4704 HARBOR LN 2018-01-02 MF Import

Geotechnical Engineering Evaluation Anderson Landslide Repairs ' 4704 (Harbor Lane Everett, Washington September 15, 2009 I NGA File No. 816909 Page 5 During our site work, we explored the near surface soils and observed outcroppings and exposures along the ravine slopes. It appears, based on our explorations, observations and the existing geologic interpretations, that the site is underlain at depth by fine-grained deposits, consisting of interbedded silt and sand, generally considered non -glacial in origin. Ilowever, areas of overlying glacial till and the sandier phase of the advance glacial outwash also exist within and nearby this site. These types of interbedded/interworked glacial deposits can affect the geologic interpretations. The compact nature of these soils indicates that they were probably compacted by the weight of the glacial ice during the Vashon glaciation period, and have gencrahy very good to high internal strength when not saturated. However, our interpretations indicate that locally lower strength to less cohesive sandier portions of the glacial and interglacial deposits have affected this portion of ate area, and specifically this particular site. Explorations: The subsurface conditions within the site were explored on August 26, 27, and 28, 2009 by drilling five geofechnical borings ranging in depths front 12.5 to 31.5 Icet below the existing ground surface using a portable drill rig. We also excavated three hand auger holes on the slope. The locations of our borings and hand augers are shown on the Site Plan in Figure 2. The soils were visually classified in general accordance with the Unified Soil Classification System, presented as Figure A-1 in Appendix A. The logs of our borings are attached to this report and are presented as Figures A-2 through A-6 in Appendix A, and the hand augers are presented as Figure A-7 in Appendix A. We present a briel'suntntary of the subsurface conditions in the following paragraphs. ror a detailed description of the subsurface conditions, the logs of the borings and hand augers should be reviewed. Drilled Borinec: Borings 1 through 4 were drilled on the slope side of the house, and Boring 5 was drilled near the front of the house. At the surface of Borings I, 2, and 3, which were drilled along the top of the steep slope, the encountered approximately 2.0 to 4.0 Icct of very loose, light brown silty fine sand to fine sand with silt. We interpreted this material to be undocumented fill and highly weathered material. Below the loose material in Boring I, we encountered medium dense to very dense, silty fine sand with varying amounts of gravel. This material was interpreted to be native glacial soil. Boring 1 was terminated in the silty sand at a depth of 12.5 Iect below the existing ground surface. Below the fill in NELSON GEOTECHNICAL ASSOCIATES, INC.