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Cet article présente plusieurs modèles numériques pour létude des phénomènes vibratoires lors du passage dun train. Les modèles permettent destimer la propagation des ondes et les réceptances pour le sol et la voie. Le sol multicouche et le couplage voie-sol sont traités par une (double) intégration sur les nombres donde. Les raideurs dynamiques de la voie et du véhicule sont combinées et les forces dexcitation roue-rail dues aux irrégularités de la voie et des roues sont calculées. Ces forces dexcitation permettent de simuler les vibrations du sol lors du passage dun train. Les modèles sont validés par comparaison avec des mesures sur deux sites, en France et en Allemagne. Les vibrations calculées correspondent bien aux vibrations mesurées.
Ground borne environmental vibralions and the dynamic soil-slructure interaction are closely relaled lo the dynamic soil parameters at a site. There are a number of soil dynamic Methods to determine the soil parameters from field tesls. Some of these methods will he described and demonstrated for some sites. The material damping of the soil is evaluated from the attenuation of the wave amplitudes. The wave speed of the soil can he simply read from the time histories of a number of consecutive measuring points. The method can be improved by the correlation function between each two neighboured sensors. The completely different SASW method uses the phase of the cross power spectrum of two sensors and determines a dispersion curve. Regular phase spectra of a line of measuring points can also be used to get a dispersion curve. The multiple sensor MASW method is introduced as an alternative lo the SASW method. A high number of regularly spaced sensor can be used to establish a frequency-wavenumber transform of the wave field which could show also the Dispersion curves of higher modes. A method has been tested which also uses the cross power spectrum of all pairs of sensors to establish a characteristic function which includes Information about the wave velocilies al low frequencies and which can work wilh ambient noise excitation (SPAC). Experiments wilh different sensor placements and different deterministic and stochaslic excilations will be presented.
The soil-structure interaction of elastic plates with horizontally propagating waves through the soil is investigated by a combined finite-element boundary-element method (FEBEM). The frequency-dependent reduction of the soil amplitudes by the plate and the amplitude distribution along the plate are presented. The following parameters are varied, the length and the width of the plate, the stiffness and the mass of the plate or, as a combination of both, the height of the plate. The results show that a strong reduction can be achieved for higher frequencies, at some distance from the edge of the plate, and for stiff (high) plates.
The dynamics of slab tracks and floating slab tracks are analysed by multi-beam models for the track and by integration in wavenumber domain for the soil which is modeled as a layered half-space. The displacements of the rail, track plate and base plate as well as the forces or force densities on the rail pads, slab mat and soil surface have been calculated as a function of frequency and distance along the track. This article is focused on the frequency-dependent force transfer functions which are presented for a great variety of track and soil parameters. Moreover, the wave propagation perpendicular to the track and the ground vibration amplitudes of the near and far-field are shown in good correlation with the force transfer function. The floating slab track has a dominating plate-mat resonance and a strong high frequency reduction. A track-soil resonance can also be recognised for an un-isolated slab track in case of layered soils. Generally there is a strong damping of the track by the soil. The reduction effect of the slab mat is mainly due to the elimination of this strong damping. Great care must be taken when the effectiveness of the floating track is evaluated. A stiff soil seems to be advantageous, but stiffening of the soil has no effect on the high-frequency force transfer of the floating slab track. Moreover, it is shown that the floating slab track does not need a stiff base plate and therefore is well suited for surface lines. It is proved in general that the bending stiffness (of the rail, the track plate or the base plate) can not have an influence on the force transfer function of the track. The total force transfer from the rail to the soil is the best criterion to judge the effectiveness of a floating slab track in reducing ground vibration at some distance from the railway line. The total force transfer is easier to calculate than the double Fourier integrals of the ground vibration amplitudes, namely in the far field, and it has the best correlation with the reduction of the ground vibration. A good reduction of the total force and the far-field ground vibration of 0.04 at 100 Hz can be achieved by soft slab mats or a high track mass.
Different high-speed railway tracks have been analysed theoretically and experimentally, a ballasted track at a surface line, a slab track in a tunnel, and a ballasted track on a concrete bridge. Vehicle, track and ground vibration as well as their interaction are considered in a combined finite-element boundary-element (FEBEM) approach. The layered soil is calculated in frequency wavenumber domain and the solution for fixed or moving point or track loads follow as wavenumber integrals. The comparison of the dynamic compliances of the different tracks leads to an improved understanding of the different track elements. Certain maxima have been observed for certain train speeds and certain eigenmodes of the bridge. These maxima correlate with some maxima of the ground vibrations. The bridge and the ground vibrations are discussed with the axle-sequence of the train. The ground vibra tions strongly depend on the regular and random inhomogeneity of the soil. The regular lay ering of the soil yields a cut-on and resonance phenomenon whereas the random inhomogeneity yields a scattering of the axle impulses which proved to be important for high speed trains. All theoretical results are compared with measurements at a high-speed line.
There is a strong need for cost-effective mitigation measures for
turnouts. SBB has initiated a series of examinations using different methodologies to gain a deeper understanding of the excitation mechanisms at low frequencies, in addition to that obtained in the RIVAS project. To date it is not yet clear what constitutes a complete measurement data set that would enable understanding most of the vibration excitation mechanisms in turnouts. Increasing vibration at turnouts in comparison to normal track is observed for all measured frequencies.
The different methodologies are presented in the paper. Under-sleeper pads (USP) are a cost-effective method to reduce vibration at frequencies above 63 Hz (1/3 octave), but there is probably no improvement for frequencies below 63 Hz. A first test of new frog geometry did not show relevant improvements in Vibration emission in comparison to a reference frog geometry. Axle box acceleration measurements are an interesting method to identify defects in a turnout. A specialized measurement system of rail roughness could identify certain geometry Problem areas for some frogs. Noise increases also are observed at turnouts for frequencies ranging between 80 to 1000 Hz. The use of railway source models to calculate
contact forces for ballasted track and turnouts seems promising, in particular for understanding the influence of ground.
The present contribution evaluates four measuring series made by the Federal Institute of Material Research and Testing for the relations between train speed and ground vibration amplitudes. This experimental evaluation is supported by the simulation of the train passages at the different sites by using appropriate excitation mechanisms and forces as well as layered soil models which have been derived from impact measurements at each site.
This contribution presents experimental methods to detect track damage. At BAM (Federal Institute of Material Research and Testing), a measuring car with a measuring system of 72 channels, geophones, mountings, cables, harmonic and impulsive exciters is used for dynamic measurements of the track, the soil and buildings. An instrumented hammer allows force measurements and to evaluate transfer functions of the track, and the soil. Wave measurements are used to identify the soil characteristics. Train passages are measured at the track and for the train induced ground vibrations. In addition to these in situ options, tests of tracks or track elements can be performed in a large laboratory.
The ground vibrations, which are generated by trains on different tracks, have been calculated by finite-element boundary-element models. The ballasted track is modelled in detail by the finite element method. The infinite soil is modelled by the boundary element method as a homogeneous or layered half-space. The track-soil system is coupled to a simple rigid mass model of the vehicle so that the vehicle-track interaction is completely included. Transfer functions are calculated in frequency domain without and with vehicle-track interaction, the compliance of the track and the mobilities of the soil at different distances from the track. Finally, the ratios between the ground vibration amplitudes with and without mitigation measures are calculated to quantify the effectiveness of the mitigation measures.
Tracks with under-sleeper pads have been investigated in a wide parameter study for the RIVAS project. The main parameters that influence the reduction of ground vibration are the stiffness of the under-sleeper pad, the mass and the width of the sleeper. The softest sleeper pad yields the best reduction of the ground vibration. The influence of the sleeper mass is not so strong, as the characteristic frequency is ruled by the mass of the sleeper and the mass of the wheelset as well.
A finite-element boundary-element software for the dynamic interaction of flexible structures and the soil has been extended for pile foundation. The boundary element method for the soil uses the Green´s functions of the layered half-space which have been generalised for interior loads. Pile groups of 10 to 20 piles of different arrays are analysed and compared with single piles. Simplified models have been developed for a user-friendly, practice oriented prediction software for railway induced ground and building vibration.
