4801 HARBOR LN 2018-01-02 MF Import

Geotechnical Engineering k ,ort Johnson Residence Addition Everett, Washington J-1280 27 February 2002 Page 8 recommended as 12H, where H is the foundation wall height in feet, and 12H is expressed in pounds per cubic foot. Surcharges due to sloping ground, adjacent footings, vehicles, construction equipment, etc., must be added to these values. The above equivalent fluid pressures assume that the backfill was compacted to approximately 90 percent of the modified Proctor maximum dry density. Additional compaction adjacent to the wall will increase the earth pressure, while a lesser degree of compaction could permit post construction settlements. Foundation Considerations — Deck We understand that the new deck will be supported by isolated columns. The proposed deck foundations located downslope of the existing residence may be subject to disturbance in the event of a landslide, in our opinion. In order to reduce the potential for deck foundation disturbance in the event of a landslide it would be necessary to mitigate the landslide potential by regarding the slope or by implementation of structural means as discussed earlier. Our scope of services did not include analysis of landslide mitigation alternatives. Potential deck foundation disturbance as a result of landsliding would also be reduced by constructing the foundations to bearing within the at least medium dense native granular soils below the soft and loose fill and native soils, similar to the methodology described above for the dwelling addition foundation. It would be necessary to remove the existing very loose to loose fill and native soils from the slope between the deck foundations and the existing dwelling in order to reduce the potential for deck foundation disturbance in the event of a landslide. Fred Baxter & Associates has indicated that disturbance of the deck four- ..s may be tolerable. Deck support that ignores potential slope movement and its adverse effects on foundations may be achieved by installing conventional drilled piers. We recommend embedding drilled piers into the dense to very dense granular soils that underlie the fill material and loose to medium dense native soil. An allowable end bearing value on the order of 3.5 DB may be utilized, where D = embedment depth (in feet) into the dense to very dense granular soils below the soft and loose fill and native soils, and B = pier diameter (in feet). Allowable skin friction of that portion of the pier embedded in the dense to very dense soils may be taken as 0.5 tsf. Temporary and Permanent Cut Slopes Temporary excavations will be made to construct the dwelling addition foundation. Temporary slope stability is a function of many factors, including the following: 1. The presence and abundance of groundwater; 2. The type and density of the various soil strata; 3. The depth of cut; 4. Surcharge loadings adjacent to the excavation; 5. The length of time the excavation remains open. Zipper Zeman Associates. Inc. 18905 33' Avenue West, Suite 117 Lynnwood. Washington 98036 (425) 71 •3304