The Effect of Exopolymers and Void Ratio on the Erosional Resistance of Cohesive Sediments

Erosion threatens coastal infrastructure and natural habitats throughout the United States. Conventional soil amendments, such as lime and Portland cement, are effective for improving soil strength and resistance to erosion, but exopolymers have the potential to improve sediment stability without the environmental risks of caustic or toxic compounds. This paper describes how the erosional resistance of a pure kaolinite clay is enhanced using two exopolymer analogues, guar gum, a neutral polysaccharide, and xanthan gum, an anionic polysaccharide. A cohesive strength meter (CSM) is used to measure the critical value of shear stress τ_oCr of high water content muds, representative of newly placed hydraulically pumped fill. Guar gum produces a nine fold increase in τ_oCr, while void ratio increases of 9% result in approximately 25% decreases in τ_oCr. Xanthan gum provides much less improvement than guar gum in cation free mixtures because of electrostatic repulsion, but sodium and calcium cations in the pore fluid negate this effect. Practical applications of exopolymers for erosion control are discussed.