Browsing by Author "Sah, B."

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Behavior of Offshore Wind Turbine Foundation Under Seismic Loading: Numerical Simulations
(Springer Science and Business Media Deutschland GmbH, 2025) Kumar, S.; Chaudhary, B.; Sajan, M.K.; Akarsh, P.K.; Sah, B.
Offshore wind energy has emerged as a pivotal source of renewable energy, driven by the need to address climate change and reduce reliance on fossil fuels. The behavior of offshore wind turbine foundations plays a critical role in ensuring the efficiency and durability of these structures in harsh marine environments. The numerical simulations of an offshore wind turbine foundation under seismic loading are presented in this paper, with an emphasis on vertical settlement and horizontal displacement. The dynamic behavior of the foundation is evaluated under different soil properties and caisson geometry using sophisticated finite element modeling. The parametric study shows that increasing the length of suction caisson foundation there is an appreciable amount of reduction in vertical settlement of foundation due deeper embedment of caisson. A deeper embedment provides increased resistance to horizontal displacement because the foundation interacts with more stable soil layers. Because denser sand has a higher unit weight, it resists compression better, which reduces overall soil compression under load and minimizes vertical settling of foundations. Sand unit weight influences an offshore wind turbine caisson foundationâ€™s horizontal displacement by boosting seabed interaction, increasing vertical stress, and possibly offering more resistance because of its higher shear strength. The results highlight the need for strict seismic design standards to guarantee the dependability and security of offshore wind farm foundations in seismically active areas, the paper ultimately contributes to the development of more efficient, sustainable, and resilient offshore wind energy infrastructure. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Behaviour of Open Trenches for the Mitigation of Ground-Borne Vibrations
(Springer Science and Business Media Deutschland GmbH, 2025) Kumar, A.; Sajan, M.K.; Akarsh, P.K.; Sah, B.; Chaudhary, B.
With the advancement of modern technology, increased rail and road transit systems have been built to relieve traffic congestion in densely populated cities. Railway lines may inevitably pass through residential or vibration-sensitive areas where high-precision labs or factories are located. Ground vibrations associated with these railway and roadway systems have become a significant concern due to rapid urbanization and related activities. Traffic, vibrating equipment, pile driving, machine foundation, and blasting induce ground vibrations might affect the integrity of nearby structures. Therefore, vibration isolation is necessary to mitigate ground-borne vibrations with suitable techniques in the present-day context. Researchers have performed multiple studies to develop efficient mitigation techniques to counter the problem of ground-borne vibrations, such as open trenches, infilled trenches, and pile barriers. Open trench barriers are one of the prominent isolation techniques for ground vibration. In this study, the performance of open trenches is investigated for the isolation of ground-borne vibrations by performing numerical analyses by utilizing the finite element method. A parametric study was carried out to evaluate the influence of trench geometry and the number of trenches in attenuating the ground-borne vibrations. The results indicate that the depth and width of an open trench are two crucial parameters determining its performance in wave attenuation. The ground-borne vibration isolation system of the trench shows improvement in damping ground-borne vibrations. Additionally, the dual trench systems were observed to reduce the wave propagation across all distances from the vibration source. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Comprehensive Analysis of Gabion Configurations for Modelling Tsunami-Resilient Rubble Mound Breakwaters
(Springer, 2025) Sajan, M.K.; Sah, B.; Kumar, S.; Chaudhary, B.
Coastal communities face significant threats from tsunamis, which cause extensive damage to infrastructure and endanger human lives. Rubble mound breakwaters, widely adopted structures in ports and harbours globally, serve as the first line of defense against tsunami waves. However, their failures in past tsunamis highlight the need for enhanced resilience. The performance of rubble mound breakwaters under tsunami conditions has received limited research attention, and few studies have explored effective countermeasures to mitigate tsunami-induced damages. This study addresses this research gap by performing a comprehensive evaluation through physical model tests, analytical studies and numerical simulations, focusing on the behaviour of rubble mound breakwaters under tsunami overflow. Observations from the responses of conventional models during overflow tests informed the proposal of a reinforcing technique utilizing gabions as a countermeasure to enhance tsunami resilience. Measurements of crest displacements and excess pore water pressure developed in both the foundation soils and the breakwater during tsunami overflow were ascertained to comparatively analyse the performance of the proposed reinforced models. An in-depth analysis was conducted on the placement and positioning of gabions to identify the most effective configuration for transforming a conventional rubble mound breakwater into a tsunami-resilient structure. Among the various gabion placement configurations studied, the stepped configuration demonstrated a remarkable 97.8% reduction in settlement during tsunami overflow. Further analytical and numerical studies were performed to assess the performance of the proposed gabion-reinforced model under tsunami overflow conditions. This proposed technique presents significant potential for protecting a wide range of coastlines by enhancing the resilience of rubble mound breakwaters against tsunamis. © The Author(s), under exclusive licence to Indian Geotechnical Society 2025.
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.
Dynamic Analysis on the Seismic Resilience of Rubble Mound Breakwaters
(Springer Science and Business Media Deutschland GmbH, 2025) Sajan, M.K.; Chaudhary, B.; Akarsh, P.K.; Sah, B.
In the aftermath of past earthquakes causing damage to rubble mound (RM) and exposing coastal infrastructure to potential tsunami waves, this paper presents an in-depth investigation into the seismic performance of these critical coastal defenses. Employing advanced finite element analysis software, the study utilizes sinusoidal input ground motions with varying accelerations to simulate the seismic response of RM breakwaters. The research methodology entails meticulous finite element modeling of conventional breakwaters and the strategic integration of reinforcements, such as sheet piles and geogrids. A detailed analysis of displacement profiles and changes in pore pressures within the seabed soil beneath the RM breakwater is conducted, offering crucial insights into its seismic behavior. The investigation explores diverse combinations of reinforcements to assess their efficacy in fortifying the breakwater against seismic loading. Seismic response is simulated by imposing sinusoidal input waves as displacements at the bottom boundary of the soil layer, with free-field boundaries at either end to eliminate reflective effects. This research significantly contributes to the optimization of RM breakwater designs, providing practical strategies for enhancing their seismic performance in coastal engineering applications. The use of finite element analysis facilitates a nuanced understanding of dynamic interactions, allowing for the development of robust and resilient coastal structures to withstand seismic challenges and mitigate potential damages to coastal infrastructure and life. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Geosynthetic Reinforcing Technique against Earthquake-Induced Damage of Rubble Mound Breakwaters
(American Society of Civil Engineers (ASCE), 2025) Akarsh, A.P.; Chaudhary, B.; Sajan, M.K.; Sah, B.; Kumar, S.
During past earthquakes, many breakwaters were found unstable due to the loss of seabed foundation stability and the deformation of its components. Limited studies are available on the seismic stability of rubble mound breakwaters. Hence, in this study, earthquake effects on RM breakwater were investigated. A series of shake table tests were conducted, applying sinusoidal input motion at the modelâ€™s base. The conventional model has seabed soils and breakwater mound. In addition, a reinforcing technique employing geosynthetic materials for mitigating the earthquake-induced damage of RM breakwater was developed. The geosynthetic reinforcing elements like geotextile sand-filled bags and geogrids were utilized at various locations of the model. The performance of the developed reinforcing model was compared with the responses of the conventional model using various parameters. The settlement and horizontal displacement of the developed model were reduced by 45% and 43%, respectively, during the mainshock. The developed model can be utilized for real-world applications. Â© ASCE.
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
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 Ltd
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.
Numerical Analysis on Geogrid-Reinforced Coastal Structures Under Tsunami
(Springer Science and Business Media Deutschland GmbH, 2025) Sajan, M.K.; Chaudhary, B.; Akarsh, P.K.; Sah, B.
Coastal structures such as breakwaters play a crucial role in coastal protection, shielding communities from the relentless forces of waves and storms. However, historical tsunami events have exposed vulnerabilities in these breakwaters, leading to instances of collapse and extensive damage. The collapse of rubble mound breakwaters during the past 2004 Indian Ocean and 2011 Great East Japan tsunamis highlights the urgent need for effective countermeasures to improve their tsunami resilience. In response, this research investigates the tsunami behavior of these coastal structures. It examines potential reinforcement technique of adopting geogrids on the breakwater slopes to mitigate tsunami-induced damage. Through advanced numerical analysis using finite element modeling, geogrid reinforcements are introduced on either side of the breakwater to assess their effectiveness in reducing tsunami-induced settlements, horizontal displacements, and stability. The incorporation of geogrids emerges as a promising solution, offering several advantages over conventional breakwater models. Results demonstrate that geogrid effectively reduces the settlement of reinforced breakwater by up to 81% under a tsunami. Moreover, geogrids demonstrate superior performance in mitigating lateral displacements and stability, highlighting their potential to enhance the tsunami resilience of the breakwater. A parametric study was performed on the influence of the tensile strength of geogrids in improving the stability of the reinforced breakwater. This study contributes valuable insights to the field of coastal engineering and disaster resilience by providing a comprehensive analysis of geogrid reinforcements in mitigating tsunami-induced damage to rubble mound breakwaters. The findings underscore the importance of proactive measures in protecting coastal communities against the escalating threat of tsunamis, emphasizing the role of innovative engineering solutions in building resilient coastal infrastructure. Â© Deep Foundations Institute 2025.
Numerical Simulations for Response of Offshore Wind Turbine Monopile Under the Action of Dynamic Loading
(Springer Science and Business Media Deutschland GmbH, 2025) Barik, T.; Chaudhary, B.; Sah, B.; Kumar, S.; Akarsh, P.K.
Wind energy is one of the most important renewable energy sources; and specifically offshore wind turbines (OWTs) are more convenient ones because of the presence of uninterrupted high-velocity winds in the offshore area. To stabilize the OWT structure, the foundation plays the most significant role. Most of the offshore wind farms employ fixed type foundations for shallow water depth. Among the fixed type foundations, monopiles arose as the first choice for the scientists and practicing engineering because of its ease of installation and economical aspects. Besides, due to high magnitude of wind pressure and wave force in offshore areas, these OWTs face a heavy dynamic lateral loading which creates unbalanced forces and moments as well as vibrations which can make the whole structure unstable by affecting these monopiles. Research has been done in the past on monopoles, but still the responses could not be understood completely. Therefore, an attempt has been made in this study to investigate the lateral behavior of monopile-tower structure under the action of dynamic lateral loadings using Finite Element (FE) analyses. A 3D numerical model has been developed in ABAQUS program; and the numerical model has been validated with the available literature. In addition, parametric studies were conducted to understand the effects of loading conditions, pile geometric configuration, and soil shear parameters on the lateral response of the monopile-tower assembly. Results obtained from the rigorous numerical analyses demonstrate that the wind load in isolation can significantly augment the lateral displacement of OWT hubs. Moreover, an additional wave load may diminish this displacement at the hub. Additionally, the length and diameter of the monopile also exert a notable influence on governing the lateral response. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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.
Response of Offshore Wind Turbine Monopile Foundation Under Action of Wind Load and Sea Waves: Numerical Analysis
(Springer Science and Business Media Deutschland GmbH, 2025) Sah, B.; Sridhar, G.
Offshore wind turbine, being one of the most important renewable energy sources globally, has witnessed the construction of numerous offshore wind farms. These are established in offshore areas due to the steadier and stronger winds compared to onshore environments. Among the diverse fixed offshore foundation systems utilized for wind turbines including gravity, caisson, tripod, monopile, jacket, and suction, the monopile foundation emerges as the predominant choice, especially well-suited for sea beds with depths up to 35Â m. However, understanding the behavior of monopile foundations under the combined influence of cyclic wind and sea waves remains limited. Throughout the 25 year lifespan of a turbine, cyclic loading continuously affects the foundation, potentially altering soil stiffness and system frequencies. To address this issue, numerical modeling using finite element method program is employed in this study. Through cyclic loading simulations, the response of monopile foundations to wind and sea waves is thoroughly investigated. Parametric studies also conducted to explore the impact of factors such as soil properties and loading conditions. The findings of this study contribute to a deeper understanding of monopile foundation behavior under dynamic environmental conditions, offering valuable insights for design and optimization of offshore wind energy projects. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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.
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 Ltd