Long-Term Behaviour of Railway Transitions under Dynamic Loading. Application to Soft Soil Sites

Research output: ThesisDoctoral Thesis

Abstract

Transition 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 soil-ballast-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.
Original languageUnknown
QualificationDoctor of Philosophy
Awarding Institution
  • Universidade NOVA de Lisboa
Award date1 Jan 2013
Publication statusPublished - 1 Jan 2013

Keywords

    Cite this

    @phdthesis{3c7da6dca40146699af64af466cafb90,
    title = "Long-Term Behaviour of Railway Transitions under Dynamic Loading. Application to Soft Soil Sites",
    abstract = "Transition 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 soil-ballast-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.",
    keywords = "Railways, settlements, Transition Zones, Non-linear, Ballast, Dynamic, Culvert, Long-term",
    author = "Ferreira, {Jos{\'e} Nuno Varandas da Silva}",
    year = "2013",
    month = "1",
    day = "1",
    language = "Unknown",
    school = "Universidade NOVA de Lisboa",

    }

    TY - THES

    T1 - Long-Term Behaviour of Railway Transitions under Dynamic Loading. Application to Soft Soil Sites

    A2 - Ferreira, José Nuno Varandas da Silva

    PY - 2013/1/1

    Y1 - 2013/1/1

    N2 - Transition 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 soil-ballast-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.

    AB - Transition 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 soil-ballast-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.

    KW - Railways

    KW - settlements

    KW - Transition Zones

    KW - Non-linear

    KW - Ballast

    KW - Dynamic

    KW - Culvert

    KW - Long-term

    M3 - Doctoral Thesis

    ER -