Prof. D. N. Singh

SEEMA GURNANI

M.Tech.
Indian Institute of Technology Bombay, Powai, India gurnani.seema@gmail.com

SOME INVESTIGATIONS ON PARAMETERS INFLUENCING THE SOIL-WATER CHARACTERISTIC CURVE OF FINE-GRAINED SOILS

Establishment of the soil water characteristic curve, SWCC, is quite important for characterization of the fine-grained soils in their unsaturated state. As such, its accurate determination becomes essential. It has been demonstrated by earlier researchers that compaction efforts and water content, the type of the soil and its mineralogy, the void ratio, fabric and stress history influence the SWCC of such soils to a great extent. However, it should be noted that compacting such soils and retrieving specimens from the compacted soil mass, for suction measurements, is a tedious task and may not result in specimens with similar compaction state. Under these circumstances, soil specimens in the form of slurry, of adequate consistency, would be quite handy for suction measurements. However, the basic issues such as the initial water content and the thickness of these slurried specimens and how these parameters influence the SWCC has not been investigated in detail, yet. Also, it has been observed that SWCC is not a unique curve and it depends on whether the measured suction corresponds to the drying or wetting of the soil specimen. Usually, drying-path is adopted for establishing the SWCC of the fine-grained, mainly due to the ease of measurements of soil suction and corresponding water content. However, it has been noted that it is quite cumbersome to establish the SWCC based on the wetting-path. In this situation, AquaSorp Isotherm Generator (manufactured by Decagon Devices Inc., USA) has been found to be quite useful for establishing both drying- and wetting- path SWCCs. Incidentally, this device has been primarily employed for food products, powders and amorphous materials and hence its utility and limitations for characterizing such soils becomes essential.
With this in view, suction measurements were conducted with the help of a Dewpoint Potentiameter, a Pressure Membrane Extractor and the AquaSorp Isotherm Generator on commercially available Kaolinite (white clay) and Bentonite, by varying the initial water content and thickness of the slurries and the results have been evaluated critically. The study highlights the limitations of these devices and proposes some recommendations for their proper and effective utilization for precise suction measurements. Further, efforts have been made to develop a mathematical algorithm, which is user friendly and can yield wetting- and drying- path SWCCs, in the absence of these sophisticated devices, just by inputting the basic soil properties (viz., particle size characteristics, Atterberg limits), which can be determined, easily, in a conventional geotechnical laboratory.