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

Pearson Property Slope Stabilization NGA File No 945216 1907 West Mukilteo Boulevard February 19,2016 Everett,Washington Page 6 opinion, construction of a retaining wall should aid in stabilizing the top of slope area along the yard area and limit potential impacts associated with potential slope movements on the yard area and residence. Due to site constraints, and based on our explorations and site observations, we recommend the use of a "light" retaining wall to protect the top of the slope along the entire extent of the yard area, along with erosion control and drainage systems to be utilized below the new retaining wall. We have provided recommendations for design and installation of a new soldier pile wall with timber lagging and tie-back anchors to protect the top of the slope. The anchor system should consist of grouted tiebacks anchors or mechanical helical anchors. The approximate location of the proposed retaining wall along with a schematic detail of the proposed new wall are shown on the Schematic Stabilization Site Plan and Schematic Retaining Wall Details in Figures 7 and 8, respectively. Detailed recommendations regarding the proposed retaining wall construction have been included in the Retaining Wall Design and Construction subsections of this report. The surficial soils encountered on this site are considered moisture-sensitive and may disturb easily when wet. To lessen the potential impacts of construction and to reduce cost overruns and delays, we recommend that construction take place during the drier summer months if possible. If construction takes place during the rainy months, additional expenses and delays should be expected. These extra expenses could include additional erosion control and temporary drainage measures to protect the proposed development area including placement of a blanket of rock spalls to protect exposed subgrades, and the need for importing all-weather materials for structural fill. 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 NELSON GEOTECHNICAL ASSOCIATES, INC.