1617 EDGEMOOR LN 2016-11-10 - Laserfiche WebLink

McKinnon Residence Retaining Wall 1617 Edgemoor Lane Everett, Washington SCOPE NGA File No 910614 December 2, 2014 Page 2 The purpose of this study is to explore and characterize the site subsurface conditions, and provide our opinions and recommendations regarding the existing slope stability and proposed retaining wall. Specifically, our scope of services includes the following: 1. Review available soil and geologic maps of the area. 2. Explore the subsurface soil and groundwater conditions within the site and in the vicinity of the retaining walls using a limited -access drill rig. Drill rig was subcontracted by NGA. 3. Map the conditions on the slope, perform hand -tool excavations, and evaluate current slope stability conditions. 4. Provide recommendations for retaining wall design and construction. 5. Provide recommendations for drainage improvements. 6. Document the results of our findings, conclusions, and recommendations in a written geotechnical letter. SITE CONDITIONS Surface Conditions The site consists of an irregular -shaped parcel covering approximately 0.68 acres. The site is occupied by an existing single-family residence with a daylight basement within the gently sloping central portion of the site. The site layout within the vicinity of the residence is shown on the Schematic Site Plan in Figure 2. The site generally slopes gently to the northeast within the western and central portions of the site from Edgemoor Lane to the northeastern side of the residence. A level lawn area is located to the northeast of the residence with a short timber wall located along the top of a steep northeast- to east -facing steep slope. This steep slope descends from the northeastern side of the relatively level yard area at gradients in the range of 28 to 38 degrees (53 to 78 percent) to a creek located at the toe of the steep slope. The overall height of the steep slope below is approximately 125 feet. It appears that undocumented fill soils had been placed within the yard and slope areas along the top of the steep slope. This fill was likely placed during construction of the residence. The slope below the wall is generally vegetated with grass, thick underbrush, and young to mature evergreen and deciduous trees. A profile of the existing ground surface, and the interpreted subsurface conditions is presented as Cross Section A -A' in Figure 3. We did not observe surface or seeping water on the slope during our site visit on November 7, 2014. We also did not observe significant signs of global slope movement during our site visit. NELSON GEOTECHNICAL ASSOCIATES, INC.