Effects of Biopolymers on the Liquid Limit and Undrained Shear Strength of Soft Clays

Document Type


Publication Title

Bulletin of Engineering Geology and the Environment

Publication Date



Published online in: Bulletin of Engineering Geology and the Environment, August 2, 2022.


Little is known regarding the effectiveness of biopolymers in soil improvement, especially considering interactions among different clay minerals, porewater cations, and biopolymer polarities. This paper presents an experimental investigation of the effects and effectiveness of four biopolymers of varying polarity and structure (xanthan gum, guar gum, carrageenan, and dextran), on the liquid limit, undrained strength, and thixotropic hardening of soft clays consisting of predominantly kaolinite with lesser montmorillonite. The liquid limits were measured using the standard Casagrande cup method. Fall cone penetration was adapted to determine the development of undrained shear strengths of the samples with time and after remolding. Clay samples were amended by the four biopolymers with a range of concentrations as well as varying NaCl in the pore fluid. Results show different biopolymers affect the consistency and strength behavior of different clays to varying extents; such changes are dominated by the constituent clay minerals’ surface charges as well as the biopolymers’ polarity and structure. Addition of biopolymers to clays results in an immediate gain in undrained shear strength that stabilizes, and some biopolymers exhibit a concentration saturation. Moreover, the neutral biopolymers (guar gum and carrageenan) behave fundamentally differently from anionic xanthan gum and cationic dextran. Advantages and limitations of potential applications of biopolymers in terms of effectiveness, costs, and ease of application are discussed. This research can aid the decision-making processes for coastal geotechnical engineers to determine which of the tested biopolymers presents a safe, cost-effective soil improvement additive for reducing erosion of coastal cohesive soils.