Improvement in some Geo-mechanical Properties of Silty Sand by Microbially Inuced Calcite Precipitation Treatment

Abstract

Microbially-induced calcite precipitation (MICP) is an innovative technique in geotechnical engineering field that utilizes the microbiological activities of microorganisms to precipitate minerals in to the soil mass. For this research the technique was employed to improve the geo-mechanical properties of silty sand. The main objective of this study is to determine the effect of urease producing bacteria on the engineering properties of microbially-stabilized silty sand. An isolate of urease producing bacteria was used to precipitate calcite in to the soil for improving the strength and reducing the hydraulic conductivity of the soil. The performance of this improvement was assessed through measurement of properties such as; unconfined compressive strength and hydraulic conductivity of the microbially-stabilized silty sand. Variables such as treatment duration (24, 48, and 72 hours), reagent concentration (0.1, 0.25, 0.5, and 0.75Mole), and suspension density of urease producing bacteria of (1x10⁵cell/ml, 1x10⁶cell/ml, and 1x10⁷cell/ml) were considered during the MICP treatment. The results indicated a general increase in strength and reduction in hydraulic conductivity with increasing concentration of cementation reagent and increasing bacterial suspension density at higher treatment duration. The optimum improvement in strength and reduction in hydraulic conductivity were both obtained at 72 hours treatment period with maximum concentration of 0.75M cementation reagent and 1x10⁷cell/ml suspension density of bacteria.  A corresponding 295% improvement in strength and 93% reduction in hydraulic conductivity were achieved.