| 1. |
- Alhede, Andreas, 1996, et al.
(författare)
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A two-stage study of steel corrosion and internal cracking revealed by multimodal tomography
- 2023
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Ingår i: Construction and Building Materials. - 0950-0618. ; 394
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Tidskriftsartikel (refereegranskat)abstract
- Modeling of corrosion-induced cracking is limited by lacking knowledge on the behavior of corrosion products. In this work, the corrosion and cracking processes were experimentally investigated in 3D at two different stages. The processes were measured at micro-structural scale, applying nondestructive neutron and X-ray computed tomography in two scans at different stages in the corrosion process. A method to evaluate the average volumetric strain of the compressed corrosion layer was proposed and displacements in the concrete matrix were measured. Strain localization revealed cracks not directly visible in the images. Multimodal tomography demonstrated to be an effective method for investigating steel corrosion in reinforced concrete.
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| 2. |
- Alhede, Andreas, 1996, et al.
(författare)
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Monitoring corrosion-induced concrete cracking adjacent to the steel-concrete interface
- 2023
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Ingår i: Materials and Structures/Materiaux et Constructions. - 1359-5997. ; 56:9
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Tidskriftsartikel (refereegranskat)abstract
- Substantial research effort has been devoted on linking corrosion-induced cracking of concrete with the internal corrosion damage level. Still, numerical models of the corrosion and cracking process require internal parameters, that cannot be directly evaluated from experimental data. Therefore, this study provides a novel experimental method for monitoring the effects of steel corrosion adjacent to the steel-concrete interface. This non-destructive method is suited for small-scale laboratory-made specimen, and was designed to provide missing information required for subsequent calibration of numerical models. Hollow steel bars were cast into concrete and subjected to accelerated corrosion using the impressed current technique. The deformations of the hollow steel bars were measured using distributed strain sensing in an optical fibre, attached to the inner surface of the hollow steel bars. After the corrosion period, X-ray Computed Tomography scans were performed to evaluate concrete cracking and corrosion level. The results reveal a non-uniform distribution of strain around the perimeter of the steel, indicating a non-uniform radial stress distribution. The non-uniformity correlated very well with the position of the corrosion-induced cracks; with extension hoop strains in the steel at the location of these cracks and contraction hoop strains in between. Further, the corrosion level varied around the perimeter, with higher values near cracks. The combination of non-destructive monitoring techniques used in this study on small-scale laboratory-made specimens show great potential to reveal new insights on how the corrosion pattern, corrosion-induced cracking of the concrete cover and stress (indirectly measured through the strain in the steel) interact throughout the corrosion process.
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| 3. |
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| 4. |
- Amavasai, Amardeep, 1988, et al.
(författare)
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Data assimilation for Bayesian updating of predicted embankment response using monitoring data
- 2024
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Ingår i: Computers and Geotechnics. - 0266-352X .- 1873-7633. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Data Assimilation (DA) algorithms has been successfully employed in geotechnical problems to jointly estimate the state of the system and model parameters, however, the impact of the field monitoring setup on the performance of DA is often overlooked. In this paper, the impact of the field monitoring setup on the performance of DA is studied. The Ensemble Kalman Filter is used as the DA algorithm as part of a synthetic experiment which includes a fully coupled hydromechanical numerical model of an embankment constructed on soft ground. The results of the assimilated parameters show different rate of convergence toward their synthetic true value which corroborates well with the results of the global sensitivity analysis performed in this study. In order to investigate the difference in influence between the quantity and type of measurement, different monitoring strategies were chosen in this study. The results indicate that the effective friction angle and Poisson's ratio are better estimated when the horizontal displacement is included along with the vertical displacement in the observation space of the DA procedure. Finally, the strong correlation between observation type and parameter convergence is independent of the type of initial prior knowledge, but strongly depends on the measurement location.
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| 5. |
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| 6. |
- Amavasai, Amardeep, 1988, et al.
(författare)
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On the feasibility of data assimilation for uncertainty modelling in geotechnics.
- 2023
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Ingår i: Proceedings of the 10th European Conference on Numerical Methods in Geotechnical Engineering; edited by Lidija Zdravkovic, Stavroula Kontoe, Aikaterini Tsiampousi and David Taborda.
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Konferensbidrag (refereegranskat)abstract
- Advanced constitutive models are usually employed in geotechnical applications to achieve higher fidelity solutions consequently demanding more model parameters. However, due to limited data availability, characterisation becomes difficult leading to increased uncertainties in the prediction which is quite common in geotechnical problems. In view of this, simpler models are preferred but sometimes are not robust enough to capture a complex geotechnical system. In this paper, we examine the issue of system uncertainty and model selection to gain a qualitative insight regarding the question of whether a simple model can capture a complex system when augmented with a data assimilation procedure, namely Ensemble Kalman Filter, while maintaining model fidelity and robustness. Results indicate that data assimilation can help capture the behaviour of the system even if the model complexity does not match that of the in-situ geotechnical system considered. The calibrated parameters can still capture the behaviour (be it simple or complex) beyond the assimilation window, however, for system with time dependent behaviour, longer monitoring time is required to enable simple models to reasonably capture the creep settlements demonstrating that a simple model would not always be sufficiently robust for modelling alternate scenarios that substantially change the complex systems behaviour.
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| 7. |
- Amavasai, Amardeep, 1988, et al.
(författare)
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Particle Filter based on Jaya optimisation for Bayesian updating of nonlinear models
- 2024
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Ingår i: Applied Soft Computing Journal. - 1568-4946. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- Particle filter (PF) is a powerful and commonly used filtering technique based on Sequential Monte Carlo framework. The main challenge in using PF for nonlinear state and parameter estimation is the degeneracy of particles. Although resampling techniques can solve this to some extent, it would still result in particle impoverishment when a limited number of particles are used thereby affecting the accuracy. Hence, a hybrid metaheuristic optimisation algorithm that combines the PF with Jaya optimisation, (PF-JAYA) has been proposed and implemented for joint state and parameter estimation for geotechnical engineering problems. The performance of PF-JAYA has been compared against the traditional Particle Filter with Sampling Importance Resampling (PF-SIR) technique. The synthetic examples show that PF-JAYA outperforms PF-SIR in terms of accuracy, rate of convergence, parameter identification and particle diversity. Furthermore, the performance of PF-JAYA is independent of the choice of prior distribution and due to its superior convergence proves to be efficient when working with sparse monitoring information. The performance of PF-JAYA on Bayesian updating of state and parameters of an elastoplastic model for a synthetic embankment case has also been evaluated where, along with PF-SIR, the Ensemble Kalman Filter (EnKF) is also chosen for comparison. Finally a further evaluation using the Lorenz ‘63 model, shows the superior performance of PF-JAYA in terms of accuracy and precision over the classical Data Assimilation techniques.
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| 8. |
- Amavasai, Amardeep, 1988, et al.
(författare)
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Towards consistent numerical analyses of embankments on soft soils
- 2022
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Ingår i: European Journal of Environmental and Civil Engineering. - : Informa UK Limited. - 2116-7214 .- 1964-8189. ; 26:7, s. 2616 -2634
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Tidskriftsartikel (refereegranskat)abstract
- A consistent automated parameter derivation method for an advanced constitutive model, Creep-SCLAY1S, which considers anisotropy, structure and creep in soft soil is presented. The algorithms are implemented in a general purpose numerical framework and are robust for noisy data. The accuracy of the derived parameters are benchmarked against a well known test case: the Haarajoki test embankment. The results show that using the proposed methodology, a consistent parameter set is derived that enables accurate laboratory data and boundary value level simulations with limited to no major user intervention. The only remaining user input relates to the adjustment of the pre-consolidation pressure with 3 kPa. This difference between the laboratory and boundary value simulations is attributed mainly due to somewhat low quality of the samples.
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| 9. |
- Ando, Edward, et al.
(författare)
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A peek into the origin of creep in sand
- 2019
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Ingår i: Granular Matter. - : Springer Science and Business Media LLC. - 1434-7636 .- 1434-5021. ; 21:1
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of an experimental study of the particle scale mechanisms that underpin creep, on-going deformations under constant external load, in dry non-cemented sand under 1D oedometric compression loading at 2500kPa. Traditional observations on the boundary of the sample are complemented with simultaneous measurements of the 3D kinematics of both the entire grain assembly and details of grain-scale mechanisms using synchrotron based X-ray tomography at two different spatial resolutions. Both the continuum response and the local grain scale response are captured using two spatial resolutions, i.e.6.and 0.65m respectively. The results, for the first time, illustrate that small displacements measured at the boundary can be the result of rather pronounced fracturing at the individual grain scale.
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| 10. |
- Bergström, Anders, et al.
(författare)
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Field test of a floating thermal pile in sensitive clay
- 2021
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Ingår i: Geotechnique. - 0016-8505 .- 1751-7656. ; 71:4, s. 334-345
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Tidskriftsartikel (refereegranskat)abstract
- The response of floating pile foundations in deep deposits of soft clay is governed by the settlements within the clay deposit surrounding the piles. A long-duration thermal response test (TRT) has been performed to assess the impact of heating and cooling on the geotechnical performance of a vertically loaded slender tubular steel pile in a deep deposit of sensitive clay. The results from the instrumented test site indicate that negligible excess pore water pressures, up to 3 kPa during heating and down to -1·1 kPa during cooling, were generated in the soil adjacent to the pile for a 50 W/m heat flux. The heating rate was sufficiently low to facilitate the drainage of pore water. The influence radius for the excess pore water pressures, however, extended beyond the soil volume affected by temperature change. The absence of thermally triggered creep settlements could be explained by the overlap between the remoulded zone resulting from pile installation, the extent of the heating, and the low creep susceptibility of remoulded sensitive clay for moderate temperature changes. Furthermore, no difference in the ultimate bearing capacity was found between the thermal pile and the reference pile, which was only loaded with a serviceability load during the test series. The current test data, therefore, indicate that driven floating piles in a deep deposit of soft clay also function as heat exchanger piles with minimal detrimental effects, for similar operational conditions as used in the TRT. It should be noted, however, that other pile types that do not extensively remould the clay adjacent to the pile shaft may show more significant influence of the thermal changes.
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