4801 HARBOR LN 2018-01-02 MF Import

Geotechnical Engineering i ort Johnson Residence Addition Everett, Washington J-1280 27 February 2002 Page 4 Based upon conditions observed at the site and our analyses, the project is feasible from the geotechnical perspective. However, the presence of low density fill and native soils, and the proximity of the dwelling to the slope extending toward Belvedere Lane will necessitate the use of extended foundations in order to reduce the potential for foundation settlement, as well as foundation displacement in the event of a landslide. Our conclusions and recommendations regarding environmentally sensitive areas, foundations, and drainage are presented below. Seismic Criteria Figure 16-2 presented in the 1997 Uniform Building Code classifies the subject site as being within Seismic Zone 3. Based on the subsurface conditions encountered at the site and published geologic literature, it is our opinion that a Soil Profile Type of Sc should be used to describe the average properties within the upper 100 feet of soil beneath the site. This designation describes soils that are considered very dense with a shear wave velocity of 1,200 to 2,561 feet per second, Standard Penetration Test values greater than 50 and an undrained shear strength greater than 2,000 psf. Environmentally Sensitive Area Considerations Title 19, Section 2.080 of the Everett Municipal Code defines geologic hazard environmentally sensitive areas. Based upon conditions encountered on site and our analysis, it is our opinion that the slope extending below the dwelling toward Belvedere Lane meets the EMC jurisdictional criteria for a steep slope hazard and an erosion hazard. Our analysis also indicates that the slope is at risk of landsliding during a seismic event due to the combination of soil conditions and slope inclination. Section 37.080 of the EMC indicates that a 25-foot buffer shall be established from the top, toe, and sides of sensitive areas. The northeast comers of the proposed dwelling addition intrude slightly into the 25-foot steep slope buffer, as shown on Figure 1. The existing deck is located within the buffer, and at least two of the proposed new deck supports are shown within the buffer. 1 :ovided that the recommendations for foundation construction presented herein are followed during construction, it is our opinion that construction of the proposed dwelling and deck additions within the 25-foot steep slope buffer will not decrease the stability of the slope or have an adverse effect on the slope. The recommended dwelling foundation construction methodology is expected to reduce the risk of landslide activity within the dwelling footprint. Specific foundation design and construction recommendations are presented subsequently. Slope Stability Considerations The explorations completed for this study disclosed very loose and soft fill and native soils above medium dense to very dense native granular soils. The interpreted distribution of soils along a subsurface profile extending through the steep slope below the dwelling is shown on Figure 2. The subsurface profile location is shown on Figure 1. We analyzed the stability of Zipper Zeman .associates. Inc, 18905 33' Avenue West, Suite 117 LSnnwwd. Wuhington 98036 (425) 771 - 3304 CTI