Bio-Electrokinetic Improvement of Deltaic Soil

Abstract

In addressing problematic soils, geotechnical engineers employ two key strategies: compatibility and improvement. This study focuses on soft and CL deltaic sediments, and seeks to enhance cementation by investigating microbially-induced calcium carbonate precipitation (MICP). Sporosarcina pasteurii bacteria, together with a cementation solution (urea and calcium-containing salt), were electrokinetically injected into deltaic clay soil from the Telar River in Iran. The initial samples, with a dry unit weight (γd) of 12.75 kN/m³, underwent injections in two modes: simultaneous injection of the bacterial and cementation solutions and individual injection in a sequential order. Unconfined compression strength tests and laboratory vane shear tests were conducted to assess changes in soil strength parameters, while a consolidation test was performed to investigate alterations in soil settlement parameters. A comparative analysis with an electroosmosis control sample revealed a remarkable increase in compressive strength and undrained shear strength for MICP bio-electrokinetic improvement. Moreover, the consolidation test demonstrated that the compression index (Cc) and recompression index (Cr) exhibited a more pronounced decline in the simultaneous injection than individual injection. This highlights the dual impact of the bio-electrokinetic method, namely the enhancement of shear strength and the mitigation of settlement in deltaic clay soil. The calcium carbonate content was measured for the samples, and the results indicated a higher degree of participation for the samples subjected to simultaneous injection. Microstructure analyses were conducted on samples, and calcite and vaterite were observed in bio-cemented samples.