PhD Theses (Civil Engineering)


Recent Submissions

Now showing 1 - 20 of 214
  • Item
    (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
  • Item
    Hydrological Modelling of River Basin and Strategic Management of Watershed under Different Anthropogenic and Climate Change Scenarios: A Case Study of Genale Catchment, Ethiopia
    (2022) Negewo, Tufa Feyissa
    It is important to estimate the quantity and quality of water resources in terms of spatial and temporal variability to utilize it sustainably. Change in future climate conditions affects the availability of water resources by modifying the magnitude of precipitation, groundwater recharge, surface runoff, actual evapotranspiration, lateral flow, water yield, the river flows, and provoke water stress in the downstream. Local government authority around the globe is also emphasizing water resources project exploration, design, planning, and management aspect within the river basin.
  • Item
    Utilisation of Basic Oxygen Funace Steel Industry Slag in Open Graded Asphalit Friction Course Mises
    (2022) Pathak, Santanu
    Open graded asphalt friction course (OGAFC) is a special purpose bituminous mix applied as a surface course for improved skid resistance and road safety especially under wet weather conditions. These mixes are characterised by high air voids content, generally greater than 18% of the mix volume, which are achieved through a uniform aggregate gradation that predominantly comprises of coarse aggregates. For adequate load transfer in OGAFC mixes through proper stone-on-stone contact these mixes demand comparatively good quality road. The increasing cost and the shortage of good quality natural aggregates, have compelled researchers and practitioners to explore alternate aggregate materials to attain sustainability in road construction. Steel slag is an industrial bylco-product obtained during the conversion of pig iron or steel scrap to industrial quality steel. Steel slag is classified as ether basic oxygen furnace (BOF) slag or electric-arc fumace (EAF) slag, depending on the fumace/process employed in its conversion.
  • Item
    Investigation of engineering properties and vegetation performance of biochar-amended soil for the application in the bioengineered structures
    (2022) Hussain, Rojimul
    Soil bioengineered structures are comprised of soil for stability and vegetation for protection. These structures are commonly adopted because of their multiple beneficial impacts. The stability and performance of these structures depend on the soil engineering properties and vegetation performance. Further, the vegetation performance i.e., the vegetation growth and health status are interrelated to the soil engineering properties. The vegetation in these structures provides additional stability and protection from erosion and failure. The vegetation roots act as soil reinforcement by anchoring or bridging the soil particles together through mobilization of its tensile strength. The root water uptake by the roots induces suction in soil that in turn increases soil shear strength or stability in terms of apparent cohesion. Further, the above ground mass of vegetation protects the soil surface from erosion along with the aesthetic view. Therefore, suitable growth and health status of vegetation are utmost important for the effective functioning of bioengineered structures. Many a times soil does not provide suitable condition for the growth and health status of vegetation and therefore several amendments have been adopted for improving the vegetation performance. Among these amendments, biochar has been regarded as more suitable soil amendment due to their stable structure i.e., microbial non-degradable and organic nature. Biochar is a carbon-rich material obtained after pyrolysis of biomass under oxygen deficit condition. The conversion of biomass into biochar is also the sustainable way of managing wastes, mitigating climate change and producing energy. Biochar as soil amendment is often used for soil carbon sequestration, improving the soil fertility as well as crop growth and yield, and removing the organic and inorganic pollutants from soil. Application of biochar as soil amendment majorly focused on loose agricultural soil. Soil in bioengineered structures is different from the agricultural soil i.e., often compacted for achieving stability and subjected to a prolong drying due to the irregular irrigation pattern. Therefore, the engineering properties of biochar-amended soil (BAS) and the vegetation performance in BAS need to be investigated under compacted state for ensuring effective stability and performance of bioengineered structures. In the present thesis work, the engineering properties i.e., the hydro-mechanical and physicochemical properties of biochar-amended compacted soil and the vegetation (grass species) growth and health status in biochar-amended compacted soil have been investigated for potential application in bioengineered structures. The results revealed that the amendment of biochar improved the soil engineering properties by increasing the soil pH, CEC, water retention capacity, shear strength and load bearing capacity, and decreasing the dry density, infiltration rate, saturated hydraulic conductivity, unsaturated hydraulic conductivity and desiccation crack potential. Further, the biochar amendment found to be improved the vegetation performance by increasing the vegetation (roots and shoot mass) growth, delaying the wilting (higher permanent wilting point), decreasing the stomatal conductance (pathogen resistance or good health) and allowing complete photosynthetic activity at relatively large suction. The amendment of different types biochar found to be exhibited variable responses on the soil engineering properties and vegetation performance. Adversely, the undrained shear strength or UCS of the soil was found to be decreased after biochar amendment which needs to be further investigated. However, the magnitude of UCS obtained for 5% (w/w) biochar amendment rate was found to be higher than the minimum (200 kPa) required strength for most of the bioengineered structures and suggested by the united state environmental protection agency (USEPA). Based on the present thesis work, it is suggested to use 5% BAS in bioengineered structures; however, considering field trials before application would add more reliability.
  • Item
    (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.
  • Item
    Seismic performance evaluation of RBS-CFT connections with bidirectional bolts under cyclic loads
    (2022) Paul, Subhra
    This thesis presents experimental investigation on evaluation of performance of a new type of steel reduced beam section (RBS), designated as V-cut, and on its role in improving overall safety of RBS-CFT connections subjected to cyclic load. Detailed design steps adopted for design of the V-cut RBS with lower depth of cut, as compared to that in the conventional radius cut RBS, are reported in this paper. Behavior of four types of steel RBS and concrete filled tube (CFT) connections with bidirectional bolts were examined. An experimental study was performed to compare the performance of V-cut RBS with that of the other conventional radius cut RBS under cyclic loading. It exhibited improved hysteretic behavior, and the new RBS-CFT connection is found to be semi-rigid in nature. Test results show that the energy dissipation in the composite steel connections with V-cut RBS is higher than that with radius cut RBS. The application of V-cut steel flange beam effectively enhanced ductility and reduced the residual torsional deformation. It reached a rotational capacity of 0.04 radians without any damage in the joint panel region, and thereby meets the seismic provisions of the AISC as a special composite moment-resisting frame. Detailed and simplified nonlinear finite element analysis of RBS-CFT connections with bidirectional bolts was performed using the general-purpose software ABAQUS and OpenSees respectively. The failure patterns of the connections were obtained by the ABAQUS software. Simplified model was proposed in OpenSees to regenerate the hysteresis loops as obtained from the experimental study. Finally, seismic vulnerability assessment has been done by developing experimental fragility curves.
  • Item
    Hydrological Assessment of LULC and Climate Change within the Water Resource Development Scenarios of Omo Gibe Basin, Ethiopia
    (2021) Chaemiso, Shiferaw Eromo
    The hydrological functions of river catchments are affected by numerous natural and man-made changes. Climate change is also one among them that has a complex effect on river basins. The river basins are vulnerable to natural and anthropogenic disruptions, changes in land use and land cover, and changes in hydrological characteristics because of water resources developments. The present study utilized hydrological modelling and remote sensing methods to determine the catchment response due to LULC changes at spatial and temporal scales for a river basin in Ethiopia. The study envisages hydrological assessment of LULC and climate change within the water resources development scenarios of the Omo Gibe Basin in Ethiopia.
  • Item
    Development of Smart Thickening Fluid based Ultra Resilient Adaptive Kinematic Soft Human Armour (SURAKSHA)
    (2022) Kumar, Suman
    With the progress of great development occurring in society, day by day a greater number of threats arises against humanity. The history of the conflicts between two parties is not new. In the present era, the form of war has been changing constantly, and it has taken various shapes such as guerilla warfare, insurgency, and similar. With the rapid development in technology, arms and ammunition have modernized. This increases the threat to the personnel who is directly participating in the conflict. The main objective during combat situation is survivability of the engaged personnel. Due to the rapid development in the lethality of bullets, there is an immense demand for the development of enhanced protective suit which can safeguard against these threats and are simultaneously flexible and light. This thesis presents the design and development of liquid ballistic body armour to counter extreme threats arising from the bullet (direct and indirect effect) from standard arms and ammunition (as per National Institute of Justice (NIJ) specifications). The effect of inter-yarn friction on the ballistic performance of the fabric is analyzed. The fabric consisting of varying yarn density (fabric sett) is considered to select optimum yarn density. From the numerical modelling, the ballistic performance of the fabric is optimized as a function of coefficient of friction and a critical coefficient of friction is obtained. The modelling of Shear Thickening Fluid (STF) treated Kevlar is presented and the ballistic performance of the STF treated fabric is evaluated. The numerical model of (STF) treated fabric utilizes the friction-based models and is implemented by adopting very high coefficients of inter-yarn friction. The present study shows that there is enhancement of ballistic performance due to increasing coefficient of friction up to a critical coefficient of friction for a specific fabric sett. Beyond critical level, no appreciable improvement in the ballistic performance of the fabric is observed. There is a decrease in the ballistic performance beyond critical friction level. After that, the Multi Material – Arbitrary Lagrangian Eulerian (MM-ALE) approach of modelling STF treated fabric is found to be an efficient option as compared to the friction-based model to evaluate the ballistic performance of the STF treated fabric. The different configurations of STF treated fabric are evaluated and optimum configuration is arrived to completely stop the projectile conforming to Ballistic Rating (BR) I, II A, II and III A as per NIJ standards. After that, the ballistic performance of STF encapsulated in bubble wrap configuration is analyzed and evaluated. The STF encapsulated bubble wrap configuration consists of STF filled in bubbles and these bubbles are either uniformly or randomly placed to prepare a layer of bubbles. The numerical strategies for modelling of STF encapsulated bubble wrap configuration is proposed and presented in this thesis. In this study uniformly placed cylindrical bubbles of diameter 5 mm and height 5 mm is investigated and presented. This new configuration is found to be more efficient as compared to STF treated fabric in terms of ballistic performance against projectiles of different ballistic rating. The STF encapsulated bubble wrap is investigated under the impact of projectile of BR I, II A, II, and III A as per NIJ standards. The optimum configuration is arrived to completely stop the projectile conforming to BR I, II A, II and III A as per NIJ standards. Based on the outcome of the investigation a design guidelines and methodology are proposed in this thesis.
  • Item
    Rock Physics Modelling and Seismic Inversion for Reservoir Characterisation
    (2022) Garia, Siddharth
    Rock physics modelling is vital in various stages of exploration and production to comprehend the fluctuations in the seismic response to variations in the physical and fluid properties of rock. Rock physics explores the quantitative relationships of seismic, sonic or ultrasonic velocities to the petrophysical properties so as to predict beyond the existing data range facilitating the initial phase of seismic interpretation. This can be achieved through a forward or an inverse rock physics model, with the primary aim being linking the elastic properties of rocks to porosity, lithology etc. Therefore, rock physics is an integral part of reservoir characterisation, seismic reservoir monitoring and lithology discrimination.
  • Item
    Biochemical Treatment of Acid Mine Drainage by Constructed Wetlands in Northeast India
    (2022) Singh, Shweta
    India is one of the largest producers of coal and coal mines are the major backbone of India’s economy. Amongst various pollution concerns of coal mining, the incidence of acid mine drainage (AMD) is widespread and globally regarded as the most challenging wastewater. The management of AMD remains a great challenge as many remediation measures fail to attain a satisfactory economical and sustainable approach. AMD from the North Eastern Coalfield (NEC), Assam, India, is highly polluted and critical investigation of the AMD pollution for the potential remedial measures is scarce. The present study demonstrates a passive treatment strategy for AMD from the NEC using constructed wetlands (CWs). The influence of climatic variables on AMD characteristics and its deleterious impact on the surrounding soil was investigated. Elevated concentration (in mg L–1) of Fe (0.12–302), Al (6.73–32), Mn (0.10–16), Co (< 1.47), Ni (< 5.24) and Cr (< 0.54) were found in the AMD. The release of pollutants increased in the monsoon season, followed by highly concentrated pollutants in the post-monsoon season. The change in the season had a predominant effect on the oxidative leaching of sulfide minerals. Horizontal subsurface flow CWs (HSSF-CWs) were designed to treat simulated AMD. The treatment performance of HSSF-CWs (A and C) utilizing various organic wastes as the wetland media were compared. Partial to complete removal of metals with negligible Mn removal and moderate sulfate removal (57–62%) was obtained. Media accounted major retention (58–95%) and plants (Typha latifolia) exhibited negligible metal uptake. Toxicity Characteristic Leaching Procedure suggested safe media disposal. The release of weakly bound Mn, Al, Co and Ni was indicated under an adverse environmental state. The role of plants and the impact of hydraulic loading rates (HLRs) in the remediation of AMD and metal attenuation were studied in planted (PCW) and unplanted (CCW) CWs. Significant impairment of sulfate reduction was observed in PCW (24–90%) than CCW (37–93%). Effluent water quality deteriorated and metal removal efficiency reduced drastically on increasing HLR. HLR has an important role in the passive treatment of AMD than the presence of plants in CWs. The application of a chelating agent and organic acids revealed high metal extraction from wetland media. Organic acids achieved comparable extraction efficiency with ethylenediaminetetraacetic acid (EDTA) and further good metal recovery values were obtained. The influence of seasonality on the efficacy of CW microcosms was studied. Rainfall has a stronger influence in the northeastern region of India. The effect of rainfall on sheltered (SCW) and unsheltered (UCW) CWs was investigated under natural conditions. Findings revealed a significant difference in the sulfate reduction of SCW (60%) and UCW (51%). Heavy rainfall imposed a highly sensitive and poor treatment response in UCW, resulting in a significantly lower treatment efficiency for all constituents due to possible shortening of hydraulic retention time in UCW with minimal or insignificant dilution effect. In addition, the long-term treatment appraisal of HSSF-CW (B) comprising gravel media was evaluated under varying COD/ratios using lactate as a carbon source. The high average metal removal efficiency was attained for Fe (73%), Al (79%), Zn (98%), Co (95%), Ni (99%) and Cr (100%), but Mn (21%). As COD/ reduced from 0.67 to 0.33, sulfate reduction decreased from 74% to 44% and metal removal efficiency subsided. Dissimilatory sulfate reduction was identified as the major biological pathway. The formation of insoluble metal precipitates (oxides, hydroxides and sulfides) accounted for about 32–76% of metal removal. Major sulfate-reducing and iron-metabolizing microbial groups were identified to control the biochemical cycling of iron (oxidation or reduction) and its bioavailability.
  • Item
    Behavior of Bentonite and Kaolin Clays at Different Particle Interactions under Chemical, Hydraulic, and Mechanical Loadings
    (2022) Das, Dhanesh Sing
    Volume change behavior of clays under mechanical, hydraulic, and chemical loadings is of great importance in various applications in the field of Geotechnical and Geoenvironmental engineering. The presence of a rich percentage of clay minerals such as montmorillonite and kaolinite in the clay soils results in heaving and subsidence problems, respectively. On the other hand, compressibility behavior and swelling pressure of bentonites is a significant concern in the Geoenvironmental applications viz., landfills, low-high-level nuclear waste repositories, and impounding facilities. Equilibrium sediment volume is often used as a surrogate compatibility test for assessing the expansiveness of clays and the identification of different clay minerals. In this study, a theoretical model was proposed based on the diffuse double layer theory to estimate the equilibrium sediment volume of clays. Further, a simple technique for routine estimation of the surface area of plastic clays was proposed based on the developed theoretical framework for sediment volume. The method utilizes equilibrium sediment volume measurement of clay soil in 0.1 N NaCl solution and used the theoretical equation for the surface area estimation. A generalized semi-empirical model was proposed for predicting the compressibility behavior of clayey soils of different plasticity over a wide range of consolidation pressures. The proposed model has validated over 114 compressibility datasets from 88 clayey soils and bentonites with different inundation fluids from the literature and the present study. Further, the Stern diffuse double layer model for the constant charge condition was developed for the first time to study the compressibility behavior of clays theoretically. The influence of compaction density and bentonite plasticity on the temporal swelling pressure evolution was analyzed using microstructural analysis. Further, the volume change behavior of air-dry kaolin due to wetting was studied at various compaction densities and under different applied loadings. Surface forces were evaluated at various pore scales at the air-dry and fully saturated state to explain the observed kaolin behavior.
  • Item
    Evaluation of the Properties of Pyrolytic Char Modified Asphalt Binders and Mixtures
    (2022) Kumar, Abhinay
    The total road network length of 6.2 million kilometres in India is the second largest in the world. The major share of roads in India is built as flexible pavements. The most common types of distresses in flexible pavements have been recognised as rutting, moisture damage, and fatigue. To alleviate pavement distresses and address the challenges associated with higher: temperatures, tyre pressures, and axle load levels experienced by pavements, asphalt binder is frequently modified for enhanced performance and extended pavement service life. In recent years, there has been a strong push toward developing sustainable solutions for managing post-consumer tyre and plastic waste streams. In this regard, pyrolysis technology has garnered scientific attention for its ability to minimise waste volume while also allowing for energy valorisation. The two primary pyrolysis products are liquid oils and gases, which have high potential as fuels and precursors to important petrochemicals. The third product, solid carbonaceous pyrolytic char, is considered a by-product with relatively few applications/uses. This study evaluated the utilisation of tyre pyrolytic char (TPC) and plastic pyrolytic char (PPC) as asphalt modifier and evaluated the effect of their incorporation on the properties of asphalt binders as well as on the design and performance attributes of bituminous concrete mixes. The study focused on a multi-faceted investigation that included: (a) characterisation of the two pyrolytic chars (TPC and PPC), (2) characterisation of the TPC and PPC modified asphalt binders focusing on conventional, storage stability, rheological, ageing, microscopic, and thermo-chemical evaluations, and (3) characterisation of asphalt mixtures fabricated with TPC and PPC modified asphalt binders with a focus on their design, rutting performance, moisture damage performance as well as on cracking and fatigue life attributes. A total of nine modified binders/mixtures were studied with a control binder and four binders, each with TPC and PPC modification levels of 5, 10, 15, and 20% by weight of binder.
  • Item
    Effect of cation type of chloride salts, and sulfate ion on chloride diffusion, chloride binding and rebar corrosion in concrete containing corrosion inhibitors
    (2022) Das, Jyotish Kumar
    Corrosion damage of steel reinforcement embedded in concrete is one of the major factors that affects the durability and decreases the service life of reinforced concrete structures, which results in huge economic losses. Chloride ions are the primary cause for corrosion of steel reinforcement that leads to the deterioration and failure of reinforced concrete structures exposed to chloride-laden environment. The cation type of chloride salts plays a major role in the process of chloride ingress, chloride binding, and steel reinforcement corrosion in concrete. Further, sulfate ions also exist concomitantly with chloride ions in saline and marine environment. Due to huge repair costs for the corrosion damages in reinforced concrete structures, it is essential to effectively minimize the corrosion damage of reinforced concrete structures exposed to aggressive environment. Among different methods, the use of corrosion inhibitors is proved to be the long term efficient method to prevent corrosion of steel reinforcement due to several benefits such as convenience, cost-effectiveness, easy availability and high resistance to corrosion.
  • Item
    Evaluating the Influence of Production Parameters on the Performance of Microsurfacing Mix
    (2022) Bhargava, Nishant
    Microsurfacing is a mixture of crushed mineral aggregates, polymer modified emulsion, mineral filler, water and additive, mixed and produced at ambient temperature. The performance of microsurfacing depends on mix ingredient optimization and process control during production. Hence, the objective of this study was to investigate the influence of different production parameters on the performance of microsurfacing mix during the mix design stage, production stage, and service life
  • Item
    Reliability Analysis and Performance-Based Code Calibration for Blast Resistant Panels Subjected to Air and Contact Blast
    (2022) Bhuyan, Kasturi
    Blast threats call for an evolution of design approach for protective structure that can address both resiliency and sustainability aspects of construction. Blast resistant design is performed based on the empirical design charts, where the blast loading is simply characterized by charge weight and stand-off distance. These empirical formulations assume either a spherical free air blast or a hemispherical surface blast and do not account for variation in charge shape, orientation, point of detonation. The peak overpressure and its duration is applied on the structure uniformly which is non-uniform in case of contact blast. Therefore, while facing a contact blast problem, which is directly placed on a structure these empirical design charts are not much helpful. A multilevel Performance-based Design (PBD) framework is developed for slabs/walls of Protective structure subject to different blast loading to improve the present Blast resistant design approach in Code provisions which is currently based on ultimate strength of the structure only. The present research develops probabilistic deflection-based capacity and air blast demand models for three performance levels associated with four damage states of reinforced Normal Strength Concrete (NRC) and reinforced Ultra-High Strength Concrete (UHSC) slabs/walls of protective structures. It also investigates the NRC and UHSC Panel under contact blast and presents the probabilistic capacity and demand models for three performance levels of damage. For this, a set of data is generated through experimental design of numerical modeling and simulations that are carried with the help of commercial simulation software package LS-DYNA. The influence of blast on slabs/walls of protective structures is modeled using a validated Finite Element (FE) approach on a square panel arrangement. Validations are in close agreement with the previous experiments available. Fragility estimates are developed for effect of air and contact blast on NRC and UHSC panel to show the consistency of the developed FE model and probabilistic formulations. Hazard curves are also established for mass of blast charge and stand-off distance to determine the distribution of the dataset. The reliability-based code calibration is performed for the development of PBD Load and Resistance Factors at the three performance levels based on the established probabilistic models and hazard curves; which circumvents the limitations of present Code provisions. The developed Load and Resistance Factors for Code provisions can be used for the design of NRC and UHSC panel when subject to air and contact blast without performing exhaustive analysis and/or experiments. A High Strength Concrete (HSC) matrix is also developed in reference with earlier studies in site with locally available materials under uncontrolled conditions for show the feasibility of adopting high strength concrete in practical field. The High Strength Concrete developed is then used in a blast resistant building frame and ground floor slab with analysis and simple design with SAP software.
  • Item
    Urban Flash Flood Modeling Framework Using Weather RADAR and Advanced Geospatial Technologies
    (2021) Akkimi, Anjaneyulu
    In recent years, the frequency of flash floods in urban regions has increased all over the world. Flash floods in cities creates a water logging situation to devastated water related catastrophes. These events are sequence of meteorological systems with a specified hydrological condition in a watershed. The forecasting of such type of events can reduce the fatality rate, property damage and helps to design flood mitigation preparedness system. To forecast flashfloods, efficient early warning system is to be designed for urban landscapes. In this thesis, it has attempted to design an early warning flash flood forecasting framework. This framework is designed by considering the key elements such as precipitation, topography and hydrological modeling, which influence the flood forecasting conditions in the cities. In this research it has designed a machine learning based precipitation nowcasting system after retrieving the rainfall rate from weather radar reflectivity using developed gravity-based gravity-based Z-R relationships. In this research, a new methodological framework is also designed to select appropriate topographic models which can be used in urban hydrological models. In this it is also developed a simple numerical solving scheme to simulate the surface runoff, water depths and flow velocities in urban landscapes. This study is quite relevant to local scale to large city scale studies, and the designed model can be applicable to any cities in an international level.
  • Item
    The Limnology of Wetlands: Understanding their Dynamic Physico-Chemical and Biotic Responses to Anthropogenic Exploitations within the Aquatic Ecosystems
    (2022) Dash, Siddhant
    This doctoral dissertation revolves around understanding the anthropogenic contamination dynamics within a wetland [Deepor Beel, Guwahati, India (a Ramsar site)], and assessing their impacts on the natural ecosystems. This incorporated four distinctive components; water column, sediment column, floral samples, and fish biota (representative of the faunal samples). Each element was assessed for its responses to the contamination levels in the event of an anthropogenic intervention. The first and foremost objective was identifying the latent pollution sources and their apportionment. For this purpose, different multivariate statistical and factorization models were employed. This followed an evaluation of the water quality employing indexing techniques, wherein novel approaches were developed and proposed to determine a water body's health status. This included developing generalized and specific (depending upon water's end-use) water quality indices (WQIs) incorporating different Chemometrics methods (i.e., multivariate statistics and Probability estimation through the water quality dataset's randomness). For the sediment column, the pollution sources were identified and apportioned through source apportionment models, which were further validated through different elemental analyses such as X-ray powder diffraction (XRD), and Scanning electron microscope - Energy Dispersive X-Ray Spectroscopy (SEM-EDS). Additionally, the sediment pollution loadings were also evaluated through various indices, such as contamination factor, pollution load index, enrichment factor, and the geo-accumulation index. Their associated potential ecological risks were also estimated, which provided the impact of one or more elements (heavy metals) on a wetland's natural ecology. Finally, chemical speciation analyses of all the heavy metals were conducted to determine their available forms in the sediment column. Furthermore, a detailed investigation was carried out on correlating the heavy metal contamination, distribution, and human health risk associated within an aquatic ecosystem. For this purpose, water, sediment, and fish samples were considered, and their heavy metal contamination and distribution were determined. The corresponding health risks were then evaluated for six different heavy metals; Cr, Cd, Fe, Mn, Cu, and Pb, upon exposure for both adults and children. The contributions to the bioaccumulation of heavy metals in the aquatic ecosystems were also assessed and compared for both water and sediment columns. Finally, the water, sediment and floral components were integrated to develop a eutrophication-based ecological model, to understand the eutrophication levels induced by different pollution loadings and providing insights into curbing the eutrophication levels.
  • Item
    Climate Change Impacts in a River Basin having Flow Regulating Structures
    (2022) Marak, Jeffrey Denzil K
    The hydraulic structures constructed for the benefits of society can cause perturbations in the streamflow. Such perturbations to natural conditions may affect the river ecosystem. The assessment of the changes in the hydrological regime due to man-made structures requires a comparison between the existing and the counterfactual scenario. It is a challenging task to carry out such assessments when pre-impact condition data do not exist. In this paper, a methodological framework is proposed and applied to Umiam watershed to generate natural streamflow by using the post-impact data when pre-impact data is not available. The Soil and Water Assessment Tool (SWAT) model is applied for simulating streamflow under the presence of reservoir and water transfer out of the watershed. The Indicators of Hydrologic Alteration (IHA) method was used for the analysis of changes in streamflow. The results reveal a reduction in the monthly median flow rate by at least 21% in all the months during the five-decade period. The large floods and small floods are found to be reduced in the presence of the reservoir, whereas it also causes more frequent low flows which last for longer durations. The extreme annual minimum flow conditions (1-day, 3-day, 7-day, 30-day, 90-day minima) shows low alteration while the corresponding annual maximum flow conditions show medium alteration. The frequency and duration of high and low pulses are greatly affected by the reservoir. The rising-rate, falling-rate, and the number of reversals show a significantly decreasing trend. The results indicate a high overall degree of alteration in streamflow. The analysis of individual reservoir effects revealed increase in monthly flows due to Kyrdemkulai, Nongmahir, Umiam Stage IV and Umtru Reservoirs. The individual effect of Umtru Reservoir was found to be highest among the four. The second highest effect was due to Nongmahir Reservoir. The cumulative effect of all reservoirs could increase the yearly median flows by 38.49% as compared to unaltered flow without IBWT and reservoirs. The change in yearly median flows were 95.43% in Umtru Basin if no water was transferred from Umiam Basin. Since rainfall plays a significant role in hydrologic response of a watershed, the spatial and temporal trends in rainfall over Umiam and Umtru watersheds were analyzed. The analysis used the gridded rainfall data from the Indian Meteorological Department from 1901 to 2018. The Innovative Trend Analysis (ITA) method was used to identify the trends in low, medium, and high-intensity rainfall. The results indicated a decreasing trend in low and medium intensity rainfall while high-intensity rainfall is increasing across annual and seasonal time scales. For the assessment of climate and landuse change CORDEX data of IITM_RegCM4, MPI-CSCREMO2009 and SMHI-RCA4 were considered. Under dammed condition, highest flow in January to March occurs in S3 and S4 (RCP 8.5). In April, June highest flow occurs in S3 and S4 (RCP 4.5). Under undammed scenario, the timing of highest flow shifts to September for S3 and S4 scenarios under RCP 8.5. In all the scenarios, sub-basin 4 is found to have the highest change in flow due to climate and landuse change.
  • Item
    Repairing and Strengthening of Reinforced concrete beam with web opening using alkali activated geopolymeric material
    (2023) Sinha, Arnab Kumar
    Transverse opening in the web of RC beam is a source of weakness which leads to early cracks when subjected to its service load and beam may collapse before its service life. The present work introduces and validates noble retrofitting technique for restoring damaged reinforced concrete beam with web opening using geopolymer-based retrofitting material (GM) and strengthening material (FRGC). Therefore 16 RC beams with transverse opening in the flexure zone (BMS) and the shear zone (BSS) are prepared along with a solid beam (SB) to study the effect of opening in RC beams. The beam specimens are initially tested to investigate the effect of the opening and are repaired and strengthened with different. The test result shows that GM as a repair material exhibits better adherence with the damaged beam. The noble retrofitting technique is capable of full restoration of all the structural integrity even on the 3rd day of repair. The load carrying capacity of the damaged BMS is enhanced by 18 %, while that of BSS is enhanced by 41 %. While the Jacketed beam of BMS types exhibits improved stiffness and with enhanced load carrying capacity of 1.3 times higher than the original beam. However, the effect of FRGC jacketing is found to be more effective in enhancing the load carrying capacity of the BSS type by 1.75 times higher than the original specimen. All the jacketed specimens exhibit improved deformation capacity leading to improved ductility.
  • Item
    Evaluating the Effect of Aging and Moisture Conditions on the Performance of Bituminous Mixtures
    (2021) Das, Bhaskar Pratim
    Environmental factors such as aging and moisture intrusion significantly influence the performance of the bituminous mixture. Hence, the study’s objective was to evaluate the effect of aging and moisture conditions on the performance of bituminous mixtures. In this study, the effect of aging and moisture conditioning on Hot and Warm bituminous mixtures were evaluated using an indirect tensile strength (ITS) test, indirect tensile stiffness modulus (ITSM) test, fatigue test, and creep tests. In addition, adhesive failure (AF) in moisture conditioned (MC) fractured specimens and the loose bituminous mixture was determined using image analysis and photodetection technique. This study noticed that an increase in moisture conditioning cycles or reduction in test temperature increased the coefficient of variation (CoV) of different cracking parameters. A one-way analysis of variance showed that ITS, fracture work density, and fracture energy parameters were sensitive to different aging and moisture conditioning levels. Furthermore, the cracking resistance parameters indicate that the WMA mixture was relatively moisture-resistant than HMA, attributed to additive characteristics. The AF was higher at 15 °C when compared to 25 °C. However, both HMA and WMA mixtures exhibited comparable adhesive failure. In conjunction with the tensile strength ratio, AF was used to classify moisture susceptibility into three zones. The study also highlights that fracture energy can serve as a measure of cracking resistance in the presence of moisture.