Bacterial Treatment of Remoulded Fine-Grained Cohesive Soils

Abstract

The main objective of this research is to study the effect of microbial-induced calcite precipitation on the geotechnical properties of fine-grained soils. For this purpose, a high plastic cohesive soil retrieved from a special zone of Tabriz city, located in east Azerbaijan province in Iran, and two cultured Pseudomonas and Bacillus bacteria with various concentrations were added to the soil samples, and then compaction and consolidated undrained triaxial tests were performed on them. The results of compaction tests indicated that bacterial treatment did not affect meaningfully maximum dry density of soil, while it reduced the optimum moisture of soil from 30.46% up to 23.83%. Moreover, bacteria inclusion increased shear strength of soil about 27.0% and 35.0%, respectively, for consolidation pressures of 200 kPa and 300 kPa. SEM analysis revealed that after treatment, the soil particles arrange in an aggregative structure with a number of small pore spaces and form a few large pore spaces. The formation of the new structure in treated soil has led to strength improvement. In general, calcite participation led to an increase in shear-induced pore water pressure, which is due to formation of calcite crystals between clay particles. Obtained results revealed potential ability of these bacteria in treatment of fine-grained soils, but it needs more researches in this field.