Browsing by Author "Sajan, M.K."

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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.
Effects of High Cyclic Strains on Dynamic Properties of Cohesionless Soils
(Springer Science and Business Media Deutschland GmbH, 2025) Akarsh, P.K.; Chaudhary, B.; Sajan, M.K.; Chikkanna, T.; Talkad, P.
Soils can experience large cyclic shear strains (>1%) under dynamic loading circumstances such as earthquakes. Determining dynamic properties such as damping ratios and shear modulus is crucial in the design of earthquake-resistant structures. From past studies, it was understood that the dynamic behaviour of soils at higher strains (>0.01%) is different from soils subjected to lower strains (<0.001%) because of nonlinear stressâ€“strain behaviour and damping characteristics at higher strains. Furthermore, it was evident that the majority of tests were carried out on lower strains and only few numbers of studies were reported on tests for higher strains. Hence in this study, the dynamic properties for locally available cohesionless soils tested under high cyclic strains are presented. Generally, the dynamic properties were determined up to strain levelsâ€‰<1% considering a symmetrical hysteresis loop. But the loop becomes asymmetric as the strain level increases and due to which, dynamic properties are over-estimated. So, in this study, the dynamic properties of saturated sand were determined by an actual asymmetric hysteresis loop. Strain-controlled cyclic triaxial tests were conducted on reconstituted soil specimens at a low frequency (0.25Â Hz) for variable peak strain levels (0.15â€“1.5%). The specimens were prepared at different relative densities (30â€“90%) and consolidated at an effective confining pressure of 100Â kPa. The findings of the study revealed that the soilâ€™s shear modulus would degrade more quickly or that the modulus reduction ratio would reduceÂ at higher strain levels (Î³â€‰â‰¥â€‰1%) due to an increase in pore water pressure during undrained cyclic loading. It also turns out that at higher strain values (>1%), the damping ratio significantly decreased. Hence, it is not obvious to extrapolate the trend seen for Î³â€‰<â€‰1% to get the results for Î³â€‰>â€‰1%. This work would be helpful for geotechnical practicians and researchers to have insights into the existing methodology for finding the dynamic properties of cohesionless soils at higher cyclic strains. 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
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.
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 Foundation Subjected to Earthquakes, Sea Waves and Wind Waves: Numerical Simulations
(Springer Science and Business Media Deutschland GmbH, 2024) Kumar, S.; Chaudhary, B.; Sajan, M.K.; Akarsh, P.K.
Offshore wind turbines are an economical and sustainable method for generating renewable energy over extended periods. They efficiently harness wind power and are strategically located far from residential areas in the sea, resulting in minimal noise pollution. These towering structures rely on wind as their primary energy source and are installed at varying water heights from shallow to medium depths. The critical aspect of ensuring the stability of the foundation for such massive and tall structures becomes particularly important, especially in regions prone to earthquakes. This research paper focuses into the influence of wind loading on offshore wind turbine platforms, with specific emphasis on the suction caisson foundation. To assess the effects of wind loads, numerical analyses were performed using the finite element software PLAXIS. The findings reveal that horizontal deflection and shear stress increase as the angle of internal friction and unit weight decrease. Additionally, the study conducts parametric analyses to explore the impact of other variables on the behaviour of the turbine. These conclusions emphasize the significance of designing resilient foundations for offshore wind turbines, considering factors such as wind loads, soil characteristics, and structural parameters. This ensures their long-term stability and effectiveness as a sustainable source of energy. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
Seepage Analysis of Resilient Rubble Mound Breakwater Under Tsunami Overflow: Numerical Analysis
(Springer Science and Business Media Deutschland GmbH, 2023) Sajan, M.K.; Chaudhary, B.
A breakwater is an offshore structure which is constructed to protect ports and harbours from the destructive effects of sea waves, currents, typhoons, and even tsunamis by reflecting and dissipating their wave energies. Among the various types of breakwaters, the rubble mound (RM) breakwater is the most common type constructed near the seacoasts of many countries across the globe. The most devastating natural hazard that a breakwater could possibly encounter during its design life is a tsunami wave. Several breakwaters were severely damaged or completely collapsed in several countries during past tsunamis. The coastal areas of India bore the brunt of the damage during the 2004 Indian Ocean tsunami. Therefore, it is utmost important to develop new techniques such as placing special gabions and rows of sheet piles as countermeasures for making RM breakwaters tsunami resilient. One of the longest breakwaters in India, the north breakwater at the Ennore Port (Chennai) has been chosen as prototype. The numerical modelling of the RM breakwater along with the seabed soil with two layers has been done in Plaxis 2D to observe the effectiveness of these countermeasures during tsunami-induced seepage through the breakwater and seabed soils. It was found that the provision of special gabions with impermeable layer and sheet piles beneath the mound can effectively prevent the seepage of water that occurs during tsunami overflow. Â© 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Seismic Responses of Rubble Mound Breakwater: Numerical Analyses
(Springer Science and Business Media Deutschland GmbH, 2024) Akarsh, P.K.; Chaudhary, B.; Sajan, M.K.; Kumar, S.
Rubble mound breakwater is a coastal structure, which is constructed to provide tranquil conditions in and around the port areas. Generally, the rubble mound structures are subjected to vigilant waves throughout the year. After the earthquakes of Kobe (1995), Kocaeli (1999), Tohoku (2011) etc. it is observed that the breakwaters can collapse due to failure of foundation and by seismic activity. Hence, in order to assess this problem, the current investigation deals with the study of rubble mound breakwaters and it is behavior against the seismic forces using numerical analysis. A finite element software PLAXIS is used for the numerical simulations. For study, a prototype has been selected and numerical model developed is a conventional rubble mound breakwater. In countermeasure model, the sheet piles in the foundation soil on extreme side of mound were considered. The numerical analyses have been done for constant seismic loading and soil properties. The parameters like vertical settlement and horizontal displacement were determined at different nodes. The vertical settlement was observed to be predominant in the crest region and it was reduced by 38% in countermeasure model. The displacement contours were significantly seen in core and armor units. The horizontal displacement of mound was seen by lateral movement of outer layers and it was 23% lesser for sheet pile reinforced model. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
Stability Analysis of Rubble Mound Breakwaters Under Tsunami Overflow
(Springer Science and Business Media Deutschland GmbH, 2024) Sajan, M.K.; Chaudhary, B.; Akarsh, P.K.; Kumar, S.
Rubble mound (RM) breakwaters are the most commonly constructed breakwaters across the globe. Even though the breakwaters are designed to withstand to dynamic wave loadings, a natural disaster such as tsunami could impart additional loadings beyond the designed limits and thereby reduce the stability of the structure. Unfortunately, several RM breakwaters were severely damaged or even collapsed under the impact of past tsunamis such as the 2004 Indian Ocean tsunami and 2011 Great East Japan tsunami. The failure of these breakwaters would lead to the inundation of tsunami waves to the coastal areas causing devastating damages to life and property. Therefore, it is relevant to make the RM breakwaters resilient against tsunami impacts, so that the breakwater can either completely prevent or at least reduce the impact height of tsunami waves. In order to design a RM breakwater resilient against tsunami, the failure mechanisms under tsunami overflow conditions have to be properly understood. The present study thus aims to numerically evaluate the stability of RM breakwaters under tsunami overflow conditions. The cross-section details of the North breakwater at the Ennore Port, Chennai, India have been modelled at full scale in the finite element software Plaxis. The model was then subjected to a tsunami overflow condition. The corresponding deformations and stability of the RM breakwater were estimated. It was observed that the stability of the breakwater was considerably reduced under tsunami overflow conditions. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
Stability of Reinforced Soil Quay Wall Subjected to Combined Action of Earthquake and Tsunami
(Springer Science and Business Media Deutschland GmbH, 2021) Sajan, M.K.; Chaudhary, B.
Reinforced soil quay walls are used as shore protection systems. Generally, horizontal layers of geogrids are provided as reinforcement in the backfill soil of the quay wall. These structures are internally stabilized by mobilized tensile strength of reinforcements. A quay wall can be subjected to tsunami load and earthquake load simultaneously. This condition occurs when an earthquake aftershock reaches the quay wall structure at the same time of a tsunami impact. Therefore, a combined analysis of quay walls subjected to earthquake and tsunami at the same time is necessary. In this study, horizontal slice method is used to evaluate the stability of the reinforced soil quay wall subjected to earthquake and tsunami. The failure surface is generated by optimizing the angle of failure plane of each slice, so that the mobilized tensile force on the reinforcement is maximum. Thus, the generated failure surface could justify the actual failure surface. It was observed that normalized force acting on the reinforcement is considerably increased under the combined effect of earthquake and tsunami. Stability of the wall is evaluated by varying several parameters, such as acceleration coefficient of earthquake motion, internal friction angle of soil, inclination and height of the quay wall, height of seawater level and height of tsunami waves, to find out the effect of these parameters on normalized reinforcement strength. Â© 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.