Laserfiche WebLink
<br />:1...32 <br /> <br />Dispersion. - -The terms dispersive clay or dispersion refer to the <br />stability of soil aggregates when exposed to water. Dispersive soils <br />are highly erosive. When dispersed soils are exposed to weathering, <br />they are easily distinguished by field observation. They tend to <br />melt down like sugar, develop land forms that resemble typical "bad- <br />land" relief (macro or micro) and form "slick spots" that are gener- <br />ally bare of vegetation. <br /> <br />e <br /> <br />There are several tests that identify dispersive soils. <br /> <br />1. The field "crumb" test identifies dispersive soils by the formation <br />of a colloidal cloud around a small clod of moist soil dropped into <br />distilled water or very dilute sodium hydroxide. <br /> <br />2. The laboratory dispersion test identifies most dispersive soils by <br />comparing the amount of 0.005 rom. material in a suspension without <br />de flocculating chemicals to the total amount of 0.005 rom. material <br />determined by mechanical analysis. <br /> <br />3. The field dispersion test is an abbreviated version of the labora- <br />tory dispersion test. <br /> <br />4. Chemical tests identify dispersive soils by comparing the amount of <br />soluble sodium and the total salt content in the saturation extract <br />or pore fluid of the soil. <br /> <br />None of these tests always correlates with the others or with field <br />performance. It is sometimes necessary to run all tests in order to <br />properly evaluate the adverse effects of dispersive soils. <br /> <br />e <br /> <br />Whenever dispersion is suspected in an area, laboratory tests should <br />be run to verify and evaluate the problem. <br /> <br />Soluble salts. - - Soils that contain considerable soluble salts, <br />particularly gypsum, are highly erodible and may slough badly. It <br />appears that the recrystallization of gypsum and other salts during <br />sedimentation results in an open, honeycombed soiL structure that may <br />be compared to loessial materials. These soils have sufficient stab- <br />ility to stand on vertical banks as long as they are dry, but they <br />slough and erode rapidly when exposed to moisture. Sodium salts have <br />a dispersive effect on soils and generally increase the erodibility <br />of soils. Although high soluble salt content in soils tend to keep <br />the soil in a flocculated or aggregated (erosion resistant) ~tate, <br />these salts would gene~ally me removed or leached back into channel <br /> <br />e <br />