Browsing by Author "Akarsh, P.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.
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 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 Ltd
Graphene oxide as nano-material in developing sustainable concrete – A brief review
(Elsevier Ltd, 2022) Akarsh, P.K.; Shrinidhi, D.; Marathe, S.; Bhat, A.K.
Nanomaterials are the most happening research field in material science. Hydration of cement grains and nano pore filling actions in cement matrix occurring at microscopic levels is greatly benefited by the superior surface area, aspect ratios, size, and greater mechanical characteristics of nano sized materials. Many researchers have used nanoparticles as cementitious materials in concrete. Graphene oxide (GO) is one among many nanomaterials with one of its sides in nano sized measurement and the other two sides are on a bigger scale. One of the advantages of GO over other nanoparticles is that the oxygen functionalities and can be easily dispersed under an aqueous medium. This paper sheds light on brief information about nanotechnology, nanomaterials application in concrete, characterization of GO, and various key researches in the usage of GO in producing concrete of desirable properties. Mainly, GO increases the performance of the resulting cement concrete by creating a strong covalent bond with hydration results like C-S-H. Using polycarboxylate ether and silica fumes the dispersion properties can be effectively improved without forming GO agglomerates. High-Performance cement concrete mixes can be produced by making GO form great bonds with other admixtures. © 2021
Incorporation of Sugarcane Bagasse Ash to investigate the mechanical behavior of Stone Mastic Asphalt
(Elsevier Ltd, 2022) Akarsh, P.K.; Ganesh, G.O.; Marathe, S.; Rai, R.
Stone Mastic Asphalt (SMA) is one kind of new generation gap graded hot mix asphalt with higher content of asphalt with coarse aggregate proportions. The stone-on-stone interlock in SMA makes it superior rut resistant mix and favorable in adverse conditions. The usage of conventional fillers in SMA will lead to the creation of many environmental nuisances and entail additional cost during the production. The use of industrial by-products in the place of the conventional filler can be proven favorable to overcome enhanced production cost of SMA. In the present research work, one such largely produced industrial waste called, Sugarcane Bagasse Ash (SBA) is used as a filler in SMA by replacing conventional Ordinary Portland Cement (OPC) filler, and the engineering performances and cost effectiveness is examined. The SMA mixes were cast with 6.25% optimum binder content are varied with SBA of 2.5% (ACS1), 5.0% (ACS2), 7.5% (ACS3) and 10% (ACS4) by weight of the mix as filler and the results were compared with conventional SMA mix (ACS0). The results showed that, the inclusion of SBA demonstrated superior performances indicating the enhanced stiffness of mix (in terms of Marshall and flow characteristics). Moisture resistance of the SMA mix was improved up to 7.5% SBA replacement. Further, the drain-down test results revealed that, SBA can be effectively used as stabilizing agent. The mix ACS 1 and ACS2 shown a minimum rut depth in reference with ACS0. The mix with 5% SBA resists more number of repetitive loads than all the mix tested. © 2022 Elsevier Ltd
Investigations on Stone Matrix Asphalt Mixes by Utilizing Slag and Cellulose Fiber
(Springer Science and Business Media Deutschland GmbH, 2023) Marathe, S.; Akarsh, P.K.; Bhat, A.K.; Mahesh Kumar, M.
Stone Matrix Asphalt (SMA) has become one of the most admired Asphalt Pavement layers due to its superior deformation-resistant capacity through a coarse stone skeleton providing more stone-on-stone contact than the other Dense Graded Asphalt (DGA) mixes. SMA has proved superior on heavily trafficked roads and in industrial applications. SMA has distinct advantages as a Surfacing, due to its potential for high resistance to fatigue and rutting. In the present study, the SMA specimens were prepared by incorporating Ground Granulated Blast Furnace Slag (GGBS) as filler and the Marshall properties were studied. Further, for the optimum Marshall mix (containing 2.5% of GGBS), the cellulose fiber was added. The results have shown that the maximum strength was obtained for the SMA mix containing 7% of bitumen content with 2.5% of GGBFS and 0.3% of cellulose fiber. Â© 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Mitigation Technique Against Earthquake-Induced Damages by Using Scrap Tire Chips in Shallow Foundations
(Springer Science and Business Media Deutschland GmbH, 2025) Akarsh, P.K.; Shivasharan, S.; Ujwal, B.; Udaykiran, L.V.; Chaudhary, B.
In recent years, earthquakes like the 2016 Kumamoto earthquake, the 2018 Sulawesi earthquake, and the 2023 Turkey-Syria earthquake have seriously damaged buildings and their foundations. This paper investigates the effectiveness of utilizing scrap tire chips beneath shallow foundations to mitigate earthquake-induced building damage. Shake table tests were conducted on physical models, including conventional foundations and foundations augmented with scrap tire layers. The objective was to assess the seismic performance and compare their behavior under sinusoidal input motion. The results of shake table tests demonstrated that incorporating a scrap tire chip layer beneath foundations significantly improves their ability to withstand seismic forces. The settlement of footing in the countermeasure model was reduced by 65.6% compared to the conventional one. The acceleration amplitude recorded at the top of the footing was decreased by 68.8% in the countermeasure model. Thus, the presence of the scrap tire layer effectively dissipates and redistributes seismic energy, thereby reducing the transmission of damaging forces to the superstructure. The enhanced damping characteristics and increased flexibility offered by the scrap tire layer contribute to improved seismic performance. The findings of this study highlight the potential benefits of using scrap tire chips as a cost-effectiveÂ material for mitigating earthquake-induced damages on foundation structures. Using scrap tire chips not only offers a sustainable alternative for waste management but also provides an efficient approach to enhancing buildingsâ€™ seismic resilience. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 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 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.
Review of Literature on Design of Rubble Mound Breakwaters
(Springer Science and Business Media Deutschland GmbH, 2023) Akarsh, P.K.; Chaudhary, B.
Breakwaters are offshore structures constructed to protect the coastal and port structures from uncertain and extreme wave conditions. It creates tranquility in and around the harbor side for smooth transactions of ships. Depending upon the availability of rocks, depth of water, geotechnical nature of the sea bed, and its functional requirement, breakwaters are classified as rubble mound breakwaters, caisson type, and composite breakwaters. Rubble mound is a flexible, heterogeneous, trapezoidal structure consisting of quarried rocks in the core and artificial armor as a protection cover. Armor units at the outer layer absorb most of the energy and under-layers prevent transmission of the wave energy. The main advantage of the rubble mound is its failure is not immediate and can be repaired by adding the stones in the flushed-out part. More than 50% of breakwaters constructed around the world are of rubble mounds. Looking at its importance for coastal structures, this paper gives an overview of the basic aspects of rubble mound breakwaters, design considerations, and its failure conditions. The design of rubble mound breakwaters include hydraulic stability of it against wave actions, structural components design, and geotechnical considerations. The common modes of rubble mound failure are hydraulic damage, erosion of subsoil, slope failures, toe erosion, overtopping, liquefaction of subsoil, crest erosion, and leeside damage. The failure of rubble mound breakwater at Ergil fishery port, Turkey due to Kocaeli earthquake of 1999 has been explained to support this part. 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.
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
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.
Stabilized Lithomargic Soil Subgrades for Low Volume Road Design Using Industrial Wastes
(Springer, 2024) Marathe, S.; Bhat, A.K.; Ashmitha, N.M.; Akarsh, P.K.
Lithomargic soil is considered a major group of “residual soil” which is identified as a problematic soil in the coastline region of Karnataka state of India. Previous studies reveal that the soil will cause several serious pavement deterioration problems when used as a pavement material. The present study focuses on the stabilization of this problematic shedi soil to make it suitable as a pavement subgrade material using fly ash (FA) and copper slag (CS) additives as stabilizers. In this investigation, various geotechnical properties were investigated to study the improvements in the mechanical soil properties with different percentages of FA and CS additions. For this investigation, relevant Indian standard (IS) codal guidelines were used. Initially, the effect of CS is studied by adding the various trial dosages of the CS from 0 to 50% (by weight) to the soil. The unconfined compressive strength (UCS) test revealed that the soil sample with 25% of CS has shown satisfactory results. Further, by maintaining the 25% CS dosage as constant, the FA dosage was introduced at an increment interval of 2% (by weight). The IS light compaction and UCS results revealed that a 6% dosage of FA had led to maximum strength gain. The improved mechanical performance includes an improvement in standard maximum proctor density from 15.22 to 18.16 kN/m3, soaked CBR value from 2.40 to 10.51%, and UCS value from 93 to 312 kPa. Further, the developments in the UCS and california bearing ratio (CBR) were studied by subjecting the virgin and modified soil to sustained desiccator curing at different intervals up to 56 days, the corresponding results indicated a strength gain of about 22% for the modified lithomargic soil. The durability tests were performed by subjecting the UCS specimens to alternate wetting–drying conditions and alternate freezing–thawing cycles. The test results were compared with that of the un-modified shedi soil. The test results were satisfactory for the application as the pavement subgrade material. The pavement design for the low-volume roads has been carried out using IRC: SP-72 guidelines and the pavement analysis is carried out using KENPAVE software. The results indicate that the use of 25% of CS along with 6% of FA in lithomargic soil could lead to a reduction of 46.15% of design pavement thickness and a reduced maximum deflection value upon stabilization. © The Author(s), under exclusive licence to Chinese Society of Pavement Engineering 2023.