An investigation of bacterial calcium carbonate precipitation and its effect on permeability, strength, and compressibility of organic soil

Bacterial calcium carbonate precipitation (BCCP) become a new an attractive soil improvement method in the last three decades. Most of the studies were carried out on granular soil and very encouraging results were obtained. But this new improvement technique was not used for organic soil that was known as a problematic soil in geotechnical applications. This laboratory scale work investigates feasibility of this new improvement technique in organic soil. For this purpose, two-stage works were carried out. In the first stage, ureolytic bacteria were isolated from local soil and its ability for calcite precipitation was investigated. In the second stage, bacteria (B. pasteurii) were induced into the organic soil with treatment solution that was injected into the organic soil by gravity for a specified time intervals. The amount of precipitated calcite was determined at the end of the treatment. Shear strength, consolidation and permeability tests were performed on treated and untreated samples to investigate effect of calcite precipitation on geotechnical properties of the organic soil. The test results showed that ureolytic and calcite precipitating bacteria can be isolated from local soils. Microscopic scale investigation indicated that solid calcite particles were precipitated in the organic soil. It was found that the amount of precipitated calcium carbonate in treated organic soil was increased about 20% by weight. Also, the test results revealed that the BCCP method increased the shear strength and reduced compressibility and permeability of the organic soil. The finding of the study encourages the geotechnical engineers to use this technique as an alternative improvement method for the organic soil.