4626 HARBOR LN 2018-01-02 MF Import

r i Geotcchnical Engineering Evaluation NGA File No.853512 Fox Residence Underpinning and Retaining Wall Design August 3, 2012 Everett, Washington Page 7 The site soils are considered to be moisture -sensitive and can disturb when wet. We recommend that construction take place during the drier summer, months if possible. However, if construction takes place during the wet season, additional expenses and delays should be expected due to the wet conditions. Additional expenses could include the need for placing a blanket of rock spalls on exposed subgrades, construction traffic areas, and paved areas prior to placing structural fill. Wet weather grading will also require additional erosion control and site drainage measures. Some of the on -site soils may be suitable for use as structural fill, depending on the moisture and organic content of the soil at the time of construction. NGA should be retained to evaluate the suitability of all on -site and imported structural fill material during construction. Foundation Improvements We recommend that the foundation lines on ilia western and northern sides of the garage be supported on pin piles to transfer the vertical loads to the underlying competent materials below to limit any future movement and settlement damage to the foundations. The approximate extend of the areas to be underpinned is shown on Figure 8. Structural brackets should he used to attach the pin piles to the footing. The structural engineer should design the new foundation supports and determine the location of the supports based on the recommendations provided in this report. A qualified contractor specializing in foundation retrofit should be retained to complete the repairs. Considering the limited site access conditions, it is our opinion that the most feasible foundation underpinning system is 2-inch diameter pin piles dtiven to refusal using it hard operated 140-pound jackhammer. If large particles or debris are present within the fill, there is a possibility that this material may obstruct some piles at shallow depths. There should be contingencies in the budget and design for additional/relocated piles to replace piles that may be obstructed by larger particles such as gravels or cobbles. For 2-inch diameter pipe piles driven to refusal using a hand-held, 140-pound jackhammer, we recommend a design axial compression capacity of two tons for each pile. The refusal criterion for this pile and hammer size is defined as less than one inch of movement during 60 seconds of continuous driving. We recommend using galvanized extra strong (Schedule 80) steel pipe. Some of the piles may have to be driven at a batter from vertical to resist lateral forces. Final pile depths should be expected to vary somewhat and will depend out the nature of the underlying soils. The pin piles should advance a minimum of 10 feet in order to provide the recommended design capacity; however, actual pile depths will likely be greater than 10 feet. Piles that do not meet the 10- NELSON GEOTECHNICAL ASSOCIATES, INC.