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DAVID L.NELSON AND ASSOCIATES, INC. � <br /> Consulting Enginccring Gcology - <br /> September 28, 198� <br /> Project No. 7884 <br /> Page five <br /> li <br /> soils prior to placement of granular structural fill up to � <br /> finish slab subbase . A base of at leasi: 4" of concrete sand I <br /> or pea gravel should be placed over a plastic vapor barrier 'I <br /> prior to placement of the slabs. The enclosed Subdrain and I <br /> Backfill Scheme graphically shows the recommended slab prepara- I <br /> tion within the structure areas. � <br /> Site development within the three story retail/office building _ <br /> and southern most retail building may require additional exca- <br /> vation to achieve 3esired foundation stabili2ation: We suggest <br /> that the areas be totally stripped of. all unsuitable surface I <br /> organic material, fill and loosened soils, and backfilled using <br /> structural fill up to proposed footing elevation. It appears <br /> that approximately 4' to 5' of unsuitable soils occur surficially I <br /> and would require removal . Alternately, the foundation areas i <br /> onl�� could be excavated down to the natural soils and replaced �I <br /> within footing trenches up to finish footing elevation, if some I <br /> risk of interior slab settlement is acceptable . The footing <br /> trenchers or total excavation should be performed at least 6" I <br /> ir_to the na'cursl soils prior to structural filling. Footing ,I <br /> trenches, iY utilizad, sliould be at least 8' wide for the 4' to i <br /> $' excavation, and extended to 10' wide within areas where �'I <br /> additional e:ccavation to reach the natural soils is necessary. <br /> Struc'�ural fill intended for use within these areas should <br /> consist of granular pit-run type soils, generally apnroved for ' <br /> use within the area. Structural fill should be placed in 6" <br /> to 8" lifts and compacted to 95/ of ASTM D-1557. Slab preparation <br /> for the footing trench excavation alternative should anticipate i <br /> removal of the surficial organic soils and placement of strur.tural <br /> fill up to slab base elevationo Slabs should then be performed <br /> as shovm on the enclosed Subdrain and Backfill Scheme . Antici- ' <br /> pated maximum allowable soil nre�sures of 2500 psf should be i <br /> expected for foundations placed a minimum of 18" below finish <br /> grade within tlie prepared struc'tural fill�footing trench areas . <br /> ' I <br /> � <br /> I <br />