 14-inch diameter helical anchors installed successfully, Load carrying capacities anywhere between 4 and 20 kips could be achieved usin�; Manta Ray anchors installed successfully, depending on the size of the anchor. We recom�nend, however, that we review anchor design and proposed instaIlation methods. We should also observe anchor installation and testing. 'Tietaack �nstaifla#ion and Testi�g: The contractor should be responsible for using equipment suited for the site conditions. �Ve do not recommend tlie use of open-hole methods for the purpose of installing the tiebacks due to the potential for soil caviug. Secondary grouting to increase soil adhesion may be used; howe�>er, if secondary arouting is used, the anchors should be tested using the methods outlined for the performance testing. NELSDfV GEO�ECHNICAL ASSOCIATES, IIdC.