Faculty Publications
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Item A Study on the Seismic Behaviour of Embankments with Pile Supports and Basal Geogrid(Springer, 2020) Patel, R.M.; Jayalekshmi, B.R.; Shivashankar, R.For constructing the roads on soft grounds, basal geogrid-reinforced pile-supported embankments are a suitable solution over other conventional ground improvement techniques like preloading, embankment slope flattening, removing and replacing the soft soil, etc. Many studies are available on these basal geogrid-reinforced piled embankments to understand their behaviour under static loading conditions. But it is necessary to understand the behaviour of these geogrid-reinforced piled embankments under seismic excitations. Hence, finite element analysis of three-dimensional models of embankment having crest width of 20 m, height above ground of 6 m, with side slopes of 1V:1.5H consisting of pulverized fuel ash, overlying soft marine clay of 28 m thickness is carried out under seismic excitations corresponding to Zone III (IS:1893). Soft marine clay layer is improved by the addition of piles arranged in square grid pattern with 5.75% area replacement ratio. Geogrid with a tensile modulus of 4600 kN/m is used as the basal reinforcement. Initially, the embankment is analyzed without geogrid reinforcement and pile supports. Then, it is analyzed with (i) Basal geogrid (ii) With pile supports (iii) With basal geogrid and pile supports. The influence of various parameters of the embankment on maximum crest displacements, differential settlements at crest, toe horizontal displacements, stresses at pile head and foundation soil between piles and pile bending moment along the depth at peak acceleration are studied. Analysis of results shows that the embankment supported over piles with basal geogrid reinforcement will experience less crest settlements, differential settlements at crest and toe horizontal displacements due to earthquake load. © 2020, Springer Nature Singapore Pte Ltd.Item Seismic Response of Basal Geogrid Reinforced Embankments Supported on a Group of Vertical and Batter Piles(Springer Science and Business Media Deutschland GmbH, 2021) Patel, R.M.; Jayalekshmi, B.R.; Shivashankar, R.; Surya, N.R.Basal geogrid reinforced embankments supported on vertical piles are proven to be a feasible and effective solution for constructing embankments over thick soft clay deposits and bridge approaching embankments. These solutions minimize the lateral displacements, total and differential settlements of embankment crest and toe by transmitting embankment loads into the deeper stratum through pile foundations and arching action of geogrid. Basal geogrid reinforcements provide good restraint against lateral spreading of the toe. Providing batter piles near the toe will further enhance this restraint against lateral spreading. Not many studies are available in literature on performance of batter piles below embankment toe, especially under seismic excitations. The present study aims to find the advantages of providing batter piles below embankment toe under seismic excitations. A 6 m high basal geogrid reinforced embankment having 1 V:1.5H side slope constructed over 28 m thick soft clay is considered for the 3-Dimensional finite element analysis. The soft clay is stabilized with 22 m long 300 mm diameter vertical and batter piles spaced at three times the pile diameter. Embankment crest vertical displacements, toe horizontal displacements, maximum differential settlements at the crest and crest lateral accelerations are analysed for different batter angles of 0°, 5°, 10°, 15°. Analysis of results reveals that larger the batter angle more is the reduction of toe horizontal displacements. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Effects of prestressing the reinforcement on the behavior of reinforced granular beds overlying weak soil(Elsevier Ltd, 2014) Shivashankar, R.; Jayamohan, J.The effects of prestressing the reinforcement on the strength improvement and settlement reduction of a reinforced granular bed overlying weak soil are being investigated through a series of laboratory scale bearing capacity tests. The influences of parameters such as strength of underlying weak soil, thickness of granular bed, magnitude of prestressing force, direction of prestressing forces and number of layers of reinforcement are being examined. Finite element analyses are carried out using the FE program PLAXIS to study the effect of prestressing the reinforcement. Results obtained from finite element analyses are found to be in reasonably good agreement with the experimental results. © 2013 Elsevier Ltd.Item 3D soil–structure interaction analyses of annular raft foundation of tall RC chimneys under wind load(Springer, 2014) Jisha, S.V.; Jayalekshmi, B.R.; Shivashankar, R.Three dimensional soil–structure interaction (SSI) analyses of tall reinforced concrete chimneys with annular raft foundation subjected to wind loads are presented in this paper. Different ranges of height and slenderness ratios of the chimneys and different ratios of external diameter to thickness of the annular raft were selected for the parametric study. To understand the significance of SSI, four types of soils were considered based on the stiffness. The chimneys were assumed to be located in terrain category two and subjected to a maximum wind speed of 50 m/s as per IS:875 (Part 3)-1987. The alongwind and across-wind loads were computed according to IS:4998 (Part 1)-1992. The linear elastic behavior was assumed for the integrated chimney-foundation-soil system and it was analysed using finite element software ANSYS based on direct method of SSI. The radial and tangential moments and settlement of annular raft foundation were evaluated through SSI analysis and compared with that obtained from conventional method of analysis as per IS:11089-1984, assuming foundation system is rigid. From the analysis, it is concluded that the SSI analysis results in higher radial moments and lesser tangential moments as compared to conventional method. All these variations depend on the geometric properties of chimney and annular raft foundations. © Indian Geotechnical Society 2013.Item Analysis of Foundation of Tall R/C Chimney Incorporating Flexibility of Soil(Springer India sanjiv.goswami@springer.co.in, 2017) Jayalekshmi, B.R.; Jisha, S.V.; Shivashankar, R.Three dimensional Finite Element (FE) analysis was carried out for 100 and 400 m high R/C chimneys having piled annular raft and annular raft foundations considering the flexibility of soil subjected to across-wind load. Stiffness of supporting soil and foundation were varied to evaluate the significance of Soil-Structure Interaction (SSI). The integrated chimney-foundation-soil system was analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic material behaviour. FE analyses were carried out for two cases of SSI namely, (1) chimney with annular raft foundation and (2) chimney with piled annular raft foundation. The responses in raft such as bending moments and settlements were evaluated for both the cases and compared to those obtained from the conventional method of analysis of annular raft foundation. It is found that the responses in raft vary considerably depending on the stiffness of the underlying soil and the stiffness of foundation. Piled raft foundations are better suited for tall chimneys to be constructed in loose or medium sand. © 2017, The Institution of Engineers (India).Item Study on Behaviour of Two Adjacent Strip Footings on Granular Bed Overlying Clay with a Void(Springer, 2020) Anaswara, S.; Shivashankar, R.This paper numerically examines the behaviour of two adjacent strip footings on granular bed over weak soil having a void. Voids could be formed in weak soil strata due to various reasons such as due to water leakage from the water supplying lines or sewer lines, poor drainage and erosion of soil, animal burrows, etc. A parametric study is carried out to understand the influence of granular bed thickness, width of footings, spacing between the footings, and the presence of a void beneath the footing in the weak soil, on the behaviour of footings. To understand the failure mechanism, shear strain contours, for different cases, are being studied. It is observed that there is a certain critical spacing between the two adjacent footings at which the footing/s carry the maximum load. This critical spacing depends on the type of loading, whether equal and simultaneous loading or unequal and sequential loading. The presence of voids also affects the performance of footings. Such voids tend to reduce the load carrying capacity of the footing/s and alter failure pattern. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item Stress Distribution in Basal Geogrid Reinforced Pile-Supported Embankments Under Seismic Loads(Springer, 2021) Patel, R.M.; Jayalekshmi, B.R.; Shivashankar, R.Basal geosynthetic reinforced pile-supported embankments are proven as the more appropriate ground improvement technique for constructing embankments for roads over very soft clay deposits and approach roads or embankments to bridges. Numerous experimental and analytical works are available on the soil arching phenomenon of geosynthetic reinforced piled embankments subjected to static loading conditions. This study attempts to evaluate the stress distribution and soil arching in geosynthetic reinforced pile-supported embankments subjected to seismic excitations. Time-history analysis has been performed on the basal geogrid reinforced pile-supported embankments by varying the height of embankment and tensile modulus of geogrid. Analyses of results show that for ? (the ratio of height of embankment to pile centre to centre spacing) less than or equal to 4.5, a geogrid tensile modulus of 3000 kN/m is sufficient to withstand vertical stresses due to earthquakes. And for the considered embankment height and pile diameter when ? nearly equal to 4.5, differential settlements are very less irrespective of seismic excitations. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.Item Effect of Reinforcement Width on Dynamic response of Basal Geosynthetic-Reinforced Embankment(Springer, 2022) Patel, R.M.; Jayalekshmi, B.R.; Shivashankar, R.High compressibility and poor shear strength properties of soft clayey foundation soils are problems to be dealt with in the design and construction of embankments or roads. The inclusion of geosynthetic at the embankment base is one of the ground improvement techniques used to construct roads or embankments over soft clayey subsoils. This article aims to present the seismic behaviour of basal geosynthetic-reinforced embankments, and various parameters are analysed to identify the suitable width of basal geogrid using time-history analysis. Embankments of heights 4 to 10 m with varying side slope angles are studied. Analysis of results shows that the addition of basal geogrid not only improves the stability of the embankment under static loading conditions but also improves the seismic performance of the embankment. From the results of this study, it is found that the basal geogrid reinforcement of a total width equal to the embankment base width plus embankment height and with a high tensile modulus of 4000 kN/m is required to effectively withstand the seismic forces in seismic regions with peak ground accelerations up to 0.6 g. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.