Performance Studies of Microbial Induced Calcite Precipitation to Prevent the Erosion of Internally Unstable Granular Soils

Abstract

Migration of fine particles within internally unstable granular soils under water seepage flow (suffusion) is one of the most common causes of earth infrastructures’ failure. To assess the ability of Microbial Induced Calcite Precipitation (MICP) to prevent the segregation in an internally unstable soil, internal erosion tests were conducted upon soil samples treated by bacteria and cementation solutions. MICP experiments were carried out with concentrations of urea/CaCl2 equal to 1.4 M. Volumes of injected bacteria solutions were equal to the volumetric water content corresponding to different tested degrees of saturation (Sr): 30, 60 and 80%. Cementation solutions were injected three times for each sample. Biochemical properties of MICP were examined to predict bacterial movement through soil matrices as a function of Sr. The amount of the CaCO3 produced was examined depending on Sr. Following their treatment, samples were saturated and submitted to increment of hydraulic gradients varying from 0.1 to 10. Eroded fine particles masses, seepage flow rates and effective hydraulic gradients along samples were measured throughout the experiment. The results of our study pointed out that MICP stabilized internally unstable granular soils as the critical gradient went from 0.7 for untreated samples to 5 for biocemented samples.