The given soil’s strength and intrinsic properties are major parameters that guide the decisions during the conception of a construction work. Soil improvement techniques offer engineers a framework of tools that allows interfering into soil’s structure in order to enhance its properties. A whole new field in geotechnical engineering has therefore been developed aiming at the conception and implementation of soil improvement techniques targeting to specific areas and foreseen improvements.
One such technique is cement grouting and it is being implemented in several applications including slope stability works, embankments, marine structures, foundations of typical buildings etc. Nevertheless, cement-grout has aroused concerns mainly around the potentially pollutant chemical agents employed. The foreseen improvement passes through an erosive process entailing the injection of viscous fluids under high pressures, thus destroying the initial state of the soil to replace it with a mixture of cement and grains forming a cement column. The improved area is limited to the diameter of this column and in this sense the technique needs to be repeated multiple times at a given area to scale-up its positive effects.
Biologically induced calcite mineralization has been recently brought into focus as an alternative cementation mechanism for soils. The whole process lies on the metabolic activity of unicellular microorganisms that are responsible for generating those conditions that allow for the formulation of calcium carbonate crystals to take place. The technique has its base at two chemical reactions; the hydrolysis of urea catalyzed by the enzyme urease, produced by the bacteria strain Sporosarcina pasteurii, and the calcite precipitation. This knowledge is put to use in an emerging grouting technique called microbial induced calcite precipitation (MICP). By temporarily regulating the concentration of bacteria and chemical constituents in a soil, a new engineering material can be generated through the nucleation of calcite crystals inside the soil matrix. Understanding, controlling and predicting this alternative environmentally friendly soil reinforcement technique, exposes innovative applications, such as restoration of weak foundations, seismic retrofitting, erosion protection, seepage flow or pollution mitigation and construction of floating beaches.
Research around this promising technique at the Laboratory of Soil Mechanics, EPFL, focuses on the conception of a geo-mechanical model to describe the enhanced behaviour of the bio-treated soil and on the adaptation of the teto quantify the resulting bonding effect with respect to the calcite content.
Research group for Bio-improved soils:
PhD Research Projects
Efficient Long-Distance Treatment of Soils with Microbially Induced Calcite Precipitation: from micro to macro: Ariadni Elmaloglou
In pursuit of innovative and more environmentally-friendly geo-engineering solutions for soil stabilization, Microbial-Induced Calcium Carbonate (CaCO3) Precipitation (MICP) has emerged as an alternative to traditional grouting techniques. MICP harnesses microbial activity that facilitates the formation of calcium carbonate precipitations that fill the pores and can improve the mechanical properties of the soil. MICP has been extensively studied in the macro-scale but the need for upscaling in real engineering problems requires further control and prediction on the time and location of precipitates, as well as their size, shape and the thermodynamic stability of polymorphs, in order to achieve an homogeneous MICP treatment over a long distance. The need for answering fundamental questions regarding the micro-scale characteristics of MICP treated soils has led, most recently, to the utilization of microfluidic and optical microscopy tools that enable real-time monitoring of MICP injections under saturated conditions. This PhD study further develops an approach that utilizes the most recent advances in real-time monitoring of MICP to probe how a single MICP treatment adapts to two different microfluidic geometries over a meter-long idealized path, focusing mainly on the chemical efficiency and the effect of induced precipitation on pore-scale morphology. The knowledge acquired from the microfluidic experiments, will be further used to enhance the efficiency and homogeneity in MICP-treated soils in the macro-scale.
Mechanical performance and upscaling of bio-improved soils – Ray Harran
Biogeotechnical engineering has inspired revolutionary solutions that have been the subject of abundant research in the last decade, out of which Microbially Induced Calcite Precipitation (MICP) remains one of most promising. The process aims to bio-cement soils in order to mitigate multiple problems of the underground. In this optic, the work targets the current challenges of MICP treated soils, namely, their mechanical performance and upscaling. Gaps of knowledge in the mechanical response are best tested in the lab, specifically targeting strength, compressibility, and creep. Findings are then be used to filter through the available constitutive models and assess their potential improvement. Concerning the upscaling effort, a state-of-the-art basin was constructed to host large-scale experiments, where MICP can be tested in different soils and hydraulic conditions. With direct contributions to mechanical performance and upscaling of the technique, the work is in line with the global effort to better establish MICP as a sustainable alternative to current soil improvement methods.
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D. Terzis, R. Bernier-Latmani and L. Laloui. Géotechnique Letters, vol. 6, num. 1, 2016.
S. Venuleo, L. Laloui, D. Terzis, T. Hueckel and M. Hassan. Geotechnique Letters, vol. 6, num. 1, 2016.
D. Terzis, L. Laloui, V. Rinaldi, Z. Marcelo and J.J. Claria. Proceedings of the 6th International Symposium on Deformation Characteristics of Geomaterials, 970-977, 2015.