1921 W MUKILTEO BLVD 2018-01-02 MF Import

II Preliminary Geotechnical Engineering Evaluation 1919 Mukilteo Boulevard I� October 20, 2005 NGA File No. 718805 Page 9 the top of the slope so that ample room is allowed for normal slope recession during a reasonab:e life span of the structure. In a general sense, the greater the setback, the lower the risk of slope failures to impact the structure. From a geological standpoint, the setback dimension is based on the slope's physical characteristics, such as slope height, surface angle, material composition, and hydrology. Other factors such as historical slope activity, rate of regression, and the type and desired life span of the development are important considerations as well. We recommend that structures placed on shallow spread foundations be set back at least 35 feet from the top of the steep slope. The downhill footing lines should be cast on competem native material at least three feet below the finished ground surface. For structures placed closer than 35 feet from the top of the steep slope we recommend the down slope footing lines be deepened to maintain an effective setback of 35 feet between the bottom of the footing and the face of the slope. This effecLve setback is shown on the Schematic Effective Setback Detail in Figure 13. To .,atisfy 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 residences with respect to the steep slopes. We are available to provide recommendations for pier foundation design parameters if needed as the project plans develop. We do not recommend construction closer than 25 feet from the top of the steep slope regardless of the effective setback from the face of the steep slope. We should be retained to evaluate the residence foundation setback distances and subgrade soil prior to placing foundation forms. Any proposed development within the setback area, other than light decks or patios, should be the subject of a specific geotechnical evaluation. Under no circumstances should water be allowed to concentrate on the slopes, during or after construction. Foundations The north footing line of the residence should be embedded or supported on drilled piers to maintain and effective setback of at least 35 feet from the face of the steep slope. We do not recommend that foundations be placed within 25 feet of the top of the steep slope. The portions of the foundation more than 35 feet from the top of the steep slope could be designed as conventional shallow spread foundations. NELSON GEOTECHNICAL ASSOCIATES, INC.