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� <br />C� <br />Adapt Engineering <br />Subgrade Verification: Footings or slabs-on-grade should never be cast atop soft, loose, organic, or <br />frozen soils; nor atop subgrades covered by standing water. A representative from Adapt should be <br />retained to observe the condition of footing subgrades before concrete is poured to verify that they have <br />been adequately prepared. <br />Bearin,g Sub r� ades: The proposed shallow spread footing system is expected to be founded on very dense <br />sand with gravel, crushed rock, and rock spalls. Before concrete is placed, any localized zones of loose <br />soils encountered in the footing subgrades should be compacted to a firm, unyielding condition, if <br />warranted by soil moisture conditions. Any uncontrolled fill material containing a significant amount of <br />organic or debris/deleterious materials within the basement footprint area will need to be overexcavated <br />and replaced with structural fill, as previously discussed. <br />Footin� Dimensions: For a poured-in-place, concrete slab-on-grade with thickened-edge footings, we <br />recommend that the spread footing elements be constructed to have a minimum width of l2-inches. For <br />frost protection, we recommend that the footings at this site penetrate at least 18-inches below the lowest <br />adjacent exterior grades, or deeper, according to Snohomisli County jurisdictional code. <br />Bearin�Pressure and Lateral Resistance: A maximum allowable static soil bearing pressure of 2,500 <br />pounds per-square-foot (ps fl may be used for thickened-edge pad footings designed as described above. <br />For the alternate equipment support pad design using a uniform thickness, structural slab-on-grade, we <br />recommend a�naximum allowable static soil bearing pressure of 750 psf across the pad area. These <br />bearing pressure values can be increased by one-third to accommodate transient wind or seismic loads. <br />An allowable base friction coefficient of 0.32 and an allowable passive earth pressure of 300 pounds per <br />cubic foot (pc�, expressed as an equivalent fluid unit weight, may be used for that portion of the <br />foundation embedded more than 1-foot below finished exterior subgrade elevation. These lateral <br />resistance values incorporate a minimum safety factor of 1.5. <br />Gradin� and Capp�: Final site grades should slope downward away from the structure so that runoff <br />water will flow by gravity to suitable collection points, rather than ponding near the structure. Ideally, the <br />area surrounding the structure would be capped with concrete, asphalt, or compacted, low-permeability <br />(silty) soils to reduce surface-water infiltration into the subsoils adjacent to/below the foundation. <br />Settlements: We estimate that total post-construction settlements of properly designed thickened-edge <br />footings bearing on properly prepared subgrades will be less than 1-inch, with differential settlements <br />approaching one-half of the total. For a structural slab-on-grade equipment pad with a uniform thickness <br />(without thickened edges), somewhat greater movements may be experienced. <br />Tower Mat Foundation <br />A mat foundation would provide adequate resistance to horizontal, axial and overturning loads associated <br />with the proposed tower, provided it is adequately sized and embedded. The following sections provide <br />our recommendations and comments for mat foundation design and construction, in the event that this is <br />the preferred foundation option for the proposed tower. <br />AT&T Mobility c/o Ryka Consulting May 5, 2014 <br />Adapt Project No. WA14-18929-GEO Page 6 <br />