Faculty Publications
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Item Strength behaviour of geogrid reinforced shedi soil subgrade and aggregate system(2006) Ravi Shankar, A.U.R.; Suresha, S.N.Shedi soil (Lithomargic clay), a yellowish-white silty soil underlying lateritic soil, is densely deposited along Konkan belt of India. The strength behaviour of Shedi soil under varying moisture content is major problem for road construction projects in this region. In the present investigation, the subgrade is stabilized with geogrid, keeping the geogrid at different positions from top of subgrade, to locate its optimum position. The plate load tests were also conducted at soaked and unsoaked conditions for unreinforeced, reinforced (with Geogrid) subgrade with aggregate base course. An equation has been established based on load-deflection values recorded for subgrade of un-reinforced and reinforced with geogrid at different levels. The deflection values obtained from equation and from the laboratory investigation were compared. In the case of reinforced subgrade with aggregate base course, the theoretical deflection values were computed based on Burmister's theory and compared with laboratory deflection values.Item Surface displacements due to tunneling in granular soils in presence and absence of geosynthetic layer under footings(Techno Press technop2@chollian.net, 2018) Rebello, N.E.; Shivashankar, R.; Sastry, V.R.This paper presents the results of numerical modeling studies on the effect of displacements of tunneling in granular soils. Presence of building loads is considered, to find displacement generated at the surface on tunnel. Effect of varying eccentricities of building is simulated, to find influence of building on vertical and horizontal displacement. Studies were carried out in two cases of with and without a geosynthetic layer installed at the bottom of the footing. Results of analysis revealed, the presence of geosynthetic layer under footing, with building placed on centre line, reduced the surface displacements compared to displacement generated without geosynthetic layer. Presence of geosynthetic layer under footing had a dominant effect in reducing displacements in high storey structures. However, when the building was shifted to greater eccentricities from centre line, presence of geosynthetic layer, led to insignificant reduction of displacements on the centre line at the surface. © 2018 Techno-Press, Ltd.Item 3-dimensional numerical modelling of sand bed reinforced with 3D geogrids of triangular form(Australian Geomechanics Society, 2019) Makkar, F.M.; Sreya, M.V.; Chandrakaran, S.; Sankar, N.In this paper, the bearing capacity improvement of a square footing resting on sand bed reinforced with 3D geogrids of triangular form is numerically studied with the help of Plaxis 3D software. The performance of 3D geogrid reinforced sand is also compared with planar geogrid reinforced sand to understand its effectiveness. In the numerical modelling, the soil behaviour is simulated by linear elastic-perfectly plastic Mohr-Coulomb model. The 3Dgeogrid and planar geogrid is modelled using geogrid structural elements available in the software. The model was validated with the experimental results and found to be in fairly good agreement with each other. The effect of various parameters on the behaviour of reinforced soil system was also investigated. It was found that the bearing capacity of multilayered planar geogrid reinforced sand bed improved by 3.68 times, while, the 3D geogrid reinforced sand bed shows 6.8 times improvement compared to the unreinforced sand bed. © 2019 Australian Geomechanics Society. All rights reserved.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 Model Footing Tests and Analytical Studies on Clayey Soil Bed Reinforced with Coconut Shell Mat(Springer Science and Business Media Deutschland GmbH, 2022) Kolathayar, S.; Gadekari, R.S.The cellular confinement systems are becoming popular in ground improvement because of their efficiency in improving the bearing capacity of soil due to the lateral confinement effect. The commercially available geocells are made from polymer materials and they are costly. This study presents the performance evaluation of coconut shell mat as a cellular confinement system in clayey soil. It is the first of its kind application of coconut shells for soil reinforcement through a lateral confinement mechanism. This soil reinforcement system using coconut shells is termed “Geococoshell” by the authors. A series of model plate load tests were conducted on unreinforced soil, soil reinforced with High-Density Polyethylene (HDPE) geocells, and soil reinforced with coconut shell mats to evaluate the performance of coconut shell mat reinforced soil bed. The results of the experiments showed that coconut shells reinforced clayey soil improved bearing capacity up to 1.5 times compared to HDPE geocell reinforced clayey bed. The effect of different patterns of placing coconut shell mat was also studied and discussed in the paper. The analytical studies have been conducted considering the reinforcement mechanisms of coconut shell mat embedded in the soil bed. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Geosynthetic reinforced rubble mound breakwater for mitigation of tsunami-induced damage(Elsevier Ltd, 2024) Sajan, M.; Chaudhary, B.; Akarsh, P.K.; Kumar, S.Several rubble mound breakwaters (RMB) were damaged and even collapsed during the past tsunamis. The main reasons for the failure of the breakwaters occurred due to the combined effects of seepage and scouring. Limited articles are available dealing with the behaviour of RMB during the tsunami. Furthermore, few available articles are related to developing countermeasures for the RMB against tsunamis. Therefore, an attempt has been made in the study to determine the exact behaviour of the RMB under the action of the tsunami. In addition, the main aim of the present study is to develop countermeasures to make the breakwater tsunami resilient. The present study proposes a novel geosynthetics-reinforced RMB to mitigate tsunami-induced breakwater damage. Based on the available information, this is the first time geosynthetics have been used in the RMB to mitigate tsunami-induced damage. Geogrid layers, geobags, sheet piles and crown walls (with shear keys) are adopted as countermeasure elements against the tsunami. Since the height of a tsunami can exceed its design tsunami height, tsunami waves were allowed to overflow the breakwater in physical model tests. Comparative analyses between the reinforced and unreinforced RMB were performed by conducting physical model tests, analytical tools, and numerical simulations. © 2023 Elsevier LtdItem Novel Techniques for Reinforcing Rubble-Mound Breakwater against Tsunamis(American Society of Civil Engineers (ASCE), 2024) Sajan, M.; Chaudhary, B.; Akarsh, P.K.; Kumar, S.; Sah, B.The widespread use of rubble-mound (RM) breakwaters along coasts across the world highlights the importance of understanding their behavior during natural disasters such as tsunamis. The failure of these breakwaters during tsunamis can have far-reaching consequences, potentially causing damage to coastal infrastructure and loss of life. Many breakwaters failed during past tsunamis. Despite this, studies on the behavior of RM breakwaters during tsunamis are minimal. The present study thus attempts to elucidate the behavior of RM breakwater subjected to a tsunami. Furthermore, efforts were made to develop effective countermeasures that can safeguard the breakwater against tsunamis. To the end, a novel technique of using geogrids for reinforcing the RM is proposed. This study could be a pioneering application of geogrids as reinforcing elements in RM breakwaters to mitigate damages from tsunamis. Geogrid layers are provided on both the seaside and harborside to mitigate tsunami-induced damage to the breakwater. In addition, a crown wall (with shear keys) is also introduced to prevent the scouring of the crest and sheet piles from preventing excess seepage through the seabed. Physical model tests, analytical studies and numerical simulations were carried out to assess the performance of the proposed countermeasures by comparing it with the behavior of conventional RM breakwater during the tsunami. The tsunamis can overflow the breakwater, potentially exceeding its design limits. Hence, provision was made in the study for overflow, where the breakwater may overflow by the tsunami. It was observed that excess seepage through the body of the breakwater and the scouring of the crest were significant factors that led to the failure of RM breakwaters under tsunami overflow. A novel reinforced model was proposed to address these issues. This model effectively withstood tsunami-induced damages without significant deformations, demonstrating its potential as a reliable solution. © 2024 American Society of Civil Engineers.Item Novel technique to mitigate the earthquake-induced damage of rubble mound breakwater(Elsevier Ltd, 2024) Akarsh, P.K.; Chaudhary, B.; Sajan, M.; Sah, B.; Kumar, S.In past, the 2004 Indian Ocean earthquake and the 2011 Great East Japan earthquake had caused collapse of many breakwaters due to failure of their foundations. The seismic behaviour of rubble mound (RM) breakwater is not well understood may be due to limited number of research works done in the area. Therefore, in the present study, a series of shaking table tests were conducted for RM breakwater in order to determine the exact reasons and mechanisms of failure of the breakwater during an earthquake. In addition, a novel countermeasure technique was developed to mitigate the earthquake-induced damage of RM breakwater. The countermeasure model dealt with geobags as armour units on the both sides instead of conventional armours to increase the stability. The developed model has geogrid and sheet piles in seabed foundation soils of the breakwater. The effectiveness of countermeasure model was examined by comparing with conventional RM breakwater model considering parameters like settlement, horizontal displacement, acceleration-time histories, excess pore water pressure and deformation patterns. Numerical analyses were done to elucidate the failure mechanisms. Overall, the developed model was found to be resilient breakwater against the earthquakes; and the technique could be adopted in practical use on the real ground. © 2023 Elsevier LtdItem Performance Assessment of Geosynthetic Reinforced Quay Walls under Concurrent Tsunami and Earthquake Aftershocks(American Society of Civil Engineers (ASCE), 2025) Sajan, M.K.; Sah, B.; Chaudhary, B.; Akarsh, P.K.Coastal structures are built against the dynamic loadings from waves, tides, and storms. However, natural disasters such as earthquakes and tsunamis can impart additional loadings on these structures that might exceed their design specifications. In the past, several earthquakes and tsunamis had resulted in severe damages even on coastal structures engineered to withstand tsunamis. It is reasonable to suggest that the tsunami waves succeeding the earthquake had impacted the coastal structures along with an aftershock, imparting the most critical loading conditions. However, limited studies are available, evaluating the performance of coastal structures when subjected to the combined loading conditions. Among various coastal structures, quay walls stand out due to their distinctive loading patterns, concurrently sustaining vertical live loads, active pressure from retained backfill, and dynamic wave forces from the sea. Therefore, the present study paper puts forth a comprehensive analysis of geosynthetic reinforced quays under the influence of a tsunami withdrawal and an earthquake aftershock. Since the magnitudes of seaward-directed loads during tsunami drawdown are unknown and difficult to assess practically, this study assumes a worst-case loading condition to represent these effects. The analytical approach adopted employs the horizontal slice method, encompassing the influence of outboard seawater, backfill submergence, tsunami impact, and pseudo-static earthquake loads. Results indicate that combined loading conditions substantially increase reinforcement forces, reducing the internal stability of quay walls. Critical parameters influencing stability include the shear strength of backfill soil, quay wall inclination, and surcharge loads. © 2025 American Society of Civil Engineers.