1617 EDGEMOOR LN 2016-11-10 - Laserfiche WebLink

McKinnon Residence Retaining Wall NGA File No 910614 1617 Edgemoor Lane December 2, 2014 Everett, Washington Page 10 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 Drainage and Slope Improvements We recommend that after the pin piles are installed, a 4-inch perforated PVC pipe be placed behind the base of the wall and extended 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 crushed rock 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. If tiebacks are utilized, extreme care should be used, as to not disturb the tiebacks during fill placement. We should be retained to evaluate the crushed rock placement during construction. The areas along the top of the slope below the proposed wall should be improved by gently re -grading the over-steepened/loosened areas, removing the vegetative cover, compacting the exposed surface to a non - yielding condition, placing suitable erosion control systems on the prepared areas, and re -vegetating with deep-rooted drought -resistant plants. The actual improvement methods for these areas will be highly depended on the conditions encountered during construction. We should work with your contractor to determine the best course of action at the time of construction. We recommend that the exposed soil be covered with heavy duty jute netting. The jute netting should be staked at the top of the slope with 2- to 3-foot long metal rebar that has a metal "T" welded to the end. The mat should be staked to the surface every five feet. 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 (Symphoricarpos albus), Nootka rose (Rosa nutkana), Ocean Spray (Holodiscus discolor), and Oregon -grape (Manhonia nervosa). We should be retained to review and comment on the slope vegetation plan and observe the slope repairs. We also recommend that all residence downspouts and yard drains be investigated to understand where they are directed. We observed numerous PVC, and corrugated pipes placed along the steep slope to the NELSON GEOTECHNICAL ASSOCIATES, INC.