A STUDY ON THE STRENGTH AND COMPRESSIBILITY BEHAVIOUR OF ORGANIC CLAYS FROM KUTTANAD, KERALA

 

ABSTRACT: This paper presents the study on the strength and compressibility behaviour of soil samples collected from Thakazhy, Thayankary, Kandamkary, and Champakulam villages belonging to Kuttanad taluk in Kerala. The influence of organic matter on the strength and compressibility behaviour is also presented. The compression indices and the liquid limit of soils increased with increase in organic content. Also, the influences of various pore fluids like water, NaCl, CaCl₂ and FeCl₃. 6H₂O solutions of different concentrations on the index and strength properties are presented. Regression equations for compression index based on simple parameters obtained in the laboratory are developed.

Following were the conclusion of the study.

The natural water content of undisturbed soil samples collected from Thakazhy, Thayankary, Kandamkary, and Champakulam vary from 23 % to 50% with organic content varying from 1.25% to about 7.66%. The soil samples from all the places except Thakazhy fall in the USCS classification of clay with high compressibility, and that from Thakazhy being clay with low compressibility due to the higher percentage sand content in the soil collected from Thakazhy.

Consistency limits tests conducted on modified soils from Thakazhy, Thayankary, Kandamkary and Champakulam, whose organic content has been varied by the addition of starch solutions, indicate that there is an increase in the liquid limit and plasticity index, while plastic limit and shrinkage limit decrease with increase in % organic content.    Consolidation tests on these modified soils indicate that with increasing % organic content the compression index was found to increase.

When different concentrations of NaCl, CaCl₂ and FeCl₃.6H₂O solutions were used as the pore fluid in oven dried soil samples, the liquid limit of all the samples show a decreasing trend as the pore fluid concentration increased. At higher concentrations the diffused double layer is suppressed causing decrease in liquid limit. The liquid limits of oven dried samples amended with organic content show an increasing trend whereas the plastic limits and shrinkage limits were found to be decreased.

The UCC strength of the oven dried samples mixed with NaCl, CaCl₂ and FeCl₃.6H₂O solutions increased marginally and then decreased with the increase in their respective concentrations.

Regression analysis of results for compression index and other basic soil parameters for undisturbed soil samples from the four locations gave way to a new empirical relationship between compression index and initial void ratio which suited the results in the best possible way.