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L'évaluation de l’aléa sismique doit tenir compte des différents aspects qui interviennent dans le processus sismique et qui affectent le mouvement du sol en surface. Ces aspects peuvent être classés en trois grandes catégories : 1) les effets de source liés au processus de rupture et à la libération d'énergie sur la faille. 2) les effets liés à la propagation de l'énergie sismique à l'intérieur de la Terre. 3) l'influence des caractéristiques géotechniques des couches peu profondes ; appelé effet de site. Les effets de site sont pris en compte dans la mitigation des risques par l'évaluation de la réponse sismique du sol. Lors de sollicitations cycliques, le sol présente un comportement non-linéaire, ce qui signifie que la réponse dépendra non seulement des paramètres du sol mais aussi des caractéristiques du mouvement sismique (amplitude, contenu en fréquence, durée, etc.). Pour estimer la réponse non-linéaire du site, la pratique habituelle consiste à utiliser des simulations numériques avec une analyse linéaire équivalente ou une approche non-linéaire complète. Dans ce document, nous étudions l'influence du comportement non-linéaire du sol sur la réponse du site sismique en analysant les enregistrements sismiques des configurations des réseaux de forages. Nous utilisons les données du réseau Kiban Kyoshin (KiK-Net). Les 688 sites sont tous équipés de deux accéléromètres à trois composantes, l'un situé à la surface et l'autre en profondeur. À partir de ces données, nous calculons les amplifications du mouvement du sol depuis la surface jusqu'aux enregistrements en fond de puit à l'aide des rapports spectraux de Fourier. Une comparaison entre le rapport spectral pour le faible et le fort mouvement du sol est alors réalisée. Le principal effet du comportement non-linéaire du sol sur la fonction de transfert du site est un déplacement de l'amplification vers les basses fréquences. Nous proposons une nouvelle méthodologie et un nouveau paramètre appelé fsp pour quantifier ces changements et étudier les effets non-linéaires. Ces travaux permettent d'établir une relation site-dépendante entre le paramètre fsp et le paramètre d'intensité du mouvement du sol. La méthode est testée sur les données accélérométriques du séisme de Kumamoto (Mw 7.1, 2016). Nous proposons ensuite d’utiliser des corrélations entre moment seismic et la duration de la faille (Courboulex et al., 2016), obtenues à partir d’une base de données globale de fonctions source et une méthode basée sur l’approche des fonctions de Green empiriques (EGF) stochastiques pour simuler les mouvements forts du sol dus à un futur séisme. Cette méthodologie est appliquée à la simulation d’un séisme de subduction en Équateur et comparée aux données réelles du séisme de Pedernales (Mw 7.8, 16 avril 2016) dans la ville de Quito. Nous proposons enfin de combiner la méthode de simulation de mouvements forts par EGF et la prise en compte des effets non-linéaires proposée dans les premiers chapitres. La méthode est testée sur les données accélérométriques d’une réplique du séisme de Tohoku (Mw 7.9). / Seismic hazard assessments must consider different aspects that are involved in an earthquake process and affect the surface ground motion. Those aspects can be classified into three main kinds. 1) the source effects are related to the rupture process and the release of energy. 2) the path effects related to the propagation of energy inside Earth. 3) the influence of the shallow layers geotechnical characteristics; the so-called site-effects. The site effects are considered in risk mitigation through the evaluation of the seismic soil response. Under cyclic solicitations the soil shows a non-linear behavior, meaning that the response will not only depend on soil parameters but also on seismic motion input characteristics (amplitude, frequency content, duration, …). To estimate the non-linear site response, the usual practice is to use numerical simulations with equivalent linear analysis or truly non-linear time domain approach. In this document, we study the influence of the nonlinear soil behavior on the seismic site response by analyzing the earthquake recordings from borehole array configurations. We use the Kiban Kyoshin network (KiK-Net) data. All 688 sites are instrumented with two 3-components accelerometers, one located at the surface and the another at depth. From these data, we compute the ground motion amplifications from the surface to downhole recordings by the computing Fourier spectral ratios for the aim to compare between the spectral ratio for weak and strong ground motion. The main effect of the non-linear behavior of the soil on the site transfer function is a shift of the amplification towards lower frequencies. We propose a new methodology to quantify those changes and study the nonlinear effects. This work results in a site-dependent relationship between the changes in the site response and the intensity parameter of the ground motion. The method is tested analyzing the records of the earthquake of Kumamoto (Mw 7.1, 2016). Posteriorly, we propose to integrate a correlation between seismic moment and the duration of the fault (Courboulex et al., 2016) in the empirical Green’s function method. This methodology was applied to simulate one seduction event in Equator, and we compare the results with the records of the Pedernales earthquake (Mw 7.8, 2016) in the city of Quito. We attempt to take in account the nonlinear effects in the empirical Green’s function method. We use the methodologies of the first part of this document based on the frequency shift parameter. The procedure could be implemented in other methodologies that can predict an earthquake at a rock reference site, such as the stochastic methods. We test the procedure using the accelerometric records for one of the aftershocks o the Tôhoku earthquake (Mw 7.9).

[pt] Esta pesquisa apresenta um estudo sobre a influência de técnicas de saturação, empregadas em laboratórios comerciais e de pesquisa, no comportamento tensão-deformação-resistência de solos residuais quando submetidos a ensaios de compressão triaxial tipo CIU. Os solos avaliados são provenientes de litologias distintas e apresentam diferenças na composição mineralógica, grau de intemperismo e estrutura. Um dos solos pertence ao perfil de alteração de uma rocha alcalina encontrada no município de Tanguá-RJ. Os demais solos são oriundos das feições melanocrática e leucocrática de um migmatito da baixada fluminense (Duque de Caxias-RJ). A variação de volume total dos corpos de prova durante a saturação foi monitorada em alguns ensaios para auxiliar na interpretação dos resultados. Para tanto, foi desenvolvida uma câmara triaxial dupla com sistema de medida de variação de volume total de fácil montagem e custo reduzido, cujas características técnicas são competitivas com as existentes no mercado. O método de saturação que consiste na percolação de água por meio de sucção com baixa tensão confinante seguida de aumento contínuo e simultâneo de tensões (saturação automática) mostrou ser o mais adequado para o solo residual de rocha alcalina, que apresenta estrutura frágil, sem agentes cimentantes e com elevado índice de vazios. Já o solo residual de migmatito (feição melanocrática), que apresenta agentes cimentantes e elevada tensão de cedência, é menos susceptível à técnica de saturação, tendo seu comportamento afetado apenas pelo emprego da técnica de incremento único de contrapressão. / [en] This research presents a study on the influence of saturation procedures, used in commercial and research laboratories, on the stress-strain-strength behavior of residual soils when subjected to CIU triaxial tests. The selected soils are derived from different lithologies and show differences in mineralogical composition, structure and weathering degree. One of them belongs to the weathering profile of an alkaline rock located at the city of Tanguá-RJ. The others are the result of weathering processes on melanocratic and leucocratic features of a migmatite from Duque de Caxias, in Rio de Janeiro Metropolitan Area. Variation of the total volume of the test specimens was monitored during the saturation process in some tests to assess the influence of this procedure on the soil structure. For this purpose, it was developed a double-walled triaxial cell with a system based on the measurement of variation of the volume of the fluid filling the inner cell. The equipment has competitive technical features, besides the low cost and easy to assemble. The saturation technique based on percolating water by suction with a low cell pressure followed by continuous and simultaneous increase of backpressure (automatic saturation) was the most suitable method for the residual soil from the alkaline rock, which presents a weakly cemented structure, without bonding, and high voids ratio. However, the residual soil from the migmatite rock (melanocratic feature), which has strong cementation and high yielding stress, shown to be less susceptible to the saturation procedures, having its behavior affected only by the saturation technique of elevation of backpressure in just onestage.

The aim of the thesis has been to evaluate and understand the effect of caustic alkali solution of varying composition on the behaviour of expansive soil containing mixed layered minerals. Mixed layered minerals are formed of two or more kinds of inter grown layers, not physical mixtures. Illite - smectite is the most abundant and wide spread of the mixed layered clay minerals in sedimentary rocks and soils and also more common than either discrete illite or smectite. In geotechnical engineering much attention has not been paid to the behaviour of soils containing mixed layered minerals. Much less is known about the behaviour of these soils in polluted environment. Mixed layered minerals are more susceptible to environmental changes as the structural linkages between the layer minerals are weak compared to normal layered phyllosilicates. One important pollutant that can have considerable effect on the behaviour of soils is the caustic alkali contamination released from various industries. Recent studies have shown that the behaviour of even stable minerals is affected by alkali contamination. However, the effect of caustic alkali contamination on the behaviour of soils containing mixed layered minerals is not known and has been chosen for detailed study. Also to understand the mechanism of their interaction with alkali, it is necessary to study the effect of alkali solutions on the constituent clay minerals viz., montmorillonite and illite under similar conditions. To elucidate the mechanism of soil alkali interaction limited tests were conducted with simple electrolyte solution, as the alkali solution also acts as electrolyte apart from being alkaline. To confirm the mechanism of interaction, tests are also conducted on these soils with industrial spent liquor containing high caustic alkali and suspended alumina obtained from an alumina extraction plant treating bauxite with high alkali solutions at high temperatures. The results obtained in the laboratory are compared with the soil samples contaminated with leaking industrial Bayer's liquid in the field. Studies are also conducted to suggest remedial measures to control the adverse effects of alkali solutions on soil containing mixed layer minerals. The content of the thesis is broadly divide into 8 Chapters - viz., Introduction, Background and overview, Experimental program and procedures, Behaviour of soils containing mixed layer mineral illite - smectite (BCSI), Behaviour of montmorillonite and illite, Influence of Bayer's liquor and study on the field contaminated soils, Measures to control the influence of alkali contamination on BCSI and Summary and conclusions. The broad outline of these chapters is given in Chapter 1. A review of literature on the behaviour of soils containing different types of clay minerals with emphasis on mixed layer minerals has been presented in Chapter 2. The influence of different inorganic contaminants on the properties of soils in terms of their physical and chemical characteristics as well as their concentration has been summarized. The importance of changes in surface characteristics of soil particles and the changes in the thickness of diffuse double layer in altering the property of soils at low concentration of contaminants and changes in the mineralogy with high concentrated contaminants such as acids and alkalis has been highlighted. This forms the background information necessary to bring out the scope of the study. Four soils having different mineralogy have been used in this study. These soils are, black cotton soil containing predominantly mixed layer mineral illite - smectite mineral called rectorite, illite, montmorillonite (common smectite) and black cotton soil containing predominantly montmorillonite. The properties of the soils used are described in Chapter 3. Caustic alkali solutions of 1N, 4N concentration prepared in the laboratory and industrial alkali-spent liquor are used as contaminants. The spent Bayer's liquor had about 4N alkali concentration and 10% alumina in suspension. To simulate the effect of suspended alumina, two more caustic alkali solutions of 1N and 4N solutions containing 10% alumina by weight of solutions are also prepared. To isolate the effect of electrolyte solutions from that of alkali solution, two electrolyte solutions of 1N and 4N sodium chloride solutions are also used. Test procedures for conducting various tests such as pH, water adsorption characteristics, X-ray diffraction studies, SEM studies, thermal characteristics and geotechnical properties such as Atterberg limits, Oedometer tests and Shear Strength are given in this chapter. The test procedures are modified, wherever necessary, to bring out the effect of contaminants, particularly the effect of duration of interaction on the properties of soils. The source and properties of black cotton soil are presented in Chapter 4. Detailed x-diffraction studies have confirmed the presence of inter layered illite-smectite mineral viz., rectorite, which is uncommon in Indian expansive soils, and is classified as CH (Clay of high compressibility) as per ASTM soil classification. Effect of alkali and salt solutions of 1N and 4N concentration on all physico chemical and geotechnical properties are studied in this chapter. As it is known that presence of certain elements such as aluminium influence the soil alkali interaction, the effect of suspended alumina along with alkali solution has also been investigated. The effect of contaminating fluids such as 1N NaOH, 4N NaOH with and without alumina, 1N NaCl and 4N NaCl on the geotechnical properties of the soil has been studied. Mineralogical changes were observed by XRD and thermal studies in the soil treated with 4N NaOH solution and 4N NaOH + 10% alumina. The interlayer potassium of illite is released and potassium hydroxide is formed in soil treated with 4N NaOH. Swelling compounds such as sodium aluminium silicate hydroxide hydrate (SASH) has formed due to attack of 4N NaOH + 10% alumina on silica rather than on rectorite. Thus the studies clearly bring out that the rectorite present in the soil is dissociated only in the presence of strong alkali solutions of concentration of about 4N. The liquid limit of soil decreased with increase in the electrolyte concentration in the case of NaCl solutions. With 1N NaOH, the liquid limit of soil increased due to increase in the thickness of diffuse double layer due to increased pH. However, Proctor's maximum dry density increased and optimum moisture content decreased with 1N NaOH. With increase in the concentration of alkali solution to 4N, the rectorite dissociates into constituent minerals with the formation potassium hydroxide. The liquid limit of soil decreased probably due to the dominating influence of electrolyte nature of hydroxide solution over the effect of increased negative charge on clay particles due increase in the pH on the constituent minerals. Proctor's maximum dry density decreased and optimum moisture content increased with 4N NaOH. Sediment volume and oedometer free swell at seating/nominal surcharge load of 6.25 kPa of soil increased in 1N and 4N caustic alkali solutions, though by different mechanisms. The increase with 1N solution is essentially due to increased negative charges on clay mineral surface. However, the increase in swelling with 4N solution is associated with the dissociation of rectorite mineral and occurs in two distinct phases unlike in the case of 1N solution. While the first phase can be attributed to the effect of alkaline nature of the solution after reduction in its concentration due to reaction with rectorite and the consequent reduction in its electrolyte nature. The second phase is due to the swelling of the separated constituent minerals in the presence of excess of alkali and occurs after much delay. Consolidation behaviour of rectorite in 1N and 4N alkali solutions has been studied in two ways: 1). Loading without waiting for the second stage of swelling to occur, as in standard consolidation procedure and 2). Loading after completion of second stage of swelling which is occurring after considerable delay as explained earlier. Normally one would initiate loading after equilibrium is reached at the end of first stage of swelling and second stage of swelling is not suspected. As there is no second stage of swelling with 1N solutions, these two types of consolidation tests produced the same results. Abnormal rebound is observed during unloading with 4N solution in which loading cycle is initiated without waiting for second stage of swelling to complete. It is interesting to note that while the liquid limit of soil decreased with increase in the concentration of alkali solution, the swelling increased. The testing procedure and period of interaction as well as the concentration of alkali solution during the test in these two tests are different. The effects of alkali solution are more severe in case of liquid limit because of thorough mixing and consequent effective reaction during testing. Similarly, the volume changes in soil that has already reacted with 4N alkali solution when exposed to further to alkali contamination are considerably less compared to uncontaminated soil exposed to fresh contamination. The shear strength of soil treated with 4N-alkali solution has increased particularly after long period of interaction. This indicates that the soil after mineralogical changes posses good strength. Chapter 5 presents the effect of alkali and salt solutions on the physico chemical and geotechnical properties of component minerals of mixed layered illite/smectite. For this study, commercially obtained montmorillonite (bentonite), naturally occurring black soil containing montmorillonite and commercially pure illite are used. It was observed that montmorillonite alkali reactions would not produce significant mineralogical changes where as illite is dissociated into smectite with the formation of potassium silicate by the interaction of released potassium with soluble silica. This confirms that the ultimate products of rectorite with alkali solutions would be smectite and compounds of potassium. In the absence of mineralogical alterations the liquid limit of montmorillonite decreases due to suppression of diffuse double layer thickness due to dominating influence of alkali solutions on this highly active clay. However a small increase in liquid limit is observed in illite with alkali solutions. Thus the net effect of alkali on rectorite is to decrease the liquid limit with increase in alkali concentration. While the free swell and oedometer swelling of montmorillonite generally decreases with increase in the alkali concentration, they increase in illite. However, in both the minerals the swelling occurs only in one phase. Thus the second phase of swelling that has been observed in rectorite can be attributed to delayed swelling of montmorillonite that has been released by the attack of alkali on rectorite. The behaviour of black soil containing mixed layer mineral contaminated in the field and laboratory by leaking Bayer's spent liquor in an alumina extraction plant has been studied in Chapter 6. The Atterberg limits of the samples treated with liquor are reduced and sediment volume increased. Similarly the swelling at seating load in consolidation test is higher in sample compacted with water and inundated with liquor. X-ray diffraction studies showed that the mineralogical changes are similar to those occurred with 4N caustic alkali solution. The mineralogical and micro structural changes in the soil samples that are contaminated by leaked spent liquor in the field are relatively more marked. Also the behavior of highly montmorillonite clay, bentonite, has been studied contaminated with liquor in the laboratory. The study on the effect of high concentrated alkali solutions on montmorillonite can be useful to study the effect of interaction on the dissociated montmorillonite. These studies are helpful to suggest some possible remedial measures to control the adverse effect of alkali on soils. Possible Remedial schemes that can be adopted before and after contamination of the soil to control the adverse effect of alkali solutions on the black cotton soil containing mixed layered mineral are listed and their effectiveness examined in Chapter 7. The suggested remedial measures include flushing with water to dilute the effect of alkali, neutralisation with dilute hydrochloric acid, stabilisation of soil with lime and calcium chloride and use of impervious membrane to separate the foundation soil from alkali solution. The effectiveness of different measures as well as the method of their application has been described. Efforts are made to understand the mechanism of remedial action. Consolidation tests conducted on soil contaminated with 4N alkali solution and inundated with water showed increased swelling due to dilution of the alkali concentration. Though the swelling of contaminated soil can be controlled by passing dilute hydrochloric acid (1N), the method is not advocated as it can lead to ground water contamination. Mixing the soil with solutions containing up to 5% by weight of calcium compound in water could not prevent the alkali induced heave in the long run when inundated with 4N alkali solution. This was due to dissolution of silica by the strong alkali solutions and formation of swelling compounds such as sodium aluminium silicate hydroxide hydrate (SASH). The formation of sodium aluminates occurred only when the alkali solution contained alumina or soil contained calcium compounds. There are no significant variations in the effects of calcium chloride or calcium hydroxide on contaminated soil. Replacing the foundation soil with soil thoroughly contaminated with 4N alkali solutions and controlling the migration of contaminants into the foundation soil using high-density polyethylene (HDPE) geosynthetic membranes can be an effective measure to control the heaving in alkali contaminated foundation soil containing interstratified illite – smectite. Summary and the major conclusions of the thesis are presented in Chapter 8.

Sub-surface soil pollution by various processes with high concentration of contaminants can significantly alter geotechnical properties of soils causing unexpected failures of structures founded on them. The changes can occur due to alteration in soil water interaction processes and/or by intense chemical interactions leading to mineralogical and microstructural changes. Behaviour of soil upon contamination with alkali pollutant is one of the major concerns faced by the geotechnical researchers in recent years. In the present study an attempt has been made to understand the role of mineralogical and morphological changes on the volume change (swelling and compressibility) behaviour of soils by prolonged interaction with caustic alkali pollutant. Based on the results it has been proposed to develop remedial measures to nullify and/or control the detrimental effects. A comprehensive experimental program has been planned to achieve these objectives. The experimental investigations carried out and results obtained are presented in eight chapters as follows. The broad outline of thesis is given in Chapter 1. A detailed review of literature on the type of phyllosilicate minerals present in various soils is presented in Chapter 2 with a view to select most common soils for the study. Various sources of contaminants and their effect on the properties of soils have been summarised. Present understanding on the mechanisms leading to changes in the soil properties has been elucidated. The occurrence of alkali contamination has been reviewed in this chapter which enabled to select the ranges of alkali concentration for the study. Based on the review of various methods employed to improve the soil behaviour, the use of salt solutions such as potassium chloride (KCl) and magnesium chloride (MgClB2B) and pozzolanic fly ash has been considered to counteract the alkali effects. Based on this detailed survey, the scope of the present investigation has been elaborated at the end of the chapter. Chapter 3 presents different materials used and various methods adapted in the current study. Three soils having different mineralogy have been used in this study to bring out the effect of alkali solutions on their volume change behaviour. While two soils were classified as CH, the third one was of CL. The CH soils used in this study are called Black Cotton Soils in India. One soil contained predominantly mixed layer illite-smectite mineral (BCS I) and the other contained predominantly montmorillonite mineral (BCS M). The locally available CL soil used is referred as red earth (RE) whose predominant mineral is kaolinite. Alkali solutions of concentration ranging from 1N to 4N are prepared using sodium hydroxide pellets (NaOH). Slat solutions viz. potassium chloride and magnesium chloride and pozzolanic fly ash obtained from Neyveli thermal power plant (NFA) are used as additives. Procedures to determine the geotechnical properties of the soils such as Atterberg limits, specific gravity, grain size distribution and compaction characteristics are given in this chapter. Procedures for identifying the mineral and microstructure of the soils such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) are also presented in this chapter. Standard oedometer tests with fixed ring apparatus were performed to study the volume change behaviour of soils under various conditions. Volume change behaviour of soils in the presence of alkali solutions is presented in Chapter 4. In order to assess the effect of alkali solution on the volume change behaviour of soils it is necessary to study their behaviour in water. Relatively very high swell was observed in BCS M, whereas the swell in RE and BCS I soil specimens was very low and moderate respectively. Adsorption of water to form diffuse double layer near the negative surface of clay mineral particles leads to swelling in soils. The thickness of the double layer depends on the cation exchange capacity of soil. Higher cation exchange capacity leads to development of higher thickness of double layer thereby inducing swell. The higher is the swell the higher would be the compression. The effect of different concentrations (1N, 2N and 4N) of alkali solutions on volume change behaviour of three types of soil is presented in this chapter. All the three soils studied, irrespective of their mineralogical composition, exhibited high swell when contaminated with alkali solution compared to water. However, the extent and nature of swell varied both with the type of mineral present in the soil and concentration of sodium hydroxide solution. The swell in BCS I increases with increase in the concentration of the alkali solution. In 1N alkali solution the high swell occurred is due to the breaking up of interstratified mineral into constituent minerals initiated by the leaching of potassium from soil due to high pH. In 2N and 4N alkali solutions, the observed high swell occurs in two stages: the first stage of swelling is due to breaking up of interstratified mineral into constituent minerals initiated by the leaching of potassium from soil due to high pH, and the second stage of swelling is due to the formation of new minerals (Zeolite P in case of 2N NaOH and Sodalite in case of 4N NaOH). The nature of swell is influenced by the formation of minerals depending on the concentration of alkali solution. Thus the studies clearly indicate that the swelling is due to the release of potassium from soil at higher pH and due to mineralogical changes depending upon the concentration of alkali solution. Confirmative tests were conducted to support the release of potassium during first stage of swelling and mineralogical alteration after second stage of swelling. The high swell in BCS M becomes higher in 1N alkali solution. The increased swell in the soil with 1N alkali solution is due to increase in the ion exchange capacity of soil at higher pH. The swell which is very high with 1N alkali solution decreases with 2N alkali solution. With increase in concentration of alkali solution to 2N, the increase in the negative charges due to alkalinity becomes less and the swell decreases due to dominant influence of electrolyte effect. With increase in the concentration of alkali solution to 4N, both these influences become less and the amount of swell remains the same. Significant increase in the amount of swell is observed with alkali solution even in non-swelling red earth. The nature of swell as well as the formation of minerals is not altered by the change in the concentration of alkali solution. At any concentrations of alkali solution the observed swell is noticed in two stages – very small first stage of swell due to lower ion exchange capacity and considerable second stage of swell due to the formation of new mineral (Sodalite) with any concentration of alkali solution. It has been observed that the normal hyperbolic swell – compression relationship does not apply for the alkali contaminated soils. The higher swell does not result in higher compression, as the swollen soil remains fairly incompressible. Analysis of the results and detailed studies on micro-structure and mineralogy of soils bring out mechanism of alkali effects. Comparing the swell behaviour of soils with alkali solutions brings out the relative importance of various mechanisms proposed for induced heave. The effect of salt solutions used viz., potassium chloride and magnesium chloride to restrict the influence of alkali solution on the volume change behaviour of BCS I is presented in Chapter 5. These salts react with alkali solution to form partly soluble potassium hydroxide (KOH) and sparingly soluble magnesium hydroxide (Mg(OH)B2B) respectively. Presence of ionic potassium can bring out potassium linkages, by bridging potassium ion between the unit layers of expansive minerals reducing the swell. Magnesium ions can restrict swell, by replacing the monovalent exchangeable ions present in soil and/or by formation of magnesium hydroxide which is a weak cementing agent. The effect of potassium hydroxide on the volume change behaviour of soil has been studied and the results clearly indicate that fixation of potassium is facilitated by high pH of KOH solution. Addition of potassium chloride has partially controlled the alkali induced heave in soil. Of the two stages of swelling observed in soil in the presence of 4N alkali solution, only the first phase of swelling is reduced which may be due to electrolyte effect and/or due to fixation of potassium. The second phase of swelling that occurs in soil due to mineralogical changes can not be controlled with the use of potassium chloride. Addition of magnesium chloride salt solution also reduced the effect of alkali solution mostly due to suppression of thickness of diffuse double layer that develops near clay surface. The nature of reduction in the swell of alkali solution during the two stages by magnesium chloride is similar to that of potassium chloride. The partial reduction in swell of soil in the presence of salt solutions leads to reduction in the compressibility of soil. Detailed data and analysis, presented in this chapter, bring out the role of microstructure and mineralogy on soil behaviour. The abnormal volume changes due to mineralogical changes affected by high concentration of sodium hydroxide could not be controlled with salt solutions, attempts are made to utilize fly ash to control the alkali induced heave. The pozzolanic compounds produced by hydration of compounds presented and/or produced by lime silica reactions can bind the soil particles controlling the swelling. The results on the effectiveness of fly ash on BCS I soil are presented in Chapter 6. The physical and chemical properties of fly ash along with the mineralogical composition and the microstructure of the fly ash are also presented in this chapter. Before studying the effect of fly ash to control the volume change behaviour of soils in presence of alkali solutions, the effect of alkali solutions on the volume change behaviour of fly ash itself has been studied. The results showed no noticeable changes in swell and compressibility of fly ash, encouraging its use for controlling the alkali induced swell. The ability of different percentages (10%, 20% and 50%) of fly ash to control alkali induced volume changes in soil with varying concentrations of alkali solutions, viz., 1N, 2N and 4N has been studied. The results indicate that the addition of fly ash effectively reduces alkali induced swell in BCS I. The effectiveness of fly ash increases with increase in its content. The reduction in swelling of soil is partially due to replacement of soil with fly ash and mainly due to cementation of soil particles by pozzolanic compounds produced. More than 25% of fly ash is generally required to significantly reduce the swell in alkali solutions. The reduction in swell with addition of fly ash also leads to lower compressibility of soil. The role of microstructure and mineralogy in controlling the volume change behaviour are also presented in this chapter. The effectiveness of fly ash in controlling the volume changes in RE and BCS M due to alkali solutions are studied in Chapter 7. The addition of fly ash completely eliminates the swelling in both the soils. The reduction in swelling up on addition of fly ash is essentially due to efficient binding of particles by pozzolanic reaction compounds. Addition of even 10% of fly ash is sufficient in completely arresting the swelling of RE and BCS M by alkali solution. Detailed data and analysis of the results to bring out the role of microstructure and mineralogy on the behaviour of soils are presented. It is clear that relatively higher amounts of fly ash is required to control the alkali induced heave in BCS I than in other soils at higher concentrations of alkali solution. The major conclusions from the study are presented in Chapter 8. The thesis demonstrates that alkali contamination alters mineralogy and morphology of soils affecting the volume change behaviour significantly. The study also brings out that fly ash can control the undesirable swell that occurs in most types of soils by cementing the soil particles to resist swelling. Though the amount of fly ash required to control the alkali induced heave varies, 25% of fly ash is often sufficient.

Rammed earth is a monolithic construction formed by compacting processed soil in progressive layers. Rammed earth is used for the construction of load bearing walls, floors, sub base material in roadways, airport runways, taxiways, aprons, foundations and earthen bunds. Soil, sand, cement and water are the ingredients used for the preparation of cement stabilized rammed earth (CSRE) specimens. The cracking in a rammed earth structure is due to the development of tensile stresses. The tensile stresses are generated due to various causes like unequal settlement of foundation, eccentric loading and / or lateral loading such as wind pressure and earthquake on an earth structure. The cracking in a rammed earth structure causes the failure of its intended function. For example formation of crack may lead to the instability of an embankment slope. And earthen dam can be destroyed gradually by erosion of soil at the crack surface (Harison et al. 1994). Hence, it becomes important to understand the fracture behaviour of cement-stabilized rammed earth structures. Well focused studies in understanding the fracture behaviour of CSRE structures are scanty. The present work attempts to address some issues on the fracture behaviour of CSRE including size effect. Through an experimental programme material properties viz. compressive strength, tensile strength and stress-strain relationships are generated for two chosen densities, 17 and 18.5 kN/m3 of CSRE both in dry and saturated condition. Soil composition, density, cement content and moisture content of the specimen during testing influence the characteristics of CSRE. In the present investigation keeping the cement at 10%, the density is varied choosing a soil-sand mixture having optimum grading limits. The basic raw materials used are soil, sand, cement and water in the ratio of 1 : 1.5 : 0.25 : 0.34 by weight. The strength properties studied alone are inadequate to predict the mechanics of fracture due to the presence of microscopic flaws, cracks, voids and other discontinuities. Therefore, some linear elastic fracture parameters such as mode I fracture toughness (KIc), critical energy release rate (GIc), net section strength (f net) and notch sensitivity are calculated, presuming that CSRE is still a brittle material because it is yet to be confirmed that CSRE is a quasibrittle material. In fact, in the present work, it is shown that CSRE has significant amount of softening. A comprehensive experimental work has been undertaken to test CSRE beam specimens for two densities, three sizes of beam and three notch to depth ratios under three point bending (TPB) in a closed loop servo-controlled machine with crack mouth opening displacement control. Results indicate that the CSRE in dry condition exhibits a greater resistance to fracture than the saturated specimen. The variation of net section strength with the notch depth is not significant. Therefore the CSRE material is notch insensitive, implying that it is less brittle. An experimental program was undertaken to determine the nonlinear fracture parameters of beam specimens both in dry and saturated condition. The influence of moisture content, density, size of the specimen as well as notch to depth ratio of the specimen on RILEM fracture energy (G F ) are presented. The GF values increase with increase in density and size of the specimen, while they decrease with increase in notch to depth ratio. Results clearly show that the total energy absorbed by the beams (W OF ) and RILEM fracture energy (G F ) for all specimens tested in dry state are higher compared to the specimens tested in saturated state, indicating that the dry specimen offers higher resistance to the crack propagation. The RILEM fracture energy GF , determined from TPB tests, is said to be size dependent. The assumption made in the work of fracture is that the total strain energy is utilized for the fracture of the specimen. The fracture energy is proportional to the size of the fracture process zone (FPZ), which also implies that size of FPZ increases with increase in the un-cracked ligament (d - a) of beam. This also means that FPZ is proportional to the depth d for a given notch to depth ratio, because for a given notch/depth, (d - a) which is also is proportional to d because is a constant. This corroborates the fact that fracture energy increases with size. Interestingly, the same conclusion has been drawn by Karihaloo et al. (2006). They have plotted a curve relating fracture process zone length and overall depth the beam. In the present study a new method namely Fracture energy release rate method proposed by Muralidhara et al. (2013) is used. In the new method the plot of GF /(d - a) versus (d - a) is obtained from a set of experimental results. The plot is found to follow power law and showed almost constant value of GF /(d - a) at larger ligament lengths. This means the fracture energy reaches a constant value at large ligament lengths reaffirming that the fracture energy from very large specimen is size-independent. This Fracture energy release rate method is used to determine size-independent fracture energy GRf , based on the relationship between RILEM fracture energy and the un-cracked ligament length. The experimental results from the present work agree well with the proposed new method. Similarly, the method is extended to determine nominal shear strength τv for large size beam. Results show that for both densities GRf decrease in saturated condition, while in dry condition as the density is increased from 17 to 18.5 kN/m3 the GRf decrease by 7.58%, indicating that the brittleness increases with higher density. The τv for large size beam increases with density both in dry and saturated condition. The size effect method for evaluating material fracture properties proposed by Bazant (1984) is applied to cement stabilised rammed earth. By measuring the peak loads of 2D geometrically similar notched beam specimens of different sizes, nonlinear fracture parameters such as fracture energy (Gf ), fracture toughness (KIc), effective length of the fracture process zone (Cf ), brittleness number (β), characteristic length (l 0) and the critical crack tip opening displacement (CT ODc) are determined for both dry and saturated conditions. The crack growth resistance curves (R-curve) are also developed for dry and saturated specimens. In the size effect method, for both densities 18.5 and 17 kN/m3 the values of nonlinear fracture properties, namely G f , Cf , KIc, CT ODc and l 0 are lower for the saturated specimen compared to those of the dry specimen. In dry condition as the density is increased from 17 to 18.5 kN/m3 the Gf decreases to 13.54%, indicating that the brittleness increase with higher density. The areas under the load-displacement and load-CMOD curves are a measure of the fracture energy and these areas are low for saturated specimens. The crack growth resistance curves (R-curve) plotted using the size-effect law from peak loads are the measure of resistance against crack growth R. The value of R is high for dry specimen compared to that of the saturated specimens. During aggregate pullout or the opening of crack, the interlock or friction between the crack surfaces may cause the energy dissipation through friction and bridging across the crack. Therefore the wet friction in case of saturated specimen must be smaller resulting in more brittleness compared to the larger dry friction for dry specimen. In the present investigation the Digital Image Correlation (DIC) technique is used to study the FPZ properties in cement stabilised rammed earth. The MATLAB package written by Eberl et al. (2006) is suitably modified and used for image correlation to suit our requirements. CMOD measured using DIC technique is validated by comparison with the CMOD measured using clip gauge. The FPZ properties such as the development of FPZ and crack opening displacements at different loading points as well as the influence of notch/depth ratio on FPZ length (lFPZ ) are evaluated for both dry and saturated conditions. At peak load the lFPZ are about 0.315 and 0.137 times the un-cracked ligament length respectively for specimens tested under dry and saturated conditions. In dry and saturated states the FPZ length decreases as the ratio increases. Lower values of lFPZ in saturated specimen indicates that it is relatively more brittle compared to dry specimen.

Most soil particles loses cohesion and split up the soil mass into individual soil grains when they come in contact with water and get saturated. In dispersive soils the particles detach more spontaneously from each other and go into suspension even in quiet water. Thus the phenomenon of dispersion is common to most soils, the degree varying from soil to soil. Dispersive soils are abundantly found in various parts of the world such as Thailand, United States, Australia, Mexico, Brazil, South Africa and Vietnam. Several geotechnical failures such as piping due to internal erosion, erosion and gullying in relatively flat areas, collapse of sidewalls and topsoil removal have been reported worldwide due to the construction in dispersive soil. Failures as reported could be prevented if such soils are identified before-hand or if the quantification of dispersivity in the soil is done accurately. There are several methods of measuring dispersivity in soils which include several physical tests, chemical tests and some common laboratory tests. It is reported in literature that no method could be completely relied upon to identify dispersive soils with absolute confidence. In addition, when these methods were studied in detail, several flaws surfaced needing a better estimation of dispersivity. In order to develop a new method of estimation of dispersivity, the mechanism of dispersion in soils was studied in depth, which revealed that the existing concepts regarding dispersivity are incomplete in many aspects. An exhaustive philosophy of dispersion which addresses every detail is non-existing. To solve these problems, the concept of dispersivity was investigated in detail. It was found out that the observed dispersivity is a result of repulsion in the soil overcoming the attractive force. Thus a list of factors that could possibly affect the repulsion and attraction (and hence the dispersivity) in soils were found out. Even though literature focuses on exchangeable sodium as the principal reason for dispersivity, from fundamental theoretical considerations several other factors such as Cation exchange capacity (CEC), pH, structure of the soil, electrolyte concentration in the pore fluid, presence of organic matter, clay minerals involved in the soil and dissolved salts in the soil could possibly have an influence on dispersivity. Several studies have reported soils of high dispersivity to possess a high pH, high CEC, high amounts of sodium. The influence of these factors on dispersivity of other soils (or generally in any soil) is not well explored. Research on understanding their mechanism of action led to the conclusion that these parameters could be generalized for any soil. Through the analysis of these parameters, it was found that the fundamental parameter governing the dispersivity of soils is the number of charges on clay particles and that the repulsion in the soils is mainly contributed by the electrostatic repulsion. The attractive force in a soil/clay mass is primarily contributed by the van der Waal’s attraction and dispersion occurs when the electrostatic repulsion (resulting due to permanent and pH dependent charges) dominates over the van der Waal’s attraction. A practical estimation of charge with least effort could be possibly carried out through the measurement of zeta potential of soils. In order to verify whether the effect of all the factors is completely and sufficiently reflected in the zeta potential values, experiments were conducted on various soils. Three soils namely Suddha soil (a locally available dispersive soil), Black cotton soil and Red soil were selected for the study. These soils were chosen as the soil samples as they could display wide ranges of dispersivity values. In order to perform dispersivity tests, soil fraction finer than 75µ (75 micron meter sieve size) was fixed as the sample size as dispersivity pertaining to the finer fractions play a greater role than that of the coarser particles. All the three soil samples were treated with sodium hydroxide and urea solutions to alter the dispersivity so that the influence of all parameters could be studied. The dispersivity of the treated and untreated soils was found out through the various conventional tests and it was found that there exists a good correlation between the dispersivity and the zeta potential of soils. It was also observed that the increase in the dispersivity is higher when treated with salts of monovalent cations. Increase in the organic content also increased zeta potential, but not as significantly. One of the popularized theories on colloidal dispersions is the classical DLVO theory which has formulated the total interaction energy of colloidal particles by estimating the electrostatic repulsion and van der Waal’s attraction energy between two particles. The total interaction energy is then expressed as the difference between them. A similar approach as taken by the DLVO is adopted in this study. The total attractive energy existing in a soil mass is mathematically derived from the expression for van der Waal’s energy between two particles and the total repulsive energy from the zeta potential values. Two different approaches namely an infinitesimal particle approach and a finite particle approach is taken for finding the energy in a soil mass. In the infinitesimal particle approach, a clay particle is assumed to be infinitely small such that any soil particle of a finite radius could be conceived to be formed by a combination of infinite number of these infinitesimal particles. With this setting, the total energy in a soil mass is computed without really bothering about what exact particles constitute the mass. The increase in energy due to the increase in radius is then integrated to obtain the final expression. The dispersivity of the soil is then estimated under defined physical conditions of the soil. In the finite particle approach, each particle is considered to be of finite radius and to estimate the total energy, the total number of particle ombinations is then taken and the total energy is expressed as a sum of all the possible combinations. The dispersivity of a soil in both approaches is expressed as a release of energy when the repulsion rules over the attraction. In order to validate the derived propositions and expressions, experiments were conducted again on soils. The soils were treated with hydroxide salt of monovalent cations such as lithium, sodium and potassium. The dispersivity of the various treated and untreated soils was measured with the conventional methods and with the derived expressions of dispersivity through zeta potential. The similarity in the trend of the dispersivity values confirmed the validity of the derived expression. It was also concluded that the infinitesimal particle approach could be adopted when information about the physical properties are available and when they are not, the finite approach could be used. An accurate determination of zeta potential is critical for representation of dispersivity with zeta potential. Thus the procedure for measurement of zeta potential was standardized. The standardization was primarily focused on establishing the ideal conditions for zeta potential measurement. The role of Brownian motion, in electrophoretic mobility measurements were studied by employing the usage of zeta deviations. Untreated, potassium hydroxide treated, sodium hydroxide treated and lithium hydroxide treated samples of Suddha soil, Black Cotton soil and Red soil (finer than 75µ) were used for the study. Zeta potential measurements on unfiltered soil water suspensions, suspensions passing 2.5µ and suspensions passing 0.45µ were conducted along with recording their zeta deviations. It was observed that soil suspensions finer than 0.45µ show acceptable values of zeta deviations and thus could be used as a standard procedure for estimating zeta potentials. It was also concluded that the presence of Brownian motion makes the assessment of zeta potential through electrophoretic measurements easier and accurate. In an alternate perspective it as deduced that the amount of total monovalent ion concentration in the soil (dissolved and adsorbed) could adequately serves as an ideal parameter that could be used to quantify dispersion in soils. In order to verify the speculation, the variation of repulsive pressure with monovalent cation concentration was studied for the above mentioned treated and untreated soils. Within the monovalent cations, the role of ionic size in repulsion along with physical factors was also studied with the help of Atterberg limits, compaction characteristics, and dispersivity measurements. It could be concluded that even though there are several chemical factors such as CEC, pH, electrolyte concentration, type of clay minerals, dissolved salts etc. and physical factors such as plasticity, water holding capacity, density and structure which influence dispersion in soils, these factors affect either directly forces between the particles or the surface charge of clays which again affect the forces. The two phenomena can be combined through the hydration behaviour of the adsorbed cations on the clay surface in view of dispersivity. It is that force due to hydration which acts as the principal reason to separate the clay particles apart. As the radius of the inner hydration shell is higher for monovalent cations than those of higher valency ions, more force would be offered by the monovalent ions. Higher the charge and higher is the number of monovalent cations, higher will be the repulsion and thus the dispersivity. The repulsive force offered by the monovalent cations in soil was calculated through osmotic pressure differences and the dispersivity was expressed as the release of energy as earlier. In order to validate the proposal, the dispersivity of the samples as measured with the conventional methods was compared and studied with the derived expression. The similarity in the trend of the dispersity values confirmed the validity of the derived expressions. Thus, it can be seen that there are primarily two different methods of quantifying dispersivity of soils. When one method estimates dispersivity by calculating the electrostatic repulsion through zeta potential, the other method gives a dispersivity value based on the repulsive pressure offered by the monovalent cations in the soil. Two methods could be regarded as two different measurements of the electrical double layer. Any method could be used based on the property that could be easily quantified. The applicability of the new approaches – calculation of monovalent cations and zeta potential- for estimating the dispersivity in soils through a complete development of philosophy of dispersion and is presented, in this thesis, in nine chapters as follows: In Chapter 1 the background of the study and review of literature connected with the present study is presented. The mechanism of dispersion and the geotechnical problems associated with dispersion is elaborately presented in this section. As the dispersive soils cannot be identified through conventional tests, a description about the various tests designed to identify dispersive soils is presented. Earlier works relevant to the topic and the shortcomings of those studies are discussed. Finally, the objectives of the current research along with the scope of the work are explained in the concluding part of this chapter. Various factors that could have influence on the dispersivity of soils and their mechanism of action are presented in Chapter 2. The relationship of the factors with zeta potential is discussed. Theories dealing with dispersivity, conventional methods of measurement, role of geotechnical characteristics in assessing dispersivity are being presented. Chapter 3 deals with the various materials and methods used for the study. A locally available dispersive soil called Suddha soil along with Black Cotton soil and Red soil were chosen as the soils for the study of dispersion. The basic material properties and testing programs adopted for the study are presented in this chapter. The codal procedures followed to determine the physical, chemical, index and engineering properties are described in detail. The experimental investigations carried to bring out the role of zeta potential in dispersivity of soils are described in Chapter 4. Detailed analysis of the results showed estimation of zeta potential is possible and can sufficient quantify dispersivity of soils. The formulation of the equation for estimating dispersivity from zeta potential is described in Chapter 5. The estimation dispersivity based on attraction and repulsion energies in a soil mass is presented here. The adoption of the approach and methodologies used based on classical DLVO theory for the current work is explained in detail. The values of dispersivity obtained from the derived equation are compared with those obtained from the conventional tests. The validity of the expression is confirmed with the results of the experiments. Chapter 6 deals with the standardization of the measurement procedure of zeta potential. Role of Brownian motion in the accurate measurement of electrophoretic mobilities are brought out here. Chapter 7 brings out an alternate perspective of quantifying dispersivity through monovalent cations. The role of monovalent cations and the mechanism in which they contribute to the repulsive pressures (hence the dispersivity) are discussed. Experimental research design adopted has brought that the effect of monovalent and ionic size on repulsive pressures leading to dispersivity is described. The results of the experiments added with the inferences drawn are explained at the end. The estimation of repulsive pressures for measuring dispersivity from monovalent cations is discussed in Chapter 8. The dispersivity of a soil mass is derived from monovalent ion concentration and experiments were carried out for verification purposes. The experimental investigation procedure adopted followed by the results are presented in this chapter. It was observed that a good co-relation exists with the dispersivity obtained from the monovalent ion concentration and that obtained from conventional methods. Chapter 9 compares the dispersivity obtained through the various methods proposed in this thesis. The comparison is made in light of the classical electrical double layer theory. The major conclusions of the study are brought out at the end of this chapter.