23 research outputs found
Effects of push–pull injection–suction spacing on sand biocementation treatment
No full textThe process of ureolysis-driven biocementation is used to improve granular soils. The precipitation of calcium carbonate (CaCO3) crystals results from the reactions of urease generated by ureolytic bacteria and chemical reagents, which strengthen or bind soil particles together. Using a lab-based scaled physical model, this study investigated the influence of selected spacing intervals (107, 214 and 321 mm) on the effectiveness of biocementation through the injection–suction or ‘push–pull’ approach. Polystyrene moulds were used to create soil specimens. These were then injected with six cycles of treatment solutions at the intervals stated. The compressive strengths and calcium carbonate contents of the biocemented soil specimens were measured after curing. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy and effluent analysis (pH and ammonium measurements) were also performed. The biocemented soil specimens with different spacing intervals obtained compressive strengths of 2.53 ± 1.06 to 4.2 ± 2.3 MPa, while the calcium carbonate contents were from 2.78 ± 0.3 to 11.16 ± 1.5%. The elemental compositions and bonding of calcium carbonate precipitates in the biocemented soil were confirmed by EDS and FTIR spectra, while SEM micrographs revealed chip-like and irregular rhombohedral crystal forms. The results demonstrated that injection spacing had an effect on biocemented soil treated by microbially induced carbonate precipitation.Full Tex
Biogeochemical processes and geotechnical applications: Progress, opportunities and challenges
No full textConsideration of soil as a living ecosystem offers the potential for innovative and sustainable solutions to geotechnical problems. This is a new paradigm for many in geotechnical engineering. Realising the potential of this paradigm requires a multidisciplinary approach that embraces biology and geochemistry to develop techniques for beneficial ground modification. This paper assesses the progress, opportunities, and challenges in this emerging field. Biomediated geochemical processes, which consist of a geochemical reaction regulated by subsurface microbiology, currently being explored include mineral precipitation, gas generation, biofilm formation and biopolymer generation. For each of these processes, subsurface microbial processes are employed to create an environment conducive to the desired geochemical reactions among the minerals, organic matter, pore fluids, and gases that constitute soil. Geotechnical applications currently being explored include cementation of sands to enhance bearing capacity and liquefaction resistance, sequestration of carbon, soil erosion control, groundwater flow control, and remediation of soil and groundwater impacted by metals and radionuclides. Challenges in biomediated ground modification include upscaling processes from the laboratory to the field, in situ monitoring of reactions, reaction products and properties, developing integrated biogeochemical and geotechnical models, management of treatment by-products, establishing the durability and longevity/reversibility of the process, and education of engineers and researchers.Geoscience & EngineeringCivil Engineering and Geoscience
Improvement of erodibility of a sand (sandy soils) treated by microbially induced urea-based carbonate precipitation: (Abstract)
No full text
Testing and modeling the hydraulic permeability evolution of Permeable reactive Barriers clogged by colloids
No full textAn Experimental Procedure to Assess the Erosional and Hydraulic Behaviour of Cohesionless Soils
No full textABSTRACT: Selective erosion of fine particles from granular soils can affect the draining properties of hydraulic structures with time, and it is important to identify unstable soils and characterise their hydraulic and erosional behaviour. To this end, this study focuses on the design and set-up of a new laboratory device for testing the suffusion and piping phenomenon occurring in an internally unstable cohesionless material. The proposed procedure offers the possibility of quantifying the hydraulic gradient at which erosion starts and evaluates the mass of fine particles washed out of the sample under controlled hydraulic conditions. The quantity of eroded particles, the exit water flow rate and the hydraulic gradient distribution along the flow paths are also measured during the process. The procedure was tested on an erosive soil under saturated conditions and under unconfined seepage, allowing the assessment of the hydraulic behaviour of this internally unstable material
Influence of Precipitates on Hydraulic Performance of Permeable Reactive Barrier Filters
No full textInternational audienc
Amélioration des propriétés mécaniques des sols par biocimentation : étude mécanique et microstructurale
No full textLe procédé de bio-cimentation est une technique prometteuse pour renforcer les sols lâches et de faible résistance mécanique. Cette technique a montré une très bonne efficacité pour plusieurs types de sols lors d’essais en laboratoire, dans des modèles physiques ou lors d’essais sur site. Dans le présent article, un protocole de biocimentation de sol par injection a été élaboré en laboratoire pour préparer des éprouvettes de sable de Fontainebleau à différents niveaux de cimentation. Des mesures de perméabilité et des essais triaxiaux drainés à différentes contraintes de confinement ont été réalisés sur ces éprouvettes. Ces essais ont été suivis par des observations microscopiques et aux rayons-X afin de comprendre l’impact microstructural de la précipitation de calcite. Dans l’ensemble, les résultats montrent une bonne répétabilité de la biocimentation par le protocole suivi, ainsi qu’une faible hétérogénéité dans le profil des éprouvettes biocimentées. Ces résultats ont montré aussi une augmentation importante de la résistance mécanique des éprouvettes de sable biocimenté. Par ailleurs, du point de vue microstructural, la précipitation de calcite est quasi-localisée au niveau des contacts entre grains, ce qui donne une très bonne efficacité mécanique (forte augmentation de cohésion), avec une faible diminution de perméabilité surtout pour les faibles niveaux de calcification
Characterization of contact properties in biocemented sand using 3D X-ray micro-tomography
No full textInternational audienceThe mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within the pore space (localized at the contact between grains, over the grain surfaces) and the contact properties: coordination number, contact surface area, contacts orientation and types of contact. In the present work, all these micromechanical properties are computed, for the first time, from 3D images obtained by X-ray tomography of intact biocemented sand samples. The evolution of all these properties with respect to the volume fraction of calcite is analyzed and compared between each other (from untreated sand to highly cemented sand). Whatever the volume fraction of calcite, it is shown that the precipitation of the calcite is localized at the contacts between grains. These results are confirmed by comparing our numerical results with analytical estimates assuming that the granular medium is made of periodic simple cubic arrangements of grains and by considering two extreme cases of precipitation: (1) The calcite is localized at the contact, and (2) the grains are covered by a uniform layer of calcite. In overall, the obtained results show that a small percentage of calcite is sufficient to get a large amount of cohesive contacts
