BITS Faculty Publications

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Start date: 2010End date: 2019

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    Improvement of cohesive soils by using stone columns
    (International Journal of Technical Research and Applications, 2018) Showkat, Rakshanda
    Soil being natural and non-manufactured material has proven itself to be most potentially problematic and complex materials to tackle with. The complexity does not arise only because of soil as a material, but also by the fact that various methods to characterize the soil for estimations of constituents, behavior and strength are potentially difficult. In this paper , a study on the effect of stone columns on the behaviour of cohesive soils has been done, it was found that the installation of the stone columns plays a very significant role in improving the bearing capacity of the cohesive soils. The main improvement in cohesive soils takes place by virtue of densification while inserting the stone column, the increase in drainage also plays a great role. The length of the stone columns was found to greatly influence the behaviour of the improvement of the soils. The improvement is very significant for a length of 1B where B is the width/diameter of the footing.
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    Soil constitutive models and their application in geotechnical engineering: a review
    (International Journal of Engineering Research & Technology, 2018-04) Showkat, Rakshanda
    Various constitutive models have been developed for modeling the stress strain behavior of soils and apply such models in finite element modeling for application in geotechnical engineering and also for analysis of soil structure problems under different loading conditions. Simple as well as complex models have been formulated based upon the mechanical principle (hooks law of linear elasticity and columbs law of perfect plasticity).However soils are not entirely linearly elastic and perfectly plastic for the entire range of loading. In fact, actual behavior of soils is very complicated to understand and it shows range of behaviors under different conditions. Hence, different models have been proposed to describe its response. Moreover, no model can completely describe the complex behavior of soils. This paper presents brief introduction of various soil models and particularly the cam clay Model and also their application.
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    Machine learning and spectral techniques for lithological classification
    (SPIE, 2016-04) Thakur, Sanchari
    Experimentations with applications of machine learning algorithms such as random forest (RF), support vector machines (SVM) and fuzzy inference system (FIS) to lithological classification of multispectral datasets are described. The input dataset such as LANDSAT-8 and Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) in conjunction with Shuttle Radar Topography Mission (SRTM) digital elevation are used. The training data included image pixels with known lithoclasses as well as the laboratory spectra of field samples of the major lithoclasses. The study area is a part of Ajmer and Pali Districts, Western Rajasthan, India. The main lithoclasses exposed in the area are amphibolite, granite, calc-silicates, mica-schist, pegmatite and carbonates. In a parallel implementation, spectral parameters derived from the continuum-removed laboratory spectra of the field samples (e.g., band depth) were used in spectral matching algorithms to generate geological maps from the LANDSAT-8 and ASTER data. The classification results indicate that, as compared to the SVM, the RF algorithm provides higher accuracy for the minority class, while for the rest of the classes the two algorithms are comparable. The RF algorithm effectively deals with outliers and also ranks the input spectral bands based on their importance in classification. The FIS approach provides an efficient expert-driven system for lithological classification. It based on matching the image spectral features with the absorption features of the laboratory spectra of the field samples, and returns comparable results for some lithoclasses. The study also establishes spectral parameters of amphibolite, granite, calc-silicates, mica-schist, pegmatite and carbonates that can be used in generating geological maps from multispectral data using spectral matching algorithms.
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    Laboratory-based, field-based, and satellite-borne spectroscopy for lithological discrimination
    (SPIE, 2016-04) Thakur, Sanchari
    Spectroscopic analysis is carried out for lithological discrimination in a study area in the Pali and Ajmer districts of Rajasthan, western India using laboratory-based, field-based and space-borne data. We first explored the feasibility of the Landsat-8 (Operational Land Imager (OLI), Thermal Infrared Sensor (TIRS)) and Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) imagery for lithological mapping. Laboratory spectra of the samples of rocks exposed in the area were collected using FieldSpec3 spectroradiometer in the VNIR-SWIR region and resampled to the LANDSAT 8 and ASTER spectral bands. The spectral angle mapper (SAM) algorithm was used to map the lithologies using the resampled laboratory spectra as references. The resulting map was validated based on field geological mapping. Fourier Transform Infra-Red (FTIR) spectroscopy of selected rock samples was carried out to correlate spectral absorption features in the TIR-IR regions with the vibrational energy.
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    Sub-surface paleochannel detection in DeGrussa area, Western Australia, using thermal infrared remote sensing
    (SPIE, 2016-05) Thakur, Sanchari
    Thermal Infrared (TIR) remote sensing measures emitted radiation of Earth in the thermal region of electromagnetic spectrum. This information can be useful in studying sub-surface features such as buried palaeochannels, which are ancient river systems that have dried up over time and are now buried under soil cover or overlying sediments in the present landscape. Therefore they have little or no expression on the surface topography. Study of these paleo channels has wide applications in the fields of uranium exploration and ground water hydrology. Identifying paleo channels using remote sensing technique is a cost-effective means of narrowing down search areas and thereby aids in ground exploration. The difference in thermal properties between the paleo channel-fill sediments and the surrounding bed-rock is the key to demarcate these channels. This study uses five TIR bands of day-time Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) L1A data for delineation of paleo-systems in the DeGrussa area of the Capricorn Orogen in Western Australia. The temperature-emissivity separation algorithm is applied to obtain kinetic temperature and emissivity images. Sharp contrasts in kinetic temperature and emissivity values are used to demarcate the channel boundaries. Profiles of topographic elevation, temperature and emissivity values are plotted for different sections of the interpreted channels and compared to distinguish the surface channels from sub-surface channels, and also to interpret the thickness and nature of the paleo channel-fill sediments. The results are validated using core-drilling litho logs and field exploration data.
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    Study of geological analogues for understanding the radar sounder response of the rime targets
    (American Geophysical Union, 2017) Thakur, Sanchari
    Radar for Icy Moon Exploration (RIME), the radar sounder onboard the Jupiter Icy Moons Explorer (JUICE), is aimed at characterizing the ice shells of the Jovian moons - Ganymede, Europa and Callisto. RIME is optimized to operate at 9 MHz central frequency with bandwidth of 1 MHz and 2.7 MHz to achieve a penetration depth up to 9 km through ice. We have developed an approach to the definition of a database of simulated RIME radargrams by leveraging the data available from airborne and orbital radar sounder acquisitions over geological analogues of the expected icy moon features. These simulated radargrams are obtained by merging real radar sounder data with models of the subsurface of the Jupiter icy moons. They will be useful for geological interpretation of the RIME radargrams and for better predicting the performance of RIME. The database will also be useful in developing pre-processing and automatic feature extraction algorithms to support data analysis during the mission phase of RIME. Prior to the JUICE mission exploring the Jovian satellites with RIME, there exist radar sounders such as SHARAD (onboard MRO) and MARSIS (onboard MEX) probing Mars, the LRS (onboard SELENE) probing the Moon, and many airborne sounders probing the polar regions of Earth. Analogues have been identified in these places based on similarity in geo-morphological expression. Moreover, other analogues have been identified on the Earth for possible dedicated acquisition campaigns before the RIME operations. By assuming that the subsurface structure of the RIME targets is approximately represented in the analogue radargrams, the difference in composition is accounted for by imposing different dielectric and subsurface attenuation models. The RIME radargrams are simulated from the analogue radargrams using the radar equation and the RIME processing chain and accounting for different possible scenarios in terms of subsurface structure, dielectric properties and instrument parameters. For cross-validation, the database is compared with radargrams simulated from the analysis of radio wave propagation through geo-electrical models representing the subsurface hypotheses for the RIME targets.
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    Calcrete-hosted surficial uranium systems in Western Australia: Prospectivity modeling and quantitative estimates of resources. Part 1 – Origin of calcrete uranium deposits in surficial environments: A review
    (Elsevier, 2018-11) Thakur, Sanchari
    This three-part paper reports the results of geochemical modeling, prospectivity modeling and quantitative resources assessments of calcrete-hosted surficial uranium deposits in the palaeochannels of geologically, physiographically, and climatologically permissive part of Western Australia. In this Part 1, geochemical dynamics of uranium mobilization and precipitation in near-surface oxidized groundwater systems are reviewed in order to understand the processes responsible for precipitation of uranyl vanadate minerals in valley/lacustrine calcrete within palaeochannels in arid and semi-arid desertic regions. The review indicates that uranium precipitation is essentially a function of concurrent changes in three mutually interdependent parameters of groundwaters, namely, (i.e. activities of all the carbonate bearing species), Eh-pH, and the activities of other ionic species. Geochemical modeling of groundwater data from northern part of the Yilgarn craton in Western Australia indicates that opening of the groundwater aquifer system to the atmosphere and consequent evaporation is likely the key process leading to precipitation of uranyl vanadate minerals in valley calcrete and playa lake sediments. Fluid mixing could also induce the precipitation below the water table, provided that the mixing groundwaters have contrasting geochemistry. These processes may operate in diverse geomorphic traps in palaeochannels. A generalized conceptual model of calcrete-hosted uranium systems is presented and regional-scale targeting criteria and their spatial proxies are identified, which, in turn, are used in Part 2 to develop a targeting model for calcrete-hosted uranium deposits in Western Australia.
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    Global grade-and-tonnage modeling of uranium deposits
    (International Atomic Energy Agency, 2018) Thakur, Sanchari
    This contribution presents models of grade and tonnage distribution of various uranium deposit types and sub-types. A p-value derived from the Kolmogorov-Smirnov test is used for evaluating the goodness-of-fit of the frequency-grade and frequency-tonnage distributions to the log-normal distribution. The results indicate that both frequency-grade and frequency tonnage distributions of most deposit types and sub-types conform to the log-normal distribution at the 95% confidence level. Models created by dividing deposits into sub-types show significant improvement in the goodness-of-fit. The t-tests reveal that the grade and tonnage distributions of sub-types of the sandstone-hosted type (namely, roll-front, tabular, basal channel and tectonic-lithologic sub-types) are significantly different from each other. Furthermore, country-wise models of the roll-front deposits in different countries do not necessarily correlate, which explains the lower goodness-of-fit for the global frequency grade and frequency-tonnage models for sandstone-hosted deposits. This implies that sandstone-hosted deposits may differ in their geological settings from country to country, thus requiring some reclassification. The same applies to basement-hosted and unconformity contact deposits in Canada and Australia.
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    Surficial uranium mineral systems in Western Australia: Geologically-permissive tracts and undiscovered endowment
    (International Atomic Energy Agency, 2018) Thakur, Sanchari
    This contribution describes a novel, integrated approach to prospectivity analysis and quantitative resource assessment of surficial uranium deposits in Western Australia that may serve as a universal, best practice template for the estimation and the planning and managing of undiscovered uranium resources elsewhere. The key objectives of and principal steps taken in this study were: (I) development of a process-based, mineral systems-type targeting model for surficial uranium deposits; (2) delineation of areas where the geology is permissive for the existence of surficial uranium deposits (i.e., geologically­permissive tracts) using mineral prospectivity analysis and employing a combination of knowledge-driven fuzzy inference systems (FIS) and data-driven weights-of-evidence and artificial neural networks; and (3) estimation of the number of undiscovered surficial uranium deposits and total amount of undiscovered uranium endowment utilizing regression models of deposit density and endowment density, the USGS three-part assessment and Zipfs Law analysis. The approach described in this contribution is a world first in that it is the first published quantitative mineral resource assessment employing three different methods and building upon the results of a systematic, multi-pronged knowledge- and data-driven prospectivity analyses. The results of these analyses indicate that the study area (the -1,700,000 km2 deserts and xeric shrublands region of Western Australia) contains a total undiscovered endowment (i.e., speculative resources) of >180,000 t U, contained in identified and up to 145 additional, undiscovered deposits. Based on the prospectivity analysis, undiscovered surficial uranium deposits are most likely to be found within geologically-permissive tracts in the remote, commonly sand dune-covered northern and eastern parts of the study area, which to date have recorded little, if any, uranium exploration.
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    Probing the cryosphere with an Earth Observation orbiting radar sounder
    (European space Agency Living Planet Symposium, 2019) Thakur, Sanchari
    The dynamic changes in the cryosphere, such as the ice calving fed by seaward flowing glaciers, have a significant impact on the society and environment, by contributing to the increase of the sea-level rise. This requires a continuous monitoring of the processes occurring within the ice-sheets to predict the dynamics and stability of the polar ice-caps. Radar sounders can acquire profiles of the subsurface (radargrams) that provide rich information for estimating the Essential Climate Variables (ECV) and better understanding the processes and structures in the ice. Subsurface targets detected from the radargrams can be used to determine: (i) the surface and the basal interface topography, ii) the ice sheet thickness and the internal layering, (iii) the characteristics of ice shelves and the position of the grounding line, (iv) the basal boundary conditions and ice flow regime, and (v) the ice mass balance. Currently, there are a number of airborne radar sounders (e.g., POLARIS [1] and MCoRDS [2]) that have been acquiring data over the Earth’s icy areas over the last decades. Significant information on the glacier structure and processes in Greenland and Antarctica have been extracted from the analysis of these radargrams [5-7]. However, these data are acquired seasonally and over specific regions, and thus they do not provide uniform coverage in space and time nor have homogeneous data quality. These limitations can be addressed by a satellite-mounted radar sounder, which would provide continuous, homogeneous, and uniform coverage of the cryosphere. The Earth-orbiting radar sounder should be designed to operate at a central frequency in the HF-VHF range with a bandwidth of 10 MHz, to have a penetration depth up to 5 km and a vertical resolution about 10 meters in ice. However, data acquired by orbiting radar sounders are subjected to the cosmic microwave background, path loss, relatively low transmit power, ionospheric effects, and poor resolution due to the altitude of the platform and the constraints on the bandwidth. In this paper, we analyze the detectability of subsurface targets in icy radargrams acquired by an orbiting radar sounder taking into account these limitations. To this purpose, we defined a simulation procedure for estimating radargrams acquired by such a radar sounder. Further, we analysed the simulated radargrams with existing techniques developed for airborne acquisitions, in order to understand the detectability of the subsurface targets. The simulation approach is based on reprocessing the available airborne radargrams to match the range of possible characteristics of the orbiting radar sounder. The simulation technique accounts for the radar and target parameters (e.g., the central frequency, bandwidth, sampling frequency, and the medium dielectric properties) that are related to the radargram characteristics (e.g., the resolution, received power, and sample spacing). Moreover, the cosmic microwave background noise is stochastically added to the simulated radargram to represent the real scenario. Simulated radargrams of a set of important ice subsurface targets are analyzed using state-of-the-art analysis techniques developed for airborne or planetary radar sounder data. The algorithms are applied to detect the important radargram targets, such as (i) the bedrock and the surface [3] - useful for estimating the ice sheet thickness; (ii) the number and strength of the layers [4, 6] - useful for understanding the paleoclimatic records and glacier aging; (iii) the ice-shelves for better understanding processes in the grounding zone; (iv) the basal features such as subglacial lakes [8] and refreezing ice [7] - useful for understanding the basal conditions and the mass balance. Our analysis confirms that an EO orbiting radar sounder can image important subsurface targets