Primary and Secondary Consolidation Characteristics of Chitosan-Treated Low Organic Clay

The occurrence of secondary compression is a peculiarity of soils rich in organic matter derived from plant remains. The ratio of secondary compression to primary compression (C_α/C_c) has been considered a valid parameter for predicting secondary compression behavior in peats or organic soils. In the present study, a low organic soil sourced from the Kuttanad region of Kerala State, India, has been studied for its consolidation characteristics. The inclusion of chitosan for the modification of compressibility is a novel method as it contributes to the recycling of 8 million tonnes of crustacean wastes yearly. One-dimensional fixed ring consolidation tests were conducted on samples treated with chitosan (at 0.5%, 1%, 2%, and 4% dosages added by dry weight of soil) and prepared at optimum moisture content (OMC) and maximum dry density (MDD) conditions. The increase in chitosan concentration reduced the compression index by 78% for 2% amended samples at a consolidation pressure of 50 kPa. With an increase in consolidation pressure up to 800 kPa, C_c increased indicating higher stiffness of the soil matrix. At 50 kPa, C_α declined to 0.007 for 2% and 4% chitosan which falls outside the normal range of organic soils. The variation in C_α/C_c was marginal with an increase in consolidation pressure and fell in the range of 0.03–0.05 at 2% chitosan which indicated the transformation of soil into inorganic material. The scanning electron microscopic images revealed that a flocculated and aggregated soil structure was observed with chitosan treatment up to 2% dosage. However, the higher concentration of chitosan particles led to aggregation with soil particles and resulted in interaggregate voids. Based on the study’s findings, crustacean biopolymers stipulate detailed research to explore their suitability for soil amelioration.