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ABSTRACT: The impact of vibrations due to underground trains on Beijing metro line 15 on sensitive equipment in the Institute of Microelectronics
of Tsinghua University was discussed to propose a viable solution to mitigate the vibrations. Using the state-of-the-art three-dimensional
coupled periodic finite element-boundary element (FE-BE) method, the dynamic track-tunnel-soil interaction model for metro
line 15 was used to predict vibrations in the free field at a train speed of 80 km/h. Three types of tracks (direct fixation
fasteners, floating slab track and floating ladder track) on the Beijing metro network were considered in the model. For each
track, the acceleration response in the free field was obtained. The numerical results show that the influence of vibrations
from underground trains on sensitive equipment depends on the track types. At frequencies above 10 Hz, the floating slab track
with a natural frequency of 7 Hz can be effective to attenuate the vibrations.
Key wordsvibration prediction-underground trains-coupled periodic FE-BE method-track types
Journal of Central South University of Technology 04/2012; 17(5):1109-1118. · 0.36 Impact Factor
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Soil Dynamics and Earthquake Engineering. 01/2012; 39:113-127.
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International Journal for Numerical Methods in Engineering. 01/2012; 90(7):819-837.
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ABSTRACT: The Detailed Vibration Assessment is an empirical procedure developed by the U.S. Federal Railroad Administration (FRA) for
the prediction of railway induced vibration and re-radiated noise. The vibration velocity level in the free-field is predicted
with a force density, characterizing the source, and a line transfer mobility, characterizing the transfer of vibration due
to a line load. The line transfer mobility is determined with in situ measurements of transfer functions. The force density
is obtained by subtracting the line transfer mobility from the vibration velocity level due to a train passage. It is assumed
that the resulting force density can be used to predict the vibration velocity level at other sites with similar train and
track characteristics. In this paper, the influence of the soil characteristics on the force density and the resulting vibration
velocity level predicted with the FRA procedure is investigated. Numerical simulations are used to compute the vibration velocity
level and the line transfer mobility at three sites with different soil characteristics. From these results, the force density
due to a train passage is determined for each site. Finally, the three force densities are used to investigate the influence
of the soil characteristics on the predicted vibration velocity level due to a train passage.
10/2011: pages 239-247;
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Proceedings of the 8th International Conference on Structural Dynamics EURODYN 2011; 07/2011
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Near Surface Geophysics. 01/2011; 9(6):515-527.
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Proceedings of the 5th International Conference on Earthquake Geotechnical Engineering; 01/2011
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Proceedings of the 4th European Conference on Computational Mechanics; 05/2010
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Geophysical Journal International 01/2010; 182(3):1493-1508. · 2.42 Impact Factor
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ABSTRACT: This paper presents a general 2.5D coupled finite element–boundary element methodology for the computation of the dynamic interaction between a layered soil and structures with a longitudinally invariant geometry, such as railway tracks, roads, tunnels, dams, and pipelines. The classical 2.5D finite element method is combined with a novel 2.5D boundary element method. A regularized 2.5D boundary integral equation is derived that avoids the evaluation of singular traction integrals. The 2.5D Green’s functions of a layered halfspace, computed with the direct stiffness method, are used in a boundary element method formulation. This avoids meshing of the free surface and the layer interfaces with boundary elements and effectively reduces the computational efforts and storage requirements. The proposed technique is applied to four examples: a road on the surface of a halfspace, a tunnel embedded in a layered halfspace, a dike on a halfspace and a vibration isolating screen in the soil.
Computer Methods in Applied Mechanics and Engineering 01/2010; · 2.65 Impact Factor
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10th US National Congress on Computational Mechanics; 07/2009
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ABSTRACT: Repeated small amplitude dynamic loading of the soil in the vicinity of buildings, as arising from traffic or construction activities, may cause differential foundation settlements and structural damage. In this paper, a numerical model for soils under repeated dynamic loading is formulated. It is assumed that the dynamic part of the loading is small with respect to the static part, reflecting the stress conditions in the soil underneath buildings. As the plastic deformation in the soil is only observed after a considerable amount of dynamic loading cycles, only the accumulation of the average plastic deformation is considered. The model accounts for the dependency of the deformation on the stress conditions and the dynamic loading amplitude. The accumulation model is implemented in a finite element framework, using a consistent tangent approach in combination with a backward Euler integration scheme. A triaxial test is considered in a first numerical example. The available analytical solution for this problem allows to validate the numerical implementation. Second, the differential settlement of a two-storey building founded on loose sandy soil under repeated vehicle passages is considered. The differential foundation settlement causes the stresses to increase at the bottom of the wall, which may result in damage. Copyright © 2009 John Wiley & Sons, Ltd.
International Journal for Numerical and Analytical Methods in Geomechanics 06/2009; 34(3):273 - 296. · 0.94 Impact Factor
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ABSTRACT: The ElastoDynamics Toolbox (EDT) version 2.1 offers an extensive set of MATLAB functions to model elastodynamic wave propagation in horizontally layered media. The toolbox is based on the direct stiffness method and the thin layer method. These methods provide stiffness matrices for a homogeneous layer and a homogeneous halfspace, which are formulated in the frequency-wavenumber domain. EDT 2.1 can be used to solve a variety of problems governed by wave propagation in the soil, such as (1) site amplification, (2) the computation of dispersive wave modes in layered soils, and (3) the calculation of the forced response of the soil due to harmonic and transient loading. The toolbox serves as an electronic learning environment for the simulation and processing of seismic wave propagation in layered media. It has also been used by various authors to model wave propagation in layered soils
Computers & Geosciences 01/2009; 35(8):1752-1754. · 1.43 Impact Factor
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ABSTRACT: This paper presents a new method for calculating vibration from underground railways buried in a multi-layered half-space.
The method assumes that the tunnel’s near-field displacements are controlled by the dynamics of the tunnel and the layer that
contains the tunnel, and not by layers further away. Therefore the displacements at the tunnel-soil interface can be calculated
using a model of a tunnel embedded in a full space. The Pipe-in-Pipe (PiP) model is used for this purpose, where the tunnel
wall and its surrounding ground are modelled as two concentric pipes using elastic continuum theory. The PiP model is computationally
efficient on account of uniformity along and around the tunnel. The far-field displacement is calculated by using another
computationally efficient model that calculates Green’s functions for a multi-layered half-space using the direct stiffness
method. The model is based on the exact solution of Navier’s equations for a horizontally layered half-space in the frequency-wavenumber
domain.
The results and computation time of the new method are compared with those of an alternative coupled Finite-Element-Boundary-Element
(FE-BE) method that accounts for a tunnel in a multi-layered half-space. It is shown that the results of the two methods are
in a good agreement for typical parameter values of a tunnel. The new method is computationally more efficient, i.e. requires
significantly less running-time on a personal computer with much less use of memory.
10/2008: pages 136-142;
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Seismic Risk. Earthquakes in North-Western Europe; 09/2008
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Proceedings of ISMA2008 International Conference on Noise and Vibration Engineering; 09/2008
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Book of Abstracts of the Inaugural International Conference of the Engineering Mechanics Institute (EM08); 05/2008
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ABSTRACT: This paper deals with the influence of the train speed on vibrations induced by high speed trains. In the past 10 years, free
field as well as track vibrations have been measured at several sites on the Belgian part of the European high speed rail
network. These experimentswere performedwithin the frame of homologation tests, which has allowed data collection for a wide
range of train speeds.
This paper concentrates on the analysis of track as well as free field vibrations for different train speeds at a site along
the line L2 between Brussels and Köln. At this site, 11 passages of the IC train at speeds between 156 km/h and 225 km/h have
been recorded and 11 passages of the Thalys HST at speeds between 218 km/h and 326 km/h. The experimental data for different
train speeds are analysed and compared to numerical predictions that have been performed by means of a numerical model that
accounts for the dynamic interaction between the train, the track and the soil.
04/2008: pages 19-25;
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Proceedings of Leuven Symposium on Applied Mechanics in Engineering; 03/2008
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ABSTRACT: The Spectral Analysis of Surface Waves (SASW) method is a technique for the identification of the thickness, dynamic shear modulus, and damping ratio of shallow soil layers. The method consists of an in situ experiment to determine the dispersion curve of the soil and the solution of an inverse problem where the corresponding soil profile is identified. The SASW method has been used to investigate pavement systems, to assess the quality of ground improvement, to determine the thickness of waste deposits, and to identify the dynamic soil properties for the prediction of ground vibrations. In this paper, the focus is on the last application.The information on the dynamic soil properties provided by the dispersion curve is limited. The dispersion curve is insensitive to variations of the soil properties on a small spatial scale and at a large depth. As a result, the solution of the inverse problem in the SASW method is non-unique and hence uncertain. The prediction of ground vibrations is therefore based on a soil model with uncertain properties.In this study, a Bayesian approach is followed to solve the inverse problem in the SASW method. A prior stochastic soil model is first formulated using the information that is available before the SASW test is performed. A Markov chain Monte Carlo method is used to transform the prior model into a posterior stochastic soil model that accounts for the SASW test results. Finally, the prediction of ground vibrations is addressed. The posterior soil model is used to assess the robustness of the predicted vibrations, accounting for the uncertainty on the results of the SASW test. As an example, the free field vibrations due to a hammer impact on a concrete foundation are considered. More complicated problems, such as the prediction of road and rail traffic induced vibrations, can be addressed in a similar way.
Geophysical Journal International 12/2007; 172(1):262 - 275. · 2.42 Impact Factor
