Ageing Effect On Shear Strength Of Mixed Kaolinite-Bentonite And Sand Clay Minerals

Abstract

Fine-grained soils are mainly composed of kaolinite, montmorillonite, illite clay mixtures in various ratios beside sand in the natural world. Only demographically significant areas are being studied for the shear behavior of these soils, which takes a lot of time and money. Clay's basic behaviour demonstrates a lower shear strength magnitude, In order to solve this issue, extensive research was done to boost clay's shear strength. In view of increasing shear strength of clay , in this experimental study , different proportions of clay minerals were taken  namely kaolinite ,bentonite  and natural sand, which depict the kaolinitic , montmorillonitic and sand in nature. At the outset, out of 3 ingredients, Bentonite was kept constant at 10% and other ingredients namely kaolinite & sand were varied with minimum and maximum fines in the mix proportions. Further similar sets of experimentation were done with Kaolinite & Sand variations as explained, each time keeping the bentonite proportion constant at variation from 20 to 80%. Each sample with the pre-decided proportion was tested for its unconfined compressive strength by fixing the OMC and MDD as per required value which were done precedingly. Prepared samples were kept in plastic pouch for the period of 30,60 and 90 days .  These samples were also observed  for SEM analyses for microstructure study. From this experimental analysis it was observed that the unconfined compressive strength and shear parameters like  cohesion, and angle of internal friction were increased with different ageing span varying from zero to 90 days and also analysed in terms of their respective microstructures.

The results shows that the trend of increasing shear strength with 0 to 90 days of ageing effect  as well as increase in Bentonite content in the mix proportion .  Unconfined compressive strength (q_u) increased from 78 kpa to 110 kpa(for minimum bentonite of 10%)  with increase in ageing from 0 to 90 days and observed  140 kpa to 204 kpa with the increase of bentonite in the mix proportion (maximum content of 80%) subjected to ageing effect from 0 to 90 days . From SEM analysis it was observed that crystalline white lumps and agglomerate structure were formed with increasing bentonite content in the mix proportion and ageing effect from zero to 90 days. It was responsible for the increase in strength and shear parameters of the mix proportion.