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Retaining Wall Installation Final Letter NGA File No.8710B13 Packer Retaining Wall February 17,2015 Everett,Washington Page 2 "Geotechnical Engineering Evaluation—Packer Property—Retaining Walls and Steep Slope Evaluation— Everett,Washington,"dated March 11,2013. During that study,we recommended a retaining wall within the ravine in the area of the landslide to stabilize the affected area along with drainage improvements and covering the slope within the vicinity of the new wall with erosion control material and vegetation. We subsequently prepared a plan review letter for the proposed retaining wall dated June 30, 2014 that provided recommendations for a shotcrete wall supported on pin piles and restrained using grouted tie back anchors. We have since monitored wall installation. Site Observations We monitored wall installation activities on a part-time basis from September 17, 2014 through November 21, 2014. Our observations during wall installation at this project were documented in Field Reports 1 through 11, which have been submitted to you. The wall is located along the lower tier of a series of tiered block walls within the steep slope ravine area to the north-west of your residence. We observed the installation of six grouted tieback anchors throughout the wall alignment. The tiebacks consisted of 4-inch diameter holes that were drilled to a depth of 40 feet behind the face of the excavation. The anchors were installed at an approximate angle of 20 degrees below horizontal. After the holes were drilled, 20-foot pvc pipe bond breakers were installed in the upper portion of the anchor along with threaded hollow metal anchor rods connected with threaded couplers to the depth of the drilled holes. Grout was pumped through the 32-mm diameter hollow steel anchor rods into the holes until the grout was observed flowing out of the drilled holes. After the grout was allowed to cure, we returned to conduct a load test on one of the grouted tieback anchors to verify the load carrying capacity. We conducted the test on Tieback A4. The tieback was tested in 25% increments of the design load to a maximum load of 150% of the design load of 9.9 kips. We observed minimal movement of the anchor during the testing and the hold periods, and the tested anchor appeared to perform well. In our opinion, all of the anchors were installed in accordance to the plans and our recommendations. We observed the installation of 11, 2-inch diameter schedule 80 piles that were driven with a 140-pound air hammer to a total embedment depth in the range of 7.0 feet to 10.9 feet below ground surface along the wall alignment. All of the piles were driven to the recommended refusal rate of less than 1-inch of movement in 60 seconds of driving. In our opinion, the pin piles were installed in accordance with our recommendations and the approved plans, and should support the wall. NELSON GEOTECHNICAL ASSOCIATES, INC. 3l � I