Faculty Publications
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Item Seismic stability evaluation of rubble mound breakwater: Shake table tests and numerical analyses(Elsevier Ltd, 2024) Akarsh, P.K.; Chaudhary, B.; Sajan, M.; Kumar, S.; Sah, B.Rubble mound (RM) breakwaters are coastal structures constructed to provide tranquil condition around the port areas. After past earthquakes such as the 2004 Indian Ocean earthquake and the 2011 Great East Japan earthquake, it was found that stability of breakwater not only depends on the wave action but seismic motions also play an important role for this. Very limited studies are available for the stability evaluation of RM Breakwater under earthquake motions by conducting physical model tests. To the end, an attempt has been made in the study to evaluate the stability of RM breakwater subjected to earthquake loadings. A series of shaking table tests conducted to evaluate the seismic behaviour of the RM breakwater. A prototype RM breakwater is modelled on two layers of seabed foundation soil. Different amplitudes of sinusoidal seismic motions (foreshocks and main shock) are provided at the base of the model. Later, the breakwater stability was evaluated for real earthquake motions. Various parameters such as settlement, horizontal displacement, acceleration-time histories and excess pore water pressure were measured during the tests. Deformation pattern was also studied by photos and videos captured during the tests. During the mainshock, the crown wall settled by 111 % more comparable to second foreshock; and the structure laterally displaced by more than 200 % comparable with first foreshock. The peak acceleration of input wave amplified while it was travelling from bottom to the crest of breakwater. The excess pore water pressure was maximum beneath the rubble mound, in loose sand and it was five times more during the mainshock compared to first foreshock. Due to loss in bearing capacity of foundation soil, the breakwater collapsed. Also, the effects like rolling down of armor units, densification and slumping of core material, shear deformation of breakwater body were observed during the main shock. Thus, the breakwater failed during the mainshock. Numerical analyses were also executed for both sinusoidal and real earthquake motions to make clear the mechanism of the breakwater behaviour subjected to the earthquake loadings. © 2024 Elsevier LtdItem 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 Response of Suction Caisson Foundations for Offshore Wind Turbines Subjected to Earthquake Loading: Numerical Simulations(Springer, 2025) Kumar, S.; Sah, B.; Chaudhary, B.Installation of offshore wind turbines (OWTs) increases exponentially in order to meet the demand of energy and to achieve a huge target of renewable energy for reducing carbon emission. Several OWTs are being built in seismic zones. The safety of OWTs that utilize suction bucket foundations is significantly depended on earthquake threat and liquefaction. This study examined the suction bucket's performance for OWTs situated in liquefiable sand when exposed to wind and seismic forces. To conduct nonlinear dynamic assessments, three-dimensional numerical models were created by using FEM program PLAXIS 3D, simulating the sandy seabed using the Mohr–Coulomb constitutive model. The study concentrated on evaluating a number of variables, including wind forces, seismic effects, bucket aspect ratios, and sand densities, that affect the way suction bucket foundations behave seismically. The investigation looked at how the OWT responded to combined earthquake and wind loading circumstances in terms of acceleration, horizontal displacements, excess pore water pressure ratios, and settlements. It was observed in the study that the OWT could undergo permanent tilting that surpasses the state of the serviceability limit, a result of the combined impact of wind, earthquakes, and liquefaction. The research also examined the deformation mechanisms of the foundation for the suction bucket, when subjected to these forces. The outcomes of this study offer valuable information for the engineering of OWTs in regions prone to seismic activity. © The Author(s), under exclusive licence to Indian Geotechnical Society 2025.Item A Three-Dimensional Investigation on the Efficacy of Different Configuration Settings of Micropiles in Enhancement of Seismic Slope Stability(Springer Science and Business Media Deutschland GmbH, 2025) Kumar, S.; Anand, A.; Sarkar, R.; Nainegali, L.Micropiles have emerged as an effective measure to strengthen the stability of slopes. However, its efficacy in improving the stability of slopes under seismic loading conditions has not been fully established. This paper intends to investigate the performance of micropiles with different configurations to improve the stability of a slope under static and seismic loading conditions. A clayey slope of height 10 m underlain by a sandy soil layer was adopted for the investigation. Three-dimensional nonlinear finite element models were developed for the slope-micropile systems. Five different configurations of micropiles, considering a single micropile on two faces of the slope, were adopted for investigation. Further, a study was carried out with eight different combinations of these configurations of micropiles for strengthening the slope. Initially, static analyses were carried out for the different configurations of micropiles. Next, for seismic loading, pseudo-static analyses were carried out for all the configurations. The efficacy of different configurations of micropiles was compared through the factor of safety obtained. Analyses were also carried out considering the water table, and the efficacy of micropiles was established in the same way. Finally, nonlinear dynamic analyses were carried out for different configurations of micropiles with real earthquake time history, and the improvement in seismic performance of the micropile-strengthened slope was reported. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.