Performance evaluation of lime and microbial cementation in residual soil improvement

Abstract

Microbially Induced Calcite Precipitation (MICP) is a technique that utilizes the concept of microbial involvements in calcium carbonate precipitation within the soil matrix structure. This leads to the cementation of the soil particles and consequently improving the strength and stiffness of the soil. In this study microbial carbonate precipitations were induced in tropical residual soil via urea hydrolysis. An isolate of urease active strain of Klebsiella pneumoniae UM123 was used to precipitates calcite into the soil with the aim of improving the engineering properties of the soil. Bacteria concentrations of 2.9 × 106 cfu/ml and 0.5 M cementation reagents concentrations were used to evaluate the strength and hydraulic conductivity of the soil. Treatment durations of 24, 36, 48 and 60 hours were used in the study. The results obtained indicated a general increase in the strength and reduction of hydraulic conductivity of the treated soil with the increase in treatment durations up to 48 hours. It was also revealed that the higher the amount of calcite precipitated the more the strength improvement and reduction of hydraulic conductivity. Appropriate percentage of lime that satisfied the initial consumption and fixation capacity of the soil sample was found to be 6%. Though, combination of MICP with lime does not significantly improve the strength at early stage of the treatment, it has substantially reduced the hydraulic conductivity of the treated residual soil particularly at the early curing period when lime alone increases the hydraulic conductivity.