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1.
The present study pertains to the development of a foundation model for predicting the behavior of geosynthetic reinforcement railway track system rested on soft clay subgrade. The ballast and sub‐ballast layers have been idealized by Pasternak shear layer. The geosynthetic layer is represented by a stretched rough elastic membrane. Burger model has been used to characterize the soft clay subgrade. Numerical solutions have been obtained by adopting the finite difference scheme combined with non‐dimensioning the governing equations of the proposed model. The results confirm that the present model is quite capable of predicting the time‐dependent settlement response of geosynthetic reinforcement railway track system placed on soft clay subgrade. The surface settlement profile and mobilized tensile load of geosynthetics has been evaluated by considering variation in the wheel load, sleeper width, thickness of ballast and sub‐ballast layers and shear modulus of ballast and sub‐ballast layers. It has been observed that an increase in the sleeper width by 24% results in the reduction in central settlement and mobilized tensile load by 6.5% and 20.1%, respectively. It was found that with a 50% increase in the thickness of the ballast layer, the central settlement has decreased by 7.3% and the mobilized tension at the zone of maximum curvature has increased by 24.6%. However, with an increase in the thickness of the sub‐ballast layer, a considerable reduction in both central settlement and the mobilization of tension on geosynthetic has been noticed. The pattern of variation of settlement and mobilized tension for an increase in the shear modulus of ballast and sub‐ballast material was found to be almost similar. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
Najaf-sea quarry is located in Najaf city about 160 km south west of Baghdad the capital of Iraq. It is the main source that supplies track ballast for maintenance of existing railway network and construction of new railway lines in the middle and southern parts of Iraq. Track ballast experience a complex combination of stresses during its service lifetime, primarily from repeated axial loads of the trains in addition to stresses generated from the environmental conditions. The ideal evaluation of suitability of track ballast must be carried out under real field loading conditions, however such field tests are usually costly and time consuming. On the other hand laboratory model tests simulating field loads under limited boundary conditions can provide satisfactory indication about the suitability of the material. The present paper investigates the deformation characteristics of Najaf-sea track ballast, under repeated loading using model tests simulating ballast conditions under a selected track section. A test setup was designed and manufactured capable of applying both monotonic as well as repeated loading on the track section under different conditions. The repeated model tests which simulate as close as possible the field conditions shed the light on the generated settlement, modulus of deformation and degradation of the ballast particles under different repeated loading levels. Statistical analysis in terms of breakage index and repeated applied load revealed satisfactory correlations that help in understanding the overall performance of the ballast material. The results also demonstrate that 4–5 tamping are capable of controlling both the settlement and modulus of deformation of the ballast material. 相似文献
3.
In order to reduce the maintenance costs of ballasted railway track and improve passenger comfort, the railway ballast particle breakage and its effect on track settlement need to be better understood. The failure process of individual railway ballast loaded between flat platens is simulated using the discrete element method, considering its irregular shape with the incorporation of parallel bonds. The tensile strength, the stress of a survival probability of 37% of samples, is obtained and compared with laboratory results from published literature for the verification of DEM simulations. The evolution to failure of the particle is understood from the stress-strain curve and progressive failure modes. The internal breakage mechanisms are analysed by tracking the accumulation of bond breakage number and the contact force distributions. 相似文献
4.
Rail tracks undergo degradation owing to particle breakage and fouling of ballast by various fines including coal and subgrade soil. As the ballast becomes fouled, its strength and drainage capacity are compromised, sometimes resulting in differential settlement and reduced track stability. This paper demonstrates a continuum mechanics based framework to evaluate the detrimental effect of fines on the strength, deformation and degradation of coal-fouled ballast under monotonic loading. An elastoplastic constitutive model that considers the effect of fines content and energy consumption associated with particle breakage during shearing is presented. This multiphase constitutive model is developed within a critical state framework based on a kinematic-type yield locus and a modified stress-dilatancy approach. A general formulation for the rate of ballast breakage and coal particle breakage during triaxial shearing is presented and incorporated into the plastic flow rule to accurately predict the stress–strain response of coal-fouled ballast at various confining pressures. The behaviour of ballast at various levels of fouling is analysed and validated by experimental data. 相似文献
5.
《Geomechanics and Geoengineering》2013,8(3):175-181
Railway ballast particles undergo significant amount of breakage under repeated train load. Breakage of ballast particles, especially highly angular fresh ones, causes an increase in settlement, contributing to track degradation. The quantitative analysis of the influence of breakage on the stress-strain properties of ballast can be performed either experimentally or numerically. Numerical modeling has the advantage of simulating ballast breakage subject to various types of loading and different boundary conditions for a range of material properties. In this paper, ballast breakage under cyclic loading is simulated using a 2D discrete element method (DEM) utilizing the software PFC2D . A new subroutine is developed and incorporated in the PFC2D analysis to study ballast breakage and to quantify breakage in relation to particle size distribution. The influence of confining pressure on both breakage and permanent deformation is also studied and compared with laboratory observations. The findings of this paper provide an insight into the true ballast behavior under cyclic loading and are expected to assist railway practitioners in developing suitable design criteria for track stability. 相似文献
6.
基于沉降控制设计理念,无砟轨道京沪高速铁路地基处理采用筏板+垫层+疏桩的方法,形成复合桩基以实现有效减少工后沉降和充分利用地基承载力的优化加固方案。为探索该新方法沉降控制机制,选用CFG桩开展了复合桩基现场试验研究,对复合桩基在高速铁路路基填筑、静置、预压卸载过程中的地基沉降变形、桩和桩间土土压力、筏板顶与底部压力进行了长期观测,分析了路基沉降变形、桩-土应力比和荷载分担比以及筏板的受力随填筑高度和固结时间的变化规律。研究表明：筏板＋垫层＋疏桩联合加固地基方案在初期充分发挥了桩间土承载作用,导致桩与桩间土产生差异沉降;随着垫层的调节作用,筏板可集中发挥桩体的承载能力及显著提高桩顶应力集中程度,地基土沉降主要发生在加固区范围内,从而揭示了复合桩基在路基荷载下的承载机制和变形特性。现场试验结果可为指导高速铁路CFG桩复合桩基设计参数的进一步优化提供试验依据。 相似文献
7.
A railway embankment constructed on a floodplain is at risk of damage due to flooding flows. The process and critical conditions that lead to railway embankment damage during flooding are not clearly understood, rendering risk estimations impossible and hindering the development of flood-resilient rail systems. For this work, we first reviewed records of railway damage in flood plains and flows through the ballast layer. The breaching process was selected as the focus of our study. We secondly specified the fundamental characteristics of flows through a ballast layer. The critical flow rate per unit width and the minimum upstream water depth required for initiating extensive ballast breaching were experimentally evaluated using a full-scale ballast layer with rails and sleepers constructed using materials originally utilized in actual railways. A two-dimensional flow model was then employed for estimating the flow through a ballast layer that was placed on an impermeable base embankment. A simple ballast breaching model was also employed in order to explore a higher flow rate condition that could not be represented in our experiment due to limited facilities. The breaching pattern represented by the simulation model corresponded to the breaching pattern observed in the experiment. In addition to the above, here, we also discuss the ballast breaching process based on qualitative field records and quantitative experimental results, as well as the ballast breaching process as represented by the simulation. 相似文献
8.
湿陷性黄土地区客运专线路基沉降观测分析 总被引：1，自引：1，他引：0
郑西客运专线是我国第一条黄土地区时速300～350 km/h铺设无砟轨道的高速铁路,路基沉降控制是保证高速铁路运营安全的重要因素。通过郑西客运专线现场沉降观测资料的分析发现,黄土地基在较小沉降控制要求的情况下具有完成时间较短、沉降趋势符合双曲线分析法、埋设于路基中部的沉降板比埋设于路肩的观测桩沉降曲线拟合性好、路堑地段也有较小的沉降发生等特点,这些结果对进行高速铁路客运专线路基沉降观测设计很有借鉴价值。 相似文献
9.
A new macroscopic constitutive model for non‐cohesive granular materials, with the focus on coarse‐sized materials (railway ballast), is presented. The model is based on the concepts of rate‐independent isotropic plasticity. The Backward Euler rule is used for integrating the pertinent evolution equations. The resulting incremental relations are solved in the strain space that is extended with the internal (hardening) variables. The model is calibrated using data from Conventional Triaxial Compression (CTC) tests, carried out at the University of Colorado at Boulder. A function evaluation method is used for the optimization, whereby a ‘multi‐vector’ strategy for choosing the appropriate start vector is proposed. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
10.
Discrete element modeling of dynamic behaviors of railway ballast under cyclic loading with dilated polyhedra 
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下载免费PDF全文 The dynamic behaviors of railway ballast under cyclic loading are simulated with discrete element method (DEM). Dilated polyhedra are constructed based on the Minkowski sum operator in order to resemble the irregular shapes of ballast particles. The polyhedral particle generation, contact detection between particles and contact laws are presented. Ballast box tests with periodic lateral boundaries are conducted to simulate the dynamics of the sleeper and ballast particles. The settlement and effective stiffness of ballast bed are investigated under cyclic loadings with five distinct frequencies. The settlement of ballast bed is significant in the first several cycles and increases with the number of cycles gradually. The higher frequency loading generates larger displacement in the same simulation time. The effective stiffness of ballast bed increases gradually. To study the effect of particles' sharpness, dilated polyhedra with different dilating radii and spherical particles are also developed. Simulation results show the sharper the ballast particles are, the smaller the produced settlement. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
11.
The paper presents a three‐dimensional study on the steady‐state response of a track system and layered half‐space soil medium subjected to the load induced by the passages of a moving train with the substructure method. Practically, due to the ground water table being several meters beneath the ground surface, the soil profile can be divided into two layers: the upper layer modeled by an elastic medium and the lower layer by a fully saturated poroelastic medium governed by Biot's theory. In the meanwhile, the rails are regarded as an infinitely long Euler beam, and the sleepers are represented by a continuous mass. The effect of the ballast is accounted for by introducing the Cosserat model for granular medium, and the train is described by a series of moving axle point loads, depending on the geometry of the train. The influences of the thickness, the mass and the rigidity of the elastic layer and the mass of the ballast on rail's displacement responses are carefully investigated. Numerical results show that the influences of these parameters are significant for high train velocity, while vanishes for low velocity. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
Geogrids are commonly used in railway construction for reinforcement and stabilisation. When railway ballast becomes fouled due to ballast breakage, infiltration of coal fines, dust and subgrade soil pumping, the reinforcement effect of geogrids decreases significantly. This paper presents results obtained from Discrete Element Method (DEM) to study the interface behaviour of coal-fouled ballast reinforced by geogrid subjected to direct shear testing. In this study, irregularly-shaped aggregates (ballast) were modelled by clumping together 10–20 spheres in appropriate sizes and positions. The geogrid was modelled by bonding a large number of small spheres together to form the desired grid geometry and apertures. Fouled ballast with 40% Void Contaminant Index (VCI) was modelled by injecting a predetermined number of miniature spheres into the voids of fresh ballast. A series of direct shear tests for fresh and fouled ballast reinforced by the geogrid subjected to normal shear stresses varying from 15 kPa to 75 kPa were then simulated in the DEM. The numerical results showed a good agreement the laboratory data, indicating that the DEM model is able to capture the behaviour of both fresh and coal-fouled ballast reinforced by the geogrid. The advantages of the proposed DEM model in terms of capturing the correct stress–displacement and volumetric behaviour of ballast, as well as the contact forces and strains developed in the geogrids are discussed. 相似文献
13.
地铁隧道穿越角度对地表建筑物的影响分析 总被引：2，自引：0，他引：2
结合深圳地铁隧道下穿某住宅小区建筑群的工程实践,以某框架结构建筑为研究对象,按照隧道-土体-结构共同作用,利用Midas/GTS软件建立三维非线性有限元模型,计算了隧道轴线与地面建筑物成90º、60º、45º和30º夹角4种不同工况,分析隧道轴线与建筑物不同夹角条件下隧道开挖对地表建筑物基础沉降和结构受力变形分布形态的影响。计算结果表明,隧道以不同角度穿越时,地表建筑基础的沉降过程和分布形态差异明显。随着穿越角度? 的减小,基础沉降最大增幅为37.3%,建筑基础沿线沉降由对称分布转为侧向倾斜,相邻柱基沉降差增大;建筑倾斜和扭曲变形增加明显,最大增幅达10倍;由于分析部位不同,相比建筑基础及底部结构变形而言,隧道穿越角度的改变对建筑内力影响较小。 相似文献
14.
铁路客运专线路基沉降预测的新方法 总被引：3，自引：0，他引：3
路基的工后沉降控制是高速铁路建设的重要问题之一,利用铁路客运专线路基现场观测数据,找出相应的路基沉降规律有利于指导设计与施工。在分析武广铁路客运专线路基大量数据的基础上,将三点法的基本思想引入到双曲线模型,建立了基于双曲线模型的三点法。其具体做法是：在实测沉降曲线上选取3个适当的点作为预测样本,代入双曲线模型进行预测。为了检验新方法,运用常用的双曲线方法、三点法、Asaoka法、星野法、泊松曲线法进行对比分析,并且提出了新方法的取点控制条件。研究表明：基于双曲线模型的三点法的预测误差小、相关系数高、与实测数据吻合较好,具有一定的实用价值,为铁路客运专线无砟轨道铺设的沉降预测问题提供了参考。 相似文献
15.
Namir K. S. Al-Saoudi Khawla H. Hassan 《Geotechnical and Geological Engineering》2012,30(5):1097-1102
Iraq is planning to expand and rehabilitate its current railway network, thus demanding huge amounts of proper ballast material. There are three common quarries in Iraq, Sinjaar in the northern sector, Al-Qaim in western desert and Najaf-sea in the middle and southern parts of Iraq. The selection of proper track ballast material is of prime importance in design and construction of railway projects. The single particle-crushing test is a simple indirect tensile test that provides useful data for the selection of the material. Two types of railway ballast materials from (Najaf-sea and Al-Qaim) quarries are commonly used in the construction of railway in Iraq. The single particle-crushing test was performed for various ballast sizes, and the obtained data were analyzed using Weibull analysis. Najaf-sea crushed stones indicate higher tensile strength for all particle sizes compared to corresponding particle sizes of Al-Qaim crushed stone. In addition, an inverse linear relationship had obtained, between tensile strength and particle size with R 2 (0.837 and 0.979) for Al-Qaim and Najaf-sea crushed stone, respectively, such relationships are important in evaluating the suitability of the materials in terms of the survival probability 相似文献
16.
17.
Repetitive or cyclic rail loading deteriorates the engineering properties of the railway ballast by particle crushing and rearrangement. Most of the classical elasto-plastic models are unable to predict such ballast degradation despite successfully predicting the overall load–deformation behavior during cyclic densification. In this context, the present study delivers a novel hypo-plastic modeling approach coupled with breakage mechanics theory to bridge the gap of the conventional models. The hypo-plastic approach enables to predict the nonlinear load–deformation response of ballast-type granular materials for both monotonic and cyclic loading conditions, while circumventing the requirement of notional yield condition to predict the inelastic behavior. Breakage mechanics theory, on the other hand, establishes the links between particle comminution and the macroscopic deformation. The novelty of the proposed approach is threefold. Firstly, unlike the conventional hypo-plastic approaches, the development of the proposed model is within the continuum thermodynamics framework. Secondly, the model requires less number of physically identifiable parameters as compared to that of earlier models employed for assessing the particle breakage under cyclic loading. Third and finally, the numerical implementation of the model as a user-defined material is simple for solving boundary value problems. Under the compressive deformation regime, the model prediction of the ballast degradation along with the cyclic densification response agrees reasonably well with the experimental results found in the literature. 相似文献
18.
积沙对铁路道碴层反射率的影响研究 总被引：1，自引：1，他引：0
青藏铁路建成后,随着全球气温的升高及人类活动的影响,青藏高原地表沙化正在呈现加速发展的趋势,地表积沙入侵路基,填堵和覆盖青藏铁路道碴层,影响了青藏铁路道碴层的反射率。为此开展了积沙对于铁路道碴层反射率影响的研究。为此本文将测量碎石层等粗糙表面的反射率的方法进行了改进,使其适用于测量混有流动性材料（如积沙等）的粗糙表面（如铁路道碴层等）的反射率。结果表明：随着铁路道碴层模型积沙覆盖率的增大,铁路道碴层的反射率先减小后增大,当积沙完全覆盖道碴层时,其反射率达到最大。并将该测试方法与ASTM-E1918A标准测试方法进行对比分析发现,在天气晴朗、无云、无雾霾且太阳辐射入射量瞬时强度变化<20W·m-2时,两种测试方法计算非常接近,其测量差值0~0.002,综合分析认为在测量带有流动材料的反射率时,采用本测试方法方便可靠。但积沙对道碴层的热流平衡影响有待进一步研究。 相似文献
19.
地铁行车速度对盾构隧道运营沉降的影响分析 总被引：1，自引：0，他引：1
地铁行车荷载经轨道-道床-隧道结构传至地基,在土体内部产生循环动应力以及超孔隙水压力是引起盾构隧道沉降的重要原因。通过车-轨-隧道-地基竖向耦合动力模型分析隧道差异沉降对列车运行荷载的影响,以上海地铁一号线体育馆站附近区间隧道为工程背景建立三维数值模型,结合塑性累积应变及累积孔压经验公式进行计算,对比分析软土盾构隧道下卧土层有、无纵向差异沉降两种情况下,地铁行车速度对隧道运营沉降的影响。结果表明：列车运行速度越快,下卧土体波动越大,但衰减越快。地基差异沉降对其长期运营存在明显不利影响,随着列车速度增大,这种影响也愈加明显。当地基差异沉降小,轨道平顺条件好时,隧道长期沉降随地铁行车速度的增大而减小;当地基差异沉降突出,轨道存在明显不平顺时,隧道运营沉降随行车速度增大而显著增加。 相似文献