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<br />-10~ <br /> <br />Permeability - - The sealing ability of the clay samples has been <br />tested in two ways. <br />1 . The layer permeability test measures the ability of a llilYer <br />of clay to hold water. This test is pointed at the blanketing uses of <br />clays in sealing ponds and short sections of canal. From the layer <br />permeability test it is possible to calculate the approximate thickness of <br />clay or bentonite needed. For example, if it is assumed that comprehensive <br />testing of a clay from a developed deposit has revealed an average permea- <br />bility rate (K) of 1.0 x 10-3 or .001 it/day. Then if (1) the water <br />- - - - <br />level drop (Q!A or drop/day) .!! to be restricted to .2.::J!!fday, and (Z) <br />the water depth (~.) in the pond or canal is 5.0 feet, the following cal- <br />culation can be made: <br /> <br />Thickness of clay <br />layer required <br /> <br />.. <br /> <br />Kx W.D. x lZ <br />drop/day <br /> <br />.001 x 5 x lZ <br />.. <br />0.1 <br /> <br />.. 0.6 inches <br />- for <br />conditions <br />assumed. <br /> <br />Z. The filter permeability test is pointed at the float.in or wash-in <br />applications of clay. It tests the ability of a thin cake of clay, deposited <br />from a mUddy water dispersion, to hold water. The test results are in <br />volume (milliliters) per minute. A small value of loss is desired but how <br />small is yet to be determined by additional laboratory and field trial work. <br />Mixability -- The mixability index test measures the relative speed <br />with which a clay sl,lmple will soften and wash away when subjected to flowing <br />water. This procedure is pointed at the wash-in or float-in methods of <br />clay application in canals. A low index figure means that the clay is hard <br />to mix, whereas a high figure meaUI> e~tlJr mixing. Some clays may indicate <br />very favorably low layer and filter loss permeability results, while at the <br />same time show extreme resistance to dispersing in water. TheFuller's earth <br />type of bentonite displays this characteristic that seemingly limits its use <br /> <br />1034 <br />