Os resíduos de mineração, quando dispostos diretamente sobre o solo podem vir a causar contaminação do meio, em decorrência da presença de metais potencialmente tóxicos. Desta forma, a disposição adequada de tais resíduos torna-se necessária, tanto para futuras áreas de disposição como para as que foram degradadas pela disposição inadequada. Neste contexto, esta pesquisa teve por objetivo avaliar a viabilidade geotécnica e geoquímica de solos argilosos transportados, para serem empregados como barreiras selantes (liners) na disposição de resíduos de mineração. Isso visou solucionar o problema ambiental da região do Vale do Ribeira, onde tais resíduos (enriquecidos por metais potencialmente tóxicos) foram dispostos diretamente sobre o solo, contaminando esse compartimento. Desta forma foram caracterizados três solos (SA, SB e SC) coletados na região do Médio Vale do Ribeira (município de Eldorado Paulista). Nestes solos foram realizadas caracterização geotécnica (ensaios granulométricos, limites de consistência, condutividade hidráulica e ensaios de compactação) e caracterizações geológicas-geoquímicas (análises mineralógicas, análises químicas, parâmetros físico-químicos e teor de matéria orgânica). Além das caracterizações foram realizados ensaios de adsorção (batch test), sendo que a solução contaminante foi cloreto de chumbo nas concentrações de 50, 100 e 150 mg kg-1. De maneira geral, notou-se que o solo menos adequado para ser empregado como barreira selante é o SB. O solo SA apresentou características geológicas-geoquímicas mais adequadas para retenção dos metais, principalmente Pb (maior CTC, maior SE, argilominerais não expansivos, presença de ilita, maior teor de matéria orgânica e maior delta pH). Já o solo SC é mais adequado quanto aos parâmetros geotécnicos (maior fração argila, menor fração areia, maior LL, maior IP, maior umidade ótima, e maior índice de vazios). Todos os solos exibiram baixa condutividade hidráulica (10-8 a 10-9 m/s), o que é considerado adequado para uso em barreira selante. Quanto a adsorção de Pb, nota-se que os três solos atuam na retenção do mesmo, sendo que os solos SA e SC apresentaram maior capacidade de adsorção que o solo SB. Desta forma, com todos os resultados conclui-se que os solos SA e SC são viáveis para serem usados na construção de barreiras selantes na região do Vale do Ribeira, por apresentarem características de retenção apropriadas para o metal analisado. / When the mining wastes are disposed on the soil, they may cause environment contamination due to the existence of potentially toxic components. Therefore, the correct disposal of these wastes is necessary, for new areas of disposal as much for areas degraded by the incorrect disposal. In this context, this research aimed to evaluate the geotechnical and geochemical viability for transported clay soils to be applied as liners to dispose mining wastes. This way, the environmental problem of the Vale do Ribeira may be solved, where such wastes (containing potentially toxic metals) were disposed on the soil and contaminated it. Thus, three soils samples (SA, SB and SC) were collected in Eldorado Paulista so they could be characterized. In these soils were conducted geotechnical tests (gradation, Atterberg limits, hydraulic conductivity and Proctor compaction) and geological and geochemical analysis (mineralogical, chemical, physic-chemical and soil organic matter content). Besides, were conducted batch tests using a contaminating solution of PbCl2 with the concentrations of 50, 100 and 150 mg.kg-1. In general terms, the least proper soil to be used as liner is the SB. The SA soil presented the most proper geological and geochemical characteristics for metal adsorption, mainly Pb (higher CEC and surface area, its clay-minerals are not expansive, existence of ilite, higher content of soil organic matter and higher &#916pH). The SC soil is the most proper to be used as liner regarding its geotechnical properties (more clay fraction and less sand fraction, higher liquid limit and plasticity index, water content optimum and void index). All soils presented low hydraulic conductivity (10-8 to 10-9 m/s), that is considered proper to be used in liners. Concerning the Pb adsorption, the three retain it, but the SA and SC soils presented better adsorption capability then the SB soil. Therefore, considering all the results, it may be concluded that the SA and SC soils are preferable to be applied in liners in Ribeira Valley, because they present the most proper characteristics for adsorption of the analyzed metal.

En vue de la réduction des problèmes engendrés par les phénomènes de retrait-gonflement des sols dans la dépression de la Lama au Sud du Bénin, nous avons entrepris des recherches dans le but de maîtriser le comportement de ces sols. Six échantillons de sols fins dont quatre argileux de cette région ont été prélevés. Différents essais ont été réalisés : une caractérisation macroscopique concernant les propriétés mécaniques et géotechniques et les essais microscopiques prenant en compte les analyses chimiques, thermiques, minéralogiques et microstructurales. Les sols étudiés sont constitués de différents minéraux argileux. Celle à structure fibreuse est à l'origine d’un comportement macroscopique particulier décelé par l’essai de gonflement libre. Les essais ont confirmé le fort potentiel de gonflement et de retrait de certains sols qui sont donc à l'origine des fortes dégradations rencontrées.Les résultats montrent que les sols traités se distinguent par les performances mécaniques acquises et peuvent être utilisés à différents niveaux de la chaussée selon leur teneur en liant.Les différentes méthodes utilisées ont révélé des facettes particulières de l'étude de traitement des sols fins. Principalement, nous avons noté que les informations apportées par les observations au Microscope Electronique à Balayage, les analyses thermiques et les analyses de Diffraction aux Rayons X ont permis de compléter l’analyse des résultats géotechniques. En somme, les méthodes de caractérisation géotechnique permettent d’avoir une idée générale du potentiel de gonflement, mais pour les études d’envergure, la réalisation d’études microscopiques est primordiale. / To help reduce the problems caused by phenomena due to the shrink-swell soil in the depression of the Lama in southern Benin, we have undertaken research in order to control the behavior of these soils. Six soil samples, including four clay from this area were taken. Different types of tests were performed: a macroscopic characterization concerning mainly mechanical and geotechnical properties and microscopic tests taking into account the chemical, thermal, microstructural and mineralogical analysis. The soils studied consist of different clay minerals. The fibrous structure is at the origin of a particular macroscopic behavior detected by the free swell test. The tests confirmed the potential for swelling and shrinking of some soils that are causing heavy damage.Three soils treated with different contents at Binder Hydraulic Road, were subjected to several tests. The results show that these soils are distinguished by the acquired mechanical performance and may be used at different levels of the floor according to binder content.Also, the different methods revealed specific facets of fine soil treatment study. Mainly, we noted that the information provided by the observations scanning electron microscope, thermal analysis and the analysis of diffraction X-Ray are very important and helped complete the analysis of geotechnical results for soil treatment. In sum, geotechnical characterization methods used to get a general idea of the swelling potential, but for large-scale studies, conducting microscopic studies is paramount.

Copies of author's previously published articles inserted. Bibliography: leaves 173-196. The objective of this thesis is to investigate the factors affecting swelling and dispersion of alkaline sodic soils containing lime and the ways to manage these soils to improve their physical condition. Studies on pure clay systems are included to understand the fundamental process involved in swelling and dispersion of pure and soil clays.

Copies of author's previously published articles inserted. / Bibliography: leaves 173-196. / xviii, 197 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The objective of this thesis is to investigate the factors affecting swelling and dispersion of alkaline sodic soils containing lime and the ways to manage these soils to improve their physical condition. Studies on pure clay systems are included to understand the fundamental process involved in swelling and dispersion of pure and soil clays. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science

Subsurface drainage has recently become common for agriculturally productive soils and key to maintain and improve crop production in poorly drained, frigid clay soils. The first study was conducted for four years (2014-17) at Casselton, ND to determine best combination of drainage, tillage and crop rotation for higher corn yield. Our finding suggested corn yield was highest with no drainage, CS and CH combination in years with drought conditions. The second study was conducted for three years (2015-17) to evaluate subsurface drainage spacing (9, 12, and 15m) and depth (0.9 and 1.2m) combination on corn, soybean and sugarbeet yields and residual soil nitrate-nitrogen (NO3-N) contents. Results indicated that 9 m drain spacing produced highest corn and soybean yield when average across three years in contrast with drain depth that has no effect on corn and soybean yield except for sugarbeet where the 1.2m depth yielded higher than the 0.9m depth. / North Dakota Corn Council / North Dakota Soybean Council / North Dakota Water Resources Research Institute

The fact that when lime is added to clayey soils same very beneficial results are produced dates back into the remote past. It is not a new development, In the United States lime has been in use since l923. The objective of this study was to determine the effect of increasing soaking time of soil-lime mixtures on the strength, swell potential, and degree of saturation. In order to ascertain the exact composition of clay minerals, X-ray diffraction analysis was run on the soil sample. The analysis showed that the clayey soil contained a large amount of water with a greater percentage of halloysite minerals. The soil, it was concluded, was poorly crystalline and was found to be midway between montmorillonite and kaolinite group. / Master of Science

Thesis (PhD (Botany and Zoology))—University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Metal pollution is a problem of increasing global concern. It could arise from industrial activities, as well as pesticide use in agriculture, among other sources. For adequate protection of the soil ecosystem from metal toxicity, the bioavailability of metals must be properly evaluated. A plethora of soil factors affect the bioavailability of metals to soil organisms. These include pH, clay and organic matter contents, salinity among others. While much is known about the influence of some of these parameters, little is known on how clay content and salinity modify the bioavailability of metals to soil organisms. This study investigated the influence of clay content and salinity on partitioning, uptake and toxicity of two essential metals (Cu and Zn) to the earthworm Eisenia fetida in separate laboratory trials. Partitioning of the metals was evaluated with 0.01 M CaCl2, DTPA (di-ethylene-triamine-penta acetic acid), and nitric acid extractions. The metal content of worms was determined by acid digestion, while growth, cocoon production, and mortality were used as endpoints showing toxicity to metals and/or salinity. To test the validity of some of the laboratory results, a field study was undertaken, using the earthworm Aporrectodea caliginosa. Further, the study assessed the effect of salinity, using a battery of laboratory tests (acute, chronic and avoidance tests) with natural and/or artificial soils on four species of organisms (a collembolan Folsomia candida, a potworm Enchytraeus doerjesi and two earthworm species E. fetida and A. caliginosa), representing different feeding patterns and ecological roles in soil. Results showed that with increased clay content, there was increased availability of Cu in the substrate, and increased toxicity to E. fetida as shown by data for mortality and growth. The situation with Zn was less significant at sub-lethal concentrations but much so at lethal concentrations. DTPA and CaCl2 extracted metals revealed changes in partitioning of Cu and Zn with changes in clay content, but this trend was not always consistent. Both DTPA and CaCl2 revealed increased availability of Zn in substrates with increased salinity. Salinity had an additive to synergistic effect with Zn in toxicity to E. fetida. When combined with Cu, salinity also increased the availability of Cu as shown by CaCl2 extracted fraction, and had additive effect on toxicity of Cu to the earthworm. The field study did not succeed in in iv confirming the results of the laboratory study due to confounding role of flooding after heavy rainfall and subsequent leaching of salts and Cu. The results of the experiment on acute and chronic toxicity tests for NaCl on E. fetida showed LC50 of 5436 mg/kg NaCl and EC50 for growth and cocoon production of 4985 and 2020 mg/kg NaCl. These values showed that earthworms might be negatively affected in many soils containing fairly moderate concentrations of salts. Similarly, A. caliginosa could not survive in natural soil containing relatively low salt concentrations (EC = 1.62 dS/m) while reproduction was severely affected at lower EC value of 0.52 dS/m. F. candida and E. doerjesi could survive in the highest salinity soil (EC = 1.62 dS/m) used in this study but their reproduction was severely affected from 1.03 dS/m. Overall, it appears that of all the taxa used, earthworm species were the most sensitive to saline stress and could proof useful in determining ‘safe levels’ of salt in contaminated soils. The results of the avoidance test showed that A. caliginosa avoided both natural and artificial saline soil containing concentrations lower than those avoided by E. fetida. The conclusion is that the influence of clay content and salinity on the bioavailability of Cu and Zn depends largely on the metal in question, but generally speaking, bioavailability and toxicity of the metals were reduced with increased clay content while the opposite was true for salinity. If the species used in this study can be seen as fairly representative of a wide range of soil organisms, the conclusion is that salinisation of soil will be detrimental to most soil organisms at relatively low saline concentrations. Given the role of beneficial soil organisms in several soil processes which in turn contribute to soil fertility and sustainable use of land, it is recommended that any farming practices that may lead to an increase in salt content of agricultural soils should be discouraged. / AFRIKAANSE OPSOMMING: Metaalbesoedeling is ‘n probleem wat toenemende globale kommer veroorsaak. Dit kan ontstaan as gevolg van industriële aktiwiteite sowel as van plaagmiddelgebruik in die landbou en ander bronne.Ten einde die grondekostelsel genoegsaam te beskerm, moet die biobeskikbaarheid van metale ge-evalueer word. ‘n Verskeidenheid van grondfaktore be-invloed die biobeskikbaarheid van metale vir grondorganismes Hulle sluit onder andere in pH, klei, organiese inhoud en soutgehalte. Hoewel heelwat bekend is oor die rol van sommige van hierdie parameters, is min bekend oor hoe klei en soutgehalte die biobeskikbaarheid van metale vir grondorganismes kan modifieer. Hierdie studie het die invloed van kleiinhoud and soutgehalte op die verdeling/partisie, opname en toksisiteit van twee essensiële metale (Cu en Zn) vir die erdwurm Eisenia fetida in afsonderlike laboratoriumproewe ondersoek. Kompartementele verdeling van die metale is geevalueer deur middel van ekstraksie-metodes met 0.01 M CaCl2, DTPA (di-etileentriamien- penta asysnsuur), en salpertersuur ekstraksies. Die metaalinhoud van wurms is bepaal deur suurverterings en spektrofotometriese analises te doen terwyl groei, kokonproduksie en mortaliteit van organismes gebruik is as gevoeligheidseindpunte om toksisiteit van metale en soutgehalte aan te toon. Om die geldigheid van somige van die laboratoriumresultate te toets, is ‘n veldstudie ook onderneem met die erdwurm Aporrectodea caliginosa. Die effek van soutgehalte is verder ondersoek deur ‘n battery van laboratoriumtoetse met vier spesies (‘n kollembool Folsomia candida,’n potwurm Enchytraeus doerjesi en twee erdwurmspesies E. fetida en A. caliginosa), wat verskillende voedingspatrone verteenwoordig. Die resultate het getoon dat met toenmende klei-inhoud was daar ‘n toename in die beskikbaarheid van Cu vir opname vanuit die substraat, asook ‘n toename in toksisiteit vir E. fetida soos deur die gegewens vir mortaliteit en groei uitgewys. Die situasie met Zn was minder betekenisvol by subletale konsentrasies en selfs baie minder so by letale konsentrasies. DTPA en CaCl2 ge-ekstraheerde metale het veranderinge in die partisie/verdeling van Cu en Zn uitgewys met verandering in klei-inhoud, maar die tendens was nie altyd konstant nie. Beide DTPA en CaCl2 ekstraksie het toenemende beskikbaarheid van Zn in substrate uitgewys met toenemende soutinhoud. Soutinhoud het ‘n additiewe/toegevoegde tot sinergistiese vi toksisiteitseffek saam met Zn vir E. fetida. In kombinasie met Cu het soutgehalte ook die geskatte biobeskikbaarheid van Cu verhoog soos uitgewys deur die CaCl2, geekstraheerde fraksie, en het ‘n additiewe effek gehad op die toksisitiet van Cu vir die erdwurm. Die veldstudie kon nie die resultate van die laboratoriumstudie bevestig nie weens die belemmerende rol van vloede na swaar reënneerslae en daaropvolgende uitloging van soute en Cu. Die resultate van die eksperimentele ondersoek na die akute en chroniese effekte van NaCl op E. fetida het ‘n LC50 van 5436 mg/kg NaCl en EC50 vir groei en kokonproduksie van 4985 en 2020 mg/kg NaCl opgelewer. Hierdie waardes het aangetoon dat erdwurms moontlik negatief beinvloed kan word in baie gronde wat ‘n redelike gemiddelde konsentrasie van soute bevat. Soortgelyk kon A. caliginosa nie oorleef in natuurllike grond wat relatief lae soutkonsentrasies bevat het (EC=1.62 dS/m) nie terwyl voortplanting sterk ge-affekteer is by ‘n lae EC waarde van 0.52 dS/m. F. candida en E. doerjesi kon oorleef in die grond met die hoogste soutgehalte (EC= 1.62 dS/m) maar hulle voortplanting is ernstig geknou vanaf 1.03 dS/m. In geheel blyk dit dat van allle taksa wat gebruik is, erdwurms die sensitiefste was vir die stres wat deur soutgehalte veroorsaak is. Die kennis kan nuttig wees in die bepaling van “veilige vlakke” van sout in gekontamineerde gronde. Die resultate van die vermydingstoetse het getoon dat A. caliginosa beide natuurlike en kunsmatig versoute gronde vermy het by konsentrasies wat heelwat laer was as dié wat deur E. fetida vermy is Die gevolgtrekking is dat die invloed van klei en soutgehalte op die biobeskikbaarheid van Cu en Zn grootliks afhanklik is van die metale wat betrokke is en dat biobeskikbaarheid en toksisiteit normaalweg verminder het met verhoogde klei-inhoud, met die teenoorgestelde wat waar was in die geval van soutgehalte. Indien die spesies wat in die studie gebruik is beskou kan word as redelik verteenwoordigend van ‘n wye reeks van grondorganismes, is die gevolgtrekking dat versouting van gronde nadelig sal wees vir meeste grondorganismes, selfs by relatief lae soutkonsentrasies. In die lig van die rol wat nuttige grondorganismes speel in verskeie grondprosesse wat bydraend is tot grondvrugbaarheid en volhoubare gebruik van gronde, word dit aanbeveel dat enige boerderypraktyk wat mag lei tot verhoging van die soutinhoud van landbougronde ontmoedig moet word.

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

Total suction of unsaturated soils is contributed by matric and osmotic suctions. Matric suction arises from capillary actions in the soil structure and varies with changes in moisture content of the soil. Pore fluid osmotic suction is related to the dissolved salt content in soil water (soil water salinity) and increases with pore water salinity. Exposure of clay soils to chemical solutions (example landfill leachate, brine pond solutions) induces osmotic suction difference between soil water and the chemical reservoir. Soil water refers to the aqueous solution residing in soil pores that is chemically composed of H2O molecules and dissolved salt molecules. Osmotic suction difference between soil water and the chemical reservoir is dissipated through the following modes. Salt molecules diffuse from the chemical reservoir to the soil water and H2O molecules from soil water flows to chemical reservoir to equalize salt concentrations in the two chambers. This flow of H2O molecules is called an osmotic flow. During osmotic flow, if the clay particles behave as perfect semi-permeable membranes, only water exchanges between clay voids and the external solution in response to chemical concentration gradients. Clay particles however function as imperfect semi-permeable membranes and transfer dissolved salts in addition to water. The outward flow of H2O molecules from soil water (dilute solution chamber) to chemical reservoir (concentrated solution chamber) causes negative pore fluid pressures to develop within the compacted clay, which then leads to increase in effective stress and the consequent volume decrease is termed as osmotic induced consolidation. Conversely, diffusion of salt molecules from chemical reservoir to soil water in response to chemical concentration gradient reduces the thickness of the diffuse ion layers around the clay particles causing a decrease in the electrical repulsion forces between them. This in turn reduces the separation of the clay particles and, consequently, compresses the clay sample to a lower void ratio; the process being termed as osmotic consolidation. Tests described by researchers show that osmotic consolidation usually has a larger effect than the osmotically induced one. Review of the literature shows that most of the available theoretical and experimental analysis in literature only focuses on the behaviour of clay samples reconstituted from slurries and not on the one of compacted clays. Compacted clays are exposed to osmotic suction gradients under field situations such as landfills and brine ponds where compacted clay liners are in contact with leachate/brine solutions. Examining the impact of osmotic suction dissipation on the swell/compression behaviour of compacted clays forms the focus of the present thesis. Statement of Problem Compacted clays differ from clay samples reconstituted from slurries as they are characterized by both matric suction and osmotic suction. As a result, besides dissipating osmotic suction gradients by diffusion of salt molecules and flow of H2O molecules, compacted clays absorb salt solution in their partly saturated void spaces to dissipate matric suction and in the process may develop swelling strains. However, absorption of salt solution to dissipate matric suction and salt diffusion in response to osmotic suction difference will alter the diffuse double layer (DDL) thickness as the latter is affected by the dissolved salts concentration of soil water; alterations in DDL thickness will in turn affect the swelling behaviour of the compacted clays. The influence of alterations in DDL thickness from dissipation of matric suction and osmotic suction difference on the swelling magnitudes of compacted expansive clays exposed to salt solutions needs to be examined. The direction of salt diffusion in response to dissipation of osmotic suction difference will also impact the swelling behaviour of compacted clays exposed to osmotic suction gradients. Diffusion of salts from external reservoir to soil water (salinization path) in response to osmotic suction gradients will reduce the swell potential of the compacted expansive clay from increased dissolved salts concentration in soil water. Conversely, diffusion of salts from soil water to external reservoir (desalinization path) should facilitate the compacted clay to swell more from reduction in its dissolved salts concentration. The influence of direction of salt diffusion during dissipation of osmotic suction gradient on the swell behaviour of compacted expansive clays needs to be examined. The volumetric response of compacted clays exposed to salt solutions may be different compared with identically compacted specimens wetted with distilled water at same total vertical pressure value. As previously mentioned, exposure of compacted clays to salt solutions, besides destroying capillary bonds will alter the soil water chemistry of the compacted clay specimens from absorption of salt solution to dissipate matric suction and salt diffusion in response to osmotic suction gradients. Alterations in soil water chemistry in turn alter the swell pressures of compacted clay specimens from concomitant changes in electrical repulsion forces. If the modified swell pressure of the compacted specimen exceeds the total vertical pressure, diminished swelling strains result at the macroscopic level. Conversely, the compacted clay will experience compressive strains at the macroscopic level if the total vertical pressure exceeds the modified swell pressure of the compacted specimen. Alterations in the wetting induced volumetric response of compacted clays from modifications in swell pressure upon exposure to salt solutions needs to be examined. Earlier researchers had re-plotted the compressibility data for sodium- montmorillonite clays remolded with sodium chloride solutions using the osmotic suction of the remolding fluids as a stress state variable in a three-dimensional space. Along a plane in which osmotic pressure (π) is constant, the coefficient of volume compressibility (mv) was obtained. Along a plane in which the effective stress [(σ - uw)] is constant, the slope defined the osmotic coefficient of volume compressibility (mπ). The above concept is useful to predict the osmotic consolidation strains of clay specimens upon exposure to salinization paths at constant effective stress. Salt diffusion into soil water in response to osmotic suction gradients may alter the exchangeable cation composition of saturated clay specimens. Alterations in exchangeable cation composition alters the diffuse ion layer thickness of clay particles which in turn may impact the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path. Saturated saline specimens refer to saturated clay specimens that are exposed to salinization (saturated specimens are inundated with salt solution) path. Saturated desalinated specimens are obtained by exposing saturated saline specimens to desalinization (inundated with distilled water) path. Osmotic swelling refers to the swelling strains developed by saturated saline specimens on exposure to desalinization path. These strains result from outward migration of salts in response to osmotic suction gradients. The influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path needs examination. The swelling magnitudes of compacted specimens are influenced by variations in dry density, water content and consolidation pressure. However, the effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path is not known and needs examination. Based on the statement of the problem, the following objectives emerge: • To examine the influence of dissipation of matric suction and osmotic suction difference on the swelling behaviour of compacted expansive clays exposed to osmotic suction gradients (salinization path). • To examine the influence of direction of salt diffusion during dissipation of osmotic suction gradients on the swell behaviour of compacted expansive clays. • To examine alterations in the wetting induced volumetric strain response of compacted clays from modifications in swell pressure upon exposure to salt solutions at range of total vertical pressures. • To predict the osmotic consolidation strains of saturated clay specimens upon exposure to salinization paths at constant effective stress. • To examine the influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path. • To examine, effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path. The organization of the thesis is as follows: After the first introductory chapter, a detailed review of literature is performed towards highlighting the need to examine the influence of dissipation of osmotic suction gradients on the swell-compression behaviour of compacted expansive clays in Chapter 2. Chapter 3 presents a detailed experimental program of the study. Chapter 4 examines the influence of dissipation of matric suction and osmotic suction difference on the swelling behaviour of compacted expansive clays exposed to salinization path. The chapter also examines the influence of direction of salt diffusion durin dissipation of osmotic suction gradients on the swell behaviour of compacted expansive clays. Black cotton soil from Karnataka State was used as the expansive clay specimen to examine these objectives. Inundating compacted expansive clay specimens with (0.1 M to 4 M) sodium chloride solutions at a total vertical pressure of 6.25 kPa in oedometer cells exposed the clay specimens to salinization paths. Measurements of changes in swelling strains, matric suction (measured by filter paper method) and pore water chemistry with time provided insight into the relative influence of matric suction and salt diffusion on the kinetics of swell. Examining the time-axial deformation behaviour of compacted specimens exposed to salinization paths in the post-primary swell region delineated the influence of osmotic suction dissipation on the volume change behaviour of compacted expansive clays. The influence of direction of salt diffusion in response to osmotic suction gradients on the swelling behaviour of compacted expansive clay was examined in the following manner. Salt diffusion from external reservoir to soil water (salinization path) was accomplished by inundating compacted clay specimens with 0.4 M and 4 M sodium chloride solutions in oedometer cells at 6.25 kPa. Salt diffusion from soil water to external reservoir (desalinization path) was accomplished by inundating salt-amended specimens with distilled water in oedometer cells at 6.25 kPa. Salt-amended specimens refer to expansive clay specimens remolded with 0.4 M/4 M sodium chloride solution at desired moisture content and compacted to the design density. Experimental results illustrated that compacted specimens dissipated matric suction by absorption of distilled water and sodium chloride solutions. The initial osmotic suction difference was dissipated by inward diffusion of salts; salt solutions absorbed to dissipate matric suction also contributed to dissipation of osmotic suction difference. The compacted clay specimens swelled on inundation with sodium chloride solutions as dissipation of matric suction and the attendant growth of diffuse ion layer repulsion dominated compacted clay behaviour exposed to salinization paths. However exposure to salinization path reduced swell magnitudes of compacted clay specimens from reductions in diffuse ion layer thickness. The time-swell plots of the compacted clay specimens exposed to salinization path categorized into initial, primary and secondary swell regions. Rates of primary swell were 5 to 21 times larger than rates of secondary swell. Experimental data suggested that primary swell develops relatively rapidly as it is linked to rate of matric suction dissipation. Secondary swell developed more slowly as it is controlled by diffusion of salts and adsorption-desorption reactions. Increase in dissolved salts concentration in soil water during primary swell occurs from salt solution absorbed in response to matric suction and salt diffused in response to osmotic suction difference. Comparatively, increase in dissolved salts concentration in soil water during secondary swell occurs from diffusion of salts in response to osmotic suction gradients. Exposure of salt-amended clays to desalinization path caused outward diffusion of salts to dissipate osmotic suction difference and absorption of distilled water to quench the matric suction of the salt-amended specimens. The salt-amended specimens developed greater swell potentials than compacted specimens inundated with distilled water owing to reduction in dissolved salt concentration of soil water and replacement of native exchangeable calcium and magnesium ions by sodium ions. The time-swell behaviour of salt-amended specimens exposed to desalinization path categorize into four regions: small initial swell region followed by large primary swell and small secondary swell regions and lastly a large tertiary swell region. Complete dissipation of matric suction coincides with end of primary swell and both processes terminate in 120-240 minutes after inundation for salt-amended specimens exposed to desalinization paths. Further, only small fraction (16 to 18 %) of possible salt extrusion occurs at the end of primary swell and bulk of salt extrusion occurs during secondary and tertiary swell. Secondary swell developed at a slower rate than primary swell, as the rate of osmotic suction dissipation during secondary swell was smaller than rate of matric suction dissipation during primary swell. Likewise, tertiary swell developed at similar or faster rate than primary swell, as rate of osmotic suction dissipation during tertiary swell is similar or quicker than rate of matric suction dissipation during primary swell for the salt-amended clays. Analysis of the laboratory results showed that greater magnitude of outward salt diffusion mobilizes larger magnitudes of secondary + tertiary swell in response to dissipation of osmotic suction difference in case of the salt-amended clay specimens. Comparison of swelling behaviour of specimens exposed to salinization and desalinization paths revealed that the direction of salt diffusion impacts their swelling behaviour. Inward salt diffusion during salinization path reduces the swell magnitude of the compacted specimens. Bulk of the swell occurs during primary swell. Outward salt diffusion during desalinization path imparts a larger swell magnitude to the salt-amended specimens in comparison to the compacted specimen inundated with distilled water. Bulk of the swell occurs during secondary + tertiary swell. Dissipation of matric suction was rapid and coincided with the end of primary swell during salinization and desalinization paths. Bulk diffusion of salts during secondary and tertiary swell was a relatively slow process. Chapter 5 examines alterations in the wetting induced volumetric response of compacted clays from modifications in swell pressure upon exposure to salt solutions at range of total vertical pressures (6.25 kPa to 200 kPa). The chapter delineates the manner in which dissipation of matric suction (arising due to unsaturated status of compacted clay) and osmotic suction difference (arising due to chemical concentration gradients between soil water and chemical reservoir) impacts the DDL repulsion pressure/swell pressure and wetting-induced volume change behaviour of compacted expansive clays as a function of total vertical pressures (6.25 kPa to 200 kPa). Alterations in the diffuse double layer repulsion pressure of compacted clays from salt diffusion are calculated based on Gouy- Chapman diffuse double theory. The diffuse double layer repulsion pressures of compacted clays exposed to salinization paths are compared with the oedometer swell pressures. The impact of modifications in swell pressure from salt diffusion on the nature of wetting-induced volumetric strains (swell/compression) experienced by the compacted expansive clay specimens exposed to salinization paths is also examined. The nature of wetting-induced volume change behaviour is analyzed in context of the total vertical pressure to swell pressure ratio of specimens exposed to salinization paths. Salinization experiments are performed in conventional oedometers with the chemical boundary conditions imposed in an “open air” fashion. In the salinization experiments, salt solutions in the oedometer reservoir were in contact with the soil water through wet porous stones. Experimental results revealed that dissipation of initial osmotic suction difference between soil water and oedometer reservoir via salt migration impacted the diffuse double layer repulsion pressure and the wetting-induced volume change behaviour of compacted clays. Osmotic suction varies directly; while, the diffuse double layer thickness inversely varies with dissolved salt concentration of soil water. Consequently, inundation with sodium chloride solutions increase the initial osmotic suction difference at the expense of the diffuse double layer repulsion pressures developed by the compacted clay specimens. Salt diffusion in response to dissipation of osmotic suction difference reduced the theoretical (DDL repulsion pressure) and experimental swell pressures of compacted clays inundated with sodium chloride solutions. The theoretical swell pressures however greatly differed from the experimental swell pressures. The total vertical pressure to modified experimental swell pressure ratio determined the nature of axial strains (swell or compression) experienced by compacted clays on exposure to osmotic suction gradients. When the total vertical pressure to modified swell pressure ratio less than unity, the compacted clay specimens experienced net swelling on inundation with sodium chloride solutions. Conversely, when the total vertical pressure to modified swell pressure ratio exceeded unity, the compacted clay experienced net compression on inundation with sodium chloride solutions. When the total vertical pressure to modified swell pressure ratio was unity, the compacted clay did experience any net axial strains on inundating with sodium chloride solution. The ingress of sodium chloride solutions in response to matric suction saturated the void spaces of the compacted specimens prior to commencement of compression. As a result, compression strains experienced by the compacted specimens on exposure to salt solutions were mainly contributed by osmotic consolidation strains. The amount of salt diffused into soil water had direct bearing on the magnitude of osmotic consolidation strains experienced by the compacted specimens at given total vertical pressure value. The time-rates of primary consolidation are approximately 20 to 100 times quicker than rates of osmotic consolidation. The much slower rates of osmotic consolidation arise, as this process is mainly diffusion controlled in comparison to primary consolidation that is mainly dependent on the soil’s permeability to water flow under load-imposed hydraulic gradients. Primary consolidation strains exceed the osmotic consolidation strains at total vertical pressures of 100 kPa and 200 kPa on exposing the compacted specimen to 1 M sodium chloride solution. The osmotic consolidation strain exceeds the primary consolidation strain on exposing the compacted specimen to 4 M sodium chloride solution at total vertical pressure of 200 kPa. Chapter 6 develops a method to predict the osmotic consolidation strains of saturated clay specimens upon exposure to salinization paths at constant effective stress, examines the influence of cation exchange reactions on the osmotic swelling strains developed by saturated saline clay specimens upon exposure to desalinization path and osmotic consolidation strains developed by saturated desalinated clay specimens upon exposure to salinization path and effect of variation in compaction dry density and water content on the osmotic swell behaviour of saturated saline specimen exposed to desalinization path and osmotic consolidation behaviour of saturated desalinated specimen exposed to salinization path Experimental results illustrated that for a given osmotic suction difference (∆π), larger osmotic consolidation strains are predicted at the lower range of consolidation pressures (25-100 kPa), than at the higher range of consolidation pressures (200-400 kPa) as physico-chemical effects dominated the deformation behaviour at the lower stresses, while; mechanical effects (frictional effects, particle interference) became important at higher range of stresses due to proximity of particles and particle groups. Comparatively, at constant consolidation pressure, the magnitudes of osmotic consolidation strains developed by the saturated clay specimens depend on the magnitude of osmotic suction difference (∆π) imposed on the specimens. The slope of the axial strain versus osmotic suction curve defined the coefficient of osmotic compressibility (mπ). Likewise, slope of the axial strain versus effective stresses plot defined the mv values for the specimens. The mπ values are 10 to 20 times smaller than the mv values indicating that the saturated clay specimens experience smaller osmotic consolidation strains from unit increase in osmotic pressure than consolidation strains from unit increase in consolidation pressure. The predicted osmotic consolidation strains were 1.9 to 2.9 times larger than the experimentally determined values. The experimental values were lower as the saturated clay specimens did not compress sufficiently enough on exposure to salinization at concerned effective stress as the well developed diffuse ion layer of the saturated clay specimen inhibited (osmotic) consolidation of the clay specimen. Ion-exchange reaction has a profound influence on the osmotic swelling developed by the saturated saline specimens and osmotic consolidation strains developed by saturated desalinated specimens upon exposure to osmotic suction gradients. Saturated saline specimens are obtained by salinization of the distilled water aturated specimen with sodium chloride solution at desired vertical stress. During salinization ion exchange occurs between sodium ions of inundating fluid and native divalent exchangeable cations of the clay surface. Upon desalinization in distilled water environment, the saturated saline specimen developed 9.2 % osmotic swelling strain at consolidation pressure of 200 kPa over period of 2560 hours. Comparatively, the unsaturated compacted specimen developed much smaller swelling strain of 0.32 % over period of 26 hours upon inundation with distilled water at consolidation pressure of 200 kPa. The 100-fold larger duration needed by saturated saline specimen to develop larger osmotic swelling strain arose from diffusion controlled outward migration of salts from soil water to distilled water reservoir. The saturated saline specimen exhibited 29-fold larger swell magnitude than the compacted clay specimen at same consolidation pressure as the combined effects of reduction in dissolved salt concentration (from outward diffusion of salts) and enhanced exchangeable sodium concentration increased the diffuse ion layer thickness around clay particles to an extent that the saline specimens swelled by 9 % at 200 kPa. Experimental results also indicated that after ion-exchange equilibrium was established, subjecting saturated saline specimens to cycles of desalinization yielded similar magnitudes of osmotic swelling strains. Likewise saturated desalinated specimen subjected to cycles of salinization yielded similar magnitudes of osmotic consolidation strains. Also the magnitudes of osmotic swelling and osmotic consolidation strains exhibited by the saturated saline and saturated desalinated specimens were of similar magnitudes. Variations in compaction density of the compacted clay specimens had bearing on the osmotic swelling developed by the saturated saline specimens and osmotic consolidation strains developed by the saturated desalinated specimens in response to dissipation of osmotic suction gradients. Desalinization caused the 1.42 Mg/m3series saturated saline specimen to experience 2 fold larger swelling strain than the 1.28 Mg/m3 series saline specimen from outward salt diffusion in response to dissipation of osmotic suction gradient. Similarly, salinization caused the 1.42 Mg/m3 series saturated desalinated specimen to experience 1.46 fold larger osmotic consolidation strain from inward salt diffusion than the 1.28 Mg/m3 desalinated specimen. The much larger swell potential exhibited by the 1.42 Mg/m3saline specimen than the 1.28 Mg/m3 series saline specimen indicates that the influence of compaction dry density persists even after saturation and alterations in exchangeable cation composition of the compacted clay specimens. Experimental results demonstrated that variations in compaction water do not have a bearing on the osmotic swelling and osmotic consolidation strains subsequently developed by the saturated saline and desalinated specimens. Chapter 7 summarizes the main findings of this study.

The escalating pollution of the environment has been one of the greatest concerns of science in recent years. Industrial advances in agriculture, expansion of chemical industries and a general change in lifestyle all over the world has lead to release of a variety of pollutants into the environment, thus contaminating the atmosphere, water bodies and many soil environments. In general, other than some natural processes, soils are increasingly being contaminated by anthropogenic sources such as leakages from waste containment facilities, accidental spills and industrial operations. Apart from affecting biotic components of the ecosystem, these pollutants greatly affect the performance, behavior and stability of the soil ecosystem, these pollutants greatly affect the performance, behavior and stability of the soil systems, thus causing severe damage to structures founded on them. The hydraulic and/or chemical alterations which allow these polluting substances to move within soil pores lead to physico-chemical decomposition processes, chemical alterations, leaching and ion exchange reactions. Such reactions could also result from natural processes such as weathering; but the effects caused by pollutants occur at faster rates. Soils are composed of clays, silts and sands. Due to charged nature of the particles and their large specific surface, engineering properties of clays are greatly affected by pollutants. The magnitude of these effects can vary significantly depending on the type of soil, the type and concentration of contaminant, duration of interaction and the environmental conditions. Hence, an understanding of contaminant-clay interactions is important for prevention of geotechnical features, if possible, or at least for planning of remedial measures. Understanding these effects and planning remedial measures requires measurement of the affected properties of polluted soils. This may involve the modification of standard test procedures or the development of new test procedures. The main types of contaminants include inorganic acids, alkalis, sulphates, organic contaminants, toxic or phytotoxic metals and combustible substances. All of these are widely used in industries. While the adverse effects of presence of sulphate in alkaline conditions is well known, little information is available on the effect of sulphate in natural soils under acidic environments. Sulphuric acid is widely employed in the production of fertilizers, pharmaceuticals, pigments, rayon, film, iron, steel, explosives, paper and paper industry. It is also used in cleaning, etching, petroleum refining, electroplating, metallurgy, and in lead-acid batteries. Due to its widespread but often improper usage and the difficulty in safe storage, sulphuric acid is often found as a contaminant in natural soils. Sulphuric acid is also generated in natural soils by oxidation by pyrites in the presence of atmospheric oxygen. Hence, an attempt has been made in this thesis to study the behavior of soils containing different clay minerals during acid-sulphate interaction. The effect of sulphate on soils containing calcite, whose presence is quite common, has also been studied. A review of literature suggests that most common geotechnical failures due to contamination occur due to significant changes on the volume change behavior. Also, it is known that severe changes that occur in soil properties can essentially be attributed to mineralogical changes that occur during interaction with pollutants. Therefore, volume change behavior of soil and detailed mineralogical changes and the consequent morphological changes that occur in soils with acid sulphate are studied.