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.
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.
The bacteria strain S. Pasteurii that catalyzes the urea hydrolysis
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.
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Research group for Bio-improved soils:
- D. Terzis, R. Bernier-Latmani and L. Laloui. Fabric characteristics and mechanical response of bio-improved sand to various treatment conditions, in Géotechnique Letters, vol. 6, num. 1, 2016.
- S. Venuleo, L. Laloui, D. Terzis, T. Hueckel and M. Hassan. Effect of Microbially Induced Calcite Precipitation on soil thermal conductivity, in Geotechnique Letters, vol. 6, num. 1, 2016.