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Application of biopolymer-modified geomaterials in waste disposal practices is gaining wide acceptance due to their superior tensile characteristics and improved crack resistance. Permeability is an important design parameter which determines the suitability of a material as a liner for construction of engineered landfills. Given this, the permeability characteristics of sand-bentonite mixtures amended with biopolymers was studied using a modified-falling head permeability apparatus under an accelerated gravity environment. Both distilled water and synthetic leachate were utilized as permeant liquid to assess the role of biopolymer amendment on the permeation behavior of sand-bentonite mixtures. Experimental results indicate that addition of biopolymers causes aggregation of the clay platelets, which in turn enhances the permeation behavior of the biopolymer-modified sand-bentonite mixtures. These mixtures meet the regulatory requirement of the liner.

The carbonation of lime-treated soils that occurs during the short-term and long-term curing is not sufficiently explored in the domain of lime stabilization. The present study investigates the carbonation mechanism in lime-treated silty clay treated with two lime contents (4%, 8%) subjected to different curing periods (7, 90, 180, and 365 days). The cured samples were exposed to accelerated carbonation, and subsequent change in the unconfined compressive strength was compared with that of control samples tested under a nitrogen environment. The extent of carbonation was measured using phenolphthalein solution. X-ray diffraction technique and thermogravimetric analysis were used to analyze the reaction products resulted from carbonation. The morphology of carbonates and effects of carbonation on the pore structure were assessed using a scanning electron microscope and mercury intrusion porosimeter, respectively. Results show that carbonation has a deleterious effect on the performance of lime-treated clay. The strength of lime-treated soils upon carbonation decreased by 30% on average. The fabric structure of treated clay was found to vary with lime content and curing period, which determined the extent of carbonation. Decalcification of reaction products and cracking induced by the carbonation of residual lime contributed to the reduction in compressive strength of treated clay. The observed strength behavior of the carbonated samples is substantiated by quantifying the variation in pore structure characteristics.

Electrochemical treatment of soil, ECT is the technique of deploying an external electric potential for introducing stabilizing chemicals into the intended zone of soil improvement. The cur...

In recent times methanotrophs have gained immense interest due to their ability to sequester and utilize methane, which is an inexpensive carbon source as well as a very potent greenhouse g...

Geosequestration deals with the long-term storage of captured carbon dioxide into various geological formations. Previous studies have focused on the different aspects involved in geological sequestration. The need to capture carbon dioxide from the emitting sources is to curb the rise in atmospheric temperature. The colossal energy demand since the pre-industrial period and with no point known for its culmination in the future, has been sufficed by the burning of fossil fuel, which is the leading cause for the emission of CO2. The combustion of fossil fuels is prolonged from being substituted by an alternative clean source due to its ease and cheaper than the currently available technologies. Hence, for mitigating the concentration of CO2 in the atmosphere, diverse techniques, including geological sequestration, have been considered. The major components of the geological sequestration technique are capturing, transporting, and long-term storage. Depleted oil and gas fields, saline formations, unminable coal seams, and saline water-filled basalt volcanic rocks are potential formations. Various mechanisms are involved in the storage of CO2 in geological formations spread over a geological time scale. The various fundamental phenomena involve a complex behavior and have been understood from various coupled models that describe the interaction of different phases of materials present in the formation. The scientific challenge is to ensure that the CO2 remains safely in these storage sites for thousands of years. The present study attempted to highlight the role of coupled phenomena in assessing the efficacy of the storage site. The thermo-hydro-mechanical and geochemical coupling in a storage site from a geoengineering perspective is discussed.

Soil has been the most widely explored material for construction purpose, since our ancestors stepped out from the cave dwellings and went in search for alternate shelters. As it is the plasticity and consequent mouldability of the soil, that attracted the early humans; it is evident that the clay minerals are the prime contributors for the desired properties. In modern times, the scope of soil as a building material became wider (viz. embankments, landfill liners etc.) and the clay fraction still plays the key role in deciding the material suitability. In this regard, it is necessary to have a thorough understanding of the various elements that influence the behaviour of the clayey fraction within the soil. Among the different factors that influence the clay behaviour, soil pH deserves the prime position, as it can alter the charge distribution of the clay surface and promote mineral dissolution. In view of this, the following chapter address the role of pH in moulding the current personality that we assigned to the clay minerals. In the initial part of the discussion, the different sources and nature of soil acidity/alkalinity, and the role of soil type and genesis in influencing the same has been reviewed. Further, the extent of pH buffering offered by the soil system is discussed, focussing on the various mechanisms involved in the pH-neutralisation. The later section of the chapter discuss the ways with which pH modifies the soil properties such as fabric arrangement and surface charge. Also, the special case of soil-electrokinetic treatment is considered to demonstrate the implications of the property changes in a real life applications.

Soil–lime interactions involve concomitant short-term and long-term alterations of the fine-grained soil resulting in the formation of a workable material bonded by various pozzolanic compounds. These pozzolanic compounds being cementitious in nature are expected to hold the soil particles together and bring long-term strength and stability to the soil–lime composites. However, the durability of cementitious phases formed due to pozzolanic reactions is highly subjective owing to the variations in the moisture and physiochemical factors like pH under diverse environmental conditions. The relative humidity and presence of atmospheric gases like carbon dioxide have a significant impact on the performance of the stabilized system. Carbonation of reaction products, as well as the effects of seasonal moisture fluctuations, can cause the decalcification of the cementitious phases and further degradation in the stabilized system. However, the type of reaction products and their chemical composition, which is a function of the mineralogy of the soil, will determine their durability in adverse conditions. The present study attempts to review the chemistry of reaction products formed in view of its inherent mineralogy. In addition, the degradation nature of the soil–lime composites under adverse conditions like moisture ingress and carbonation is evaluated for their long-term performance.

It is essential to understand the phenomena of adhesion, deadhesion, and transport of microorganisms in porous media to scale up bioengineering processes. In this study, the adhesion and de...

The present study describes the calcium adsorption behavior of clays exhibiting distinct mineralogical composition. The adsorption characteristics were determined using conventional batch-equilibrium sorption method, and different theoretical models were applied to describe the equilibrium sorption isotherms. The variation in calcium adsorption capacity was determined as a function of clay mineralogy, temperature and pore fluid chemistry. Further, the thermodynamic parameters were also calculated to describe the nature of adsorption mechanisms. Significant variation in calcium adsorption potential was observed among the clays, primarily attributed to their mineralogical diversities and related unique surface charge properties. The adsorption density escalated with rise in calcium concentration, temperature and pH of the adsorption system. These observations can be attributed to surface charge modifications and mineral dissolution properties of the clays, which in turn resulted in higher electro-negativity of the clay surface and thereby enhancing the affinity for calcium ions.

The recent research infers that the detailed characterization of lime-treated soils using analytical techniques enables better understanding of the complex soil–lime interaction mechanisms as well as the pivotal factors influencing the efficacy of lime treatment. In view of this, the present study focuses on evaluating the effects of lime treatment on the strength properties of sodium bentonite clay in terms of the variations in thermal characteristics derived by employing analytical thermogravimetric analysis. This technique is effectively used to monitor the consumption of free lime and evolution of new cementitious hydration products (viz., calcium silicate hydrate and calcium aluminate hydrate), as well as detrimental lime carbonation phenomenon occurring in the sodium bentonite-lime composite during short-term curing. Based on the comparative evaluation of untreated and lime-treated sodium bentonite, variations in the weight loss corresponding to thermal decomposition of different chemical phases are estimated. The additional inferences from X-ray diffraction and Fourier transform infrared spectroscopy analyses substantiated the interpretations of thermogravimetric results regarding the lime stabilization mechanisms and consequent strength evolution in sodium bentonite-lime composites. Thus, the present study demonstrates that the comprehensive analysis of thermogravimetric results enables reliable interpretation of the soil–lime interaction mechanisms and the evolution of strength during curing.

Four geosynthetic clay liners (GCLs) serving as single liners were exhumed from below 0.7 m of silty sand on a 3:1 (horizontal:vertical) north-facing slope at the QUELTS site in Godfrey, Ontario, after 5 and 7 years. The 300 mm GCL overlaps with 0.4 kg/m supplemental bentonite were all physically intact. The exchangeable bound sodium was completely replaced with divalent cations. The GCL with the smallest needle-punched bundle size (average of 0.7 mm) and percentage area covered by bundles (4%) maintained low hydraulic conductivity (k) when tested under 0.07–1.2 m head with 10 mmol/L CaCl2 solution as the permeant. For GCLs with larger bundles (1.1–1.6 mm) and higher percentage area covered by bundles (9%–14%), k was low when the head was low (0.07 m). Once the applied head increased, k increased by 1–4 orders of magnitude depending on the (i) hydraulic gradient, (ii) size and number of the needle-punched bundles, and (iii) structure and mass of the bentonite per unit area. The results suggest that the GCLs can perform effectively as a single hydraulic barrier in covers providing that the head above the GCL is kept low (e.g., by a suitable drainage layer above the GCL).

The clay mineral-based soils having low permeability and high swell–shrinkage characteristics are preferred as a backfill and buffer material for containing hazardous waste. Though many factors influence the behaviour of these soils, the contribution of various particle sizes present in them is not thoroughly investigated. In order to examine the effect of particle size on electrokinetic, mineralogical and surface properties of soils, the selected soils were sieved through different size of sieves such as 75, 63, 54, 45, 36, 25 and 20 µm, and the fractions retained on them were collected. The collected fractions were processed and characterized for their electrokinetic, mineralogical and surface properties. Based on the experimental results, the role of different particle size on the micro- and macro-level behaviour of selected soils was quantified.

Surface charge properties of colloids can be studied from their point of zero charge (PZC) measurements. The point of zero salt effect (PZSE), a category of PZC, indicates the pH value at w...

The fundamental behaviour of fine-grained geomaterials compacted over a range of moisture content is strongly influenced by the resulting porosity and pore size distribution (PSD) characteristics. The majority of pertinent studies have employed mercury intrusion porosimetry (MIP) for determining these properties. Since the PSD analysis using MIP technique demands moisture free specimen, it is necessary to select an appropriate sample drying technique that minimises the alteration of soil fabric during sample preparation. In view of this, the present study evaluated the influence of various drying techniques, such as oven-drying, solvent-replacement and freeze-drying, up on the soil fabric in terms of its PSD characteristics. Further, the study investigated the role of placement moisture content on the modifications of soil fabric when soil specimens are compacted over a range of compaction states, using scanning electron microscopy. Based on the obtained results, it is demonstrated that the sample drying ...

Population explosion and rapid industrialization have led to generation of large amount of solid and liquid wastes, which require safe disposal and containment. Currently, land disposal or shallow disposal of these wastes is being practiced by industries and the municipal authorities. However, subsequent interaction of the disposed of waste with rain or ground water generates leachates, which in due course of time contaminate the geoenvironment viz., soil, rock and the ground water (Shu et al. 2018). In addition, high-level radioactive waste generated by nuclear industry comprising of radionuclides of transuranics (viz., Pu, Np and Am) and fission products (viz., I, Cs and Sr), require safe handling and disposal in the geological formations. The efficacy of these formations must be established based on detailed investigations related to their geological, hydrological, geochemical, geophysical and geotechnical characteristics and their impact on integrity of the waste form (IAEA 1993; Gurumoorthy and Singh 2004a, b). It must be noticed that the migration of radionuclides from these waste forms depends on the type and condition of the rock mass (intact or fractured) and the soil mass (saturated on unsaturated). The fractured rock mass creates a pathway for the ground water movement and thereby enhances the probability of dissolution and migration of radionuclides from the radioactive waste matrix and resulting in contamination of the geosphere (Hakanen 1993; Jedinakova 1998).

The quantification of the kinetics of short-term clay–lime interactions is a key step for optimizing the parameters during lime stabilization of fine-grained soils, and also for predicting the long-term performance of lime treated soil matrix. The existing scientific literatures often believed that monitoring of consistency limits as well as compaction characteristics of lime treated soils yield significant amount of information regarding their physico-mechanical behaviour. However, apparently limited extent of works has been carried out to assess the role of clay mineralogy and pore fluid chemistry on inherent variations in plasticity and compaction characteristics. Further, no definite single conclusion could be drawn from the previous studies conducted to comprehend the plausible mechanisms of stabilization occurring in the lime treated soils during short-term and long-term interaction periods.In order to enhance the current understanding, this study primarily focused on the critical evaluation of plasticity properties and compaction characteristics variations of lime treated soils with respect to change in pore fluid chemistry (such as pH and concentration of lime). The study employed soils with quite diverse physico-chemical and mineralogical compositions so as to highlight the role played by the clay mineralogy in governing the extent of short-term improvement that can be mobilized by lime treatment. Based on the significant observations gathered from experimental works, attempts have been made to elucidate the possible short-term mechanisms of lime stabilization which also contribute to long-term strength and durability of lime treated soil.

The benefit from using admixtures in soil to improve properties was discovered in ancient times. Various admixtures such as straw, bitumen, lime, salts and pozzolans are conventional additions to soil, while cement, petrochemicals and bacteria are currently being increasingly used in an effort to improve and stabilize soil from both mechanical and chemical aspects. The conventional techniques which utilize cement, lime, petrochemicals, etc., cause significant environmental degradation. With environmental awareness for materials and methods used in ground improvement generally growing, the trend towards using biopolymers as admixtures is expected to increase. This paper gives the concept and theory of ground improvement technique which employs biopolymers and describes the practical application of these techniques. A number of studies have been conducted in the past decades to check the suitability of various biopolymers in improving soil properties. The effectiveness of biopolymers for soil stabilization in agricultural, construction and military applications has been recognized by many researchers. More efficient and scientific usage of these materials for soil improvement requires knowledge about interaction mechanisms involved in the modification of geotechnical properties of soil. Most of the studies in clay–polymer interaction are from the field of medical engineering, where clay particles are suspended in the colloidal form and macromolecules are attached to them in different ways. The fundamental mechanism in biopolymer–soil modification proposed by various researchers is also presented in this paper. The study reveals the prospects of this green technology in the current era of rapid deterioration of natural resources. Furthermore, the need for continuing research on a number of factors which controls the mechanism is suggested.

The unconfined compressive strength is one of the influencing parameters that are used for determining the in situ strength of soft, fine-grained soil deposits. Since many previous research works have highlighted the influence of pore fluid type, electrolyte concentration, pH and valence of the pore fluid on unconfined compressive shear strength. The present study has inferred the effect of pore size distribution (PSD) on unconfined compressive shear strength (UCS) of bentonite and kaolinite minerals. It is observed that the pore size distribution of bentonite is a bimodal distribution representing both interpore and intrapore, whereas the kaolinite mineral exhibits a unimodal distribution representing only the interpore. The interpore represents the water molecules bounded between soil aggregates, whereas the intrapore represents the water molecules bounded within the soil aggregated and on the clay surface. From the obtained UCS value of bentonite and kaolinite minerals, it can be inferred that the UCS strength variation of bentonite mineral is strongly influenced by the water molecules bounded on the clay surface or diffused double layer water, whereas the UCS strength of kaolinite minerals is controlled by the net attractive force between the clay particles. The present study demonstrated that the pore size distribution is also one of the parameters that strongly influences the unconfined compressive strength of the soil.

Permeability of gases through geomaterials are critical in areas like landfill cover design, buffer material characterization in deep geological repositories for radioactive waste containment, geosequestration of greenhouse gases, oil and gas recovery. In general, there are two types of laboratory methods for determination of gas permeability of geomaterials, such as steady-state and transient or pressure decay methods. In all these methods, the sample thickness that needs to be considered is important for accurate estimation of gas permeability characteristics. In view of this, the present study discusses the effect of sample thickness on the laboratory determination of gas permeation through geomaterials. A permeability apparatus has been developed for evaluating the gas permeability characteristics of geomaterials over a range of compaction state, based on the concept of pressure decay. Further, the experiments are conducted at different sample thicknesses along the standard Proctor compaction curve and the effect of sample thickness on gas permeability has been evaluated.

Electro-kinetic properties of colloidal substance can be studied in terms of its zeta potential, which indicates the stability of the colloidal system. Numerous investigations have been made in the past several decades in areas of electro-kinetic remediation and stabilization of fine-grained soils. A proper understanding of the underlying mechanism of the above processes demands a thorough knowledge of the zeta potential of the system. Further, the electro-kinetic process can significantly alter the physio-chemical and electrical properties of the clay-water-electrolyte system which is also manifested as a change in the zeta potential value. Various environmental factors that affect the zeta potential include temperature, electrolytic concentration, cation valency and pH of the medium. The investigations made in view of understanding the role of zeta potential in determining electro-kinetic efficiency of various soils are widely scattered and no attempts have been made so far to interpret the available data, making it difficult to arrive at any conclusive inference. In this context, the present study attempts to evaluate the investigations carried out, by the previous researchers, to identify the factors that are influencing zeta potential and its role on electro-kinetic properties of clay minerals. In addition, zeta potential measurements are conducted on kaolinitic type and Na-bentonite soils over a wide range of pH and the results are compared with the data available in the literature.

Water vapour diffusion is a predominant moisture transport mechanism in an unsaturated soil due to the presence of either thermal gradient or concentration gradient. In such soils, as water content decreases, the continuity of liquid films is lost, and as a result, water movement is mainly in the form of water vapour. The knowledge of water vapour migration characteristics of geomaterials is important in the performance evaluation of underground buried services, compacted/geosynthetic clay liners, geothermal energy utilization, thermally enhanced clean-up of contaminated sites and the containment facilities for disposal of high-level nuclear waste. In view of this, the present study describes a methodology to investigate the water vapour diffusion through geomaterials under isothermal conditions. Further, the study evaluates the effect of particle size and compaction state on water vapour diffusion characteristics of the soils.

Rapid industrialization and urbanization cause release of significant quantities of hazardous contaminants, including heavy metals and radionuclides, into the biosphere. Severe accumulation of these contaminants and their exposure deteriorates human health, environment, and biota system. Conventional remediation of heavy metal, radionuclide contaminated soils includes physicochemical extraction, stabilization/solidification/immobilization, soil washing. These techniques demand large quantities of chemical reagents, huge cost apart from the generation of secondary toxic by-products, and hence, the aforementioned techniques become unsuccessful and ineffective. This necessitates an interdisciplinary approach using biomediated processes and/or derived by-products, which enhances remediation process through accelerated biogeochemical phenomenon. Bioremediation is a broad area which involves large matrix of remediation techniques such as bioaccumulation, biosorption, biosparging, bioleaching, biomineralization, phytoremediation. Among all these techniques, biomineralization or microbially induced carbonate mineral precipitation is the most fascinating, promising methods to handle the present-day challenges pertaining to remediation of contaminated soils. In view of this, the current study presents a critical review on mechanisms of microbially induced carbonate precipitation in view of solid-phase sequestration of inorganic contaminants. Further, this study assesses the suitability of various microorganisms along with the associated precipitation processes for transforming soluble inorganic compounds into stable and non-redox sensitive carbonate minerals.

Determination of thermal conductivity of buffer materials is an important aspect in the design and characterization of engineered barrier systems (EBS) in deep geological repositories (DGRs) for safe containment of high-level nuclear waste. Several factors, viz. compaction state, particle size distribution, and mineralogical characteristics of buffer materials, influence the thermal conductivity of composite buffer materials. Therefore, it is essential to give due regards to the influence of these factors while estimating thermal conductivity of buffer materials. In view of this, the present study pertains to an extensive laboratory scale determination of thermal conductivity of a wide range of sand-bentonite based buffer materials employing a thermal needle probe. Precision and accuracy of the thermal needle probe are established in relation to a contemporary and widely endorsed thermal property analyzer. Further, the efficacy of several predictive models available in the literature is evaluated to appraise the thermal conductivity of composite buffer materials in relation to the experimental data. Realizing the need of a generalized approach considering the influence of clay mineralogy and particle size fraction present in the geomaterial, the manuscript proposes generalized thermal conductivity prediction models meant for the buffer materials. The developed models are found to deliver satisfactory performance and accuracy in appraising thermal conductivity of sand-bentonite buffers used in DGRs.