1921 W MUKILTEO BLVD 2018-01-02 MF Import

Preliminary Geotechnical Engineering Evaluation 1919 Mukilteo Boulevard October 20, 2005 NGA File No. 718805 Page 6 our recommendations are incorporated into the design and construction of this project. The site slope is considered stable with respect to deep-seated failures. There is a potential for shallow sloughing and erosion event- to occur on the steeper portions of the slope. We have provided recommendations for structure setback and deep foundation embedment to lessen the impacts of the proposed development on the slope and to allow for normal slope recession during a reasonable life span of the structures. This is further discussed in the Structure Setback subsection of this report. We recommend that the residence foundations be designed to provide a minimum effective setback of feet between the face of the slope and the bottom of the downslope footing line. This is intended to reduce potential impact of the development on the steep slope, and to also reduce the risk of undermining the residence should any slope failures take place. To satisfy this setback requirement, the downslope footing lines could be supported on reinforced concrete piers extending below finished grade to provide the effective setback as shown on Figure 13. The need for concrete piers will depend on the final location of the residence with respect to the steep slopes. We are available to provide recommendations for pier foundation design parameters if needed as the project plans develop. The footing lines further from the slopes could be designed as conventional shallow foundations. These footings should extend through any loose surficial soil or undocumented fill and be founded on the underlying medium dense or better native soils or structural fill extending to these soils. Medium dense soils should typically be encountered approximately five feet below the existing surface. NGA should be retained to evaluate foundation bearing soil at the time of construction. The soils encountered on this site are considered moisture -sensitive and will disturb easily when wet. To lessen the potential impacts of construction on the slope 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 slope, 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.