Bore cast by polymer and bentonite

The action of bentonite in stabilizing the sides of bore holes is primarily due to thyrotrophic property of bentonite. The thyrotrophic property of bentonite suspension permits the material to have the consistency of a fluid when introduced into a trench or hole. When left undisturbed it forms a jelly like membrane on the borehole wall and when agitated it becomes a fluid again. In the case of a granular soil, the bentonite suspension penetrations into sides under positive pressure and after a while form a jelly. The bentonite suspension then gets deposited on the sides of the hole and makes the surface impervious and imparts a plastering effect. In impervious clay the bentonite does not penetrate into the soil, but deposits only as thin film on the surface of hole. Under such condition, stability is derived from the hydrostatic head of the suspension. The bentonite powder and bentonite suspension used for piling work shall satisfy following requirements: a) the liquid limit of bentonite when tested in accordance with IS 2720 (Part 5) shall be 400 percent or more. b) The bentonite suspension shall be made by mixing it with fresh water using a pump for circulation. The density of the freshly prepared bentonite suspension shall be between 1.03 and 1.10 g/ml depending upon the pile dimensions and the type of soil in which the pile is to be bored. The density of bentonite after contamination with deleterious material in the bore hole may rise up to 1.25 g/ml. This should be brought down to at least 1.12 g/ml by flushing before concreting. c) The marsh viscosity of bentonite suspension when tested by a marsh cone shall be between 30 to 60 stokes; in special cases it may be allowed up to 90 s. d) The pH value of the bentonite suspension shall be between 9 and 11.5
But in these days polymer are used because it take less time for mixing and having high viscosity property its provide good lubrication with water so that’s why it is more beneficial in piling and no flushing is required when it used.
Minimum viscosity of polymer in piling is =45stokes