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Bio- and Chemo- Mechanical Processes in Geotechnical Engineering



In recent years, substantial advances have been made in understanding the coupling between chemical and biological processes and mechanical and hydraulic behaviours in soils and rocks. At the same time, experimentation and modelling capabilities have progressed significantly, allowing effective design of geotechnical applications


  • ISBN: 9780727760531
  • Edición:
  • Idioma: Inglés
  • Año: 2014

Compra bajo pedidoDisponibilidad: 15 a 30 Días

Contenido Bio- and Chemo- Mechanical Processes in Geotechnical Engineering

In recent years, substantial advances have been made in understanding the coupling between chemical and biological processes and mechanical and hydraulic behaviours in soils and rocks. At the same time, experimentation and modelling capabilities have progressed significantly, allowing effective design of geotechnical applications. The need for such analyses arises, for example, in chemical and biological soil improvement; nuclear, hazardous and municipal waste containment; petroleum and natural gas extraction; methane hydrate exploitation; CO2 sequestration; and assessment of pavement durability.

The seventeenth Géotechnique Symposium in Print took place at the Institution of Civil Engineers on 3 June 2013 and sought to address the new challenges that are emerging from the interactions between multi-physical phenomena. These proceedings bring together the international research presented at the symposium and published across two issues of Géotechnique as well as additional subsequent research published in the journal.

The papers selected for the symposium cover a wide range of geotechnical processes, including:
•Experimental analysis and constitutive modelling of the bio- and chemo-mechanical behaviour of
•Effects of changes in the pore water chemistry on soil and rock behaviour.
Interactions between geometrical scales of diverse biological, chemical, physical and mechanical processes.
•Case studies of chemical and biological soil modifications.
•Applications of bio- and chemo-mechanical models in emerging technologies.

Bio- and Chemo- Mechanical Processes in Geotechnical Engineering provides researchers and practitioners with a comprehensive introduction to the recent advances in the area and invaluable insight into the developments within this emerging field.

Contents and Preliminary Pages

Double-structure effects on the chemo-hydro-mechanical behaviour of a compacted active clay

This work presents an insight into double-structure effects on the coupled chemo-hydro-mechanical behaviour of a compacted active clay. In the first part, selected pore size distribution curves are introduced, to highlight the influence of solute concentration on the evolution of the micro structure of compacted samples. An aggregated structure with dual-pore network is induced by compaction even at relatively high water contents. This structural arrangement is enhanced by salinisation, and has a notable influence on transient volume change behaviour – that is, the occurrence of different stages of swelling upon pore water dilution and higher volume change rates upon salinisation. A coupled chemo-hydro-mechanical model, taking into consideration double-structural features from a chemo-mechanical viewpoint, is described and then used to interpret these behavioural responses and present complementary information on local transient processes. The model is designed to identify an intra-aggregate and an inter-aggregate domain, and assigns different values of hydraulic pressure and osmotic suction to each domain. Distinct constitutive laws for both domains are formulated, and the flow of salt and water between the two domains is accounted for by a physically based mass exchange term. The model is used to simulate salt diffusion tests run in an oedometer at constant vertical stress. Parameters used in the formulation are calibrated based on separate experimental evidence, both through direct test results and through back-analyses of laboratory experiments

A chemo-mechanical constitutive model accounting for cation exchange in expansive clays

The paper presents a chemo-mechanical model for expansive clays that takes into account the effects of cation content and cation exchange. These factors play a key role in the mechanical behaviour of very active clays, particularly with regard to volumetric behaviour. The model is based on an existing double-structure formulation that distinguishes specifically between microstructure and macrostructure. Chemical effects are defined at the micro structural level, the seat of the basic physico-chemical phenomena affecting highly swelling clays. The microstructural model accounts for changes in both osmotic suction and in cation content. Microstructural strains are considered to be reversible; material irreversibility arises from the interaction between the two structural levels. The formulation is developed for general unsaturated conditions; saturation is considered as a limiting case. The model is successfully applied to the reproduction of experimental behaviour observed in oedometer tests on saturated bentonite subjected to chemo-mechanical loadings, and in hydration tests of unsaturated bentonite performed using different solute concentrations.

An experimental and constitutive investigation on the chemo-mechanical behaviour of a clay

Engineering issues for which the understanding of the chemo-mechanical behaviour of soils is relevant include wellbore stability problems, the salinification of groundwater, and nuclear waste storage. However, despite the vast number of situations in which couplings between chemistry and mechanics occur, the available constitutive models rely on limited experimental evidence. This paper presents the results of an experimental programme on the chemo-mechanical behaviour of a non-swelling illite. The osmotic suction is controlled through the ion concentration of sodium chloride in the pore water. Stress paths include mechanical loading at a constant osmotic suction, and an increasing osmotic suction at a constant mechanical stress. The experimental results point out a correlation between the osmotic suction and initial oedometric modulus, as well as between the osmotic suction and yield stress. A constitutive framework for soils is extended to take the observed chemo-mechanical couplings into account. The numerical model has been calibrated for the illite using the parameters obtained through the tests under mechanical loading at a constant concentration, and validated using more elaborate stress paths. The presented experimental and constitutive investigation builds a basis for the assessment of engineering issues in which pore liquid chemistry plays a major role.

Reduction of the clogging potential of clays: new chemical applications and novel quantification approaches

Earth pressure balance machines are increasingly being used for tunnelling in difficult soils and ground conditions. In clayey soils, clogging of the working tools is among the main hazards. Attempts to reduce this risk by adding anti-clogging chemicals do not always produce the desired effect. In this paper, the limited efficiency of the existing conditioning chemicals is quantified and explained, and an enhanced interaction mechanism is proposed. This mechanism is based on sealing the clay aggregates against the penetration of water; it requires the addition of polyamine chemicals, as a newly patented application. These chemicals have been shown to dramatically reduce the clogging potential of different clay pastes over a broad range of water contents, using novel approaches for quantifying the clogging behaviour of clays in general. These methods also establish important correlations between empirical stickiness and more fundamental soil parameters, and in particular the ratio between adhesion and strength. Together with microscopic investigations and adsorption measurements, this provides insight into the working mechanism of the new chemicals at the particle level; it also highlights the differences between this mechanism and that of commercially used foams and polymers.

Coupled chemical-hydraulic-mechanical behaviour of bentonites

Bentonites are clay soils characterised by a high specific surface and a permanent negative electric charge on their solid skeleton. Their common use as hydraulic and contaminant barriers for landfill and soil remediation applications, including the final disposal of nuclear waste, needs to be supported by adequate theoretical modelling of their mechanical behaviour and transport properties, in order to assess the expected performance in the long term. To this end, a theoretical approach has been proposed in order to derive constitutive equations for their coupled chemical-hydraulic-mechanical behaviour. The phenomenological parameters that govern the transport of electrolyte solutions through bentonites – that is, the hydraulic conductivity, the reflection coefficient (which is also called the chemico-osmotic efficiency coefficient), and the osmotic effective diffusion coefficient – have been measured through laboratory tests on a bentonite with porosity of 0·81, over a range of sodium chloride concentrations in the pore solution that varied from 5 mM to 100 mM. The relevance of the osmotic phenomena has been shown to decrease when the salt concentration increases. The obtained results have been interpreted by assuming that the microscopic deviations of the pore solution state variables from their average values are negligible. In this way, it is possible to interpret the macroscopic behaviour on the basis of the physical and chemical properties of the bentonite mineralogical components

Environmentally enhanced crack propagation in a chemically degrading isotropic shale
Authors:   M. M. HU; T. HUECKEL

Crack propagation is studied in a geomaterial subject to weakening by the presence of water, which dissolves a mineral component. Such weakening is common when tensile microcracks develop, constituting sites of enhanced mineral dissolution. A previous concept is adopted of reactive chemo-plasticity, with the yield limit depending on the mineral mass dissolved, causing chemical softening. The dissolution is described by a rate equation and is a function of variable internal specific surface area, which in turn is assumed to be a function of dilative plastic deformation. The crack vicinity in plane strain is subject to a constant subcritical all-round uniform radial tensile traction. The behaviour of the material is rigid-plastic with chemical softening. The extended Johnson approximation is adopted, meaning that all fields involved are axisymmetric around the crack tip, with a small, unstressed cavity around it. Initial dissolution proportional to the initial porosity activates the plastic yielding. The total dissolved mass diffuses out from the process zone and the exiting mineral mass flux can be correlated with the displacement of the crack tip. A simplified semi-analytical solution for this model is presented

A chemo-poro-mechanical model for sequestration of carbon dioxide in coalbeds

To reduce the emissions of carbon dioxide into the atmosphere, it is proposed to inject anthropogenic carbon dioxide into deep geological formations. Deep, unmineable coalbeds are considered to be a possible carbon dioxide repository because coal is able to adsorb a large amount of carbon dioxide inside its microporous structure. However, the response of coalbeds is complex because of coupling between the flow and mechanical responses. Injection of carbon dioxide causes coal to swell, which leads to reductions in permeability and hence makes injection more difficult, and at the same time leads to changes in the mechanical properties that can affect the stress state in the coal and overlying strata. Apart from the influence of swelling on permeability, the chemo-mechanical aspects of carbon dioxide sequestration in coalbeds have been little studied. In this paper, the results of a series of triaxial tests on a bituminous coal are presented that show a reduction in elastic modulus as a result of carbon dioxide adsorption. Using these experimental results, a linear relationship between the reduction in elastic modulus and the amount of adsorbed gas was found. This relationship, in conjunction with a dual-porosity model, has been employed to simulate the hydromechanical response of a coal bed to carbon dioxide injection. The results of the numerical simulation show that the softening of the coal can change the permeability and stresses in the coal, and suggest that considering the softening effect is crucial for accurate assessment of the performance and safety of carbon dioxide storage in coalbeds.

Growth of polymer microstructures between stressed silica grains: a chemo-mechanical coupling
Authors:   R. GUO; T. HUECKEL

Laboratory tests on the micro scale are reported in which two amorphous silica cubes were compressed in a liquid environment, in solutions with different silica ion concentrations, for up to 3 weeks. Such an arrangement represents an idealised representation of two sand grains. The grain surfaces and asperities were examined in the scanning electron microscope and atomic force microscope (AFM) for fractures, silica gel growth and polymer strength. In 500 ppm solution, silica gel structures a few hundred micrometres long appeared between stressed silica cubes. In 200 ppm solution, silica deposits were found around damaged grain surfaces, while at 90 ppm (below silica solubility in neutral pH), fibres a few micrometres in length were found growing in cube cracks. AFM pulling tests found polymers with strength of the order of 100 nN. It was concluded that prolonged compression produced damage in grains, raising local silicon ion concentration and accelerating precipitation, polymerisation and gelation of silica on grain surfaces, enhancing soil strength at the micro scale, and hence most likely contributing to the ageing phenomenon observed at the macro scale.

Some unexpected effects of natural and anthropogenic chemicals on construction
Author:   S.A. JEFFERIS

From time to time chemicals present in the ground induce reactions that are sufficiently severe to cause structural damage, or risks to the health and safety of construction workers or end users of construction work. Such chemicals include those from contaminated land, which can complicate the design of underground works and may add significantly to costs. However, investigation techniques and remedial procedures are now well established for many contaminated land chemicals, and their effects should no longer come as a surprise to the construction team. In contrast, chemicals naturally present in the ground or deliberately introduced into it can lead to unexpected problems – especially if their effect is greatly out of proportion to their concentration in the ground. This paper gives brief case histories of some unanticipated effects of changes in redox potential associated with carbon, iron, nitrogen and sulfur species.

Effect of chemical treatment used in MICP on engineering properties of cemented soils
Authors:   A. AL QABANY; K. SOGA

Despite the large number of studies concerned with microbially induced carbonate precipitation (MICP) on soils, little attention has been paid to the effect of the chemical concentration used in the treatment on the precipitation pattern of calcium carbonate and their influence on engineering properties of MICP cemented soils. In this study, unconfined compressive strength tests were conducted on sand samples treated using 0·1, 0·25, 0·5 and 1 M urea–calcium chloride solutions. It was found that, although the strength of tested samples all increased after MICP treatment, the magnitude of this increase depended on the concentration used in the treatment and that the use of a low-chemical-concentration (i.e. urea and calcium chloride) solution resulted in stronger samples. Permeability test results showed that the use of a high-urea–calcium chloride-concentration solution resulted in a rapid drop in permeability at the early stage of calcite precipitation, whereas the use of a low-chemical-concentration solution was found to result in a more gradual and uniform decrease in permeability. This observed effect of chemical concentration on the strength and permeability of MICP cemented soils can have implications for the design of MICP for field applications

Mitigation of liquefaction of saturated sand using biogas
Authors:   J. HE; J. CHU; V. IVANOV

Some recent studies have indicated that the liquefaction potential of saturated sand can be greatly reduced if the sand can be made slightly unsaturated. One way to reduce the degree of saturation of sand is to inject gas into sand. This approach offers a cost-effective solution for mitigating liquefaction hazard over a large area. However, it is not easy to inject gas into sand in a uniform manner. A biogas method was developed in this study to overcome this difficulty. In this method, denitrifying bacteria are used to generate tiny, inert nitrogen gas bubbles in sand. Shaking table tests using a fully instrumented laminar box are conducted on both saturated sand and sand containing microbially generated nitrogen gas bubbles. Comparisons of the results of these tests indicate that the pore water pressure generated in the partially saturated sand was much smaller than that in saturated sand. Thus the proposed method is effective in reducing the liquefaction potential of sand.

Dynamic response of liquefiable sand improved by microbial-induced calcite precipitation

Microbial-induced calcite precipitation (MICP), a novel bio-mediated ground improvement method, was explored to mitigate liquefaction-prone soils. Geotechnical centrifuge tests were used to evaluate cementation integrity and the response of MICP cemented sands to dynamic loading. The cementation integrity testing reveals a change in behaviour from ‘soil like’ to ‘rock like’, with an increase in treatment level. Results from dynamic testing demonstrate a clear increase in resistance to liquefaction of MICP-treated sands compared to untreated loose sand. The MICP sands were treated to varying levels of cementation (light, moderate and heavy cementation levels) and assessed using nondestructive shear wave velocity measurements. The centrifuge models were all subjected to ground motions consisting of sine waves with increasing amplitudes. Accelerations, pore pressures and settlements were measured in the soil during shaking, and the changes in soil behaviour and post-shaking shear wave velocity for soils prepared to different cementation levels are discussed. Increased resistance to liquefaction was demonstrated with a decrease in excess pore pressure ratios in the MICP-treated models, as well as in reduced post-shaking settlements; however, surface accelerations were amplified at heavy levels of cementation. A tradeoff between improving liquefaction resistance and minimising undesirable higher surface accelerations needs to be considered when designing the soil improvement level.

Volumetric consequences of particle loss by grading entropy

Chemical and biological processes, such as dissolution in gypsiferous sands and biodegradation in waste refuse, result in mass or particle loss, which in turn lead to changes in solid and void phase volumes and grading. Data on phase volume and grading changes have been obtained from oedometric dissolution tests on sand–salt mixtures. Phase volume changes are defined by a (dissolution-induced) void volume change parameter (Λ). Grading changes are interpreted using grading entropy coordinates, which allow a grading curve to be depicted as a single data point and changes in grading as a vector quantity rather than a family of distribution curves. By combining Λ contours with pre- to post-dissolution grading entropy coordinate paths, an innovative interpretation of the volumetric consequences of particle loss is obtained. Paths associated with small soluble particles, the loss of which triggers relatively little settlement but large increase in void ratio, track parallel to the Λ contours. Paths associated with the loss of larger particles, which can destabilise the sand skeleton, tend to track across the Λ contours.

Biogeochemical processes and geotechnical applications: progress, opportunities and challenges

Consideration 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.

Mathematical model of electro-osmotic consolidation for soft ground improvement
Authors:   L. HU; H. WU

Electro-osmotic consolidation is an attractive, soft ground improvement technique. In this paper a theoretical model is proposed for electro-osmotic consolidation by coupling the seepage field, electric field, and the stress and strain field. The soil mass deformation, pore-water pressure and the electrical voltage are the basic variables in the governing equations. A three-dimensional numerical model based on the finite-element method was developed to simulate the electro-osmotic consolidation process, predicting the tempo-spatial variation of soil mass displacement. The numerical model is compared with previous analytical solutions. Three common electrode installation patterns are illustrated and analysed with the numerical model, and the results indicate that the triangular pattern can achieve the largest average surface settlement and the smallest differential settlement. The effect of the penetrating depth of the electrodes on the ground settlement is also investigated. An engineering field application is simulated to validate the developed numerical formulation.

Analytical solution for axisymmetric electro-osmotic consolidation
Authors:   H. WU; L. HU

Electro-osmotic consolidation is a potential method for soil improvement. An axisymmetric electro-osmotic consolidation model with coupled horizontal and vertical seepage is proposed and the analytical solution is derived without the equal strain hypothesis, which was used in previous models. The proposed analytical model can predict the distribution of pore-water pressure in the radial direction, and comparison with previous analytical models indicates that the degree of consolidation is overestimated if the model is simplified from an axisymmetric model to a planar model. A design chart is developed to facilitate the evaluation of applying electro-osmotic consolidation for soil improvement.

Improving the mechanical response of kaolinite and bentonite through exposure to organic and metallorganic compounds

The mechanical response of soft clays can be modified through change of the adsorbed ions or by adding lime or cement using deep mixing tools. This work focuses on analysing the effects induced by a new class of chemical agents, which can be driven through soft clays and lead to cementing bonds, without being associated with any deformation. The resulting technique could be of benefit for improving in situ soil properties, for instance beneath existing foundations. Both kaolinite and sodium-and potassium-bentonites are subjected to different chemical compounds, considering the effects on the liquid limit, residual friction angle and apparent preconsolidation pressure

Weathering of submerged stressed calcarenites: chemo-mechanical coupling mechanisms
Authors:   M. O. CIANTIA; T. HUECKEL

Long portions of the Apulian coast are steep cliffs in carbonate soft rocks. These, especially the calcarenite, are affected by weathering processes that markedly alter their mechanical properties with time, potentially leading to instability of coastal geomorphological structures. Such alterations are mainly due to chemical reactions between the solid and fluid phases, and are driven by chemical variables, which are internal variables and hence uncontrollable. In a search for the variables that drive the process of rock weakening, recourse is made to the micro scale, at which most of the chemical processes are observed and quantified. Observations using scanning electron microsope, thin sections and X-ray computed tomography analyses appear to be crucial for the understanding, interpretation and definition of the degradation mechanisms of the material. A chemo-mechanical coupled model at the meso scale of the chemically reactive stressed porous system is presented and framed in the context of a multi-scale scenario of an array of coupled phenomena. An analogous model at the macro scale is developed in parallel together with upscaling and identification procedures for meso-scale and macro-scale material constants. The main outcome of the study is a tool for predicting the progress of time-dependent weathering phenomena, potentially allowing the stability of geological structures to be assessed as it evolves with a progressing chemical degradation in a specific configuration and under a specific set of loads.

Massive sulfate attack to cement-treated railway embankments
Authors:   E. E. ALONSO; A. RAMON

Two access embankments to a railway bridge, having a maximum height of 18 m, experienced a continuous and severe heave shortly after construction. Vertical displacements reached 120 mm in a 2-year period. The embankments were designed, by including soil–cement-treated transition wedges, to provide an increasingly rigid support as the trains approach the stiff bridge abutments. A grid of 10 m deep jet-grouting columns was also built, with the purpose of stabilising the embankments. Instead, a sustained swelling deformation, which extended to depths of 8–10 m, was activated. The compacted soil was low-plasticity clayey material, with a variable percentage of gypsum. The embankments suffered a massive ettringite-thaumasite attack, which was triggered by the simultaneous presence of cement, clay, sulfates and an external supply of water (rain). The paper describes the field extensometer and inclinometer records, the long-term laboratory tests performed, some mineralogical observations and the reactions leading to the growth of expansive crystals, and presents a model that simulates the measured heave. Forces acting against the bridge, which was seriously damaged, were estimated. Remedial measures include removal of the active upper zone of the embankments, and the construction in stages of slabs supporting the rails and founded on piles built on both sides of the embankments. The case is considered unique because of the magnitude of the reaction developed in the embankments, and its damaging action on the nearby bridge structure

Microbial method for construction of an aquaculture pond in sand

A method to construct an aquaculture pond in sand using microbial biocementation is presented in this paper. The microbially induced calcium carbonate precipitation process was used to form a low-permeability layer in sand for the construction of a water pond model in the laboratory. The test results indicated that the permeability of sand was reduced from the order of 10–4 m/s to 10–7 m/s when an average 2·1 kg of calcium (Ca) per m2 of sand surface was precipitated. The bending strengths of the walls and the base of the model pond were in the range of 90–256 kPa. The unconfined compressive strengths for the samples taken from the walls and the base of the pond were in the range of 215–932 kPa.




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