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-lo- <br />coripressibility but when ~+etted some of the samples settled or <br />• expanded. The erratic volume change potential may be due to the <br />variable soil type and density. The lower density soils com- <br />pressed or collapsed when wetted and the higher density soils <br />swelled. Swelling pressures were measured to a maximum of about <br />5000 to 7000 psf which is between about 2 to 6 times the effec- <br />five overburden pressure. As a result of development on the <br />site, a change in soil moisture conditions should be expected. <br />The upper natural soils have adequate strength to support <br />shallow spread footings. Because: of erratic soil volume change <br />potential, there is a risk of sig~~ificant differential foundation <br />movement, The movement could cause structural damage to the <br />building. Other foundation types and subgrade treatment could be <br />• used to reduce differential foundation movement potential. <br />Drilled or driven piling, a heavily reinforced mat, and a box <br />type spread Cooting system are possible foundation types that <br />should result in lower movement. subgrade treatment may consist <br />of placing structural fill below a spread footing foundation to <br />achieve a more uniform bearing condition. The potential for <br />subgrade heave due to shallow wettings should be substantially <br />reduced by the structural fill. <br />The designer should be aware of the foundation movement risks <br />when selecting the foundation system. Dynamic loading may also <br />contribute to the foundation settlement. Rased on our limited <br />knowledY;e of the proposed dewatering structure, it appears that <br />spread footings placed on compacted structural fill can be used <br />. with the settlement potential as presented below. Recommenda- <br />Chen & Associates <br />