In recent decades, many cities have become densely populated due to increased urbanization, and the transportation infrastructure system has been heavily used. The downtime of important parts of the infrastructure, such as tunnels and bridges, seriously affects the transportation system’s efficiency. For this reason, a safe and reliable infrastructure network is necessary for the economic growth and functionality of cities. At the same time, the infrastructure is ageing in many countries, and continuous inspection and maintenance are necessary. Nowadays, detailed inspections of large infrastructure are almost exclusively performed by inspectors on site, which is both time-consuming and subject to human errors. However, the recent technological advancements in computer vision, artificial intelligence (AI), and robotics have opened up the possibilities of automated inspections. Today, semiautomatic systems such as drones and other mobile mapping systems are available to collect data and reconstruct 3D digital models of infrastructure. This significantly decreases the downtime of the infrastructure, but both damage detection and assessments of the structural condition are still manually performed, with a high impact on the efficiency and accuracy of the procedure. Ongoing research has shown that deep-learning methods, especially convolutional neural networks (CNNs) combined with other image processing techniques, can automatically detect cracks on concrete surfaces and measure their metrics (e.g., length and width). However, these techniques are still under investigation. Additionally, to use these data for automatically assessing the structure, a clear link between the metrics of the cracks and the structural condition must be established. This paper presents a review of the damage of tunnel concrete lining that is detectable with optical instruments. Thereafter, state-of-the-art autonomous tunnel inspection methods are presented with a focus on innovative mobile mapping systems for optimizing data collection. Finally, the paper presents an in-depth review of how the risk associated with cracks is assessed today in concrete tunnel lining.
Several concrete dams show cracking, and their condition and remaining service life must be determined. Assessment and service life prediction of cracked dams should include an investigation to determine the cause and consequences of cracks. Cracks can be caused by different mechanisms, which also may act together. Some mechanisms act during a short period of time, e.g. in the beginning after construction, while other mechanisms may influence the dam during the whole service-life. Therefore, it is important to combine observations, measurements, laboratory tests and theoretical analyses investigating the causes of the cracks, their future development and the influence they may have on the performance of the dam. Lessons learned and knowledge concerning crack propagation in concrete and rock, general material engineering, durability concerns caused by cracks, structural analysis issues connected to cracks, field measurements and design of remedial measures has been compiled in a Swedish guideline. The guideline highlights issues that should be looked for in inspections and contains a methodology to determine the residual strength and serviceability of cracked concrete dams and how to review dam safety criteria's. This in turn will provide the dam owner with a better means to manage and prioritize rehabilitation and maintenance work RÉSUMÉ: De nombreux barrages en béton sont atteints de fissuration nécessitant une évaluation de leur état ainsi que de leur durée de vie. Ce travail doit inclure une étude permettant d'identifier les types ainsi que les causes de fissuration affectant l'ouvrage. Les fissures peuvent être causées par plusieurs mécanismes, pouvant dans certains cas interagir entre eux. Certains mécanismes apparaissent durant un période de temps limitée, comme au début de la phase de construction, alors que d'autres peuvent être actifs durant l'ensemble de la durée de vie de l'ouvrage. Il est en conséquence important d'associer observations, auscultation et analyses théoriques lors de l'évaluation des types de fissures et de leurs causes, de leur évolution dans le temps ainsi que des éventuelles conséquences que celles-ci peuvent exercer sur la performance future du barrage. Les connaissances ainsi que le retour d'expérience concernant la propagation de fissures dans le béton et les roches, la mécanique des matériaux, les problèmes de durabilité induits par la fissuration, le calcul scientifique, les méthodes d'auscultation et la définition de solutions de confortement ont été consignés dans un guide méthodologique suédois. Ce guide met en exergue les types de pathologies qui doivent être recherchées lors des inspections et présente également une méthodologie pour estimer la résistance et la durée de vie résiduelles de barrages présentant des fissures. Une méthode de présentation des critères de sécurité est également incluse. Ce guide permet à l'exploitant d'optimiser la gestion de l'ouvrage, notamment concernant la hiérarchisation des travaux de maintenance et de confortement.
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