University of Cambridge > > Engineering Department Geotechnical Research Seminars > Applicability of Microbially Induced Calcite Precipitation (MICP) for Soil Treatment

Applicability of Microbially Induced Calcite Precipitation (MICP) for Soil Treatment

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Microbially Induced Calcite Precipitation (MICP) is a recently developed technique for soil improvement. MICP is forging ahead demonstrating its efficiency and advantages as an alternative for the traditional techniques. The distinctive characteristic of the MICP is the in-situ occurrence of the precipitation reaction. Soil treatment with MICP involves introducing a specific biological activity of the soil before injecting a stable urea solution with a calcium source. The biological activity catalyzes the hydrolysis of urea introducing carbonate ions that lead to the precipitation of the calcite. The precipitated calcite binds the soil particles together and clogs the pores changing the engineering characteristics of the soil.

The optimization of the MICP process became possible on the controlled lab-scale experiments. Nevertheless, the applicability of the MICP on the field-scale is still determined by some common natural conditions like high pore-water pressure, nonuniform flow fields, and soil heterogeneity that have not received sufficient investigation yet. This study is focused on the assessment of MICP under these conditions in terms of the precipitation efficiency and the uniformity of precipitation profiles. This assessment was carried out employing a modified flexible-wall permeability test to allow for continuous monitoring of soil stiffness (represented as by shear wave velocity) and hydraulic conductivity. In addition, an upscaled radial model was used to resemble the radial flow systems used for the treatment in the field. The radial model was used also to study the MICP in heterogeneous soils. As the uniformity of precipitation is considered one of the major challenges in the field, the study investigated the use of surfactants for the improvement of MICP profiles.

The development of soil characteristics by MICP treatment was found to follow a phased general trend that has several implications for the applicability of MICP in the field. The feasibility of MICP for different geotechnical applications was revised based on this trend of change and the possible degrees of control. Implications for the field were also interpreted based on the correlations between precipitation profiles and the flow-fields. This study proposes a design approach for MICP treatment systems that is based on the initial hydrological system of the site defining a critical minimum seepage velocity as the main design parameter. This approach could serve the design purposes better than the comprehensive numerical modeling of the treatment process which is still facing obstacles due to the complexity of the involved processes in MICP .

This talk is part of the Engineering Department Geotechnical Research Seminars series.

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