Long-term behaviour of railway transitions under dynamic loading application to soft soil sites

Dissertação para obtenção do Grau de Doutor em Engenharia CivilTransition zones in railway tracks are built to mitigate damage and wear to tracks and trains, and discomfort to passengers, caused by structural and foundation discontinuities, such as those introduced by bridge approaches or culverts. However, additional strains are still generated that cause changes of track geometry, that lead to more frequent maintenance operations and sometimes speed restrictions, that raise costs, and need to be minimized. This thesis addresses those questions and describes research undertaken to model the dynamic response of the railway tracks, taking into account the behaviour of ballast at the aforementioned railway transition zones, where the long-term settlements are amplified by dynamical loading on the ballast due to the discontinuities. Novel numerical models for the simulation of the dynamic response of the system soilballast-track-vehicle and accounting for those phenomena are presented. The models are validated by field measurements performed at a passage over a culvert, located in a soft soil site. The models include the unloaded level of the track, the possibility of voids under the sleepers, and the non-linear constitutive behaviour of the ballast, as well as representation, albeit simplified, of the vehicles. The forces transmitted to the ballast at transition areas vary considerably, both in time and space: loading of ballast reaches higher values than in regular tracks, and the additional vibrations cause larger differences between loads transmitted to consecutive sleepers. This causes higher densification of ballast at transition zones. Transition zones solely composed of approach slabs are not effective in soft soil sites. The soil and ballast at approach regions settle more than the segment on top of the much stiffer structure, leading to the appearance of hanging sleepers. The subsequent combined effect of lower load on part of the ballast and motion of the approach slabs results on increased settlement of the ballast and sub-ballast, increasing the voids under the sleepers, and causing more severe actions on the track. Possible improvement measures were modeled and tested computationally at the later stages of the thesis. The numerical simulations showed that the use of soft railpads on the stiff side of the transition is beneficial, provided the problem is mostly caused by stiffness variation of the track support. Slab track solution was also tested and showed advantages over the ballasted track by showing much smaller differential rail displacements,for identical change of the track support stiffness.Fundação para a Ciência e Tecnologia - Ph.D grant (SFRH/BD/25297/2005), through the project “Interacção solo-via férrea para comboios de alta velocidade” (POCI/ECM/61114/2004), and through the project SMARTRACK (PTDC/EME-PME/101419/2008

Dynamic Behavior in Transition Zones and Long-Term Railway Track Performance

This work was conducted in the framework of the TC202 national committee of the Portuguese Geotechnical Society (SPG) Transportation Geotechnics, in association with the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGETC202). Publisher Copyright: © Copyright © 2021 Paixão, Varandas and Fortunato.Transition zones between embankments and bridges or tunnels are examples of critical assets of the railway infrastructure. These locations often exhibit higher degradations rates, mostly due to the development of differential settlements, which amplify the dynamic train-track interaction, thus further accelerating the development of settlements and deteriorating track components and vehicles. Despite the technical and scientific interest in predicting the long-term behavior of transition zones, few studies have been able to develop a robust approach that could accurately simulate this complex structural response. To address this topic, this work presents a three-dimensional finite element (3D FEM) approach to simulate the long-term behavior of railway tracks at transition zones. The approach considers both plastic deformation of the ballast layer using a high-cycle strain accumulation model and the non-linearity of the dynamic vehicle-track interaction that results from the evolution of the deformed states of the track itself. The results shed some light into the behavior of transition zones and evidence the complex long-term response of this structures and its interdependency with the transient response of the train-track interaction. Aspects that are critical when assessing the performance of these systems are analyzed in detail, which might be of relevance for researchers and practitioners in the design, construction, and maintenance processes.publishersversionpublishe

J. R. R. Tolkien: construtor de mundos. Personagens, lugares e adaptações

J. R. R. Tolkien (1892-1973) foi, juntamente com C. S. Lewis (1898-1963), o criador da fantasia moderna. A centralidade da sua obra no espaço genológico do fantástico, a sua influência e relevância no mesmo domínio e a sua preponderância nas estratégias retóricas e narrativas mais imediatamente reconhecíveis pelos leitores do género são hoje ampla e consensualmente confirmadas pelos críticos. Pretendendo dar continuidade à reflexão crítica sobre os textos de Tolkien, que não se reduzem a O Senhor dos Anéis, surge agora este livro, que vem dar conta da pluralidade de discussões em torno dos vários temas e motivos presentes no legendarium tolkieniano. Este volume revisita personagens e lugares da Terra-Média, que, obviamente, não se esgotam nas suas dezenas de páginas. Entendemos esta publicação como uma primeira abordagem em português a determinadas figuras e espaços, que permitem uma reflexão sobre questões dos foros estético, filosófico, cultural e político, que Tolkien explorou por intermédio das suas criações literárias.Esta actividade é financiada por Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia, I.P., no âmbito do projecto UIDB/00019/2020, projectos UIDB/00114/2020 e UIDP/00114/2020 e projecto UIDB/04311/2020.info:eu-repo/semantics/publishedVersio

Towards network assessment of permanent railway track deformation

The permanent railway track deformation caused by regular train traffic is important for infrastructure managers and railway contractors, as it determines the railway track quality. Although several successful approaches have been made to address the topic of the permanent railway track deformation, these have only been applied at specific locations, and have not yet been successfully applied at a network level. This paper presents a methodology that can be applied at the network level, by making use of a stochastic subsoil model to characterise the subsoil uncertainty and variability along the railway line, and by combining it with a dynamic train-track model and a cumulative cyclic deformation model. This methodology is illustrated by analysing a railway track section of 9 km in the Netherlands. The effects of the train service, such as train speed and axle loads, on the permanent deformation of the track are quantified. The proposed methodology has been partially validated against results of the dynamic stiffness obtained during the passage of a measurement train. The results illustrate the added value of this methodology for infrastructure managers and railway contractors as it allows for the quantification, at network level, of the consequences of train service changes for the future state of the railway network

Characterisation of microbial attack on archaeological bone

As part of an EU funded project to investigate the factors influencing bone preservation in the archaeological record, more than 250 bones from 41 archaeological sites in five countries spanning four climatic regions were studied for diagenetic alteration. Sites were selected to cover a range of environmental conditions and archaeological contexts. Microscopic and physical (mercury intrusion porosimetry) analyses of these bones revealed that the majority (68%) had suffered microbial attack. Furthermore, significant differences were found between animal and human bone in both the state of preservation and the type of microbial attack present. These differences in preservation might result from differences in early taphonomy of the bones. © 2003 Elsevier Science Ltd. All rights reserved