1907 W MUKILTEO BLVD 2021-11-15 - Laserfiche WebLink

Pearson Property Slope Stabilization NGA File No 945216 1907 West Mukilteo Boulevard February 19,2016 n /] Everett,Washington Page 10 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 soldier 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. 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 dependent on the conditions encountered during construction. We should work with your contractor to determine the best course of action at the time of construction. If any irrigation systems are located near or within the steep slopes they should also be abandoned and removed. Areas of exposed soils should be covered with erosion control matting, and then planted with deep-rooted plants. For the sloping areas directly below the new wall,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 (Symphoricarpos albus), Nootka rose (Rosa nutkana), Ocean Spray (Holodiscus discolor), and Oregon-grape (Manhonia nervosa). We should be retained to review and comment on final slope improvement plans and observe the slope repairs. The actual improvement methods for these areas will highly depend on the conditions encountered during construction. We should work with your contractor to determine the best course of action at the time of construction NELSON GEOTECHNICAL ASSOCIATES, INC.