EFFECT OF BENTONITE DRILLING FLUID ON SKIN RESISTANCE OF THE PILE

Abstract

Pile foundations are found as an economical and effective foundation system for high rise buildings. With increasing use of long straight shafts necessitated accurate assessment of uplift resistance. Since last 70 years, for the construction of bored cast-in-situ piles, bentonite has been used as a borehole stabilizer. The action of bentonite in stabilizing the sides of bore holes is primarily due to thixotropic property of bentonite which permits the material to have the consistency of a fluid when introduced into a hole. When left undisturbed it forms a jelly like membrane of low permeability on the excavated borehole wall around the soil particles, helping in its stabilization but in return reduces the frictional resistance of pile. To check the effect of bentonite support fluid on skin resistance of the pile, the project work has been carried out which includes laboratory as well as experimental works. In laboratory work, influence of various parameters such as concentration of bentonite, time without agitation, effect of addition of poly-fluid and alum and silt content on the rheological properties has been studied and the dissertation also presents the results of a set of bentonite–sand interface shear tests carried out using bentonite support fluids, and a real life problem of pile is physically modeled and pull out test has been performed on a fabricated laboratory setup. The field test on modeled concrete piles has shown reduction in uplift capacity of the pile due to the formation of soft filter cake.