Faculty Publications
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Item Effect of geosynthetic stiffness on the behaviour of encased stone columns installed in lithomargic clay(Springer, 2020) Vibhoosha, M.P.; Bhasi, A.; Nayak, S.Columnar systems have been extensively used to support structures on problematic ground conditions. Encased stone columns are very effective for flexible structures such as embankments and storage tanks where a relatively large settlement is permissible. Lithomargic clay is extensively found along the Konkan belt in peninsular India and serves as the foundation for most of the structures. Construction activities in lithomargic clays are challenging due to the fact that there occurs drastic reduction in strength under saturated conditions. In this paper, the effectiveness of encased stone column in lithomargic clay has been studied and a 3D column model was developed to examine the effect of geosynthetic stiffness on the column-load-carrying capacity. © Springer Nature Singapore Pte Ltd. 2020.Item Numerical Analyses of Geogrid Reinforced Embankment Over Soft Clay(Springer Science and Business Media Deutschland GmbH, 2021) Keerthana, C.; Vibhoosha, M.P.; Bhasi, A.Construction of embankments on weak foundation soils is a challenging task for civil engineers due to excessive settlement, bearing capacity failure and slope stability issues. To solve this problem, a variety of ground improvement techniques, including vertical drains, grouting, complete soil replacement, geosynthetic reinforcement and piling, are adopted. Geosynthetics provides an alternative and economical solution and has been increasingly applied as reinforcement in embankments on soft soil. In the present study, 3D numerical analyses using the finite element program ABAQUS was carried out to study the time-dependent behaviour of geogrid reinforced embankment. Parametric studies were carried out by varying the height of the embankment. © 2021, Springer Nature Singapore Pte Ltd.Item Three dimensional modeling of geocell using membrane elements by considering the actual curvature(American Institute of Physics Inc., 2021) Vibhoosha, M.P.; Bhasi, A.Railway Networks are popular world wide because of its ride quality and low cost. In order to meet the ever growing demand, the track operational efficiency has to be improved with minimal maintenance and infrastructure cost. By providing a three dimensional honey comb structure known as geocell on track substructure, the lateral deformation of the ballast and sub ballast can be effectively reduced and the overall stability is improved. The 3D modeling of geocell is complex as it involves interaction between geocell walls and the fill material inside. Different constitutive models were used for both geocell and infill material with suitable interaction properties. By using the membrane elements the hexagonal shape of geocell was simulated. In this paper, full 3-d finite element analyses were carried out using developed numerical model to study the lateral deflection of geocell reinforced subballast system. Also a comparison was made between 3D and 2D numerical models. © 2021 American Institute of Physics Inc.. All rights reserved.Item Performance Evaluation of Stone Column Reinforced Shedi Soil(Springer Science and Business Media Deutschland GmbH, 2024) Vibhoosha, M.P.; Bhasi, A.; Nayak, S.Ground modification techniques are adequate in the present scenario, due to the scarcity of suitable construction sites. The problematic soil widespread in the Konkan region of west coast India is shedi soil. Construction over this soil is challenging because it loses strength when saturated. Among the various ground modification techniques, the use of stone columns is an ideal technique due to their higher strength and stiffness properties compared to the surrounding soft soil. The cost effectiveness and ease of installation make stone column method popular in India. In the present paper, the performance of stone column reinforced shedi soil is analysed, by developing a three-dimensional finite element model in ABAQUS. The long-term stability is imparted with the time-dependent behaviour and it is evaluated. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item A Review on the Design, Applications and Numerical Modeling of Geocell Reinforced Soil(Springer Science and Business Media Deutschland GmbH, 2021) Vibhoosha, M.P.; Bhasi, A.; Nayak, S.For improving the stability and load carrying capacity of weak subgrade, strengthening methods are to be followed in the field. Among the various approaches, geocells have been identified as an effective soil reinforcement technique for improving soft subgrade behaviour. The three-dimensional honeycomb structure of geocell offers more lateral confinement to the infill soil resulting in improved load carrying capacity. This led to the widespread use of geocells for different geotechnical applications like pavements, foundations, embankments, slope protection, erosion control etc. Many researchers in the past have confirmed the suitability of geocell reinforcement through their experimental, numerical and field studies. In this paper, a comprehensive review of the reinforcement mechanisms, design aspect and numerical modelling techniques of geocell reinforced soil is provided. In addition, this paper highlights the various field application scenarios where different types of geocells have been used and explores the research challenges and scope for further research in this field. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Numerical study of basal reinforced embankments supported on floating/end bearing piles considering pile-soil interaction(Elsevier Ltd, 2015) Bhasi, A.; Rajagopal, K.Construction sites consisting of soft soils may require ground improvement to prevent excessive settlements or bearing capacity type failures and shear movements, which results in construction delays and premature failures. Among the various ground improvement techniques, the Geosynthetic Reinforced Piled Embankment Systems (GRPES) provide a practical and efficient solution due to the low cost and short construction times. Most of the piled embankments are constructed on end bearing piles. At large depths of foundation soil, floating piles are more economical and technically feasible than the end bearing piles. The design of floating piles involves complex soil-structure interaction and there are no clear uniform guidelines available for the design of embankments supported on floating piles. This paper presents the results of numerical investigation into the performance of geosynthetic reinforced embankments supported on end bearing as well as floating piles considering the pile-soil and geosynthetic-soil interaction. 3-D Column models are employed to carry out the parametric studies on factors such as the development of arching, skin friction distribution along the pile length and axial force distribution. Full three-dimensional analyses are carried out to study the overall behavior of the GRPES system and the results obtained from the analyses were compared with those from British Standard BS8006-2010. The results indicated that the use of floating piles could considerably reduce the settlements and the embankment load transferred through the piles to the foundation soil is found to depend very much on the length of the piles. This aspect needs to be accounted for while calculating the arching factor in the empirical equations. © 2015 Elsevier Ltd.Item Effect of Column Configuration on the Performance of Encased Stone Columns with Basal Geogrid Installed in Lithomargic Clay(Springer, 2019) Nayak, S.; Vibhoosha, M.P.; Bhasi, A.Lithomargic clay is extensively found along the Konkan belt in peninsular India and serves as a foundation for most of the structures. The reduction in strength under saturated conditions makes this soil problematic causing a lot of engineering problems such as uneven settlements, erosion, slope failures, and foundation problems. This paper presents the effect of column configuration (i.e. equivalent number of columns with reduced diameter for the same surface area) on the performance of lithomargic clay reinforced with geogrid encased stone columns and basal geogrid layer. The investigations were performed both experimentally through small-scale models and through finite element analyses. The results were compared with the performance of lithomargic clay reinforced with ordinary and encased stone columns. A single geogrid encased stone column with a basal geogrid layer improved the load-carrying capacity of lithomargic clay by 180% while the percentage of increment in the case of a group of three geogrid encased stone column with basal geogrid layer having the same surface area was 210%. It was also observed that the geogrid encasement of stone columns reduced the maximum column bulging by 38%, whereas geogrid encased stone columns along with basal geogrid layer reduced the bulging by 82% compared to ordinary stone columns. © 2019, Springer Nature Switzerland AG.Item Numerical Investigation of Consolidation Induced by Prefabricated Horizontal Drains (PHD) in Clayey Deposits(Springer Science and Business Media Deutschland GmbH, 2021) Menon, A.R.; Bhasi, A.In this work, the process of prefabricated horizontal drains (PHD) induced consolidation in clayey embankment fills is investigated by a numerical approach. Based on spacing parameters, the suitability of axisymmetric and plane strain conditions for modeling the drain has been studied, and the suitability zones and matching functions have been proposed. The implications of the use of elastoplastic models to simulate the behavior of in situ soil on the suitability zones and matching functions have also been studied. The numerical results were compared with the analytical unit cell solutions for axisymmetric and plane strain conditions. Further, the effect of PHD in improving the consolidation behavior of various soil types has been analyzed in terms of pore pressure dissipation and settlement. The studies showed that the drain improved ground is best modeled under axisymmetric conditions at lower spacing ratios, and plane strain conditions simulate the more distantly spaced cases. PHD was found to accelerate the consolidation process in soft soils significantly, and the effect was found to be most prominent in highly plastic soils. © 2020, Springer Nature Switzerland AG.Item Analysis of Geocell-Reinforced Stone Column-Supported Embankment Considering Soil-Structure Interaction(Springer, 2022) Vibhoosha, M.P.; Bhasi, A.; Nayak, S.Geocells are a superior form of reinforcement due to their cost-effectiveness and three-dimensional confining properties. The effect of the basal geocell layer on the performance of the stone column-supported embankment was evaluated in this paper by carrying out time-dependent coupled analyses considering the geocell-infill soil interactions. The various parameters, such as arching, stress concentration ratio, surface settlement, column bulging characteristics, and the influence of various types of infill materials and drainage blanket thickness on column-supported embankment behavior, were analyzed. The load transfer mechanism was quantified using the term stress concentration ratio, and with the use of geocell mattress above stone columns, the stress concentration ratio increased by 1.5 times that of ordinary stone columns. Also, it was observed that compared to ordinary stone column-supported embankment, the combination of stone columns with geocell-sand mattress resulted in a further reduction of the foundation settlement by 15%. Analysis results showed that the arching behavior is not predominant in geocell-reinforced columnar structures. The various analytical methods like Guido et al. (1987), Low et al. (1994), and Abusharar et al. (2009), which were developed for geosynthetic reinforced columnar embankments, were found to significantly under-predict the stress reduction ratio values with geocells. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Three dimensional analyses of geocell reinforced encased stone column supported embankments on lithomargic clay(Taylor and Francis Ltd., 2023) Vibhoosha, M.P.; Bhasi, A.; Nayak, S.Geocells are a superior form of reinforcement due to their cost-effectiveness and three-dimensional confining properties. However, numerical modeling of geocell is always challenging due to its three-dimensional honeycomb structure. The limitations of the equivalent composite approach (ECA) led to the recent development of full 3D numerical models, which consider geocell-infill material interaction. This paper discusses the time-dependent performance of geocell-reinforced encased stone column-supported embankment considering the actual 3D nature of geocells using the finite element program ABAQUS. Parametric studies were carried out to study the stress transfer mechanism, vertical deformation of the foundation soil, and stress-strain variation inside the geocell pockets. It is found from the analyses that with the provision of a geocell layer on top of Geosynthetic Encased Stone Columns (GESC), the stress concentration ratio improved by 47% at the end of consolidation compared to GESC alone. Also, an 80% reduction in foundation surface settlement is observed with geocell-sand mattresses. The geocell-sand mattress decreased the bulging of the stone columns, and almost 80% of the stone column bulging occurred by the end of the embankment construction. The proposed model’s numerical results show that the equivalent composite approach overestimated the stress concentration ratio and bearing capacity. The tensile stresses are non-uniformly distributed in the geocell pockets, and the maximum tensile force was mobilised at the geocell mid-height. Among the various geocell infill materials analysed, the aggregates were best suited considering the stress concentration ratio and vertical settlement. The numerical results supported the idea that encased stone columns with geocells at the embankment base can perform similarly to a geosynthetic reinforced piled embankment system, which is costlier but very efficient. When the modular ratio is more than 40, geocell-reinforced encased stone column-supported embankment is similar to GRPES. © 2022 Informa UK Limited, trading as Taylor & Francis Group.