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The vibrations of railway tracks on a poroelastic half‐space generated by moving trains are investigated through a vehicle–track–ground coupling model. The theoretical model incorporates a vehicle, a track, and a fully saturated poroelastic half‐space soil medium. The source of vibration excitation is divided into two components: the quasi‐static loads and the dynamic loads. The quasi‐static loads are related to the static component of the axle loads, whereas the dynamic loads are due to the dynamic wheel–rail interaction. A linear Hertizian contact spring is introduced between each wheelset and the rail to consider the dynamic loads. Biot's dynamic theory is used to characterize the poroelastic half‐space soil medium. Using the Fourier transform, the governing equations for the track–ground system are solved and the numerical results are presented for a single axle vehicle model. The different dynamic characteristics of the elastic soil medium and the saturated poroelastic medium are investigated. In addition, the different roles of the moving axle loads and the roughness‐induced dynamic loads are identified. It is concluded that the vibration level of the free field off the track predicted by the poroelastic soil medium is smaller than that predicted by the elastic soil medium for vehicle speed below the Rayleigh wave speed of the poroelastic half‐space, whereas it is larger for vehicle speed above the Rayleigh wave speed. The dynamic loads play an important role in the dynamic responses of the track–ground system. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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基于实测资料,假设列车轮载经钢轨传递下来的荷载由5根枕木承担。根据分担比,获得了道渣层表面非均布荷载的表达式。将道渣层视为单相弹性介质,软土地基被看成是考虑水土耦合作用的饱和多孔介质。借助势函数,利用Helmholtz矢量分解法及Fourier变换技术分别对弹性土体和饱和半空间土体进行求解,得到非均布移动荷载作用下软土地基位移、应力及孔压响应在变换域内的精确解答。利用FFT算法得到了数值结果,详细分析了荷载分布形式、观察点位置、道渣性质以及软土地基渗透系数对动力响应的影响。研究结果表明：高速情况下动力响应与低速情况有很大不同;对于软土路基,应特别注意列车高速运行时路基浅层范围内产生的孔压响应。 相似文献
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The problem of the dynamic responses of a semi‐infinite unsaturated poroelastic medium subjected to a moving rectangular load is investigated analytical/numerically. The dynamic governing equations are obtained with consideration of the compressibility of solid grain and pore fluid, inertial coupling, and viscous drag as well as capillary pressure in the unsaturated soil, and they can be easily degraded to the complete Biot's theory. Using the Fourier transform, the general solution for the equations is derived in the transformed domain, and then a corresponding boundary value problem is formulated. By introducing fast Fourier transform algorithm, the unsaturated soil vertical displacements, effective stresses, and pore pressures induced by moving load are computed, and some of the calculated results are compared with those for the degenerated solution of saturated soils and confirmed. The influences of the saturation, the load speed, and excitation frequency on the response of the unsaturated half‐space soil are investigated. The numerical results reveal that the effects of these parameters on the dynamic response of the unsaturated soil are significant. 相似文献
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基于Biot饱和多孔介质U-W格式动力控制方程,采用Galerkin法和Fourier变换,推导了饱和土体2.5维有限元方程及黏弹性人工边界,建立了饱和土地基中空沟分析模型,并在波数域中进行求解,通过快速Fourier变换（FFT）进行波数展开,获得三维空间域中结果。算例分析了移动荷载作用下均质饱和土地基、分层饱和土地基、上覆单相弹性层饱和土地基3种饱和土地基模型中空沟的隔振效果。结果表明：饱和土地基中空沟的隔振效果不仅与空沟自身深度有关,还与地基中成层土体的分界面以及土体参数有关,波在不同土体分界面上的透射和反射会影响空沟的隔振效果;饱和土地基中上覆单相弹性层厚度对空沟的隔振效果影响显著,随着上覆单相弹性层厚度的增加,饱和土地基中空沟的隔振效果变好。 相似文献
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Interaction of a cylindrical thin‐walled pile with an inhomogeneous isotropic elastic medium 
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下载免费PDF全文 This paper presents a rigorous analysis for the static interaction of a cylindrical thin‐walled pile with an inhomogeneous isotropic elastic half‐space under vertical, horizontal, and torsional forces individually applied at the top of pile. The inhomogeneity is specified with the exponential variation of shear modulus along depth of the embedding medium, and the Poisson's ratio is assumed to be constant. By means of a set of Green's functions for pile and soil medium and satisfying the compatibility conditions between the 2 interacting media, the formulation is reduced to coupled Fredholm integral equations. Using the adaptive‐gradient elements, capable of capturing the singular stress transfer at both ends of the pile, a numerical procedure is developed and utilized for evaluating the relevant integral equations and studying the inhomogeneity effect on the soil‐pile interaction responses. The analysis results have been validated for different soil‐pile modulus ratios under axial load and for a Poisson's ratio of 0.3 under lateral load. The procedure does not consider the nonlinear behavior of the soil medium or plastic yielding in the pile section, and the impact of the unreliable results for the case of high Poisson's ratio is not examined. 相似文献
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Reducing vertical acceleration in ballast layers of railways to mitigate geometrical disorders in high‐speed lines 下载免费PDF全文
下载免费PDF全文 According to field feedbacks from high‐speed lines (HSL), the increase of train operating speeds is responsible for unusual fast evolving geometrical disorders in ballasted tracks. This paper deals with the search of solutions applicable at the design stage to mitigate these disorders. The starting point of the present work relies on the assumption, comforted by the literature, of a strong correlation between disorders and vertical accelerations in the ballast layer induced by the train passages. This led us focus herein on the calculation and the analysis of accelerations in the railway structure. The vertical accelerations (γz) are computed using the in‐house developed numerical program ViscoRail and on the basis of a reference HSL. These are shown to increase strongly with the train speed attesting to the link between the train speed and the geometrical disorders in ballast. Then, other simulations are run varying some structural parameters to evaluate their impact on the acceleration field γz. In that way, we show that decreasing the stiffness of the mechanical connection between the rails and the ballast, increasing the moment of inertia of the rails or the Young modulus of the sub‐ballast layer, leads to a decrease of γz and could provide solutions for the design of future HSL. The solution consisting in the incorporation of an asphalt sub‐ballast layer, as already experimented on sites, is finally examined in more details. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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The Riemann problem for an irreversibly compressible three‐phase medium has been solved. This solution introduces the maximum medium density that is attained in the process of active loading. The possible wave configurations have been analyzed, and the corresponding equations for the evaluation of the contact pressure and velocity have been obtained. The existence and uniqueness of the solution has been proven. The technique of the Riemann problem's solution for the arbitrary Lagrange–Euler mesh was developed. Examples of the Riemann problem solution for various wave configurations show that neglecting the bulk elastic plastic deformations yields significant errors in the results both quantitatively and qualitatively. The effect of the air volumetric content in a three‐phase soil medium on the Riemann problem solution has been investigated. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Three‐dimensional dynamic response of ground with a poroviscoelastic interlayer to a harmonic moving rectangular load 下载免费PDF全文
下载免费PDF全文 Stratification is a basic characteristic of ground. Due to the influence of ground water, saturated weak interlayers widely exist, particularly in soft soil area. An interlayer of high compressibility and low strength has a substantial effect on dynamic response of the ground, especially under high speed moving load. Thus, a comprehensive investigation in the influence of interlayer is essential and useful in geotechnical and transportation‐related engineering. This paper presents a three‐dimensional semi‐analytical approach to study the dynamic response of a layered ground with a soft saturated interlayer. The ground is modelled as a half‐space consisting of three parts: a viscoelastic upper layer, a saturated poroviscoelastic interlayer governed by Biot's theory and a viscoelastic half‐space. An ‘adapted stiffness matrix’ is proposed to obtain the semi‐analytical solution to the system. Comprehensive parametric study is conducted to investigate the influences of existence, geometrical and physical properties of the interlayer. Depth, thickness, hydraulic permeability of the interlayer, load speed and frequency significantly influence the dynamic response of the ground, among which the interlayer depth plays a dominant role. Resonant frequency exists, which is highly affected by the interlayer thickness, especially in low speed regime. Both hydraulic permeability and boundary conditions of the interlayer influence the characteristics of pore pressure distribution. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
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基于Biot理论,研究了饱和土中带有衬砌的圆形隧洞在移动环形荷载作用下的动力响应。假定衬砌为弹性体,土体为饱和多孔介质,引入两类势函数来表示土体、孔隙水和衬砌的位移,使隧洞的控制方程解耦。结合边界条件及连续条件,通过傅立叶变换得到频率-波数域中衬砌和土体的应力、位移和孔隙水压力解答,最后用傅立叶积分逆变换得到时-空域中的数值解。计算并比较了3种隧洞模型（弹性土体隧洞、饱和土体隧洞和饱和土衬砌隧洞）的动力响应分析。数值分析结果说明：（1）移动荷载速度对3种隧洞动力响应均具有较大影响;（2）弹性土体隧洞和饱和土体隧洞的动力响应具有明显区别,所以在富水地区的隧洞动力响应中土体应该视为饱和土体;（3）衬砌对隧洞动力响应有较大影响,故隧洞的动力分析中不能忽略衬砌作用。 相似文献
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An analytical solution is presented in this paper to study the time‐dependent settlement behaviour of a rigid foundation resting on a transversely isotropic saturated soil layer. The governing equations for a transversely isotropic saturated soil, within Biot's poroelasticity framework, are solved by means of Laplace and Hankel transforms. The problem is subsequently formulated in the Laplace transform domain in terms of a set of dual integral equations that are further reduced to a Fredholm integral equation of the second kind and solved numerically. The developed analytical solution is validated via comparison with the existing analytical solution for an isotropic saturated soil case, and adopted as a benchmark to examine the sensitivities of the mesh refinement and the locations of truncation boundaries in the finite element simulations using ABAQUS. Particular attention is paid to the influences of the degree of soil anisotropy, boundary drainage condition, and the soil layer thickness on the consolidation settlement and contact stress of the rigid foundation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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An analytical solution is developed in this paper to investigate the dynamic response of a large‐diameter end‐bearing pipe pile subjected to torsional loading in viscoelastic saturated soil. The wave propagation in saturated soil and pile are simulated by Biot's two‐phased linear theory and one‐dimensional elastic theory, respectively. The dynamic equilibrium equations of the outer soil, inner soil, and pile are established. The solutions for the outer and inner soils in frequency domain are obtained by Laplace transform technique and the separation of variables method. Then, the dynamic response of the pile is obtained on the basis of the perfect contacts between the pile and the outer soil as well as the inner soil. The results in this paper are compared with that of a solid pile in elastic saturated soil to verify the validity of the solution. Furthermore, the solution in this paper is compared with the classic plane strain solution to verify the solution further and check the accuracy of the plane strain solution. Numerical results are presented to analyze the vibration characteristics and illustrate the effect of the soil parameters and the geometry size of the pile on the complex impedance and velocity admittance of the pile head. Finally, the displacement of the soil at different depth and frequency is analyzed. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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This paper describes the influence of seasonal variations of the ground water table on free field traffic-induced vibrations. The passage of a truck on two types of road unevenness is considered: a joint in a road pavement consisting of concrete plates and a speed bump with a sinusoidal profile. Free field vibrations are computed with a two-step solution procedure, where the computation of the vehicle axle loads is decoupled from the solution of the road–soil interaction problem. The impedance of the soil is calculated using a boundary element method, based on the Green's functions for a dry layer on top of a saturated half-space. It is demonstrated that, in the low-frequency range of interest, wave propagation in the saturated half-space can be modelled with an equivalent single phase medium as an alternative to Biot's poroelastic theory for saturated porous media. The relation between the free field velocity and the depth of the ground water table is dominated by three phenomena: (1) the compressibility of the soil decreases due to the presence of the pore water, (2) the ground water table introduces a layering of the soil which may cause resonance of the dry layer and (3) refracted P-waves in the dry layer interfere with surface waves. If the depth of the ground water table is large with respect to the wavelength of the vibrations in the soil, the response tends to the response of a dry half-space. The average free field velocity is equal to the velocity in the absence of ground water. If the depth of the ground water table is small with respect to the wavelength of the vibrations in the soil, the response tends to the response of a saturated half-space and resonance of the dry layer does not occur. The average free field velocity is smaller than the velocity in the absence of ground water. The interference of refracted P-waves and surface waves causes an additional oscillation of the response as a function of the excitation frequency and the distance between the road and the receiver. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Validation of a three‐dimensional constitutive model for nonlinear site response and soil‐structure interaction analyses using centrifuge test data 下载免费PDF全文
下载免费PDF全文 The capability of a bounding surface plasticity model with a vanishing elastic region to capture the multiaxial dynamic hysteretic responses of soil deposits under broadband (eg, earthquake) excitations is explored by using data from centrifuge tests. The said model was proposed by Borja and Amies in 1994 (J. Geotech. Eng., 120, 6, 1051‐1070), which is theoretically capable of representing nonlinear soil behavior in a multiaxial setting. This is an important capability that is required for exploring and quantifying site topography, soil stratigraphy, and kinematic effects in ground motion and soil‐structure interaction analyses. Results obtained herein indicate that the model can accurately predict key response data recorded during centrifuge tests on embedded specimens—including soil pressures and bending strains for structural walls, structures' racking displacements, and surface settlements—under both low‐ and high‐amplitude seismic input motions, which was achieved after performing only a basic material parameter calibration procedure. Comparisons are also made with results obtained using equivalent linear models and a well‐known pressure‐dependent multisurface plasticity model, which suggested that the present model is generally more accurate. The numerical convergence behavior of the model in nonlinear equilibrium iterations is also explored for a variety of numerical implementation and model parameter options. To facilitate broader use by researchers and practicing engineers alike, the model is implemented as a “user material” in ABAQUS Standard for implicit time stepping. 相似文献
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The dynamic response of an end bearing pile embedded in a linear visco‐elastic soil layer with hysteretic type damping is theoretically investigated when the pile is subjected to a time‐harmonic vertical loading at the pile top. The soil is modeled as a three‐dimensional axisymmetric continuum in which both its radial and vertical displacements are taken into account. The pile is assumed to be vertical, elastic and of uniform circular cross section. By using two potential functions to decompose the displacements of the soil layer and utilizing the separation of variables technique, the dynamic equilibrium equation is uncoupled and solved. At the interface of soil‐pile system, the boundary conditions of displacement continuity and force equilibrium are invoked to derive a closed‐form solution of the vertical dynamic response of the pile in frequency domain. The corresponding inverted solutions in time domain for the velocity response of a pile subjected to a semi‐sine excitation force applied at the pile top are obtained by means of inverse Fourier transform and the convolution theorem. A comparison with two other simplified solutions has been performed to verify the more rigorous solutions presented in this paper. Using the developed solutions, a parametric study has also been conducted to investigate the influence of the major parameters of the soil‐pile system on the vertical vibration characteristics of the pile. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Previous work on three‐dimensional shakedown analysis of cohesive‐frictional materials under moving surface loads has been entirely for isotropic materials. As a result, the effects of anisotropy, both elastic and plastic, of soil and pavement materials are ignored. This paper will, for the first time, develop three‐dimensional shakedown solutions to allow for the variation of elastic and plastic material properties with direction. Melan's lower‐bound shakedown theorem is used to derive shakedown solutions. In particular, a generalised, anisotropic Mohr–Coulomb yield criterion and cross‐anisotropic elastic stress fields are utilised to develop anisotropic shakedown solutions. It is found that shakedown solutions for anisotropic materials are dominated by Young's modulus ratio for the cases of subsurface failure and by shear modulus ratio for the cases of surface failure. Plastic anisotropy is mainly controlled by material cohesion ratio, the rise of which increases the shakedown limit until a maximum value is reached. The anisotropic shakedown limit varies with frictional coefficient, and the peak value may not occur for the case of normal loading only. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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This study is conducted with a numerical method to investigate the seismic behaviour among certain soils, single piles, and a structure. A series of numerical simulations of the seismic behaviour of a single‐pile foundation constructed in a two‐layer ground is carried out. Various sandy soils, namely, dense sand, medium dense sand, reclaimed soil, and loose sand, are employed for the upper layer, while one type of clayey soil is used for the lower layer. The results reveal that when a structure is built in a non‐liquefiable ground, an amplification of the seismic waves is seen on the ground surface and in the upper structure, and large bending moments are generated at the pile heads. When a structure is built in a liquefiable ground, a de‐amplification of the seismic waves is seen on the ground surface and in the upper structure, and large bending moments are generated firstly at the pile heads and then in the lower segment at the boundary between the soil layers when liquefaction takes place. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Analytical solutions for the steady‐state response of an infinite beam resting on a visco‐elastic foundation and subjected to a concentrated load moving with a constant velocity are developed in this paper. The beam responses investigated are deflection, bending moment, shear force and contact pressure. The mechanical resistance of the foundation is modeled using two parameters ks and ts — ks accounts for soil resistance due to compressive strains in the soil and ts accounts for the resistance due to shear strains. Since this model represents the ground behavior more accurately than the Winkler spring model, the developed solutions produce beam responses that are closer to reality than those obtained using the existing solutions for Winkler model. The dynamic beam responses depend on the damping present in the system and on the velocity of the moving load. Based on the study, dynamic amplification curves are developed for beam deflection. Such amplification curves for deflection, bending moment, shear force and contact pressure can be developed for any beam‐foundation system and can be used in design. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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为研究空沟对高速列车引起地基振动的隔振效果,在已有研究基础上改进出一种新的解析研究模型。模型中首次运用了饱和半空间模型来研究地基上隔振沟对高速列车的隔振效果;隔振沟则通过在饱和半空间土体上设置3个合适宽度、截面为矩形的弹性层来模拟;中间矩形弹性层为路堤,路堤上方放置了枕木与轨道。枕木与轨道分别通过纵向异性Kirchhoff薄板与Euler梁来模拟,饱和土地基采用Biot多孔饱和介质理论来描述。控制方程通过傅立叶变换与傅立叶级数展开,在变换域中进行求解。研究表明,随着列车运行速度的提高,空沟的隔振效果明显提高;饱和土体固-液相的耦合作用对隔振沟的隔振效果的影响明显,尤其当列车运行速度超过土体表面Rayleigh波速时,随着土体渗透系数的增加,空沟隔振效果显著降低。此外,列车运行速度超过土体表面波速时,饱和土地基上空沟的隔振效果明显优于相应单相弹性地基上空沟的隔振效果。 相似文献
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An analytical solution of cavity expansion in two different concentric regions of soil is developed and investigated in this paper. The cavity is embedded within a soil with finite radial dimension and surrounded by a second soil, which extends to infinity. Large‐strain quasi‐static expansion of both spherical and cylindrical cavities in elastic‐plastic soils is considered. A non‐associated Mohr–Coulomb yield criterion is used for both soils. Closed‐form solutions are derived, which provide the stress and strain fields during the expansion of the cavity from an initial to a final radius. The analytical solution is validated against finite element simulations, and the effect of varying geometric and material parameters is studied. The influence of the two different soils during cavity expansion is discussed by using pressure–expansion curves and by studying the development of plastic regions within the soils. The analytical method may be applied to various geotechnical problems, which involve aspects of soil layering, such as cone penetration test interpretation, ground‐freezing around shafts, tunnelling, and mining. © 2014 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd. 相似文献