FRICTIONAL RESISTANCE OF POLYMER FLUID AS A BOREHOLE STABILIZER

Abstract

Since last 60 years, for the construction of bored cast-in-situ piles, bentonite has been used as a borehole stabilizer, which forms a filter cake of low permeability around soil particles, helping in its stabilization. But the filter cake, required to be formed for borehole stabilization, in return reduces the shaft resistance of the pile, as it forms a soft interface layer between concrete and soil. To overcome the problems associated with bentonite as a stabilizer, in the present work polymers as a substitute has been analyzed. To achieve the objectives the effect of polymer fluid on the frictional resistance of pile has been studied. Laboratory tests were conducted to determine the effect of various parameters such as polymer concentration, silt content, bleaching powder etc. on the rheological properties of the drilling fluid. The results shows that a small amount of polymer can increase the marsh funnel viscosity of water as compared to bentonite. The effect of pH and time on the viscosity of polymer fluid helped to optimize the drilling fluid which was used to perform the direct shear test, with a layer of different concentration of polymer fluid along the predefined failure plane, to check its effect on internal angle of friction and cohesion of soil. A real life problem of pile is physically modeled and pull out test has been performed on a fabricated laboratory setup. The results of the pull out test marked decrease in the shaft resistance of pile with the increase in polymer concentration. The theoretical relations, given by various researchers, and the experimental results were then compared to give a modification factor ‘F’, depending on the internal angle of friction of soil.