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4.2. Shallow Foundations <br /> The planned building addition is underlain by 2 to 8 feet of compressible loose to medium dense fill soils. <br /> Unsuitable fill soils and highly weathered glacial till deposits will vary across the planned building addition. <br /> We anticipate that competent dense glacial till deposits will be encountered about 2 feet below existing <br /> site grades (boring B-3) at the south end of the planned addition and about 8 feet below existing grade <br /> (boring B-1) at the north end of the planned addition. <br /> We recommend that foundations for the building addition be supported on: (1) undisturbed dense to very <br /> dense glacial till, (2)structural fill extending to dense glacial till deposits, or(3)at least 2 feet of structural <br /> fill. Exposed subgrade soils consisting of fill or weathered glacial til! ';ir)uld be compacted prior to placing <br /> the 2-foot-thick structural fill layer below footings. The structural liii zone should extend at least 2 feet <br /> beyond the edges of the foundations. <br /> Footings supported on undisturbed dense to very den . : glacial till Pahosits may be designed using a <br /> maximum allowable bearing pressure of 5,000 psf. F, oti ;gs supported on rr_ictural fill that extends down <br /> to undisturbed glacial deposits or is supported 'tr l oot least 2 feet of comp ,.;lied structural fill may be <br /> designed using a maximum allowable bearing pressuro of 3,000 psf.The allowai it hearing pressures may <br /> be increased by one-third for short duration loads such O:, wind or r;oi•mic events. <br /> The design frost depth for the Puget Su,ii t,J ,.,.ra is 12 inches; therefore, we recommend that all exterior <br /> footings be founded at least 18 inches boirw IL st adjacent Li shed grade. Interior footings should be <br /> founded at least 12 inches below bottom of,lob or adj is .''.nt finished. ide. For shallow foundation support, <br /> we recommend widths of at least 18 and 24 I ches, respoci ively,for cc o;nuous wall and isolated column <br /> footings supporting the proposed building additihci. <br /> 4.2.1.Foundation Settlement <br /> We estimate that the post-construction settlement of footings founded on the undisturbed dense glacial till <br /> deposits or oc feet of structural fill c , I,.rommonded above, will be less than 1 inch. Differential <br /> settlement l etween coin,rorably loaded column io()iings or along a 25-foot section of continuous wall <br /> footing sih{OL ld be less than inch ovc ra distance of 25 feet. We expect most of the footing settlements <br /> will occur a t leads are applied. I or li-,turbed soils not removed from footing excavations prior to <br /> placing concrete result in addi i trial settlement. <br /> 4.2.2.Lateral Resistance <br /> Lateral loads can be resit,I by live resistance on the sides of the footings and by friction on the base <br /> of the footings. Passive resist, e should be evaluated using an equivalent fluid density of 350 pounds <br /> per cubic foot (pcf) where footings are poured neat against native soil or are surrounded by structural fill <br /> compacted to at least 95 percent of MDD, as recommended. Resistance to passive pressure should be <br /> calculated from the bottom of adjacent floor slabs and paving or below a depth of 1 foot where the adjacent <br /> area is unpaved, as appropriate. Frictional resistance can be evaluated using 0.35 for the coefficient of <br /> base friction against footings. The above values incorporate a factor of safety of about 1.5. <br /> If soils adjacent to footings are disturbed during construction, the disturbed soils must be recompacted, <br /> otherwise the lateral passive resistance value must be reduced. <br /> GEOENGINEERS_g December6,2021 Page4 <br /> File No.24459-003-00 <br />