The field of soil bio-improvement, through microbial-induced calcite mineralization, has gained significant momentum in scientific literature in the past years. The phenomenon, which is inspired from natural environments, has been extensively applied at laboratory bench-scale, leading to a surge of expectations around its potential fit as a mainstream solution to real-world construction and environmental problems. The present study aims to break out of the laboratory and deliver a benchmark, large-scale application of ground bio-reinforcement which was designed and implemented in the canton of Vaud, Switzerland. The work aims to mitigate landslide risk in a slope hit by extreme rainfall in early 2018. This resulted in increased pore water pressure within the failure surface, therefore reducing the soil's effective shear strength and triggering the slip of roughly 3,000 cubic meters of earth mass. A grouting solution was designed to induce the bio-mineralization of calcite binders within the targeted slip zone. In order to present obtained results in the best possible light, we combine laboratory tests, in situ monitoring, microstructural inspections, and post-stabilization aerial surveillance. Obtained data reveal slower displacement rates for the bio-stabilized zone compared to the rest of the slope. Overall, our global analysis aims to offer new prospects towards bio-mediated geotechnical practice under real-life conditions.

Soil biocementation represents an emerging technique that has dominated the development of sustainable and innovative geotechnics during the past decade. Despite numerous studies focusing on peak strength behavior and the ensuing softening response, less is known about the stress-and time-dependent deformability of biocemented geomaterials even though it remains central for most envisaged applications. This study comprised an experimental campaign on two microbially induced carbonate precipitation (MICP)-treated sands with different initial characteristics. Samples with various calcite contents were subjected to uniaxial and incremental loading and to long-term monotonic loading to evaluate their compressibility and capture the principles of their deformation. Furthermore, the use of the porosity-tocement ratio, originally developed for artificially bonded soils, is herein evaluated as a parameter to capture and express the behavior of MICP-treated sands. Observations from the incremental loading campaign revealed that for a range of calcite contents between 3% and 8% and for applied stress levels up to 1,000 kPa, MICP treatment significantly enhanced the stiffness properties of the geomaterials and reduced their overall deformability. Medium-grained sand required lower bond contents to achieve a similar compressibility to fine-grained sand and was more compatible with the porosity-to-cement ratio. The effects of time dependency were also assessed under different sustained monotonic loads over a long time (>75 days). Under sustained high stresses exceeding the apparent preconsolidation stress, the coefficient of secondary compression reached up to a threefold increase compared with the untreated state. Based on the behavioral characterization, stress and time considerations were shown to be interdependent. The cementation achieved by the treatment shifted a portion of immediate settlement, which was released as delayed deformation after bond breakage took place, depending on loading configuration and bond quality (deposition and imperfections), as determined via microstructural observations.

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