Compaction, permeability and direct shear tests for investigation of the biopolymer effect on the engineering behavior of clayey soils.

The improvement techniques for soil engineering properties are needed in geotechnical applications. For example, the natural soil mixtures (bentonite-sand and bentonite-zeolite) in the landfill liner applications lose their function and performance and become permeable because of changes in ionic concentration, temperature and water level. Hence subsurface layers contaminate and economical cost increases. There are a lot of methods for the improvement of soils; however some of them cannot effectively works for improvement and the others are too expensive for practical purposes. Moreover, the applications of biopolymers in geotechnical and geoenvironmental engineering are relatively unexplored, compared to other areas. In this study, xanthan gum, chitosan and chitin biopolymers were used which are used in ındustry frequently. In this study, two different types of biopolymers, xanthan gum and chitosan, with different proportions were used in the compaction, permeability and direct shear tests for investigation of the biopolymer effect on the engineering behavior of clayey soils. In the experiments, the mixtures of kaolin, bentonite and sand were used with 0.25%, 0,5%, 0.75%, and 1% concentrations of xanthan gum, chitosan and chitin biopolymers. As a results of this study, the effect of biopolymers were investigated on the engineering properties of soils. Some sugesstions are given for the use of biopolymers on ground improvement applications.In this study, the mixtures of natural kaolin, bentonite and sand mixtures were investigated in the presence of 0.25%, 0.5%, 0.75% and 1.0% concentrations of three different biopolymers namely, xanthan gam, chitosan and chitin. The used biopolymers were increased the dry density of the 40% sand, 40% kaolin ve 20% bentonite mixtures. There was no significant change on the optimum water contents. There was 2.7% increase in dry density of 40% sand, 40% kaolin ve 20% bentonite mixture in the presence of 1% chitosan. When xanthan gum and chitosan biopolymers were compared there is similar degree of improvements in dry denstities. In the presence of different concentrations of xanthan gum the decrement was observed in the permeablity of 70% sand-30% kaolin mixtures. The 1% concentration of xanthan gum decraesed the permeablity almost 30 fold. The effect of xanthan gum decreased with time because of degradation effect. However, after three weeks xanthan gum still have signifant effect on the permeability. Chitosan also have similar effects like xanthan gum, it decreased the permeability characteristics of the mixtures. In general, 0.25% concentration can be used as the optimum concentration for permeability applications. The biopolymers increase the cohesion and internal friction angle of the samples. The 1% concentration of xanthan gum and chitosan increased the shear strength parameters of the samples around %10-15. The results of this study have shown that the biopolymers can be used in dams and landfill liner applications. However, the effect of degradation should be investigated for long term applications of the biopolymers.