Bio-mediated soil improvement

[1] Methane gas hydrates, crystalline inclusion compounds formed from methane and water, are found in marine continental margin and permafrost sediments worldwide. This article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate-bearing sediments. Formation phenomena include pore-scale habit, solubility, spatial variability, and host sediment aggregate properties. Physical properties include thermal properties, permeability, electrical conductivity and permittivity, small-strain elastic P and S wave velocities, shear strength, and volume changes resulting from hydrate dissociation. The magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate-bearing sediments to changes in mechanical, thermal, or chemical boundary conditions. These predictions are vital for mitigating borehole, local, and regional slope stability hazards; optimizing recovery techniques for extracting methane from hydrate-bearing sediments or sequestering carbon dioxide in gas hydrate; and evaluating the role of gas hydrate in the global carbon cycle.

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Physical properties of hydrate-bearing sediments

The century-old Hazen formula for predicting the permeability of sand is based only on the D10 particle size. Whereas, the half-century-old Kozeny-Carman formula is based on the entire particle size distribution, the particle shape, and the void ratio. As a consequence, the Hazen formula is less accurate than the Kozeny-Carman formula. It is recommended that the former be retired and the latter be adopted.

Goodbye, Hazen; Hello, Kozeny-Carman

Aims: To gain an understanding of the environmental factors that affect the growth of the bacterium Sporosarcina pasteurii, the metabolism of the bacterium and the calcium carbonate precipitation induced by this bacterium to optimally implement the biological treatment process, microbial induced calcium carbonate precipitation (MICP), in situ.

Methods and Results:  Soil column and batch tests were used to assess the effect of likely subsurface environmental factors on the MICP treatment process. Microbial growth and mineral precipitation were evaluated in freshwater and seawater. Environmental conditions that may influence the ureolytic activity of the bacteria, such as ammonium concentration and oxygen availability, as well as the ureolytic activities of viable and lysed cells were assessed. Treatment formulation and injection rate, as well as soil particle characteristics are other factors that were evaluated for impact on uniform induction of cementation within the soils.

Conclusions:  The results of the study presented herein indicate that the biological treatment process is equally robust over a wide range of soil types, concentrations of ammonium chloride and salinities ranging from distilled water to full seawater; on the time scale of an hour, it is not diminished by the absence of oxygen or lysis of cells containing the urease enzyme.

Significance and Impact of Study:  This study advances the biological treatment process MICP towards field implementation by addressing key environmental hurdles faced with during the upscaling process.

Effects of environmental factors on microbial induced calcium carbonate precipitation

This paper presents the results of a comprehensive experimental study of the desiccation of fine-grained soils. Air drying of initially saturated soil slabs in controlled conditions is investigated by performing three kinds of tests: free desiccation tests, constrained desiccation tests (prevented shrinkage), and crack pattern tests. Strains, suction, water con- tent, and crack geometry are investigated. Results reveal that unconstrained drying exhibits two stages: a domain with large, mostly irrecoverable deformations and degree of saturation close to 100%, followed by a domain with lower defor- mations at a decreasing degree of saturation. Homogeneous soil macroscopic cracking is possible only in the presence of boundary constraints and (or) moisture gradients, inducing the build-up of tensile stresses. Results also show that, for the initially saturated remoulded soils tested here, in the whole sample and near a crack initiation point, the degree of satura- tion remains very close to 100% until cracking, while cracking onset, the air-entry suction, and the shrinkage limit are close to each other. Cavitation nuclei and the formation of an irregular drying front at cracking initiation are commented upon in light of this observation. Finally, results suggest that the crack pattern geometry is the result of energy redistribu- tion. A quantification of the process is proposed. Resume´ : Cet article presente les resultats d'une etude experimentale complete de la dessiccation de sols fins. Le sechage de sols initialement satures est etudiedans des conditions controlees et atemperature ambiante. Trois types d'essais ont eteeffectues : essais de dessiccation libre, essais de dessiccation avec contraintes (le retrait est empechedans une direc- tion) et essais de plans de fissures. Les deformations, la succion, la teneur en eau et la geometrie des fissures ont eteinves- tiguees. Les resultats demontrent que le sechage sans contrainte presente deux etapes : un domaine durant lequel les deformations sont grandes et irreversibles et le degrede saturation reste pres de 100 %, suivi d'un domaine durant lequel les deformations sont plus faibles et le degrede saturation diminue. Pour un sol homogene, des fissures macroscopiques apparaissent seulement lorsqu'il y a des contraintes aux frontieres et (ou) des gradients d'humidite ´, ce qui induit des contraintes en tension. Les resultats montrent aussi que pour les silts et argiles remanies initialement satures utilises dans cette etude, le degrede saturation reste tres pres de 100 % jusqu'ala fissuration. De plus, la fissuration, l'entree d'air et la limite de retrait sont proches les unes des autres. Suite a ces observations, l'existence de germes de cavitation et la forma- tion d'un front de sechage irregulier lors de l'initiation des fissures sont discutees. Finalement, les resultats suggerent que la geometrie des fissures resulte d'une redistribution de l'energie a travers le corps. Une quantification du processus est proposee. Mots-cles: dessiccation, initiation de fissure, succion, succion a l'entree d'air, geometrie des fissures.

https://people.duke.edu/~hueckel/desiccationpapers/2009.can.fundam of cracking.pdf

Fundamentals of desiccation cracking of fine-grained soils: experimental characterisation and mechanisms identification

This manual presents data on soil behaviour, with emphasis on practical and empirical knowledge, required by geotechnical engineers for the design and construction of foundations and embankments It deals with: index and classification properties of soils; soil classification; clay minerals and soil structure; compaction; water in soils (capillarity, shrinkage, swelling, frost action, permeability, seepage, effective stress); consolidation and consolidation settlements; time rate of consolidation; the Mohr circle, failure theories, and stress paths; shear strength of sands and clays Four appendices deal with the following: application of the "SI" system of units to getechnical engineering; derivation of Laplace's equation; derivation and solution of Terzaghi's one-dimensional consolidation theory; pore pressure parameters (TRRL)

William D. Kovacs

Papers

An Introduction to Geotechnical Engineering

A New Soil-Reinforcement Interaction Model