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L • Field penetration tests conducted in the clay material indicate that it has a very stiff to <br />hard consistency, the lowest two results being I1 and 15 blows per foot, and the average more <br />than 40 blows per foot. The in-place density of the material averaged around I IS pounds per <br />cubic foot. In-place moisture content varied between 10 and 24 percent with an avenge of about <br />15 percent, which is considered somewhat dry of optimum for the material. The samples of silty <br />clay from Borings 1-4 were low expansive upon wetting at a pre-load of 500 pounds per square <br />foot (psf). The more plastic clay samples, particularly from Borings 5-10, were considerably <br />more expansive, with percent swell measured at 8 to 13, considered highly expansive. <br />Unconfined compressive tests revealed generally high internal cohesion strength, with test <br />results from 900 psf (low strength) to almost 29,000 psf (high strength), with the avenge of 12 <br />tests being 12,800 psf (high strength). Unconsolidated, undrained (UU) triaxial compression <br />• tests on a composite sample of avenge silty lean clay soil from the upper 25 feet of Boring 17 <br />revealed an angle of internal friction of 23 degrees and an apparent cohesion of 2,200 psf. UU <br />testing on deeper samples of clay from a depth of 55 feet in Boring 17 and 75 feet in Boring 23 <br />indicated friction angles of 6 and 4 degrees and cohesion of 4,350 and 3,050 psf, respectively. <br />Clearly, most of the clays on this site would be considered sensitive to loss of strength and/or <br />volume change upon increases in moisture content or pore pressure. However, where the soils <br />are dry of saturation, they have considerable strength via high internal stresses and negative pore <br />pressures. Where structures are founded on the clays, it is important that foundations bear in <br />materials of stable moisture content. <br />Our strength testing is necessarily conducted on small samples, chosen to represent the <br />avenge conditions for the matrix soils. The overall nature of the gravelly and cobbly clay will <br />10 <br />