10200 25TH AVE SE Geotech Report 2018-01-02 MF Import

/ . � Proposed Modernization and Addirions tn Subsurface Fxplorruion, Geolagic Hazards, Eisenhower Middle Schoof and Geotechnica[Engineering Report Everett, Washington DesiRn Recommendatinns A representative from our firm should inspect the stripped/overexcavated subgrade and be present during placement of structural fill to observe the work and perform a representative number of in-place densiry tests. In this way, the adequacy of the earthwork may be evaluated as filling progresses and any problem areas may be wrrected at that tune. It is :mportant to understand that taking random compaction tests on a part-time basis will not assure uniformity or acceptable performance of a fill. As such, we are available to aid the owner in developing a suitable monitoring and testing program. 10.0 FOUNDATIONS Our explorations indicate that the foundation bearing stra[um, consisting of inedium dense to very dense till underiies the proposed buil j.ing area at depths ranging from approximately 0 to 7 fee[. Where suitable bearing stratum is shallow, conventional spread footings may be us;.d. If the existing fill is shallow, the fill can be recompacted Co a firm and unyielding condition and used for foundarion support. In those area� where the fill is deep or where space limitations or economic considerations make excavation to [he foundation bearing stratum impractical, we recommend the n;e of a deepened foundation system for foundation support. Jeotechnical design recommendatioas for conventional spread footin,� foundations, driven pipe piles, and GeopiersT"' or rock trenches are presen[ed belc�w. i0.1 Conventional Spread Footines Spread footings may be used for building support when founded on suitable native till, recompacted existing fill, or new structural fill placed as previously discussed. To limit differential setdements betwc,:n footings that bear on scructural ii;l and those on dense till, we recommend that an allowable foundation soil bearing pressure of 3,000 pounds per square foot (ps� be utilized for design purposes, including both dead and live loads. If higher bearing pressures are needed, a value of 5,000 psf may be used in areas where all footings are placed entirely on dense till. An increase of one-third may be used for short-terni wind or seismic loading. Perimeter footings should be buried at least 18 inches into the surrounding soil for � frost protection; interior footings require only 12 inches burial. However, all footings must penetrate to the prescribed bearing s[ratum and no footing should be founded in or above loose, organic, or existing fill soils. [t should be noted that the area bounded by lines extending downward at 1H:1V from any footin, must not intersect another footing er intersect a filled area which has not been compac:ed to at least 9� percent of ASTM:D 1557. In addition, a 1.SH:1V line extending down from any foo[ine must not daylieht because sloughing or raveling may eventually undermine the footing. 1'hus, footines should nut be placed near [he edge of steps or cuts in the bearing suils. Jmiunrr•?3, ZOOd ASSOClA7'ED E,IR7'f!SGENCES, LYC. ,tlT�d-REOJ:�faJ-Prt;•rttsi]2);'Jy'�ti�ItC!'-IY.K Page 14 i7