Abstract Soils are unconsolidated and heterogeneous materials that induce numerous geotechnical c... more Abstract Soils are unconsolidated and heterogeneous materials that induce numerous geotechnical challenges due to poor bearing capacity, uniform and differential settlement of building, seepage, scouring, and erosion. Recently developed microbially induced calcite precipitation (MICP) technique is an environmentally friendly and sustainable technique that works on nature's concept of forming rocks and minerals. The natural mineral formation is a quiet slow process that can be expedited by adding a sufficient amount of nutrients to the soil including urea and calcium sources to form calcite crystals between soil grains. However, the application of MICP requires a proper understanding of the kinetics of biogeochemical reactions in the urea hydrolysis and biocementation process. The study includes numerical modeling of precipitation kinetics of calcium carbonate with time and distance in granular soil media, including the factors affecting the rate of urea hydrolysis (i.e., pH and electrical conductivity). The laboratory investigations were also carried out on sand using Sporosarcina pasteurii strain with two different cementation media concentrations, i.e., 0.25 and 0.50 M. The experiments were conducted and analyzed after 10 and 20 days of biotreatment for calcite precipitation using calcimeter. The presence of calcite between sand grains was identified by SEM images. The predicted results were found in concurrence with experimental results, which proves the validation of the numerical model.
The influence of soil-structure interaction in the Natural Frequency of a parabolic reflector ant... more The influence of soil-structure interaction in the Natural Frequency of a parabolic reflector antenna is investigated. The main free vibration characteristic of an antenna is natural frequency. The analysis model simulated with fixed base condition and soil structure interaction. A parametric study is conducted to understand the antenna structure soil behavior (soil structure interaction (SSI)) by changing the antenna orientation, soil properties with impedance functions (spring constants) as per ASCE 4-16 and 3D (three dimensional modeling of founding medium) model methods. To address this problem, Finite Element Method is used to model soil structure interaction analysis of antenna structure with foundation by MSC PATRAN & NASTRAN using direct method and impedance method. The soil considered as homogeneous and analyzed for shear wave velocity (Vs) 100 m/s, 180 m/s, 250 m/s, 450 m/s, 760 m/s for antenna with 90° elevation. To study the embedment effect, soil around the footing and pedestal is considered. The frequency results are compared for antenna with four orientations with Vs 100 m/s soil properties. Considerable reduction in frequency observed with soil structure interaction in higher modes. Soil structure interaction study in antennas helps in finding what extent the natural frequency falls when the soil interaction is incorporated in the model.
Journal of Hazardous, Toxic, and Radioactive Waste, Oct 1, 2020
Abstract Metabolites generated from microorganisms have a high potential for the strength improve... more Abstract Metabolites generated from microorganisms have a high potential for the strength improvement and contaminant remediation of soils. The consortium of naturally available bacteria and microa...
The Himalayan region has been severely affected by landslides especially during the monsoons. In ... more The Himalayan region has been severely affected by landslides especially during the monsoons. In particular, Kalimpong region in Darjeeling Himalayas has recorded several landslides and has caused significant loss of life, property and agricultural land. The study region, Chibo has experienced several landslides in the past which were mainly debris and earth slide. Globally, several types of rainfall thresholds have been used to determine rainfall-induced landslide incidents. In this paper, probabilistic thresholds have been defined as it would provide a better understanding compared to deterministic thresholds which provide binary results, i.e., either landslide or no landslide for a particular rainfall event. Not much research has been carried out towards validation of rainfall thresholds using an effective and robust monitoring system. The thresholds are then validated using a reliable system utilizing Microelectromechanical Systems (MEMS) tilt sensor and volumetric water content sensor installed in the region. The system measures the tilt of the instrument which is installed at shallow depths and is ideal for an early warning system for shallow landslides. The change in observed tilt angles due to rainfall would give an understanding of the applicability of the probabilistic model. The probabilities determined using Bayes' theorem have been calculated using the rainfall parameters and landslide data in 2010-2016. The rainfall values were collected from an automatic rain gauge setup near the Chibo region. The probabilities were validated using the MEMS based monitoring system setup in Chibo for the monsoon season of 2017. This is the first attempt to determine probabilities and validate it with a robust and effective monitoring system in Darjeeling Himalayas. This study would help in developing an early warning system for regions where the installation of monitoring systems may not be feasible.
In recent years, due to the reduction in available natural resources, the attention of many resea... more In recent years, due to the reduction in available natural resources, the attention of many researchers has been focused on the reuse of recycled materials and industrial waste in common engineering applications. This paper discusses the feasibility of using seven different materials as alternative fillers instead of ordinary Portland cement (OPC) in road pavement base layers: namely rice husk ash (RHA), brick dust (BD), marble dust (MD), stone dust (SD), fly ash (FA), limestone dust (LD), and silica fume (SF). To exclusively evaluate the effect that selected fillers had on the mechanical performance of asphalt mixtures, we carried out Marshall, indirect tensile strength, moisture susceptibility, and Cantabro abrasion loss tests on specimens in which only the filler type and its percentage varied while keeping constant all the remaining design parameters. Experimental findings showed that all mixtures, except those prepared with 4% RHA or MD, met the requirements of Indian standards with respect to air voids, Marshall stability and quotient. LD and SF mixtures provided slightly better mechanical strength and durability than OPC ones, proving they can be successfully recycled as filler in asphalt mixtures. Furthermore, a Machine Learning methodology based on laboratory results was developed. A decision tree Categorical Boosting approach allowed the main mechanical properties of the investigated mixtures to be predicted on the basis of the main compositional variables, with a mean Pearson correlation and a mean coefficient of determination equal to 0.9724 and 0.9374, respectively.
The Indian Himalayan regions have been significantly affected by the increase in the frequency of... more The Indian Himalayan regions have been significantly affected by the increase in the frequency of landslide occurrence. Thirty percentage of the worldwide landslide incidents occur in the Himalayan region with 42% of India's landslide region belonging to Darjeeling-Sikkim Himalayas (NDMA Report, 2011). Several studies have been carried out worldwide on early warning systems considering rainfall history. Although rainfall is one of the criteria which can successfully predict the probability of landslides on a regional scale, it is indeed difficult to understand the risk associated with slope failure. The reason is the spatial variation of rainfall intensity, local soil conditions, geology, hydrology and topography. An early warning and monitoring system is one of the most effective techniques to minimise the disasters influenced by slope instability as it is less expensive and easier than slope reinforcement. A reliable and robust system fitted with microelectromechanical systems tilt sensor and volumetric water content sensors were installed. The sensor monitors the tilting angle of the instrument which was installed at shallow depths, and the variation of tilting angle corresponds to lateral displacement at slope surface. The primary objective was to monitor the tilting angles at various slope sites and to formulate a dependable warning system with a low probability of false alarms in Chibo Pashyor region in the Indian state of West Bengal. Such system would assist in the installation of several low-cost sensors over an active slope as it was difficult to determine the particular section of slope which could fail in the next heavy rainfall. The change in tilting rate would help in establishing thresholds determined empirically. Such system would help in developing an early warning system and also help in calibrating thresholds calculated using empirical techniques.
Abstract Microbially induced calcite precipitation (MICP), an emanating, sustainable and potentia... more Abstract Microbially induced calcite precipitation (MICP), an emanating, sustainable and potentially sound technique for biocementation of granular soils. The method is based on the metabolic activity of urease-producing microbes. Bioaugmentation through individual microorganisms has been investigated till now, and synergistic effect of bacteria mixtures (hybrids) for bioaugmentation is under-explored yet. Durability aspect of biocemented soils in terms of wetting–drying resistance and ageing also requires special attention and thorough investigation before adopting in field application. Thus, considering these limitations of MICP, present study has been carried out to aim multiple objectives, including optimization of cementation solution injection strategy. Poorly graded liquefiable sand was treated in polyvinyl chloride (PVC) tubes by augmenting it with Sporosarcina pasteurii, Bacillus sphaericus, and their mixed culture for hybridized activity. The biotreatment was continued by using 0.50 M cementation solution using injection frequency 12 and 24 h, and injection pore volumes (PV) 1, 0.75, and 0.5 up to 18 days. Permeability and calcite content of biocemented specimens were determined after treatment. For durability analysis, biocemented specimens were subjected to 0, 5, 10, 15, and 20 wetting–drying (W-D) cycles and kept in an uncontrolled temperature environment for 0, 1.5, 3, 4.5, and 6 months to investigate ageing effects. After W-D cycles and ageing time, samples were tested for ultrasonic pulse velocity (UPV), shear modulus, unconfined compressive strength (UCS), and split tensile strength (STS). The mass-loss rate of biocemented specimens was also determined after cyclic W-D actions. The liquefaction resistance of biotreated sand was compared with untreated dense sand specimen using dynamic cyclic simple shear (DCSS) tests. The results showed W-D resistance of biocemented sand even after 20 W-D cycles, and ageing effects showed more than two times increase in mechanical properties. The DCSS test results showed that excess pore pressure ratio was not reached to 1 in biocemented sands up to 100 cycles.
Establishing of parabolic reflector antennas is required for any satellite communications. The im... more Establishing of parabolic reflector antennas is required for any satellite communications. The important parameters of antenna structure are Gain, Pointing accuracy and Natural frequency. This research intends to understand the free vibration characteristics of antenna structure with field test and numerical analysis. Antenna servo system band width depends upon antenna stiffness and structure fundamental frequency. Generally, String-Snap method is followed for finding the frequency physically. But it is a destructive test. Hence frequency obtained from numerical analysis is only considered for deciding the servo system. Nowadays, using microtremor (velocity sensor) frequency of antenna can be measured without any damage or destruction to antenna. In this paper, 7.2m diameter full coverage antenna is considered for field test and numerical analysis and the results are compared.
Abstract Landslide hazards in hilly areas are causing destructions to properties and lives all ar... more Abstract Landslide hazards in hilly areas are causing destructions to properties and lives all around the globe. Increasing population demands for the urbanization of mountainous areas which in turn escalates the risk associated with landslides. In India, the Himalayan belt is highly susceptible to landslides and contributes a major share of the total landslides across the world every year. Rainfall is identified as the major triggering factor of landslides in Indian Himalayas, and this chapter summarizes the case study conducted to establish an early warning system for Kalimpong town, in the Darjeeling Himalayas of India. Different approaches in defining rainfall thresholds were followed and real time field monitoring has been carried out using Micro Electro Mechanical (MEMS) tilt sensors and volumetric water content sensors. The study proves that the rainfall thresholds can be used as a first line action for issuing early warning to the public and its performance can be improved by using real time monitoring data.
Microtremor method is the most inexpensive and convenient technique for dynamic site characteriza... more Microtremor method is the most inexpensive and convenient technique for dynamic site characterization of sedimentary basins. This study was carried out in Delhi NCR at 144 different stations and field measure-ments were taken using velocity sensors for a period of 1 hr at each station point. The data was analyzed us-ing VIEW 2002 software for the estimation of fundamental resonance frequency. The results of the all 144 stations were divided into four categories (T1, T2, T3, and T4) based on the shape of the H/V spectra, reso-nance frequency and soil type. Since the detailed (bore hole data) soil profile at all these locations is availa-ble, the resonance frequency is compared with sedimentary thickness. It is observed that the resonance fre-quency is high at ridge areas and very low in places with high sedimentary thickness close to Yamuna.
Abstract Soils are unconsolidated and heterogeneous materials that induce numerous geotechnical c... more Abstract Soils are unconsolidated and heterogeneous materials that induce numerous geotechnical challenges due to poor bearing capacity, uniform and differential settlement of building, seepage, scouring, and erosion. Recently developed microbially induced calcite precipitation (MICP) technique is an environmentally friendly and sustainable technique that works on nature's concept of forming rocks and minerals. The natural mineral formation is a quiet slow process that can be expedited by adding a sufficient amount of nutrients to the soil including urea and calcium sources to form calcite crystals between soil grains. However, the application of MICP requires a proper understanding of the kinetics of biogeochemical reactions in the urea hydrolysis and biocementation process. The study includes numerical modeling of precipitation kinetics of calcium carbonate with time and distance in granular soil media, including the factors affecting the rate of urea hydrolysis (i.e., pH and electrical conductivity). The laboratory investigations were also carried out on sand using Sporosarcina pasteurii strain with two different cementation media concentrations, i.e., 0.25 and 0.50 M. The experiments were conducted and analyzed after 10 and 20 days of biotreatment for calcite precipitation using calcimeter. The presence of calcite between sand grains was identified by SEM images. The predicted results were found in concurrence with experimental results, which proves the validation of the numerical model.
The influence of soil-structure interaction in the Natural Frequency of a parabolic reflector ant... more The influence of soil-structure interaction in the Natural Frequency of a parabolic reflector antenna is investigated. The main free vibration characteristic of an antenna is natural frequency. The analysis model simulated with fixed base condition and soil structure interaction. A parametric study is conducted to understand the antenna structure soil behavior (soil structure interaction (SSI)) by changing the antenna orientation, soil properties with impedance functions (spring constants) as per ASCE 4-16 and 3D (three dimensional modeling of founding medium) model methods. To address this problem, Finite Element Method is used to model soil structure interaction analysis of antenna structure with foundation by MSC PATRAN & NASTRAN using direct method and impedance method. The soil considered as homogeneous and analyzed for shear wave velocity (Vs) 100 m/s, 180 m/s, 250 m/s, 450 m/s, 760 m/s for antenna with 90° elevation. To study the embedment effect, soil around the footing and pedestal is considered. The frequency results are compared for antenna with four orientations with Vs 100 m/s soil properties. Considerable reduction in frequency observed with soil structure interaction in higher modes. Soil structure interaction study in antennas helps in finding what extent the natural frequency falls when the soil interaction is incorporated in the model.
Journal of Hazardous, Toxic, and Radioactive Waste, Oct 1, 2020
Abstract Metabolites generated from microorganisms have a high potential for the strength improve... more Abstract Metabolites generated from microorganisms have a high potential for the strength improvement and contaminant remediation of soils. The consortium of naturally available bacteria and microa...
The Himalayan region has been severely affected by landslides especially during the monsoons. In ... more The Himalayan region has been severely affected by landslides especially during the monsoons. In particular, Kalimpong region in Darjeeling Himalayas has recorded several landslides and has caused significant loss of life, property and agricultural land. The study region, Chibo has experienced several landslides in the past which were mainly debris and earth slide. Globally, several types of rainfall thresholds have been used to determine rainfall-induced landslide incidents. In this paper, probabilistic thresholds have been defined as it would provide a better understanding compared to deterministic thresholds which provide binary results, i.e., either landslide or no landslide for a particular rainfall event. Not much research has been carried out towards validation of rainfall thresholds using an effective and robust monitoring system. The thresholds are then validated using a reliable system utilizing Microelectromechanical Systems (MEMS) tilt sensor and volumetric water content sensor installed in the region. The system measures the tilt of the instrument which is installed at shallow depths and is ideal for an early warning system for shallow landslides. The change in observed tilt angles due to rainfall would give an understanding of the applicability of the probabilistic model. The probabilities determined using Bayes' theorem have been calculated using the rainfall parameters and landslide data in 2010-2016. The rainfall values were collected from an automatic rain gauge setup near the Chibo region. The probabilities were validated using the MEMS based monitoring system setup in Chibo for the monsoon season of 2017. This is the first attempt to determine probabilities and validate it with a robust and effective monitoring system in Darjeeling Himalayas. This study would help in developing an early warning system for regions where the installation of monitoring systems may not be feasible.
In recent years, due to the reduction in available natural resources, the attention of many resea... more In recent years, due to the reduction in available natural resources, the attention of many researchers has been focused on the reuse of recycled materials and industrial waste in common engineering applications. This paper discusses the feasibility of using seven different materials as alternative fillers instead of ordinary Portland cement (OPC) in road pavement base layers: namely rice husk ash (RHA), brick dust (BD), marble dust (MD), stone dust (SD), fly ash (FA), limestone dust (LD), and silica fume (SF). To exclusively evaluate the effect that selected fillers had on the mechanical performance of asphalt mixtures, we carried out Marshall, indirect tensile strength, moisture susceptibility, and Cantabro abrasion loss tests on specimens in which only the filler type and its percentage varied while keeping constant all the remaining design parameters. Experimental findings showed that all mixtures, except those prepared with 4% RHA or MD, met the requirements of Indian standards with respect to air voids, Marshall stability and quotient. LD and SF mixtures provided slightly better mechanical strength and durability than OPC ones, proving they can be successfully recycled as filler in asphalt mixtures. Furthermore, a Machine Learning methodology based on laboratory results was developed. A decision tree Categorical Boosting approach allowed the main mechanical properties of the investigated mixtures to be predicted on the basis of the main compositional variables, with a mean Pearson correlation and a mean coefficient of determination equal to 0.9724 and 0.9374, respectively.
The Indian Himalayan regions have been significantly affected by the increase in the frequency of... more The Indian Himalayan regions have been significantly affected by the increase in the frequency of landslide occurrence. Thirty percentage of the worldwide landslide incidents occur in the Himalayan region with 42% of India's landslide region belonging to Darjeeling-Sikkim Himalayas (NDMA Report, 2011). Several studies have been carried out worldwide on early warning systems considering rainfall history. Although rainfall is one of the criteria which can successfully predict the probability of landslides on a regional scale, it is indeed difficult to understand the risk associated with slope failure. The reason is the spatial variation of rainfall intensity, local soil conditions, geology, hydrology and topography. An early warning and monitoring system is one of the most effective techniques to minimise the disasters influenced by slope instability as it is less expensive and easier than slope reinforcement. A reliable and robust system fitted with microelectromechanical systems tilt sensor and volumetric water content sensors were installed. The sensor monitors the tilting angle of the instrument which was installed at shallow depths, and the variation of tilting angle corresponds to lateral displacement at slope surface. The primary objective was to monitor the tilting angles at various slope sites and to formulate a dependable warning system with a low probability of false alarms in Chibo Pashyor region in the Indian state of West Bengal. Such system would assist in the installation of several low-cost sensors over an active slope as it was difficult to determine the particular section of slope which could fail in the next heavy rainfall. The change in tilting rate would help in establishing thresholds determined empirically. Such system would help in developing an early warning system and also help in calibrating thresholds calculated using empirical techniques.
Abstract Microbially induced calcite precipitation (MICP), an emanating, sustainable and potentia... more Abstract Microbially induced calcite precipitation (MICP), an emanating, sustainable and potentially sound technique for biocementation of granular soils. The method is based on the metabolic activity of urease-producing microbes. Bioaugmentation through individual microorganisms has been investigated till now, and synergistic effect of bacteria mixtures (hybrids) for bioaugmentation is under-explored yet. Durability aspect of biocemented soils in terms of wetting–drying resistance and ageing also requires special attention and thorough investigation before adopting in field application. Thus, considering these limitations of MICP, present study has been carried out to aim multiple objectives, including optimization of cementation solution injection strategy. Poorly graded liquefiable sand was treated in polyvinyl chloride (PVC) tubes by augmenting it with Sporosarcina pasteurii, Bacillus sphaericus, and their mixed culture for hybridized activity. The biotreatment was continued by using 0.50 M cementation solution using injection frequency 12 and 24 h, and injection pore volumes (PV) 1, 0.75, and 0.5 up to 18 days. Permeability and calcite content of biocemented specimens were determined after treatment. For durability analysis, biocemented specimens were subjected to 0, 5, 10, 15, and 20 wetting–drying (W-D) cycles and kept in an uncontrolled temperature environment for 0, 1.5, 3, 4.5, and 6 months to investigate ageing effects. After W-D cycles and ageing time, samples were tested for ultrasonic pulse velocity (UPV), shear modulus, unconfined compressive strength (UCS), and split tensile strength (STS). The mass-loss rate of biocemented specimens was also determined after cyclic W-D actions. The liquefaction resistance of biotreated sand was compared with untreated dense sand specimen using dynamic cyclic simple shear (DCSS) tests. The results showed W-D resistance of biocemented sand even after 20 W-D cycles, and ageing effects showed more than two times increase in mechanical properties. The DCSS test results showed that excess pore pressure ratio was not reached to 1 in biocemented sands up to 100 cycles.
Establishing of parabolic reflector antennas is required for any satellite communications. The im... more Establishing of parabolic reflector antennas is required for any satellite communications. The important parameters of antenna structure are Gain, Pointing accuracy and Natural frequency. This research intends to understand the free vibration characteristics of antenna structure with field test and numerical analysis. Antenna servo system band width depends upon antenna stiffness and structure fundamental frequency. Generally, String-Snap method is followed for finding the frequency physically. But it is a destructive test. Hence frequency obtained from numerical analysis is only considered for deciding the servo system. Nowadays, using microtremor (velocity sensor) frequency of antenna can be measured without any damage or destruction to antenna. In this paper, 7.2m diameter full coverage antenna is considered for field test and numerical analysis and the results are compared.
Abstract Landslide hazards in hilly areas are causing destructions to properties and lives all ar... more Abstract Landslide hazards in hilly areas are causing destructions to properties and lives all around the globe. Increasing population demands for the urbanization of mountainous areas which in turn escalates the risk associated with landslides. In India, the Himalayan belt is highly susceptible to landslides and contributes a major share of the total landslides across the world every year. Rainfall is identified as the major triggering factor of landslides in Indian Himalayas, and this chapter summarizes the case study conducted to establish an early warning system for Kalimpong town, in the Darjeeling Himalayas of India. Different approaches in defining rainfall thresholds were followed and real time field monitoring has been carried out using Micro Electro Mechanical (MEMS) tilt sensors and volumetric water content sensors. The study proves that the rainfall thresholds can be used as a first line action for issuing early warning to the public and its performance can be improved by using real time monitoring data.
Microtremor method is the most inexpensive and convenient technique for dynamic site characteriza... more Microtremor method is the most inexpensive and convenient technique for dynamic site characterization of sedimentary basins. This study was carried out in Delhi NCR at 144 different stations and field measure-ments were taken using velocity sensors for a period of 1 hr at each station point. The data was analyzed us-ing VIEW 2002 software for the estimation of fundamental resonance frequency. The results of the all 144 stations were divided into four categories (T1, T2, T3, and T4) based on the shape of the H/V spectra, reso-nance frequency and soil type. Since the detailed (bore hole data) soil profile at all these locations is availa-ble, the resonance frequency is compared with sedimentary thickness. It is observed that the resonance fre-quency is high at ridge areas and very low in places with high sedimentary thickness close to Yamuna.
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Papers by Neelima Satyam