Effect Of Additives on Geotechnical Properties of Soil in Relation to Erosion Generation Under Simulated Rainfall Conditions

The vulnerability of soil erosion towards erosion may be reduced by having a good vegetative cover over the soil surface, slope improvement and improving soil properties so that it is not easily detached and transported. However, establishment of proper vegetative cover is time taking process as it takes time for a seed to germinate and attain maturity. As an alternative approach, if soil resistance is increased by increasing the shear strength of soil against erosive forces offered by eroding agents, the soil system will become capable of withstanding the detachment of its particles on the application of shear stress. Under this practice, an additive is mixed to the soil which increases the shear strength of soil.

Accordingly, in this study, additives namely jute fibre and guargum and their combinations were mixed with soil in different proportions to study various geo-technical properties such as dry density, optimum water content, California bearing ratio (CBR) and tri-axial shear parameters. There were nine treatments for which CBR values were determined. for two stages i.e., for the1^st day of treatment and on the 4^th day after the treatment. The tri-axial test was performed to obtain values of shear parameters at three confining pressures of 1kg/cm², 1.5kg/cm² and 2 kg/cm² for a particular percentage of additives.

To produce rainfall a small size portable rainfall simulation system was developed in the laboratory which was1m x1m in size and operated from a height of 5 meter. The simulation system was calibrated for producing rainfall intensities of 12.8 cm/h and 17.5 cm/h for water pressures of 0.4 kg/cm² and 0.5 kg/cm² which occurred almost uniformly over the entire test plot. The soil was treated with guargum having 0.3%, 0.5%, and 0.7% concentration by weight and with jute fiber having 0.3%, 0.5%, and 0.7% by weight and there combinations.

The recorded observations clearly revealed that as the value of shear strength of soil increased, the soil loss rate/ sediment outflow rate decreased for every combination of land slope and rainfall intensity. It was also found that for a particular value of cohesion and angle of internal friction, the runoff rate increased with rainfall intensity for every land slope while the sediment concentration and sediment outflow rate increased with rainfall intensity as well as land slope.