Browsing by Author "Sarkar, R."

Now showing 1 - 8 of 8

A Three-Dimensional Investigation on the Efficacy of Different Configuration Settings of Micropiles in Enhancement of Seismic Slope Stability
(Springer Science and Business Media Deutschland GmbH, 2025) Kumar, S.; Anand, A.; Sarkar, R.; Nainegali, L.
Micropiles have emerged as an effective measure to strengthen the stability of slopes. However, its efficacy in improving the stability of slopes under seismic loading conditions has not been fully established. This paper intends to investigate the performance of micropiles with different configurations to improve the stability of a slope under static and seismic loading conditions. A clayey slope of height 10 m underlain by a sandy soil layer was adopted for the investigation. Three-dimensional nonlinear finite element models were developed for the slope-micropile systems. Five different configurations of micropiles, considering a single micropile on two faces of the slope, were adopted for investigation. Further, a study was carried out with eight different combinations of these configurations of micropiles for strengthening the slope. Initially, static analyses were carried out for the different configurations of micropiles. Next, for seismic loading, pseudo-static analyses were carried out for all the configurations. The efficacy of different configurations of micropiles was compared through the factor of safety obtained. Analyses were also carried out considering the water table, and the efficacy of micropiles was established in the same way. Finally, nonlinear dynamic analyses were carried out for different configurations of micropiles with real earthquake time history, and the improvement in seismic performance of the micropile-strengthened slope was reported. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.
Characterization of Thermal Stability and High-Temperature Tribological Behavior of Electroless Ni-B Coating
(2018) Pal, S.; Sarkar, R.; Jayaram, V.
A preliminary study has been conducted using sequences of isothermal heat treatments and unidirectional high-temperature wear test following ball-on-flat geometry against an alumina counterface, to assess thermal stability and high-temperature tribological properties of the crystalline electroless Ni-B coating, a potential candidate for high-temperature solid lubricant coating. Isothermal heat treatment of 450 C/15 h causes a significant amount of B diffusion into the Fe substrate without altering the coating s through-thickness hardness and nanostructure. At room temperature, a very low wear rate is observed, which increases up to two orders of magnitude above a testing temperature of 100 C. Room-temperature wear behavior is mostly governed by oxidative wear, where friction-induced heating produces a thick oxide scale on the wear track, which subsequently decreases the wear rate by preventing direct contact between the coating and counterface. In the case of wear tests above 100 C, removal of the same oxide layer occurs through local plastic deformation, essentially plastic ratcheting at the contacting region by flow softening of the contacting surface layer due to a local rise in temperature. Worn track morphology shows similarity with the severe wear seen in steel steel contacts. Experimental observations have been explained and validated using the concept of contact point flash temperature. A quantitative assessment of contact point flash temperature has been carried out adopting the methodology, proposed by Ashby et al. The effects of applied normal load, test geometry, choice of counterface material, and testing temperatures on the transition of wear mechanism are critically discussed. 2018, The Minerals, Metals & Materials Society and ASM International.
Characterization of Thermal Stability and High-Temperature Tribological Behavior of Electroless Ni-B Coating
(Springer Boston, 2018) Pal, S.; Sarkar, R.; Jayaram, V.
A preliminary study has been conducted using sequences of isothermal heat treatments and unidirectional high-temperature wear test following ball-on-flat geometry against an alumina counterface, to assess thermal stability and high-temperature tribological properties of the crystalline electroless Ni-B coating, a potential candidate for high-temperature solid lubricant coating. Isothermal heat treatment of 450 °C/15 h causes a significant amount of B diffusion into the Fe substrate without altering the coating’s through-thickness hardness and nanostructure. At room temperature, a very low wear rate is observed, which increases up to two orders of magnitude above a testing temperature of 100 °C. Room-temperature wear behavior is mostly governed by oxidative wear, where friction-induced heating produces a thick oxide scale on the wear track, which subsequently decreases the wear rate by preventing direct contact between the coating and counterface. In the case of wear tests above 100 °C, removal of the same oxide layer occurs through local plastic deformation, essentially plastic ratcheting at the contacting region by flow softening of the contacting surface layer due to a local rise in temperature. Worn track morphology shows similarity with the severe wear seen in steel–steel contacts. Experimental observations have been explained and validated using the concept of contact point flash temperature. A quantitative assessment of contact point flash temperature has been carried out adopting the methodology, proposed by Ashby et al. The effects of applied normal load, test geometry, choice of counterface material, and testing temperatures on the transition of wear mechanism are critically discussed. © 2018, The Minerals, Metals & Materials Society and ASM International.
Deterministic seismic hazard analysis for Phuentsholing region of southern Bhutan considering local site effects
(Springer Science and Business Media Deutschland GmbH, 2022) Sengupta, S.; Sarkar, R.; Kolathayar, S.; Drukpa, D.
Phuentsholing is a thriving border town in the southwestern part of Bhutan. With the development of infrastructure over time, the safety of the residence and lifeline buildings becomes a matter of concern. Bhutan lies in the Himalayan mountain ranges, which is considered one of the most active regions for seismic events. The Indian seismic code, IS 1893-2016, has assigned Zone IV for the region, which signifies the large risk that exists for all the structures. Therefore, conducting a seismic hazard assessment for the site becomes extremely necessary before any major construction. The present study focusses to perform the deterministic seismic hazard analysis (DSHA) around certain points of interest in the town of Phuentsholing, in Bhutan. Furthermore, site-specific response spectra for Pipaldhara-1, Pipaldhara-2, Kabreytar-1, Kabreytar-2 and Phuentsholing town were plotted from the results of the DSHA. It is estimated that a peak ground acceleration ranging from 0.11 to 0.14 g can be anticipated at the level of bedrock in the study region. Response spectra were plotted for the ground level using appropriate soil-amplification coefficients, derived from the analyses in the DEEPSOIL program. © 2022, Springer Nature Switzerland AG.
Effects of Uncertain Parameters on the Performance of Single Batter Piles Embedded in Laterally Spreading Ground
(Springer Science and Business Media Deutschland GmbH, 2025) Kumar, S.; Sarkar, R.; Nainegali, L.
The seismic performance of batter piles is still the least investigated in comparison to vertical piles, though batter piles may offer a prospective solution in case of laterally spreading ground. In this study, a comprehensive investigation is presented for the performance of a single batter pile (both positive and negative) in comparison to the vertical pile considering spreading ground movement. Beam on Nonlinear Winkler foundation (BNWF) approach is considered for modelling the soil-pile systems, and models are developed in the open-source programmer OpenSees. The study considers a three-layer soil profile with a liquefiable layer sandwiched between a non-liquefiable surface crust and the base layer. The following five critical parameters were considered to be uncertain in considering the effects of uncertainty on performance: batter angles, thickness of liquefiable layer, ground slope, relative density of liquefiable layer, and slenderness ratio. An exhaustive probabilistic investigation through response surface methodology was carried out to evaluate the effects of different uncertain parameters on the performance of the pile foundations. The study indicated that the performance of negative batter piles is superior to the vertical and positive batter piles. Further, prediction equations for maximum pile head displacement and bending moment have been developed for piles with different batter angles. The study is supposed to be helpful for practising design engineers to adopt batter piles in seismic conditions. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Effects of uncertainty of critical parameters on performance of piles with different batter angles in laterally spreading ground: development of prediction models
(Taylor and Francis Ltd., 2025) Kumar, S.; Sarkar, R.; Nainegali, L.
Failures of vertical piles are common under earthquake loading, especially in laterally spreading ground conditions. Performance is supposed to be better for batter piles due to their higher lateral load-carrying capacity. However, the framework of the design of batter piles is still not available for laterally spreading ground for different degrees of batter, considering the associated uncertainties. This paper investigates the effects of uncertainties on the performance of batter piles in laterally spreading ground. The beam on nonlinear Winkler foundation (BNWF) approach was considered for modelling the soil-pile systems. Nonlinear analyses were carried out for cosine-shaped ground deformation profiles. Effects of the uncertainty of critical parameters such as ground slope, relative density and thickness of the liquefying layer, batter angle, and slenderness ratio of the piles were investigated through a factorial design approach. A central composite design approach was adopted to investigate the curvature effects of the uncertain parameters. It was observed that the negative batter piles perform significantly better than their counterparts of vertical and positive batter piles. This study proposes prediction models for maximum bending moment and pile head displacement for piles with different batter angles, considering a three-layered laterally spreading ground. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Near-surface seismic refraction tomography and MASW for site characterization in Phuentsholing, Bhutan Himalaya
(Springer Nature, 2021) Sarkar, R.; Kolathayar, S.; Drukpa, D.; Choki, K.; Rai, S.; Tshering, S.T.; Yuden, K.
It is essential to understand the soil characteristics of the subsurface layers for any engineering construction. In difficult terrains like hilly areas, conventional methods of investigation are expensive and difficult to conduct. It calls for nondestructive testing methods to get reliable estimates of subsurface properties. In the present study, seismic refraction tomography (SRT) technique and multichannel analysis of surface waves (MASW) methods were carried out along five selected profiles in Phuentsholing region of Bhutan Himalaya. The profile length ranges from 37 to 81.5 m, and depth of imaging down to 10 m. While the SRT data imaged the P-wave velocity (Vp) structures, the MASW imaged the shear wave velocity (Vs) structures. The P-wave images provide a fair knowledge of geological layers, while the MASW images provide S-wave velocity structures (Vs). These results are useful to estimate soil parameters, like the density, Poisson’s ratio, Young’s modulus, shear modulus, N-value and the ultimate bearing capacity. The seismic images reveal the presence of sand, sandy clay, gravels and shale layers below the selected sites. Bhutan Himalayas being seismically vulnerable, the obtained results in terms of shear wave velocity were accustomed to categorize the sites as per NEHRP site classes, and a ground response analysis was performed to determine the reliable amplification factors. From the study, it is suggested that the engineering construction is feasible at all the sites except in one site, where an indication of saturated soil is observed which is vulnerable for liquefaction, and ground needs to be improved before construction at that site. © 2021, The Author(s).
Static and dynamic performance of single batter piles embedded in slope
(Springer, 2024) Kumar, S.; Najar, D.S.; Sarkar, R.; Nainegali, L.
The performance of pile foundations embedded in the sloping ground has received the least attention. Further, considering piles with batter angles, the investigation is even more limited. In this study, 3D non-linear finite element analyses were conducted to investigate the lateral load-carrying behaviour of vertical and batter (with angles -5°, +5°, -10° and +10°) pile foundations embedded in slope. Firstly, static analyses were performed, and the behaviour of the batter piles was compared with the vertical piles, considering the piles are embedded in a 30° slope of height 5.0 m with medium-stiff clay. It was observed that the capacity of piles reduces when they are installed on sloping ground. Negative batter piles were found to be more effective than the vertical piles in the slope. Next, the performances of the piles were investigated for dynamic lateral loading. It was inferred that the negative batter piles provide better resistance under lateral loading than the vertical and positive batter piles in sloping ground under dynamic loading as well. © Indian Academy of Sciences 2024.