A study of geotechnical applications of biopolymer treated soils with an emphasis on silt

Biopolymers are natural polymers produced by live microorganisms such as bacteria, yeast, and fungi. A major potential application of soil treated with biopolymers is in construction of impervious barriers which prevent or delay the transportation of hazardous materials and leachate to the surrounding environment. The focus of this thesis is on application of biopolymers, particularly xanthan gum, to silty soil matrices to reduce soil permeability through enhancement of soil aggregate binding and clogging.; Experiments were conducted on compacted samples of silt (Bonnie silt) treated with biopolymers. Samples were prepared using mixture of silt with either xanthan gum powder or xanthan gum solution, compacted both wet and dry of optimum. Laboratory experiments indicated that the permeability of Bonnie silt is reduced approximately 100-fold by application of xanthan gum solution to the soil. Similar results were obtained by mixing xanthan gum powder with Bonnie silt. The reduction in permeability of Bonnie silt was found to have a direct relationship with the percentage of xanthan gum powder in the soil. The application of other biopolymers such as sodium alginate solution to Bonnie silt, also resulted in a decrease in the hydraulic conductivity of the silt. Application of xanthan gum (2%) solution to Silver sand at moisture content of approximately 14 percent results in a decrease of about 100 fold in the sand's hydraulic conductivity.; Results of several long-term permeability tests (up to one year) of Bonnie silt treated with xanthan gum indicated that the reduction in permeability can be maintained. Similar results were obtained for long-term permeability tests on xanthan gum powder with Bonnie silt.; Triaxial shear strengths of compacted Bonnie silt samples were increased approximately 30 percent by mixing the silt with xanthan gum solution with similar non-brittle stress-strain behaviour. Sodium alginate additive was less effective than xanthan gum.; The test program clearly demonstrated the promise of this new technology for construction of impervious barriers using silty soils. However, some aspects of this technology remain a challenge such as practical and economical construction in the field and long term biodegradation.