High-pressure compaction studies (up to 200,000 p.s.i.) were conducted on kaolinite, illite, and montmorillonite clays and a natural organic colloid of Iranian origin, gum tragacanth. The remaining moisture content in percent (dry weight) was plotted versus the logarithm of pressure in p.s.i. For kaolinite clay there is a straight-line relationship between 40 and 200,000 p.s.i. (M=33.9-5.96 log P), and for illite clay the relationship between the moisture content (%) and pressure (p.s.i.) can be expressed by the formula M=50-8.7 log P. For montmorillonite clay, on the other hand, there is a break in the curve at about 1,000 p.s.i. and from 1,000 to 200,000 p.s.i. the curve is a straight line: M=104-18.06 log P. For gum tragacanth, moisture versus pressure curve has a "hyperbolic" shape; and it appears to be harder to squeeze water out of the crystalline clays than it is from the amorphous gel at low pressures. The moisture versus pressure curves of the more plastic (higher swelling) clays have steeper slopes than those of the clays having low plasticity; however much longer time is needed for the establishment of equilibrium in more plastic clays.

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