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Geotechnical Engineering Evaluation NGA File No. 870113 Packer Property March 11,2013 Retaining Walls and Steep Slope Evaluation Page 13 Everett;Washington In the case of the helical anchors, the contractor should determine the torque values required to achieve the desired capacity. However, the anchors should advance a minimum of 20 feet from the face of the wall and one anchor be tested to confirm design capacities. One anchor should be performance tested to 200 percent of the anchor design capacity. The performance test should consist of cyclic loading in increments of 25 percent of the design load, as outlined in the Federal Highways Administration (FHA) report No. FHWA/RD-82/047. The test location should be determined in the field, based on soil conditions observed during anchor installation. All other tiebacks should be proof-tested to at least 130 percent of design capacity. Wall Backfill and Slope Improvements We recommend that after the pin piles and tiebacks are installed, a 4-inch perforated PVC pipe be placed behind the base of the retaining wall that is allowed to flow through the face of the retaining wall to aid in drainage through the wall. The pipe should be surrounded by a minimum of one foot of drain rock and the drain rock entirely wrapped in a heavy-duty filter fabric prior to the placement of the rock spall backfill. The drain should be tightlined into the existing drain system or independently down to the base of the slope and adequately anchored to the slope. After the drain is installed, the loose soils from behind the entire extent of the wall should be removed and replaced with 2-to 4-inch rock spalls. Extreme care should be used as to not disturb the tiebacks or drainage during rock spall placement. The removed soils could be placed near the bottom of the slope as directed by NGA. Areas of exposed soils and substantial unstable debris, including, if possible, the extent of the slope onto the neighboring property, should be cleared of the unstable material, covered with erosion control matting, and then planted with deep-rooted plants. For the steep area directly below the new wall (20 feet or so) and, if possible, the portion of the slide and exposed areas on the neighbor's property, we recommend that the exposed soil be covered with heavy duty erosion control matting such as Tensar C350 Turf Reinforcement Mat, or equivalent. The erosion control matting should be staked to the surface at a minimum of five feet on center using 2- to 3-foot long metal stakes with a "T" welded to the end. After the matting is placed, we recommended that deep-rooted vegetation be planted on the slope and grass seed be placed to re-establish vegetation growth. The vegetation should be maintained until established. We recommend a mixture of 25% each of the following vegetation: Snowberry NELSON GEOTECHNICAL ASSOCIATES, INC.