Dali Naidu Arnepalli

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.

A series of fluorinated high density polyethylene (f-HDPE) geomembrane (GM) samples of different thickness (1, 1.5 and 2.5 mm) was exhumed from the backfill immediately upstream of a barrier system constructed to contain a hydrocarbon spill in the Canadian Arctic. The samples were tested for oxidation induction time (OIT), crystallinity, melt index (MI) and tensile properties. The results of these tests are reported and it is shown that the durability of the GM was maintained well beyond the initial 3-year design life of the barrier system. Based on 7 years of field data, the std-OIT depletion time for the 1.5 mm thick GM used in the barrier system was inferred to be over 140 years while the antioxidant depletion time based on the HP-OIT is estimated to be about 200 years. No significant temporal changes in the crystallinity, MI or tensile properties of the exhumed GM samples were detected. © 2009 Elsevier Ltd. All rights reserved.

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.

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.

This study investigates effect of liquid to solid ratio, initial concentration of heavy metals, pH and composite heavy metal solution and nature of sorbent on sorption capacity of two different geomaterials such as clayey soil and moorum. The batch sorption experiments were carried out with the selected geomaterials using different heavy metal solutions such as Copper, Manganese, Zinc, Lead and Chromium. Based on the experimental results, the following conclusions are drawn i) increasing liquid to solid ratio decreases the removal rate of heavy metal, however heavy metal sorbed on unit mass of the sorbent increased at equilibrium ii) increase in pH and the initial heavy metal concentration leads to an increase in the heavy metal uptake by the geomaterials iii) nature of the clay mineral present in the geomaterials plays significant role in controlling the sorption characteristics of the geomaterials compared to amount of clay content present in the geomaterials iv) observed order of selectivity of heavy metals is Cr >Pb >Cu >Mn ∼Zn.

The knowledge of adsorption characteristics of bentonite (B) is mandatory for heavy metals removal from the wastewater and contaminant retention in landfill liner. Adsorption characterization of geomaterials requires the use of a buffer for pH adjustment. Previous studies have not investigated the impact of using a buffer on the adsorption characteristics of swelling soils such as B. This study quantified the influence of sodium acetate (Na-Ac) buffer on the adsorption capacity of B and percentage removal of lead (Pb2+) using a batch adsorption study (BAS). The solution was adjusted using either nitric acid or Na-Ac buffer to maintain pH=5. The sediment volume of bentonite suspension in water at pH 5 adjusted with Na-Ac buffer was less than that using nitric acid. The lesser sediment volume was due mainly to the agglomeration of bentonite particles in the presence of Na-Ac buffer. The experimental findings corroborate that the use of Na-Ac buffer results in a notable reduction of adsorption capacity and percentage removal of Pb2+ by B. The highest percentage removal of Pb2+ ions was observed at a liquid-to-solid ratio (L/S) of 20 when pH was adjusted with nitric acid. The lowest percentage removal was noted at L/S=100 when pH was maintained using Na-Ac buffer. The influence of Na-Ac buffer also was evaluated by conducting a BAS for Pb2+ removal under a competitive environment of Na+ using sodium chloride (NaCl) and Na-Ac buffer. The interaction of Pb2+ with B in two different environments was confirmed by mineralogical, morphological, and spectral analysis postadsorption. According to this study, nitric acid can be a better alternative to Na-Ac buffer for the adsorption study of B in a controlled pH environment. If a buffer is used for the adjustment of pH in a BAS, its effect on the adsorption capacity and percentage removal should be taken into account when characterizing B for its practical application in water decontamination, waste containment system, and chemical reactive barrier projects.

Ground improvement techniques involving chemical additives are often energy-intensive and unsustainable due to the environmental distress caused by them. Sustainable biocementation processes such as microbially induced calcite precipitation (MICP) can overcome the drawbacks of traditional ground improvement techniques. Capturing the underlying coupled mechanisms in the biocementation process requires the knowledge of diverse fields of bio-chemo-hydro-mechanics. Modeling such a complex phenomenon is imperative for the successful implementation of the stabilisation technique in the field. The existing coupled models on biocementation are chiefly intended to validate the observed behavior of laboratory-scale biocemented specimens. This scenario demands the need to develop a coupled bio-chemo-hydro-mechanical (BCHM) model for field simulations. The BCHM model was developed with finite element and backward Euler finite difference approximations in space and time. The Galerkin weak formulations are derived for the mass balance equations of the coupled model. The advective-governed transport phenomena are accommodated with the Petrov-Galerkin formulation. An overall kinetically controlled reactive model is implemented to reproduce the urea hydrolysis and associated chemical kinetics. The reduced permeability of the biocemented soil is accounted in terms of its effective porosity, using the modified Kozeny-Carman equation. The fixed-point iteration scheme is implemented for bio-chemo-hydraulics to deal with the nonlinearity in the balance equations. The mechanical constitutive response of biocemented soil is simulated using a micromechanical framework. The von Mises and Drucker-Prager plasticity models were adopted for the biocement and soil particle phases, respectively. The integration of plasticity models was carried out using a return mapping algorithm. The Newton Raphson scheme is considered for the finite element implementation of elastoplastic models. The fully coupled nonlinear finite element problem is solved in a staggered approach using the developed MATLAB routine. The contour plots of biomass and chemical concentrations and precipitated calcite content are generated. The considered elastoplastic model predicted improvement in mechanical strength of biocemented specimen. A complete bio-chemo-hydro-mechanical behavior of the two-dimensional geometry is captured.

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.

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.

The time to rupture of a 1.5-mm-thick high-density polyethylene geomembrane aged in a typical landfill composite liner configuration is investigated under a pressure of 250 kPa at 85 ° C. The geomembrane was underlain with a geosynthetic clay liner and had a 560 g=m2 needle-pinched nonwoven geotextile protection layer separating it from 50 mm of drainage gravel containing leachate. Seventeen (0.6-m-diameter) tests were conducted. In addition to 9 months required to deplete antioxidants (Stage I), the tests indicated a lag period (Stage II) of 5.5 months and a time from the start of degradation to rupture (Stage III) of 20 months, giving a total inferred time to rupture of 34.5 months (2.9 years). There were up to 61 brittle ruptures per sample (i.e. > 2 million cracks per hectare). The ruptures were predominately oriented in the machine direction and located (1) directly beneath a gravel contact, (2) at the side of a gravel indentation, or (3) between gravel indentations. The ruptures between gravel indentations were the least frequent but largest. The calculated strains perpendicular to the rupture direction were 24±6%. Rupture occurred, although the average stress-crack resistance for all ruptured geomembrane samples still was approximately 760±200 h, with a minimum of 360 h. These results indicate the importance of minimizing tensile strains in the geomembrane in the design of a liner system.