2702 59TH ST SW 2024-07-05 - Laserfiche WebLink

Geotechnical Engineering Evaluation Miller Property Slope Stabilization Everett, Washington NGA File No. 1333322 July 1, 2022 Page 2 5. Conducting numerical limit -equilibrium modeling on representative slopes affected by the stabilization methods to provide a quantitative evaluation of slope stability. 6. Providing our opinion on the cause of the recent instability within the site. 7. Providing recommendations for permanent slope stabilization, including recommendations for design and construction of a retaining wall, and slope reconstruction and protection measures, as warranted. 8. Providing recommendations for drainage and erosion control improvements, as well as long- term maintenance of the slope. 9. Documenting the results of our findings, conclusions, and recommendations in a written geotechnical report. SITE CONDITIONS Surface Conditions The site is situated on the northern flank of a tributary ravine to Powder Mill Gulch, situated to the west of the site. The site is currently occupied by a single-family residence, playset area, and concrete driveway extending from 59th Street SW within the central, southwestern, and north -central portions of the site, respectively. Surrounding the existing structures, the property is generally vegetated with grass yards areas, landscaping shrubs, and young to mature trees along the southern and eastern fringes of the site. The parcel is bordered by 591h Street SW to the north, a neighboring residential property to the west, and City of Everett - owned vacant property to the east and west. Geomorphology: Regional geomorphic features which may be imperceptible at ground level can be inferred remotely through aerial imagery and data. Light Detection and Ranging (LiDAR)-derived imagery shows mathematically interpolated ground surface elevations through vegetation interference. In general, landslides are characterized on these images by hummocky, undulating topography and steep headscarps. The most apparent geomorphic features in the area are the system of ravines that have heavily eroded the generally level, plateau -like uplands and created numerous peninsulas of land on which the subject property and overall residential development is situated. On the slopes below the site our interpretation indicates mostly diffuse erosional sloughing -type landslide features and locally oversteepened or more active conditions. An overview of the neighborhood on LiDAR also indicates a smooth and level concave feature immediately on the top of slope and below the residence structures, which we anticipate may be indicative of previous grading activities in support of the residential development. NELSON GEOTECHNICAL ASSOCIATES, INC.