The Effect of Exopolymers on the Compressibility of Clays

High compressibility of wetland clays causes subsidence, which threatens many natural habitats and coastal infrastructure. One method of combating subsidence is hydraulic pumping of dredged sediment, but this deposits high water content slurry that is highly compressible. Exopolymers can improve the stability of sediment without danger to the environment because they are naturally produced, high molecular weight polysaccharides. This preliminary study used two biopolymers, guar gum, a neutral polysaccharide, and xanthan gum, a negatively charged polysaccharide, as exopolymer analogues to determine how they change the consolidation behavior of clays, specifically a pure kaolinite. A series of 1D consolidation tests were performed on clay and biopolymer mixtures with varying biopolymer concentrations. Results show that compressibility is decreased (C_c reduced from 0.614 to 0.422) when the clay particles and biopolymer strands form a highly linked hydrogen bonding network, while compressibility is increased (C_c increased from 0.614 to 1.058) through electrostatic repulsion between the clay and biopolymer and through biopolymer displacement of clay particles. Overall, biopolymer amendment can reduce compressibility if applied at low concentration.