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 6 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 cantilever pipe pile wall with timber lagging along the top of the steep slope. We understand that the anticipated exposed wall height may be on the order of two to three feet. However, the exposed height of the proposed retaining wall may be greater and may require tieback anchors to support lateral pressures associated with the retaining wall. If tieback anchors are needed, we recommend that they consist of grouted or mechanical anchors. We have also provided recommendations for improvements on the slope below the wall to lessen the potential for future sliding on the slope within the vicinity of the retaining wall. The approximate location of the proposed retaining wall along with a schematic detail of the new wall are shown on the Schematic Retaining Wall Site Plan and Schematic Pin Pile Wall Detail in Figure 8. Detailed recommendations regarding the proposed retaining wall design and installation have been included in the following subsections of this letter. We also understand that you wish to construct a garden shed within the back yard area in close proximity to the top of slope area. In correspondence submitted to us, we understand that you intended to support the proposed garden shed on a level pad supported by landscaping type concrete block retaining wall. In our opinion, placement of this type of wall within the sloping area and supporting the wall on the undocumented fill soils encountered within the area may lead to future settlement or even failure of such wall. If a garden shed is still proposed, we recommend that a level pad be created and supported by the same pin pile retaining wall recommended in this letter. 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. NELSON GEOTECHNICAL ASSOCIATES, INC.