Faculty Publications
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Item 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 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 Developing Tsunami-Resilient Rubble Mound Breakwater: Novel Gabion-Based Technique(American Society of Civil Engineers (ASCE), 2025) Sajan, M.K.; Chaudhary, B.; Akarsh, A.P.; Sah, B.The rubble mound (RM) breakwater, which is a prevalent coastal structure worldwide, often faces the significant challenge of tsunami-induced damage. Coastal regions which are characterized by high population density necessitate robust breakwaters to withstand the destructive forces of tsunamis. The most devastating natural hazard that a breakwater could encounter during its lifespan is the tsunami. Past occurrences have revealed vulnerabilities in conventional RM breakwaters leading to failures attributed to the scouring of rubble and seabed caused by excessive seepage during tsunami overflow events. This study presents novel countermeasures aimed at mitigating the potential failure mechanisms induced by tsunamis on RM breakwaters. The proposed countermeasure elements include gabions, crown walls equipped with shear keys, and sheet piles. To assess the efficacy of these innovations, a series of tsunami overflow tests was conducted on small-scale models. The results demonstrated a marked improvement in the stability and resilience of RM breakwaters against tsunamis with the incorporation of these countermeasures. Additionally, numerical simulations were performed to determine the precise mechanisms influencing the behavior of the breakwater during tsunamis. © 2024 American Society of Civil Engineers.Item Investigations on the development of hybrid mound breakwaters for tsunami defense(Elsevier Ltd, 2025) Sajan, M.K.; Chaudhary, B.; P K, A.; Sah, B.Tsunamis significantly damage coastal infrastructure and lives, resulting in extensive economic implications. Despite the global adoption of breakwaters as a primary coastal defence measure, it was observed that the structural integrity of several of these breakwaters was compromised during past tsunamis. The present study addresses these vulnerabilities of breakwaters by particularly focusing on the most commonly adopted rubble mound type breakwater. Further, this study introduces a novel technique in order to enhance the reliability of these structures by mitigating the tsunami induced failure mechanisms. In the novel technique, wrap-faced geogrids are implemented to reinforce the rubble mound without compromising the breakwater functionality in dissipating the incident wave energy through transmission. A comprehensive evaluation was carried out, including tsunami overflow tests, analytical assessments, and numerical simulations, to ascertain the effectiveness of the novel hybrid mound breakwater. The findings indicate that the developed hybrid mound breakwater withstood level 1 tsunamis with a 96.7 % reduction in settlement. One of the critical failure mechanism of breakwaters observed during past tsunamis was due to the seepage induced scouring of the foundation. The hybrid mound breakwater showcased a 42.37 % reduction in the foundation pore water pressure during tsunami by incorporating cut off walls. The numerical simulations also reconfirmed the enhanced performance of hybrid mound breakwater to protect the coasts from future tsunamis. © 2025