ARTIFICIAL INDUCEMENT OF DISPERSIVITY IN NON DISPERSIVE CLAY SOILS

Dispersive clay soils under certain conditions deflocculate, rapidly erode and flow with water. These soils may have disastrous consequences for earth fill dams or other hydraulic structures. In nature, dispersive soil forms in old landscapes by leaching and illuviation process over a long period of time. Ground water containing carbonate / bicarbonate of sodium is one of the contributing factors in the formation of sodic soil/dispersive soil in many regions. Dispersion of soil is a complex physical, chemical and mechanical process. It has been established by authors that in laboratory also it is possible to produce dispersive soil from non-dispersive clay soil in short duration of time. Artificial synthesis of dispersive soil is possible only, if exact and actual cause of dispersivity is known. Once the reason could be identified, detailed studies can be taken up for various possible geotechnical remedies for dispersive problem. Non dispersive clay soil of CI group was treated with soda activated multani mitti (, a commonly available ordinary grade bentonite soil, activated with soda (Na2CO3) by wet method). The XRD analysis of the of the sample revealed that clay soil contains montmorrilonite mineral. Clay soil sample was blended with soda activated multani mitti in various proportions and mixed with distilled water and placed in mechanical shakers for 36 hours to ensure maximum possible exchange reactions. The resulting composite product was subjected to soil dispersity tests such as crumb test, double hydrometer test and pin hole test. Chemical pore water extract test was not conducted because soda activated multani mitti was already rich with excess sodium carbonate. All the three dispersive tests responded positive results indicating soil has become dispersive. These test results were compared with similar tests conducted on normal soil samples where no dispersion was observed. In the other technique, non-dispersive clay soil (CI group) of soil was activated with soda in various proportions by keeping soda in low and controlled concentration. The clay soil contains montmorrilonite mineral (which is one of the necessary condition for dispersivity) was revealed by XRD analysis. Clay soil sample was blended with 1% soda and 2% soda (% by wt) thus keeping soda in low and controlled concentration and mixed with distilled water and placed in mechanical shakers for 36 hours to ensure maximum possible exchange reactions. To see the effect of soda concentration, soil was mixed with excess soda by wet method. The resulting composite product was subjected to soil dispersivity tests i.e., crumb test, and pin hole test. For 1% and 2% blended soda composite samples responded positive results indicating soil has become dispersive. For 20% blended composite sample showed no dispersivity. It has been concluded based on these studies that the presence of exchangeable sodium, calcium and montmorillonite are necessary for phenomenon of