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 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 Stone Columns with Vertical Circumferential Nails: Laboratory Model Study(2010) Shivashankar, R.; Dheerendra Babu, M.R.D.; Nayak, S.; Manjunath, R.This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the improvement in stiffness, load carrying capacity and resistance to bulging of stone columns installed in soft soils. A new method of reinforcing the stone columns with vertical nails installed along the circumference of the stone column is suggested for improving the performance of these columns. Tests were carried out with two types of loading (1) the entire area in the unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the limiting axial capacity. It is found that stone columns reinforced with vertical nails along the circumference have much higher load carrying capacity and undergo lesser compression and lesser lateral bulging as compared to conventional stone columns. The benefit of vertical circumferential nails increases with increase in the diameter, number and depth of embedment of the nails. The improvement in the performance of stone column was found to be more significant, even with lower area ratio. It is found that reinforcing stone column with vertical circumferential nails at the top portion to a depth equal to three times the diameter of stone columns, will be adequate to prevent the column from excessive bulging and to improve its load carrying capacity substantially. © 2010 Springer Science+Business Media B.V.Item Performance of stone columns with circumferential nails(2011) Nayak, S.; Shivashankar, R.; Dheerendra Babu, M.R.D.Stone columns are often used as an effective technique for improving the performance of soft ground. Stone columns derive their load-carrying capacity due to lateral confinement from the surrounding soil. Very soft soils offer very low lateral confinement, leading to large settlements and low load-carrying capacities. In this paper, an alternative method of enhancing the performance of stone columns in soft soils by reinforcing the stone columns with circumferential nails driven vertically is suggested. The method was developed in laboratory-scale model tests and a series of plate load tests were performed in unit cell tanks to investigate the performance of stone columns reinforced with circumferential nails. The investigation was carried out by varying the depth of nails below ground level, the number of nails and the diameter of nails with different diameter stone columns and area ratios (orspacing). It was found that the circumferentially reinforced stone columns have much higher load-carrying capacity with a significant reduction in settlement and less lateral bulging in comparison with plain stone columns.Item Experimental Studies on Behaviour of Stone Columns in Layered Soils(2011) Shivashankar, R.; Dheerendra Babu, M.R.D.; Nayak, S.; Rajathkumar, V.Stone columns are found to be effective and economical ground improvement technique in soft grounds. Understanding its behaviour when they are installed in stratified soils, in particular when the upper layer consists of weak soil, will be of great practical significance. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behaviour of stone columns in layered soils, consisting of weak soft clay overlying a relatively stronger silty soil, for various thicknesses of the top layer. Tests were carried out with two types of loading (1) the entire area in the unit cell tank loaded, to estimate the stiffness of improved ground and (2) only the stone column loaded, to estimate the limiting axial capacity. Laboratory tests were carried out on a column of 90 mm diameter surrounded by layered soil, for an area ratio of 15%. It is found that the depth of top weak layer thickness has a significant influence on the stiffness, load bearing capacity and bulging behavior of stone columns. © 2011 Springer Science+Business Media B.V.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 A Study on the Behaviour of Stone Columns in a Layered Soil System(Springer, 2020) Nayak, S.; Balaji, M.; Preetham, H.K.Stone columns are one of the cost-effective and efficient methods for improving the ground which strengthen the soil and reduce the settlements. The study of the behaviour of stone columns in layered soils is of great importance. In this paper, results obtained from the experiments done on the stone columns with varying thickness of clayey silt soil (lithomargic clay) at bottom and the lateritic soil at the top are discussed. The lateritic layers are varied from top for a depth of 1D to 5D where D is the stone column diameter. Experiments were performed on untreated soils alone, soil with the ordinary stone column, geogrid encased stone column with and without additional horizontal reinforcement called basal layer to geogrid encased stone column in lithomargic clay. Similar experiments were conducted using lateritic soil. By considering layered combination of these two soils, experiments were also performed on ordinary stone column, geogrid encased stone column and geogrid encased stone column with basal layer. Laboratory tests were conducted in a unit cell on the floating stone column of diameter 60 mm. The load capacity of the stone column and bulging characteristics are significantly affected with the increase in the layers of lateritic soil. The encasement of stone column enhances the stone column’s capacity and reduces the bulging. The additional horizontal reinforcement layer also showed a significant impact on the load capacity of the stone column. Experiments conducted were modelled and analysed using PLAXIS 2D software package. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.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.