PhD Theses (Civil Engineering)

Browse

Now showing 1 - 20 of 228

2-D coupled surface and sub-surface flow model for river flow simulation with piedmont zone
(2018) Patowary, Sudarshan
The interaction between surface and groundwater flow in a non-prismatic river has been a topic of interest among researchers since last three decades. Existence of piedmont zone in the river bed changes the downstream flow scenario significantly. Downstream flow situation assessed by routing of upstream hydrograph may yield erroneous flow assessment, if the existence of such piedmont zone is ignored. Moreover, most of the researchers, to reduce complexity, carried out hydrodynamic studies neglecting the infiltration zone in the river bed. Therefore, for reliable flow forecasting in a river passing through a piedmont zone, consideration of surface and ground water interaction in the modelling process is quite important. To overcome above difficulties, a two dimensional coupled surface-subsurface flow model is developed, where surface and subsurface flow are linked via exchange of flux between two systems. Saint-Venant equation is the most common equation to describe free surface flow. In this study free surface flow considering piedmont zone in the computational domain is described by the Saint- Venant equation coupled with Green-Ampt. infiltration equation. The water infiltrated through the recharge zone moves as unsaturated flow and joins the mainstream at downstream. This process is modelled by the two dimensional Richards equation. The two dimensional shallow water equation and Richards equation are nonlinear equation which is not amiable to solve analytically without simplification. In this study Beam and Warming implicit scheme is used to solve free surface flow equation with Green-Ampt. infiltration equation and Alternate Direction Implicit scheme is used for Richards equation
(A) few analytical solutions for predicting one-dimensional steady infiltration in heterogeneous soils
(2022) Talukdar, Jagadish
Analytical solutions are worked out for the general one-dimensional steady state infiltration equation for a heterogeneous soil column with the sink term of the equation being treated as any valid root-water uptake function along the length of an infiltrating space. Solutions are being obtained for the governing equation (Richards’s equation) considering both the Gardner as well as van-Genuchten conductivity functions. The validity of the developed solutions is being checked by comparing with the analytical works of others for a few simplified infiltration situations; also, a few numerical checks and experimental comparisons on them have also been carried out. These solutions can predict infiltration behavior through any arbitrarily inclined soil column and can also accommodate any valid spatial variations of the root-water extraction function and the soil hydraulic parameters of the infiltration equation, along the length of an infiltrating column. The study shows that infiltration on a heterogeneous Gardner or van- Genuchten soil is a highly complex process involving many variables and the spatial variations of these variables in such a soil may greatly influence the infiltration mechanics associated with it; this is true both when a root-water function is present in an infiltrating space and when it is absent. It has also come out of the study that infiltration hydraulics related to a heterogeneous Gardner or van-Genuchten soil is mostly due to the combined effect of all the players of the system and is not due to one or two infiltration variables of the system alone. As there is currently no analytical solution to either the Gardner or van-Genuchten-based infiltration equation for a heterogeneous soil with or without the sink term, it is hoped that the proposed solutions will be worthwhile additions to the collection of analytical solutions on the subject. Keywords: Analytical solution; Gardner’s conductivity function; van Genuchten’s conductivity function; Root-water extraction function; Soil heterogeneity.
(A) Frequency Domain based Inverse Ground Response Analysis Framework for the Determination of Dynamic Soil Properties
(2023) Mondal, Joy Kumar
Effect of local soil in amplifying bedrock motion during earthquakes (EQs) is an important phenomenon, and is observed globally. As a result, the bedrock motion at times increases manifold while reaching the surface. Such amplification in ground motions due to local soil is termed as local site effect (LSE), and can numerically be quantified by performing ground response analysis (GRA). Understanding the effect of local soil requires information about subsoil type as well as shear strain dependent behaviour of each subsoil layer (known as dynamic soil properties curves or DSPCs). Literature suggests that DSPCs of local soil are not readily available at regional level. Due to this reason, while attempting to estimate LSE, majority of site-specific studies consider DSPCs developed for other region's soils. DSPCs, though can be determined using existing inverse GRA methodologies, critical review done in this work highlighted that most of the frequency domain studies target to determine change in shear modulus (G) with shear strain (γ) but no to very limited studies target to determine damping ratio (β) variation with γ (or β curve). Additionally, these methodologies are limited to finding out soil properties for the surficial layer only. During an EQ excitation however, each of such soil layers will behave distinctively
(A) Method for Analysing Episodic Air Quality and Health Risks to Sedentary Workers in an Urban Traffic Corridor
(2021) Sahu, Mitali
This research is aimed at developing a methodology to identify episodic conditions caused by air pollutants (Carbon Monoxide (CO), PM2.5 and Black Carbon (BC)) released from the traffic in an urban traffic corridor, to determine the most episodic prone locations, and to estimate chronic obstructive pulmonary disease (COPD) health risks to the sedentary workers in the traffic corridor due to PM2.5. This research has been carried out in an urban traffic corridor of the downtown of Guwahati, the fastest developing city of North-Eastern India situated in the Brahmaputra River Valley. It involves the development of indicators – one pertaining to the real CO emission scenario in the traffic corridor and second pertaining to the threshold CO emission scenario adopted from the national ambient air quality standards – which incorporate hourly average emission, population, pollutant toxicity and dimension of the corridor, and determine the time of occurrences of episodic conditions over the day. The factors which are most influencing the episodic conditions have been identified using statistical correlation analysis. The air dispersion model, AERMOD has been used to determine the episodic prone locations. The method has been applied further to BC to validate the time and spatial location of the episodic condition caused by CO. Subsequently, health risks due to PM2.5 in the episode-prone areas have been found out in terms of the risks of ischemic heart disease (IHD), stroke, COPD, and lung cancer (LC) expected upon exposure to PM2.5. The health risk estimates have been further supported with the help of a social questionnaire survey carried out in the traffic corridor on the participants who are sedentary workers in the shops located along the roadside. The results of the health relative risks show that the salesmen of air-conditioned shops1 and open shops2 are prone to risk due to exposure to PM2.5. The level of exposure of both groups to PM2.5 is different, which also resulted in different COPD symptoms for the workers of open shops having a direct exposure than the workers of air-conditioned shops having indirect exposure. The methodology developed in this research may be useful in carrying out such research in the roadside microenvironments.
(A) Study on Geotechnical Characterization of Residual Lateritic soil and Brahmaputra sand Blended with Fly Ash and Cement
(2011) Kalita, Ajanta
The shear strength of soils is one of the important aspects to be considered in any geotechnical activity. The problems concerned with the bearing capacity of road subgrade, slope stability of embankments and the design of retaining structures are all dependent on the shear strength characteristics of soils. Depending on the application in hand and the requirements, one needs to carry out modification of the soil properties. There is ample scope for the bulk utilization of fly ash in soil mixes for geotechnical applications such as in the construction of roads, embankments and backfilling behind retaining structures. In this research work, the characteristics of two soils, a fine-grained residual lateritic soil (red soil) and granular riverbank sand (Brahmaputra sand) blended with a low-calcium fly ash and ordinary Portland cement was studied through a systematic series of compaction tests, direct shear tests, CBR tests, unconfined compression tests and triaxial consolidated drained tests. Depending on the type of test, the maximum amount of soil replaced with fly ash by weight ranged from 50% to 90%. The amount of cement added was up to a maximum of 3 % to 5% by weight of the soil-fly ash mixes. This provided a wide range of gradation and texture of the mixes. Compacted specimens of the mixes were cured up to 28 days. Based on the maximum dry unit weight obtained from the compaction tests, the specimens for the remaining tests were prepared. The strength tests were conducted on the as-compacted specimens without saturating them. Direct shear tests were carried out only on specimens of sand and sand-fly ash mixes. The results from the tests were analysed to examine the compaction and strength characteristics of the modified soils due to the application of fly ash and cement. The obtained values will also be useful in judging the suitability of those proportions of the soil mixes for their use in diverse geotechnical applications that include the construction of subgrade and subbase of pavements. As the fly ashes produced in the same plant at different times can be different, and as locally available soils can vary widely in their properties, characterization of their mixes is a must for their field usage. It is to be noted that fly ash can be used to stabilize soil, and even soil can be used to stabilize fly ash as well..
(A) study on influence of control parameters on strength, durability and microstructure of fly ash-ground granulated blast furnace slag based geopolymer mortar and concrete
(2023) Prusty, Jnyanendra Kumar
Ordinary Portland cement (OPC) has been extensively used as the primary binding material in the preparation of concrete. However, over last few decades, Portland cement manufacturing industry has become one of the major contributors of emission of large volume of CO2 during the manufacturing process. On the other hand, the management of industrial waste in limited landfill space creates a massive challenge for the developing countries. To mitigate these issues, since last few decades, extensive research work has been undertaken to explore new alternate and more sustainable construction materials. In this line, there is a widespread use of industrial wastes in the production of concrete. Geopolymer concrete (GPC) has gained popularity as a potential alternative of Portland cement concrete due to its better mechanical properties and environmental benefits. The major challenges associated with the geopolymer composites are the variations in the physicochemical properties of precursor materials depending upon their sources, requirement of heat curing for the development of geopolymer composites with low calcium bearing precursor materials, limited availability of efficient and systematic mix design methodologies etc. Furthermore, the limited research works on durability performance of geopolymer composites in various aggressive environment is hindering the practical application of this material.
(A) Study on multiple Contaminant-Soil interaction and its effect on Contaminant fate Prediction
(2013) Buragohain, Poly
With tremendous urbanization and industrialization enormous amount of waste has been generated, which has significantly affected the quality of geoenvironment and the water resources. Several researchers and practitioners have stressed the importance to circumvent this environmental issue, and to find an appropriate solution to contain these wastes safely. Engineered landfill is an efficient method for meeting this challenge and soils used in these facilities and those below it (natural soil) plays a very vital role. One of the significant chemical properties of a landfill liner material is the contaminant retention capacity which determines the fate of contaminants or pollutants in the geoenvironment. It is necessary to establish the retention property of soils to evaluate its usefulness in waste containment facilities and its potential in minimizing contaminant migration into groundwater. There are several studies that evaluate contaminant retention of soils for single contaminant interaction. In, reality the presence of single contaminants seldom exists. Every contaminant is influenced by multiple ions present in the geoenvironmemt. Therefore, there is a need to evaluate multiple contaminant-soil interaction. There is also a need to further evaluate the retention capacity of locally available soils found abundantly and check its potential use as a cost-effective liner material in waste containment facilities. The present research work attempted to understand systematically, the multiple contaminant retention behavior of soils. The adequacy of existing mathematical isotherms for quantifying soil-multiple contaminants interaction was evaluated. Effort was made to quantify the influence of multiple contaminants on retention property of different soil type based on existing mathematical isotherm models. Many experimental interaction results were compared in the present study to appraise this objective. Some of the anomalies while using isotherm results for comparing different soil-contaminant retention cases have been brought forth. The contaminant retention results were used to understand the sensitivity of retention parameters on contaminant fate prediction. The influence of different ranges of contaminant concentration on fate prediction was studied. An attempt was made to understand whether there is a possibility of developing a correlation between soil specific parameters such as cation exchange capacity, specific surface area, soil pH with retention parameters. Keywords: contaminant, retention, single, multiple, isotherm, fate prediction, locally available soils, soil properties, ion chromotograph.
(A) STUDY ON PERFORMANCE IMPROVEMENT OF EXPANSIVE SOIL USING RESIDUAL SOIL AND LIME EXPANSIVE SOIL USING RESIDUAL SOIL AND LIME
(2009) Hussain, Md. Monowar
The soils which show volumetric changes due to changes in their moisture content are referred to as expansive soils. With increase in moisture content, these soils swell and with decrease in moisture content undergo shrink. This leads to seasonal movements causing heave in rainy season and subsidence in summer, giving rise to high differential settlement in the structures founded on them thereby causing distress and damage to it. Stabilization of expansive soils with additives has been used with great success. In the recent past several investigations have been reported highlighting the beneficial use of lime for performance improvement of clay soils (Davidson and Handy, 1959; Thompson, 1966; Bhasin, 1978; Bell, 1988; Sivapullaiah et al., 1998, 2000; to name a few). In spite of these studies there is still need of further investigation to understand the mechanism of lime induced modifications of soils more clearly. From literature review it is observed that lime generally improves the performance of clayey soils in terms of reduced swelling and increased strength. However, in some cases, depending on the type of soil, amount of lime added, curing period etc. the performance improvement reduces. In view of this an attempt is made to carry out a systematic study through careful variation of above parameters, to develop an understanding of the mechanisms involved.Primarily an expansive soil (ES) and a residual soil (RS) that represent the extreme types of soil are used in the present study. The non swelling and high strength residual soil was added to the expansive soil to improve its performance. Besides to cover a wide range of plasticity these two soils are mixed in different proportion (i.e. 100%ES, 80%ES + 20%RS, 60%ES + 40%RS, 40%ES + 60%RS, 20%ES + 80% RS, 100%RS) to prepare six different soil samples. Subsequenty these soils were treated with lime of varied quantity under varied curing period. The test results indicate that the liquid limit continues to reduce till 3% lime content, beyond which the increased lime content has marginal effect on it. However, at very high lime content (i.e. 13%) and long curing period (i.e. 28 days) the liquid limit of the expansive soil has shown an increasing trend. This increasing trend gradually grows more prominent with increased percentage of residual soil and curing period. It is of interest to note that irrespective of soil type the liquid limit is large for increased curing period. The plastic limit increases with increases in lime content. The increase is relatively faster till lime content reaching about 3%. From 3 to 5% of lime content the rate of increase in plastic limit is relatively slow. Beyond 5% lime content visible increase in plastic limit is noticed only for increased percentage of residual soil and higher curing period. In general soils have shown an immediate decrease in plasticity index upon addition of lime. For 100%ES, increasing the lime content beyond 5% had a marginal effect in further reducing the plasticity index. This is in line with earlier observations that immediately upon addition of lime the liquid limit reduces and plastic limit increases. In general the plasticity index increases with increase in curing period however it is more prominent for the increased percentage of residual soil. This is attributed to the silica gel that enhances the...
(A) Study on Plastic Cell Filled Concrete Block Pavement for Low Volume Rural Roads
(2011) Singh, Yendrembam Arunkumar
A systematic full scale experimental study on the structural performance of Plastic Cell filled Concrete Block Pavement (PCCBP) for various cell thicknesses subjected to live traffic conditions is presented in this research work. Five test sections of different thicknesses viz., 50 mm, 80 mm, 100 mm, 120 mm and 150 mm, of PCCBP over 100 mm thick water bound macadam (WBM) sub-base layer has been constructed at the approach road towards Indian Institute of Technology Guwahati (IIT Guwahati), India, from National Highway 31 (NH 31). In addition, to check the feasibility of PCCBP overlay to strengthen the existing old bituminous pavement, 50 mm thick PCCBP overlay test section was also constructed. Further, in order to optimize the cost of pavement construction, an attempt has been made to use waste stone dust (byproduct of aggregates crushing) in place of the traditional river sand. Custom fabricated Falling Weight Deflectometer (FWD) was used to evaluate the PCCBP by measuring the surface deflections at specified radial distance from the load center. In this work, Genetic Algorithm (GA) based backcalculation program (Reddy et. al., 2002) was used for backcalculating the layer moduli of the PCCBP test sections using pavement surface deflection data. For the thicknesses tested, elastic layer modulus of PCCBP (~1995 MPa for 50 mm thick) has been seen to increase linearly with increasing thickness (~90% increase in elastic modulus was observed for 200% increase in thickness). To evaluate the structural performance of PCCBP, surface deflections data using FWD were collected at regular intervals of 0 passes, 38,000 passes (~6 months) and 62,000 passes (~11 months). It has been observed that for the initial 38,000 ESAL passes the degradation in layer modulus of PCCBP is of the range ~3-20%, however there appears to be a stabilization after 38,000 ESAL passes with the degradation dropping to ~1-7% (from 38,000 to 62,000 ESAL passes). It has also been seen that there is a significant improvement (~230% increase) in elastic layer modulus when PCCBP is used as overlay as compared to that of bituminous overlay. Efforts have been made to assess pavement distresses of PCCBP test section using distress guidelines developed by Interlocking Concrete Pavement Institute (ICPI, 2007) based on Pavement Condition Index (PCI) for similar distress types observed. The distress type and severity level of each test section was recorded and PCI value of each section was calculated using the deduct curves given in the distress manual. From the PCI value, the rating of the test section was found to be in the range from Fair to Very Good condition even after a load repetition of 62,000 ESAL passes. Specific distresses observed for PCCBP are also reported. From the feasibility study of PCCBP overlay, it was observed that the performance is Excellent even after 62,000 ESAL passes. Economic evaluation of PCCBP vis-a-vis conventional flexible and rigid pavements was also carried out. In the absence of design guidelines for PCCBP, rutting criteria as per IRC (2001) was adopted to design the PCCBP pavement. Conventional flexible and rigid pavements were design as per IRC (2007) and IRC (2004). The construction and maintenance cost were estimated based on Government of Assam schedule rate 2007-08 (PWD, 2007) and guidelines for the estimation of the maintenance cost for construction of the rural roads......
(A) Study on response and capacity of monopod bucket foundations supporting offshore wind turbines in sandy soils
(2018) Deb, Tanmoy Kumar
With the increasing demand for renewable and environment friendly energy, wind turbine farms are moving seaward due unavailability of suitable land locations, noise pollution produced, visual impact on the natural environment, and availability of stronger and stable wind speeds. Offshore wind turbine foundations are subjected to large lateral forces arising from wind forces and water currents and the vertical self-weight loading is substantially lesser.This thesis presents the results of three-dimensional finite element analyses of bucket foundations embedded in medium dense and very dense sandy seabeds, considering the non-linear behaviour of the soil. Under vertical compressive loading, the response of bucket foundation was investigated for three diameters (12, 15 and 18 m), each having three aspect ratios (0.5, 0.75 and 1.0). The effects of skirt length and soil plug of the bucket foundation were investigated by comparing the vertical response with that of surface circular foundation and embedded solid foundation, respectively. Based on the results, predictive equations have been proposed for the bucket foundation to determine the ultimate vertical bearing capacity and settlement under superstructure load.Under lateral loading, same geometries of bucket foundation were analysed under lateral loads. The superstructure load ranged from 5 to 15 MN. The hub height was taken as 100 m and the lateral loading height was varied from 0 to 100 m. For a given loading height and superstructure load, the ultimate lateral capacity is observed to increase with increasing value of either bucket diameter or skirt length. Increasing bucket diameter shows greater influence on the ultimate lateral capacity as compared to skirt length. The influence of superstructure load on ultimate lateral capacity keeps on decreasing with an increase in bucket skirt length. Interaction diagrams of lateral load and overturning moment capacity at various loading heights have been represented graphically for serviceability limit state, fatigue limit state, worst expected transient load limit state, and ultimate limit state. Finally, predictive expressions have been proposed for the depth of point of rotation, initial stiffness, ultimate lateral capacity and allowable capacity of bucket foundations in medium and very dense sands.
(A) Study on Soil-Plant-Atmosphere Interaction for Green Infrastructure
(2020) Gadi, Vinay Kumar
The presence of vegetation in the upper layer of vadose zone results in complex moisture dynamics (soil-plantatmosphere interaction) due to the combined effects of transpiration and soil water evaporation. Unsaturated soil-root composite hydraulic properties, transpiration and soil water evaporation and effect of plant parameters (i.e., leaf area index (LAI), grass density, shoot length (SL) and stomatal conductance) on soil property are keys for understanding this complex moisture dynamics. Plant parameters and unsaturated soil properties were not considered holistically by previous researchers to understand soil-plant-atmosphere interaction. The main objective of this study is to explore the soil-plant-atmosphere interaction by considering the soil (cracks, suction and hydraulic conductivity) and plant parameters (vegetation density, LAI and stomatal conductance) together. Effect of crop and non-crop species growth on crack intensity factor (CIF) were investigated in the current study. In addition, effect of plant parameters on evapotranspiration induced suction was numerically analyzed. It is evident that large number of sensors are usually installed to monitor the suction in geotechnical infrastructure. Therefore, a non-intrusive and economical technique was developed to differentiate the 1) mix grass cover under tree shade (MUT); 2) mix grass cover under self-shade (MUS) and 3) mix grass cover without shade (MWS) in relatively large areas. Changes in stomatal conductance and surface area of vegetation at high suction ((high suction; > 100 kPa) were rarely investigated previously. Hence, effect of suction on stomatal conductance and surface area was investigated in this study. Furthermore, spatial and temporal heterogeneity of hydraulic conductivity in green space was rarely focused. Field monitoring was conducted in an urban green space to understand the spatial and temporal heterogeneity of surface hydraulic conductivity during the life period of mix grass. It is known that suction and surface hydraulic conductivity are interpreted from soil surface water content. Non-invasive and cost effective technique is vital to interpret soil surface water content. Therefore, colour analysis technique was demonstrated to interpret soil surface water content. This study on soilplant- atmosphere interaction helps to analyze the performance of green infrastructure accurately. Correlations were found between shoot parameters (SL, LAI, vegetation density) and CIF for the selected crop and non-crop species. Numerical analysis revealed that changes in shoot and root parameters could alter the suction by 11 % - 300 %. In addition, time required to attain wilting point was found to depend on plant parameters. Two new relationships i.e., Stomatal conductance characteristic curve (SCCC) and surface area characteristic curve (SACC) were found. The elementary hypothesis of spatial uniformity of surface hydraulic conductivity during life span of mix grass was not found to be true from the present study. The spatial and temporal heterogeneity of surface hydraulic conductivity was found mainly due to non-uniformity in grass growth and tree shade.
(A) Study on strength and deformation behaviour of glass fibre-reinforced clayey and sandy soils under varying moulded states
(2017) Patel, Suchit Kumar
Field applications of fibre-reinforced soil are still lagging behind the traditional planer reinforcement method. There is ample scope to increase field applications of fibre reinforcement with both clayey and sandy soils. In the present study, the strength and deformation behaviour of two soil types, a clayey soil and a sandy soil, reinforced with glass fibres, were studied through a systematic series of laboratory tests. Glass fibres of 0.15 mm diameter and of different lengths (10, 20 and 30 mm) were mixed randomly up to 1% content with the clayey soil and up to 4% content with the sandy soil. The reinforced clayey soil specimens were moulded at different combinations of dry unit weight and moisture content, close to the maximum dry unit weight and optimum moisture content of the unreinforced soil, whereas the reinforced sandy soil specimens were moulded at relative densities ranging from 35% to 85%.Unconfined compression tests, California Bearing Ratio tests and consolidated undrained triaxial tests were conducted on reinforced clayey soil specimens, whereas only consolidated drained triaxial tests were carried out on reinforced sandy soil specimens. The soaking period in CBR tests was extended up to 40 days from the standard 4 days. The laboratory results were analysed to evaluate the effect of the glass fibres on the compressive strength, CBR, shear strength, failure axial strain, specimen deformation and failure modes, secant modulus and energy absorption capability. The contribution of fibres to the soil strength improvement under varying moulded states has been examined, and a comparison has been made on the behaviour of glass fibre-reinforced clayey soil and sandy soil.
(A) Study on Strength Characterisation of Soils Mixed with Fly Ash, Scrap Tyre Materials and Cement
(2020) Barman, Pranjal
In this study, the individual or combined effect of fly ash and tyre fibre on stress-strain-strength characteristics of two soils, a fine-grained residual lateritic soil (red soil) and granular riverbank sand (Brahmaputra sand), with or without cement was investigated. The fly ash content used in this study varies from 20% to 50% content by weight. Tyre buffings and tyre crumb which were used as scrap tyre materials were added to the soil mix varying from 5% to 10% content by weight. The amount of cement added ranges from 1% to 2% by weight of the various soil mixes. Specimens were statically prepared based on the maximum dry unit weight and optimum moisture content and then subjected to strength tests. For each mix, unconfined compression and triaxial compression test was carried out on the as-compacted specimen with curing period of 0, 3, 7, 14 and 28 days. Inclusion of fly ash and tyre buffings to both the soil types reduces the dry unit weight. Improvement in unconfined compressive strength has been observed with the addition of fly ash to the sand and also with curing period which does not occur in case of the red soil mixes. Addition of tyre buffings to red soil-fly ash mixes reduces the strength, but increases the shear strength of sand-fly ash mixes especially in higher confining pressure. However, addition of cement to soil-fly ash-tyre fibre mixes can lead to considerable improvement of shear strength of the soil. Improvement in strength of different soil mixes is seen with the increase in curing period. Moreover, soil-fly ash-tyre buffing mixes containing 35% or 50% fly ash and 5% tyre buffing content along with cement have been found to have some potential for use in the construction of roads.
(A) Study on the Effect of Heavy Metals and Leachates on Engineering Behaviour of Bentonite
(2021) Ray, Saswati
A rapid increase in industrialization is leading to the generation of high metal toxicity to the ecosystem. Landfilling has been carried out as the most preferred method of waste disposal around the globe. In the present study, two bentonites of different mineralogical composition were studied for their change in the index properties, swelling, swelling potential, swelling pressure, hydraulic conductivity, consolidation parameters, shear strength properties and sorption characteristics in the presence of different heavy metals of various concentrations and different leachates. Different isotherm models were used to determine the best-fit equilibrium isotherms. Kinetic models were fitted to investigate the kinetics and mechanisms of metal sorption on both the bentonites. FESEM and FTIR studies were conducted to analyze the change in surface morphology and alteration in FTIR pattern in both the bentonites before and after sorption of heavy metals. The results showed that the liquid limit, free swelling, swelling potential and swelling pressure of the bentonites decreased with an increase in the heavy metal ion concentration and the presence of leachates. Results also indicated that compression index (Cc) and time required for the 90% of consolidation (t90) decreased. In contrast, the coefficient of consolidation (cv) and hydraulic conductivity (k) increased in the presence of heavy metals and leachates. Both the bentonites showed a reduction in the Unconfined Compression Strength in the presence of heavy metals and leachates, yet, lying within the recommended a minimum value of 200 kPa. The study showed that pH influenced the adsorption of heavy metals for both bentonites. Isotherms’ investigation reveals that both the isotherm model fits well with equilibrium data. Kinetic studies followed the Pseudo-second order model. A comparison between the two bentonites showed that bentonite, which has a high liquid limit, swelling capacity, specific surface area (SSA), cation exchange capacity (CEC) and montmorillonite content, showed higher sorption capacity and undergoes a massive change in the liquid limit, free swelling, swelling pressure and hydraulic conductivity due to the presence of the various permeants.
(A) Study on the effect of salts on the swelling, hydraulic and consolidation behaviour of bentonites
(2016) Dutta, Jagori
Due to rapid urbanization and industrialization, the geoenvironment and groundwater reserves in most parts of the world are getting damaged due to the harmful effect of pollutants disposed off into the geoenvironment. Due to its high swelling capacity, contaminant adsorption capacity and low hydraulic conductivity, bentonite is primarily used as a liner material in waste containment. This work was carried out to study the effect of inorganic salts and heavy metals present in leachates on the behaviour of bentonites. Two bentonites of different mineralogical composition were studied for their change in the index properties, free swelling, swelling potential, swelling pressure, hydraulic conductivity and consolidation parameters due to the presence of various inorganic salts and heavy metals of various concentrations, individually as well as combination of each other. The results showed that salt has a definite effect on the free swelling, swelling potential, swelling pressure, hydraulic conductivity of the compacted bentonite. The liquid limit, free swelling, swelling potential and swelling pressure of the bentonites decreased with an increase in the salt or heavy metal ion concentration. Irrespective of the initial compaction condition, the hydraulic conductivity of the bentonite increased with an increase in the salt concentrations. The compression index (Cc), coefficient of volume change (mv), and time required for the 90% of consolidation (t90) of the bentonites decreased; whereas, coefficient of consolidation (cv) increased with the increase in salt concentration indicating specimens consolidated faster in salt solution in comparison to water. A comparison between the two bentonites showed that salt has a significant effect on Bentonite-B. Bentonite-B, which has a high liquid limit, swelling capacity, SSA, CEC and ESP and termed as high quality bentonite, undergoes a large change in liquid limit, free swelling, swelling pressure and hydraulic conductivity due to...
(A) Study on the Water Retention and Contaminant Retention Behavior of Fly Ash, Bentonite and Its Mixes
(2015) Deka, Abhijit
A need to explore cost-effective and environmentally sustainable alternate materials that can be used in multi-layered hydraulic and contam inant barriers has motivated this research. Natural clays or expansive soils like bentonite mixed with cohesionless soil like sand is used for the construction of low permeable waste containment liners and covers. Sand is a costly construction material that would obviously need replacement in waste management projects such as liners and covers. Fly ash can be a viable alternative to sand in these projects. Unsaturated characteristics and contaminant interaction are important for the behavioral modeling and performance assessment of geomaterials used in liners and covers. This research was planned to investigate the unsaturated behavior and contaminant interaction of fly ash-bentonite mix. The unsaturated behavior was established in terms of water retention characteristics curve (WRCC) for four Indian fly ashes, bentonites and fly ash-bentonite mix. The study brings out the measurable range of suction in fly ash, which is otherwise missing in the literature. The importance of volumetric shrinkage curve and mandatory approach for WRCC parameterization of bentonite has been demonstrated in this study. The influence of fly ash type and content on the WRCC of fly ash-bentonite mix was investigated. The sensitivity of variation in WRCC parameters on unsaturated seepage modeling was studied for specific cases of measured WRCC. The contaminant retention capacity of fly ash, bentonite and selected fly ash-bentonite mix was determined by considering lead as a model contaminant. The study highlights the usefulness of fly ash in combination with bentonite for waste containment liners and covers. This would help in the mass utility of waste fly ash for a meaningful environmental application such as waste containment and also relieve the burden of storage space.
(A) Time Domain Approach for Bridge Fatigue Considering the Effect of Multiple Vehicles at Random Passing Rate
(2022) Pillai, Anjaly J
Bridges are lifeline structures in transportation network. Smooth flow of traffic through bridges is important consideration for socio-economic development of any regions. The bridges are generally designed with high factor of safety to cater for uncertainty in live load and material properties. With time, the structures may show various forms of degradation. This is mostly common where traffic growth is unexpectedly high and the structures are exposed to aggressive environment, which necessitates a more elaborate approach to estimate fatigue life in design phase itself. Burden of in-situ monitoring of crack growth may thus be reduced.
Aerobic Granulation in Sequencing Batch Reactors for Treating Wastewater Laden with Phenol, Thiocyanate, Ammonium and Nitrogenous Heterocyclic Compounds
(2020) Tomar, Sachin Kumar
Aerobic granular sludge (AGS) technology is developed in the last two decades for the treatment of wastewater. Because of having unique properties like high settling behavior, compact structure and ability to withstand high and toxic loading, AGS has been used in the treatment of various kinds of domestic and industrial wastewater. Phenol, thiocyanate (SCN-), ammonia-nitrogen (NH4+-N), pyridine and indole found in many industrial wastewater, such as coking industry, requiring an economic and sustainable treatment technology before being disposed to surface water bodies. In this work, AGS were developed by optimizing operational parameters for the treatment of multiple toxicants in sequencing batch reactors (SBRs). The first aim of the current research work was to optimize the cycle time followed by the air flow rate for aerobic granulation by using toxic phenol as a carbon source along with SCN- and NH4 +-N. For cycle time and air flow rate study, synthetic wastewater containing phenol (400 mg L-1), SCN- (100 mg L-1) and NH4 +-N (100 mg L-1) was treated in the three SBRs. At 6 h cycle time and 2.5 L min -1 air flow rate, granules showed good characteristics and pollutant removal performances. Furthermore, the investigation on rapid granulation seeded with the refinery sludge with two different substrates (400 mg L-1 phenol in R1 and 1220 mg L-1 of sodium acetate in R2) along with 100 mg L-1 of NH4 +-N was carried out in two different SBRs. Faster granulation in just 40 days was observed in R1 with better granular characteristics. After 75 days of stable operation, granules started to break down in R1, therefore the impact of toxic SCN- on granule reformation was evaluated in R1. Reformation of disintegrated granules were observed after gradual addition of SCN- (10-340 mg L-1) with better granular characteristics along with the recovery of nitritation efficiency. In addition, two SBRs with two different kinds of industrial sludge; refinery sludge (R1) and brewery sludge (R2), were operated to observe the impact of high loading of phenol (5.71 kg COD m-3 day-1) along with SCN- (100 mg L-1) and NH4 +-N (100 mg L-1) on the stability and performance of AGS. R2 granules were stable at an organic loading rate (OLR) of 5.71 kg COD m-3 day-1, whereas the granules of R1 started to disintegrate at an OLR of more than 3.32 kg COD m-3 day-1. Afterwards, the potential of AGS for simultaneous biodegradation of two nitrogenous heterocyclic compounds (NHCs), i.e., pyridine and indole, and NH4 +-N along with phenol and SCN- was investigated in three SBRs. R1 and R2 were operated with pyridine and indole, respectively, whereas R3 was operated with a mixture of equimolar concentrations of pyridine and indole. Pyridine did not show any inhibitory effect on characteristics of aerobic granules up to a concentration of 5.0 mM. However, Indole was having a profound adverse impact on the granular characteristics and other pollutants removal with a concentration of more than 1.0 mM (R2 and R3).
Anaerobic digestion of pulp and paper mill sludge
(2018) Veluchamy C
Anaerobic digestion (AD) of pulp and paper mill sludge (PPMS) was studied with and without pretreatment, in biochemical methane potential (BMP) assay, batch and with a semi-continuous lab scale reactor. Initially, AD of PPMS without pretreatment (as control) was carried out by using cow dung as inoculum in a BMP test. Results indicated that PPMS has a high potential for energy recovery in the form of biogas. Based on the experimental result on gas production, volatile solids (VS) reduction, F/M ratio 2.0 was perceived as best and achieved higher methane production (264±5 mL CH4/g of VS degraded). As PPMS contain inherent recalcitrant characteristics of lignocellulose content, turns hydrolysis step into a rate-limiting stage AD. Therefore, further experiment was carried out to overcome the hydrolysis step, different pretreatment were studied. The chemical and instrumental (FT-IR, XRD, FESEM) analyses exposed that all the pretreatment methods have shown improvement in solubilization. Among the pretreatments studied, in thermal pretreatment-hot air oven (80oC for 90 min), in electrohydrolysis (15 V for 45 min), in biological pretreatment (Bacillus mojavensis (CDb1)) showed the highest impact on sludge solubilization. Further, screened pretreatment (in the previous experiment) were tested for enhanced methane production in BMP assay. The result revealed that the specific methane production potential was increased from 264±5 to 303±4 mL of CH4/g VS degraded (thermal), 301±3 mL of CH4/g VS degraded (electrohydrolysis), and 295±3 mL of CH4/g VS degraded (biological). A net energy of 8,735 kJ was gained after thermal pretreatment and 13,224 kJ was gained after electohydrolysis pretreatment. In addition to that three kinetic models were studied. Among that Gompertz and logistic function models represents and reproduce the experimental data, while earlier has better fit. Designed anaerobic auger plug flow reactor (AAPFR) experimental studies were carried out in two places: one at India, IITG (Environmental lab) campus and another one at Canada, University of Guelph Ridgetown Campus. At India, the AAPFR was operated for 75 d with thermal pretreatment (30 d) and without pretreatment (30 d) at 21 d HRT with specified OLR (6.3 kg VS/m3/d). The CH4 yield obtained from the continuous study was not significantly different from the BMP and batch study, and experimental CH4 yield was an equal to 310 mL CH4/g of VS degraded in AAPFR operation. At Canada, study was majorly emphasized on the effect of increasing OLR on the CH4 production in long-term experiments (130 d) in corn silage. The increase in biogas production was observed with an increase in OLR. In addition to this, increase in OLR resulted in a decrease in CH4 content and increase in H2S concentrations. However, the reactor showed a stable operation at an OLR 6.5 kg/m3/d. The reactor lost its stability at an OLR 8.8 kg/m3/d, which was apparent by decrease in biogas yield and its CH4 content. Further, a development of mathematical modeling on a mass diffusion on effect of moisture content (MC) for the solid-state anaerobic digestion (SS-AD) was carried out. This model proposed that the decreased MC causes augmented mass diffusion resistance by the accumulation of hydrolytic product and lead to the reduced methane gas production.
Analysis and modeling of passenger car equivalents for heterogeneous traffic conditions
(2017) Ballari, Syed Omar
Passenger car equivalent (PCE) values are required while representing a non-homogeneous (mixed) traffic stream in terms of a homogeneous (base) traffic stream. For the traffic conditions prevalent in India, researchers mostly suggest individual PCEs of different vehicle types varying with traffic composition and flow rate. The objective of the present study is to estimate the constant and the aggregate PCE values for the four-lane and six-lane highways passing through the level terrain in India. PCE values are estimated based on the macroscopic relationships and the area occupancy and speed drop are selected as the performance measures. Macroscopic relationships are generated using simulation model and can be better represented by considering the stationary traffic conditions. For a particular traffic composition, constant PCEs can be used across different flow rates without much loss of accuracy. Aggregate PCEs do not vary with area occupancy in the case of four-lane and six-lane divided highways. Speed drop provides variation among the aggregate PCEs particularly at lower flow rates. The present study can be extended further by defining the thresholds of area occupancy and speed drop based on empirical data.

Browse

Browsing PhD Theses (Civil Engineering) by Title

Results Per Page

Sort Options