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 7 All construction operations and drainage improvements planned as part of this project should be planned and completed in a manner that enhances the stability of the steep slope, not reduces it. Any excavation spoils generated during site improvements should not be stockpiled on site but rather promptly hauled away. Also, all current and future runoff generated within the site should be collected and routed to a permanent discharge location at the bottom of the slope, or to an approved drainage system. Under no circumstances should water be allowed to concentrate or flow uncontrollably over the slope. The vegetation cover on the slope should be evaluated for compatibility with desired slope stability conditions, and a vegetation management plan should be devised to enhance slope stability. The proposed retaining wall and the slope should be monitored on an on -going basis after construction especially during the wet season for any signs of instability, and corrective actions promptly taken should any signs of instability be observed. Lawn clippings and any other household trash or debris should never be cast over the slope. Any future plans for structures near the slope or modifications to the slope should be specifically evaluated by NGA and approved by the City of Everett. Retaining Wall Design and Construction The proposed new retaining wall should consist of 3-inch square driven steel tubing or 2-inch pin piles bridged using pressure -treated timber lagging. We understand that the proposed retaining wall will be designed as a cantilever wall but may need to incorporate tieback anchors consisting of grouted or mechanical anchors. The new retaining wall should generally be located along the top of the steep slope in the approximate location of the existing timber wall. The final extent and heights of the wall should be determined by your structural engineer. However, we recommend that the exposed portion of the wall not exceed eight feet in height. The approximate location and cross section detail of the proposed retaining wall is shown on the Schematic Retaining Wall Site Plan Schematic Pin Pile Wall Detail in Figure 8. The retaining wall should be designed by an experienced structural engineer licensed in the State of Washington. We recommend that the square tubing or 2-inch pin piles be galvanized extra strong (Schedule 80) steel pipe sections driven into place using a hand-held, 140-pound jackhammer or larger. The piles should be spaced at a maximum distance of four feet, and should be embedded a minimum of 15 feet into the competent slope material. Piles that do not meet this minimum embedment criterion should be rejected, and replacement piles should be driven after consulting with the structural engineer on the new pile locations. Our explorations encountered loose undocumented fills within the proposed retaining wall NELSON GEOTECHNICAL ASSOCIATES, INC.