PhD Theses (Civil Engineering)

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Flow Characteristics in Multi-Layered Vegetated Channels
(2024) Barman, Jyotimoy
Riparian vegetation plays a crucial role in determining the flow behavior in the channel. The effect of flow on the slope and main channel varies based on the size, type, and density of floodplain vegetation in a compound channel. Though vegetation distribution in different water bodies is non-uniform, most studies mainly concentrate on uniformly distributed vegetation with fixed vegetation height. Laboratory studies were conducted to address this issue as it was not explored properly. Experiments were performed by taking partially vegetated rectangular channels and compound channels. Rectangular channels were considered to compare flow between homogeneous height/single-layered partially vegetated channels and heterogeneous height/multi-layered partially vegetated channels. Compound channels of three bank angles, namely 310, 450and 900 were considered with vegetated floodplains.
Numerical and experimental studies to determine the subgrade soil resilient modulus using the RLCBR test
(2023) Kaushik, Supratim
Subgrade characterization in terms of resilient modulus is an important aspect of mechanistic pavement design methods. The resilient modulus is analogous to the Elastic modulus; however, repeated loads are applied instead of monotonic load and is expressed as the ratio of deviatoric stress to the resilient strain. The most commonly used laboratory method to determine resilient modulus is the Repeated Load Triaxial Test (RLTT). However, the test is complex, requires expensive test setup, skilled personnel and is time-consuming. Therefore, an alternate simple and cost-effective method for subgrade resilient modulus characterization using the simple CBR apparatus has been explored in this study. This study aims to characterize the subgrade resilient modulus using the Repeated Load CBR (RLCBR) test and compare it with the field modulus. It combines numerical modelling of the CBR test, with laboratory studies using the Repeated load CBR (RLCBR) test to propose methodologies and predictive models to characterize the subgrade resilient modulus using the RLCBR test. A 3D Finite Element Model of the CBR test was formulated in the commercial package LS-DYNA® to understand the mechanics of the test. The objective was to obtain mathematical relationships between the octahedral shear stress and the bulk stress with the plunger stress, which can be measured experimentally. Results showed that a linear relationship between the bulk stress and octahedral shear stress with the plunger stress can be assumed under elastic conditions. A total of twelve soils were tested in the laboratory in the present study. RLCBR tests were conducted on all twelve soils in deformation-controlled mode and five soils (out of twelve) in load-controlled mode. The deformation-controlled RLCBR tests were used to standardize the test and propose a predictive model which estimates the subgrade resilient modulus at stress levels typical of a subgrade soil element.Results showed that the proposed RLCBR model agreed with the modulus calculated at the recommended stress levels using the MEPDG model. Further, statistical analysis of the proposed model showed that the model could capture the effects of moisture on the resilient modulus. In contrast, the load-controlled test results were used for stress-based non-linear elastic characterization of subgrade soils. The results showed that the proposed methodology predicted the MEPDG model coefficients with an R2> 0.8 for all the cases. Further, the model coefficients were validated with those obtained from empirical correlations and showed promising agreement. The proposed methodology can be cost-effective in characterizing resilient moduli for MEPDG Level 1 applications. The laboratory resilient modulus was compared with the field resilient modulus determined using the Light Weight Deflectometer and the Dynamic Cone Penetrometer (DCP) tests. The laboratory-resilient modulus was much higher than the field modulus obtained using the DCP and the LWD due to variations in field and laboratory moisture-density conditions. However, it was also observed that as the moisture and density conditions were nearer to the laboratory conditions, the RLCBR and field modulus approached each other. The comparison assessment of the field and RLCBR test results suggest that a reference modulus from the laboratory RLCBR test can be used to evaluate the construction quality in the field in terms of modulus in addition to traditional density checking. Hence the resilient modulus prediction model developed using RLCBR, a quick and simple test, could provide more inputs to design and quality control characteristics in the field for constructing subgrade soils.
Groundwater Dynamics in Hardrock-dominated Headwaters Regions of Paschimi Nayar River, Mid-Himalaya through Assessment of Stream Flow, Spring flow and borehole data
(2023) Tarafdar, Soukhin
Small basin research has contributed significantly to the process based understanding of internal functioning of the catchments. In this study, two microwatersheds of area < 10km2 and a small hydrological response unit (HRU) (< 0.4km2) nested within one of experimental microwatershed are being investigated through hydrological instrumentation in terms of rain gauges, water level recorders at the outlet for continuous stream gauging as well groundwater level measurements in shallow and deep fractured bedrock aquifers in the smallest HRU to better understand the hydrological functioning in the headwater regions of Paschimi Nayar Basins. The precipitation variability of ISM during 2009 to 2018 period showed inter-annual variability with drought, intermittent multiple deficient rainfall periods and normal monsoon rainfall years. Analysis of long-term records of spring flow through flow duration curve indicates a significant reduction in lowflows as well as high flow periods. Recession curve analysis using single non-linear and two exponential linear reservoir models for the recession period indicate an overall non-linearity in storage-discharge relationship. A parallel offset was observed between years in yearly-prolonged post-monsoon recession curve in -dQ/dt verses Q plot indicating the control of antecedent storage over rate of outflow. Shallow piezometer (< 4 m) and deep borewell (< 80 m) monitored over two monsoon period indicate a rapid response to any rainfall amount exceeding 5mm. The episodic recharge and water level fluctuation method indicate a monsoonal recharge of 4% to 24% for a low specific yield value (1 to 5%). The study also highlight that effectiveness of recharge is controlled by the rainfall intensity.
Characterizing Dam Augmented Flow in Downstream of a Hydropower Project to Assist Management Strategies
(2023) Devi, Dipsikha
The recent increase in human activities, such as the construction of dams along rivers, has led to significant hydrological changes in downstream regions. A significant effect of dam construction is the disruption of natural flow patterns leading to erratic water levels, seasonal fluctuations, and sporadic sediment transport. This study introduces a modelling framework to analyze the downstream flow impact of hydropower dams. The framework comprises both a reservoir operation model and a hydrodynamic model. A comprehensive investigation was undertaken to assess the hydropower dams' influence across the entire water year. Moreover, a detailed examination was conducted to characterize the outflow hydrographs from Inter Basin Water Transfer (IBWT) and Non Inter Basin Water Transfer (NIBWT) hydropower dams. For NIBWT hydropower, Lower Subansiri Hydropower Project is considered for the analysis. Results showed that with the presence of the dam, the flashy characteristic of the outflow hydrograph increases. Thus, dam-induced flood is a combination of regional flood as well as flash flood. Based on the statement ranking of the dam-induced flood was provided among the global hazards considering the factors suggested by Bryant. To assess the flow contribution by the ungauged tributaries downstream of the dam, a streamflow generation module was developed using the Drainage Area Ratio (DAR) incorporated into the developed model and applied in the operational IBWT hydropower project.
Thermal and Strength Characteristics of Soil-Biochar-Biopolymer Composite Backfill
(2023) Patwa, Deepak
Thermal backfill is essential for underground crude oil pipelines, crude oil storage tanks, and geo-energy storage units. The major function of such backfills is to prohibit heat migration from the source as well as sub-structural stability. Often the thermal characteristics of locally available soils are not adequate for thermal backfill applications. Hence, it is required to modify the native soil by amending it with appropriate materials that possess suitable thermal characteristics and provide enhanced sub-structural stability. Biochar is a low thermal conductive, highly chemically stable, and eco-friendly material and has the potential to mitigate heat loss and may increase soil strength. However, the thermal characteristics of soil-biochar composite (SBC) in the compacted condition in view of applying it as thermal backfill material have largely been unaddressed in literature. Therefore, this study aims to explore the possibility of biochar-based soil composite as thermal backfill material. In the current study, two types of locally available soil and three types of biochar (hardwood biochar, water hyacinth biochar, and sugarcane bagasse biochar) are used to investigate the applicability of SBC as thermal backfills. The experimental results revealed that the SBC has lower thermal conductivity and volumetric heat capacity compared to bare soil under dry, wet, and near-saturation conditions. However, the UCS of soil also reduces with biochar amendment, which depends upon soil type and particle size fractions. To overcome this, a biopolymer-based stabilization technique is used to make it a high-strength sustainable biochar-biopolymer-based composite thermal backfill that is capable of providing efficient thermal insulation and strength. The findings of this study establish the synergistic attributes of biopolymer and biochar amendment for developing a high-strength and low thermal-conductive soil composite. A bench-scale study on the thermal insulation efficiency of SBC and soil-biochar-biopolymer composite (SBPC) in terms of heat transfer was conducted to facilitate field-scale applications. The SBC and SBPC exhibit lower temperatures than bare soil at all radial distances. The temperature difference between bare soil and SBC varies from 4 to 20 °C. A pyrolysis temperature of 400ºC is determined to be a suitable temperature regardless of the feedstock type because of the least energy consumption, considerable yield, required thermal characteristics, and carbon stability for the design period. The finding from the current study unravels the potential of biochar-based thermal backfill to restrict heat transfer from energy storage facilities.
Development of Speed Based Consistency Evaluation of Four-Lane Highway Geometry Using Naturalistic Driving Data
(2023) Nama, Suresh
India has experienced rapid growth in its infrastructure, including the expansion of two-lane to four-lane highways and the construction of new four-lane highways in mountainous terrains. However, the safety of these highways has not kept up with their development. In 2019 alone, there were over 1,80,000 fatalities due to accidents on Indian highways mainly over curves. To address this issue, a study was conducted on a 65km four-lane highway in mountainous terrain to understand driving behavior and improve safety. Data was collected from GPS equipped passenger cars driven by various drivers, revealing that the highway covered 285 horizontal curves with varying design speeds, curve lengths, vertical gradients, and superelevation. The data showed that most drivers were traveling above the design speed, and operating speeds varied across curve from point of curvature (PC) to point of tangent (PT), indicating the need for separate four-lane consistency criteria. To evaluate the safety of mountainous terrain four-lane horizontal curves, two safety criteria were developed: Speed Synchronization (SS) and Speed Harmony (SH), which consider the variation in speed across the curve. The SS criterion evaluates safety based on speed variation between successive locations within the curve, while the SH criterion evaluates safety due to variation in operating speed from the curve design speed. These criteria were used to develop a new speed-based geometric design for four-lane highways, which, along with vehicle dynamics, can be used to evaluate the safety of existing four-lane curves. Geometric parameters influencing drivers speed over four-lane horizontal curves were also identified, including tangent length, gradient, curve length, and deflection angle. A continuous percentile speed distribution model was developed to accurately predict any percentile speed across the four-lane highway alignment using ANN machine learning models. In addition to improving highway safety through design and warning systems, the study also developed a three-level over-speed warning system using operating speed (V85) and design speed (V95) to assist drivers in identifying upcoming hazards. The studies outcomes have several benefits, including the ability to predict percentile speed values using the developed speed models to evaluate highway safety and design, overcoming the limitation of uniform speed assumptions across curves, improving four-lane highway geometric design on mountainous terrains, and enhancing driver safety through the over-speed warning system.
Novel Investigations on Potential of Balanites Aegyptiaca and Sesamum Indicum for Surfactant Preparation and Application in Foam Concret
(2023) Selija, Khwairakpam
Synthetic surfactants commonly used in foam concrete production is reported to exhibit serious environmental threat. Hence utilization of natural surfactants could present new sight in improving the environmental impact of foam concrete. However, studies on valorization and extraction of natural surfactants from different plant and animal sources for use in foam concrete is very scarce from Indian context. Considering the above facts, the current study aims to use natural surfactants valorized and extracted from two different biological sources, namely sesame seed (rich in protein) and hingot fruit (rich in saponin) as prospective supplementary alternative to conventional synthetic foaming agents in foam concrete production. Balanites aegyptiaca also known as hingot is found all over the world and studies on phytochemistry of various parts of plant indicate that fruit, seeds and bark part of plant has 22-27% of saponin. Adding to above, excellent plant's adaptability, high yield features and abundant availability are other added reasons for selection of this plant for this study as it can add economical as well as environmental benefits. Another plant source used for surfactant extraction in the present study is Sesamum indicum commonly known as sesame seed. Studies have proved that sesame seed has rich protein content of 20 to 25% and hence has excellent potential foamability. Despite the huge potential foamability of above surfactants (sesame and hingot), it is surprising to find that to date, its potential has not been assessed for use in foam concrete production. The first phase of present study comprises of the optimization of surfactant extraction and foam production processes through systematic experiment design based on response surface methodology (RSM). The possible response surface models have been developed for prediction of various foam and surfactant characteristics such as initial foam density (IFD), foam stability, foam bubble size and viscosity of surfactant solution. The validity of models is tested by ANOVA and verified experimentally. Analysis of influence of various input parameters on responses indicated that surfactant concentration has significant effect on all the responses studied. Further the parameters associated with heating process (heating temperature and duration) also have substantial influence on various foam and surfactant characteristics as it promotes the hydrolysis of protein and saponin. The obtained results established that increase in surfactant concentration, heating temperature and heating duration resulted in increase in viscosity of surfactant solution eventually leading to reduction in foam liquid fraction, foam drainage and bubble size. Hence good correlation is established between above mentioned foam and surfactant parameters. Furthermore, performance of surfactants in foam cement paste was assessed and ASTM requirements are found to be met confirming foam stability. The outcomes of the present study could help the industry to gain confidence in the usage of recommended natural surfactant for foam concrete production.
Experimental and Numerical Evaluation of Flow beneath Mini Disc Infiltrometer for Estimating Wetting Characteristics of Soils
(2023) Naik, Aparimita Priyadarshini
Precise determination of soil water infiltration and sub-surface water movement is essential for developing soil-water management practices. For modeling flow and transport in the sub-surface zone and unsaturated porous media, the knowledge of the wetting hydraulic properties, including, water retention characteristics curve (WRCC) and soil hydraulic conductivity functions (SHCF), are critical. This study evaluated the potential of mini disc infiltrometer (MDI) measurements for characterizing wetting soil hydraulic properties using both laboratory and field measurements and various soil textures. It analyzed the influence of tension head and initial soil conditions on estimated parameters from MDI measurements, evaluated time dependence on transient analysis from MDI, and compared MDI measurements with other established devices. In addition, with the help of independent measurements and inverse modelling, it demonstrated the utility of MDI for rapidly and effectively characterizing the WRCCs and SHCFs from laboratory measurements. This study demonstrated that MDI is a useful, non-intrusive, and non-invasive tool for characterizing soil hydraulic properties, with important implications for improving our understanding of infiltration at the soil surface and redistribution, and further movement of soil water in the vadose zone.
Data-Driven and Machine Learning Frameworks for Condition Assessment of Plate Structure using Elastic Waves
(2024) Kalimullah, Nur Mahammad Mussa
The evolving domain of structural health monitoring (SHM) is crucial for ensuring the integrity and extending the service life of engineering structures. This thesis presents a suite of data-driven and machine learning frameworks developed to enhance the condition assessment of plate structures, particularly focusing on the complexities of piezoelectric materials and anisotropic composites. In a comprehensive exploration of data-driven and machine learning frameworks for assessing the condition of plate structures, this dissertation presents a series of interconnected studies, each contributing to the advanced insights and application in SHM, particularly focusing on piezoelectric materials and anisotropic composites.
Studies on Enhancement of Stability, Rheology, and Mechanical Performance of 3D Printable Foam Concrete
(2024) Uday, Boddepalli
Multifunctional properties are a requirement due to the increasing need for the thermal resistance, acoustic insulation, fire resistance, and etc. for the modern construction. Nevertheless, the material must be both mechanically sound and porous in order to fulfil these requirements. One such concrete that satisfies the demands of modern building is foam concrete (FC). FC is a cellular concrete produced using binder, fine aggregate or filler, foam and water as ingredients. Proper control in dosage of foam can result in wide range of densities ranging from 300 to 1800 kg/m3. FC is a unique, non-structural and low-cost light weight concrete with special properties such as low density, high acoustic insulation, low thermal conductivity, high energy absorption capacity, good fire resistance, and good freeze and thaw resistance. The aforementioned properties of FC are mainly dependent on the microstructure of FC which is influenced by the foam production parameters (air pressure, type of foam generator), foam stability (drainage, density, size, shape, and etc.) and surfactant characteristics (type of surfactant, viscosity, surface tension, and etc.). FC has an extensive spectrum of demands to satisfy an array of applications.
Optimal Crop Planning in A Canal Command Area with Due Emphasis on Nutrient Balance and Climate Change
(2023) Debnath, Mridusmita
Rainfed agriculture plays a vital role in providing food and livelihoods globally. However, its production is adversely affected due to uncertainty in rainfall patterns which is increasing under the impact of climate change. Supplemental irrigation helps minimization of risk thus stabilizes the crop yield. Given that rice is a primarily grown crop in rainfed conditions and is the staple food of half the global population, it is under the pressure of increasing production due to the burgeoning population globally. Therefore, proper farming management such as balanced fertilization practices, irrigation etc are required. On the other hand, monocropping of cereal is a growing phenomenon among the farmers, due to known yield, reduced investment, prior knowledge of the activity calendar, insufficient irrigation and lower market risk resulting in a rice-fallow cultivation system. However, the introduction of pulses, oilseeds and vegetable crops during the fallow season is the key to providing better nutrition and improving household food security. Thus, irrigation water management is required for maximizing yield of these crops during the fallow season.
Studies on Restrained Steel Beams and its Material Characterization Under Heating and Cooling Fire
(2023) Mushahary, Suman Kumar
This thesis presents results from material level experimental tests on E350 steel and 10.9 grade level bolts as well as numerical studies on steel beams having an I shaped cross-section. The experimental program comprised of subjecting specimens to monotonic heating as well as heating followed by cooling scenarios to simulate natural conditions as expected during fire exposure. Post—fire properties were evaluated as part of the experimental studies as well. The results from the experimental program were used to derive temperature dependent mechanical properties of E350 steel during heating, cooling, and residual conditions of fire exposure. These results were then combined with studies published in literature to propose reduction factors in mechanical properties of E350 steel. Similarly, results from experiments conducted on tensile and shear capacity of 10.9 grade bolts during heating, cooling and residual phases are presented. A three-dimensional numerical model of a steel I beam was developed using general purpose software Abaqus. The numerical studies were focused on predicting evolution of axial (catenary) forces that develop in the steel beam for varying support conditions (restraint levels) and load levels. The mechanical properties derived for the heating and cooling phases through experimentation were applied in this numerical model. Furthermore, the axial (catenary) forces that develop during heating and cooling phases of fire exposure were predicted with the help of the numerical model. A parametric study was conducted using the validated numerical model. An analytical model to calculate the catenary forces and critical temperature of the beam for design purposes is also proposed.
Snow/Glacier Dynamics of Himalayan Ranges and Associated Hazards
(2023) Mondal, Sandeep Kumar
The Himalayan cryosphere, also termed “the Third Pole, " acts as a natural storehouse to several mega river systems, such as the Ganges, Indus, and Brahmaputra, serving billions of people with fresh water. However, the high mountain ranges of the Himalayas are also susceptible to various categories of hazards, such as snow/rock-ice avalanches, landslides, earthquakes, and glacial lake outburst floods (GLOFs). The present study attempts to perform a series of investigations to better understand the dynamics of snow/glaciers in the Himalayan region and their contribution to perennial river streams. It also includes studying the major types of Himalayan hazards that have occurred in the recent past.
Assessment and Modelling of River Water-Sediment Pollution Load based on Spatial and Temporal Variations
(2022) Goswami, Ankit Pratim
This doctoral thesis attempts to understand the interrelationship between the two critical components of river ecosystem, i.e., its surface water and benthic sediments, as sediments are said to source and sink many contaminants in a river. In order to fully understand the aspects of the river ecosystem, the study has been divided into five objectives to get a better understanding of pollution load in surface water and benthic sediments, their sources and the need for monitoring and treatment. In the first part of Objective I, a survey of the probable catchment area of the river was carried out to select the sampling locations from which surface water and benthic sediment samples were collected. Sampling and analysis of surface water were carried out for 21 parameters at 18 different sites, whereas sampling and analysis of benthic sediments were carried out for 9 parameters, particularly heavy metals, at 9 different sites. The analysis of surface water samples revealed that with respect to pollution load, heavy metals present a higher risk to the consumer of surface water of Kolong river. The aim of the second part of Objective I was to use the analysed surface water samples to evaluate the drinking water quality using fuzzy logic and information entropy. Fuzzy logic based index, i.e., fuzzy water quality index (FWQI) results are more stringent than information entropy based index, i.e., entropy weighted water quality index (EWQI), as it is more sensitive to parameter variation. The aim of Objective II was to assess the benthic sediment quality or load in the river using total metal concentration and metal speciation fractions based indices. Total metal concentration based indices include geoaccumulation index (Igeo), pollution load index (PLI), enrichment factor (EF), potential ecological risk of individual metal (Eir), potential ecological risk index (PERI), and metal speciation fractions based indices, include pollution index (IPOLL), mobility factor (MF), individual (ICF) and global contamination factors (GCF), modified ecological risk index (MRI). After comparing both types of indices, it was found that the speciation-based index quantifies the risk associated with heavy metal contamination better as the indices developed using this approach gave consistent results and gel well with the variation of the
Global Damage Indices for RC Structures: A Numerical Response-Driven Training Approach
(2024) Naskar, Subhadip
Any seismic damage index model can be used to compute earthquake-induced structural damage of a building. Most researchers prefer combined damage index models (e.g., modified Park and Ang-type damage indices) due to their ability to consider the effect of both maximum and cyclic deformations on structural damage. All such combined damage models require section-level responses through nonlinear time-history analysis and cannot compute the global damage index (GDI) using global-level responses alone. Utilising the structural dynamic responses recorded by modern sensors, there is a scope for developing a new combined GDI evaluation method which uses such recorded data and avoids the requirement of numerically obtained sectional responses. On the other hand, the acceptability of the computed damage of a building utilising any damage index model through the output of a representative finite element model depends on the authenticity of the experimental data with which the finite element model is calibrated. The lateral output of any finite element model is usually calibrated with experimental results of axially loaded cantilever columns subjected to unidirectional horizontal quasi-static loading. For most of the conventional experimental setups, the true lateral behaviour of a cantilever column is altered because of the undesirable orientations of the actuators and the fixing arrangements between the actuator heads and the column tip. Therefore, the results obtained from such experiments must be rectified to generate true lateral load-deformation behaviour before being used directly for the calibration of any finite element model. Many previous research works also emphasised the need to rectify such experimental data. Therefore, a novel mechanics-based formulation to reproduce the true lateral load-deformation curve of cantilever columns from experimental data and a novel combined GDI evaluation method incorporating recorded floor-displacement responses for instrumented RC buildings during any seismic event are explored in the present study. Using the new GDI evaluation methodology, four different GDI formulae based on either displacement ductility or curvature ductility of columns are introduced to estimate the damage to 2D frames and 3D buildings. Explicit expressions of global damage coefficients available in those formulae are formulated in terms of some basic structural properties and local soil conditions. For wider applicability of the new GDI formulae, the limiting ranges of computed GDI values associated with post-earthquake restoration-based different global damage states (e.g., no damage, repairable, irreparable and collapse) are also studied
Study of biogeochemical and climatological impacts on spatial and seasonal variability of air-sea CO2 fluxes over the Indian Ocean
(2023) Lekshmi, K
The role of oceans in regulating the global climate is significantly affected by the spatial and seasonal variations in CO2 gas exchange process at the marine-atmosphere interface. The concentrations of CO2 gas in the atmosphere and ocean surface are the chief factor determining the flux direction, and are regulated by the physical, chemical and biological processes in the marine environment. These processes and their impacts vary regionally and seasonally, thereby impacting the spatial and seasonal trends in the CO2 fluxes. The Indian Ocean, with its contrasting flux trends in the western and eastern counterparts, plays a unique role in the CO2 transfer process. While the Arabian Sea acts as a net annual CO2 source, the Bay of Bengal serves as a net sink. Being an under explored oceanic region, the exact reasons behind this contrasting behavior are yet to be understood.
Study of Pedestrians� Unsafe Road Crossing Behaviour at Signalised Intersection Crosswalks
(2022) Raonia, Rahul
The association between pedestrians' risk-taking behaviour and fatal crash frequency necessitated an understanding of pedestrians' risky road crossing behaviour at signalised intersections. Four objectives were formulated to fulfil research gaps, and data were gathered from 10 signalised intersections across Kolkata city. Under the first objective, the Impact of social and non-social factors on signal violation was studied. The second objective analysed the distracted road crossing behaviour using a questionnaire and video graphic survey. The waiting behaviour at signalised intersections was investigated using survival analysis to fulfil the third objective. Finally, pedestrian-vehicle interaction was studied using the pedestrian safety margin approach (fourth objective).
(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.
Hydro-Chemical Evaluation of Bentonite-Fly ash Mix as Liners in Near Surface Waste Disposal Facility
(2023) Gupt, Chandra Bhanu
Hazardous industrial wastes are contained in engineered shallow near-surface disposal facilities or landfills. To minimize the migration of waste from landfills and protection of geoenvironment and groundwater, low permeable compacted liners are provided, which act as hydraulic and contaminant barriers. In normal practice, bentonite-sand (B-S) mixtures are recommended as liner material. Due to shortage, there is a need to explore the possibility of using alternate waste materials like fly ash (FA) as a substitute for sand (S). To ensure its application in compacted liner, the B-FA mixes should qualify hydro-chemical requirements laid out by different regulatory bodies like Environmental Protection Agency (EPA). The detailed hydro-chemical evaluation includes hydraulic conductivity determination, contaminant retention properties, adequate strength and volumetric shrinkage characteristics. Additionally, when two reactive materials (B and FA) are mixed together, it is important to ensure its compatibility over a period of time. A detailed study is needed to make sure that there are no undesirable interactions between B and FA leading to poor performance of liner. This necessitate long-term interaction studies of B-FA mixes for vital properties such as hydraulic conductivity and contaminant retention. This study investigated in detail the hydraulic conductivity of B-FA mixes under constant volume (swelling completely restricted) and free swelling conditions at time (t) varying from 0 days (immediately after compaction) to four years of interaction. Every measurement was carried out for extended duration of 90 days to ensure steady state condition.
Erosion Mitigation via Bio-Mediated Soil Improvement
(2022) Dubey, Anant Aishwarya
Existing soil erosion mitigation practices that focus on cement-based hard structures and chemical grouts have limitations in terms of their environmental impact and effectiveness. Recently bio-mediated soil improvement has been proposed by several researchers as a promising eco-friendly solution for mitigating erosion. However, the bio-mediated soil improvement techniques have their own limitations, such as bacteria transportation to the site, non-uniform distribution of bio-precipitates, and generation of ammonia as a by-product.

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