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- 17 - <br />A satisfactory alternative would be spread footings placed on the <br /> • <br />natural, coarse granular material designed for a maximum bearing <br />pressure of 8,000 psf. A minimum footing dimension of 3 feet is <br />rewmmended. Footings should be placed belay potential scour depth. <br />Riprap material, such as currently in place, ouuld also be used to <br />reduce potential swot depth. Abutment walls should be designed to <br />resist an equivalent lateral earth pressure of 35 psf per foot of <br />depth above the water table and 80 psf per fwt of depth including <br />hydrostatic pressure below the water level. These pressures assume <br />compacted backfill material. Additional lateral pressures due to <br />vehia~lar traffic should also be considered. Unit weights can be <br />assumed as 125 pcf imist and :0 pcf submerged. If extensive wing <br />walls are provided, a positive joint should be provided between the <br />abutment to allow for same differential imvemnt. Resistance to • <br />sliding can be calculated utilizim~ a base friction coefficient of <br />0.5. Badcfill material would oonsist of granular soil having a <br />maximum 8-ind~ size and percent passing the 5200 sieve less than 58. <br />Subsoils encountered within the proposed treatment-site consist <br />of stiff to very stiff clays to the maximum depth drilled, 20 feet. <br />Results of swell-consolidation tests, presented on Figures 23 and 24, <br />indicate negligible swell potential and minor settlement potential <br />under natural ~misture and density conditions. However, a swell <br />potential is indicated if the upper moist clays were to bacons dry. <br />We understand that foundation loadings will be relatively light and <br />cut depth will be minimal. • <br />