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FOUNDATION SUPPORT <br /> . We recommend ffiat all footings be founded on eithcr the dense, native till or compscted <br /> structura! fill overlying dense till. If loose to medium dense weathered till is encountered at <br /> footing subgrade levds, it witl be nesessary to compact the wwthered till to s��uctu�al fill <br /> i� . speciGcations. Btcause of the dissimilar settlement chazacteristics of the dense till and fill soils, <br />� it will be imperadve that loose native soils and fill be compacted to shvctural fill specifications. <br />� Continuous strip foo6ngs should be at lea.et 18 inco�wide; isolated spread footings should have <br />� a minimum width of 2 feet. We recommend that all exterior footings be founded at least <br />. 18 inches below the lowest adjacent fmished grade. 'Ihe base of interior footings should be <br />" ' foundaJ at least 12 inches below the finished flcwr grade. <br /> • An aliowable soil bearing pressure of 2,500 psf(Fwunds per squaze foot) may be used for <br /> � design of isoiated and continuous spread footings founded on compacted weathered till or I <br /> structural fill in acwrdance with our reaammendations. M alluwable soil bearing pressure of <br /> 4,000 psf can be used for footings bearing on the dense till. Once �:e specific building location, I <br /> elevation and foundation design have been establisbed, we recommend that we evaluate the <br />. footing lacations to see if it may be possible to determine where this higher allowable bearing � <br /> pressure can be udlized to make the foundation more cost-effective. '[t�ese values apply ro the <br />� sum of ali dead plus long-te�m live loads, excluding the weight of the footing and any everlying <br /> 1; • . bac�1L These values may be increased by one-third when eanhquake or winu loads a!e <br />• considered. <br />;: 'She seWement of foundation elements bearing on dense till will be nominal (less than <br /> 1/4 inch). The ezpected settlement will increase as the structural fi!1 underlying the footings <br />' ' increases. We expect the maximum total settlement of footings founded on structural fill <br /> r' - prepaze� as recommended will be i.ss than about 1 inch. Thecefore, providr.d there is not an <br />' abrupt transidun between foodngs underlain by fill and the dense native till, we ezpect differential <br />• aettlemente will be limded to about 'b inr,�hetween comparably loaded isolated column footings <br /> or within 50 feet along continuous strip footings. If a sharp transition between the fill and the <br /> dense till is encountered during construction, the uansition can be made more gradual by <br /> ezcavating some of the dense native till and replacing it with wmpacted strucmral fi31 or taking <br /> the footings founded on weathered soil/structural fill deeper. We reco:nmend that the prepazation <br /> of the shallow foundatioa subgrades and structural fill placement be observed by a tepresentative <br /> of our staff so that our recommendations can be modified as the actual field conditions <br /> encountered during construction wazrant. <br /> FLOOR SLAB SUPPORT <br /> Slahs-on-grade should bs underlain by 2 4- to 6-inct; thickness o:capil(xry break marerial <br /> placed over the dense native till or compacted structural fill placed after compietion of the <br /> rer;ommended site prepazation procedures. Again, it is imperative that there is not a shazp <br /> ' uvisition between dense till soils and structural ftll underlying the floor slab. <br /> G e o E o y i n e e r � 7 file No.0975-017-R73/061993 <br />