基于欧标的有砟轨道道床强度及横向稳定性设计与检算

以新加坡地铁轨道系统设计项目为背景,基于欧洲铁路规范,对有砟轨道道床强度和横向稳定性进行设计与检算。结果表明:有砟道床上层道砟厚度300 mm、下层道砟厚度500 mm、砟肩宽度400 mm时,轨枕底面处、上下层道砟分界面处、道砟与路基分界面处道床压强分别为196. 477 k Pa,105. 766 k Pa,41. 810 k Pa,小于设计强度;荷载作用下的轨道横向力小于自身抵抗能力;有砟轨道道床强度和横向稳定性满足规范要求,可为其他项目特别是为国内企业承接类似海外工程提供参考。     

高速铁路弹性轨枕有砟轨道力学特性试验研究

根据我国高速铁路设计相关规定,桥上有砟轨道地段应采用弹性轨枕或砟下垫,但目前对其研究较少。基于此,本文进行了系统的高速铁路桥上弹性轨枕有砟道床静、动力学特性试验研究,得出如下主要结论:1采用弹性轨枕后,道床的纵、横向阻力均较普通道床小,但能达到高速铁路有砟轨道的开通要求;2弹性轨枕有砟道床具有较小的支承刚度,能满足高速铁路钢轨支点刚度不大于30k N/mm的要求;3相对于普通道床,采用弹性轨枕后,会显著降低钢轨及桥梁的振动加速度,具有良好的减振、隔振性能;4采用弹性轨枕能有效减小道床的应力,大大减小线路养护维修工作量,体现了良好的优越性,适合于在桥上及岩质路堑等刚性基础地段铺设;5采用弹性轨枕会增大轮轨横向作用力及钢轨、轨枕的横向位移,使列车的运营安全性有所降低。总体上研究认为,在高速铁路桥上采用普通轨枕道床与弹性轨枕道床均能满足高速铁路有砟轨道开通的要求,但在满足高速铁路安全运营的前提下,从减小道砟受力,减少养护维修,提供良好的减振、隔振等方面考虑,建议高速铁路桥上有砟轨道采用弹性轨枕结构。     

基于稀疏贝叶斯学习的有砟轨道道砟层损伤识别

在列车荷载和环境影响的双重作用下,有砟轨道道砟层支承轨枕的刚度会逐渐退化,严重威胁着行车安全.本文建立包含钢轨-轨枕-道砟层的二维有砟轨道模型,以有砟轨道系统中轨枕结构的频率和振型作为输入数据,采用稀疏贝叶斯学习方法,对枕下道砟层的单损伤和多损伤工况进行了损伤识别研究.本文首先采用室内两跨三层异型框架结构损伤试验验证了...     

基于离散单元模拟道砟力学性能研究

如今快速发展的高速和重载铁路对铁路有砟道床的要求愈加严格,同时铁路运输量的日益增加也加重了铁路道床的变形和破坏,所以研究列车荷载作用下铁路有砟道床道砟颗粒的力学特性是非常有必要的。本文运用Minkowskin sum理论发展扩展多面体颗粒单元,建立铁路道砟的颗粒模型,借助离散单元模拟方法进行力学性能的分析,重点在于定性的对道砟颗粒在列车荷载作用下的具体沉降规律及刚度变化进行了模拟分析,这对铁路道床的合理化设计和优化改良方案具有重要的意义。     

基于复合地基载荷试验的土工格栅加固分析

对土工格栅的功能与工作机理进行了分析，通过在载荷试验中桩顶盒桩间土的位置铺设土工格栅，在土工格栅的上下层埋设土压力盒来了解土工格栅对桩土应力的影响。通过对桩土压力数据进行处理，分析了土工格栅的作用机理与加固效果。     

土工格栅控制液化土体流动变形的试验研究

液化导致的土体大变形以及侧向流动是地震引起建筑物破坏的主要原因。采用土工格栅作为主要加固材料,开展建筑物荷载作用下液化场地流动变形的振动台试验研究,考虑水平层状土工格栅、包裹状土工格栅和土工格栅+无纺布联合处理等3种加固方案对结果的影响,从超孔隙水压力发展、建筑物沉降量以及格栅应变特性等分析加固方案对液化变形的处理效果。试验表明:采用上述3种加固方案所得的相同埋深处超孔隙水压力峰值基本相等,表明土工格栅的加入基本不能改变地基的液化状态,而后期超孔隙水压力在土工格栅+无纺布联合加固方案下消散速度最快。与其它两种加固方案相比,土工格栅+无纺布联合加固方案下建筑物沉降量最小,相比未加固工况沉降量减少24%,土工格栅中间位置的应变峰值小于边缘位置的应变峰值。采用土工格栅+无纺布联合加固时,具有较大表面积的无纺布对该覆盖区域液化土体有较好的约束作用,限制了砂土颗粒的竖向移动。此外,砂土颗粒对无纺布的作用力将由土工格栅承担,这种作用力将有利于土工格栅与砂土之间的摩擦效应,进一步限制液化砂土的流动变形。     

双块式无砟轨道轨枕混凝土表面露石研究

<正>目前，我国高速铁路和客运专线主要采用无砟轨道结构。其中现浇混凝土道床式无砟轨道为双块式无砟轨道。双块式无砟轨道自上而下主要由钢轨、扣件、双块式轨枕、道床板、隔离层、底座等部件组成。在实际运营过程中，由于高频列车的荷载作用下使得轨枕四周易与道床板产生离缝，这样会影响轨道结构的服役性能和耐久性。通过对双块式轨枕预制后进行凿毛处理，可以有效增加界面的粗糙度，提高轨枕四周与道床混凝土的粘结力，减少离缝的产生。     

有砟轨道路基翻浆冒泥模型试验系统的研发与应用

为研究既有线有砟轨道路基的翻浆冒泥机理，自主研发了一套能够模拟循环荷载–湿化耦合作用的模型试验系统。模型试样直径500 mm，由厚度分别为350 mm的路基土和200 mm的道砟组成，整个试样在高强度透明有机玻璃模型筒中制备完成。模型试验系统配备有监测荷载、位移、体积含水率和孔隙水压力的4种传感器，并通过高清相机对颗粒迁移过程进行图像捕捉。基于所研发的试验系统，针对辛泰铁路典型翻浆冒泥病害路段土样，开展翻浆冒泥模型试验。试验结果表明：动孔隙水压力是导致翻浆冒泥病害产生的关键因素。随着体积含水率的增加，动孔隙水压力引起的颗粒迁移量逐渐增加；在饱和状态下，会引起大量颗粒迁移，翻浆冒泥现象显著。试验结束时，道砟污染指数达到25%，在实际工程中已严重影响铁路的正常运营，有必要对污染道砟进行换填。     

列车-有砟轨道-路基系统竖向耦合振动及其响应分析

由于道砟颗粒在列车高速运行下会发生剧烈振动以至于产生颗粒破碎甚至飞溅现象,对有砟轨道系统的动力学研究显得十分迫切。为探究在列车行驶过程中车体、轨道、路基在竖直方向上的动力响应,结合刚体假设、有限单元法、离散单元法建立列车-有砟轨道-路基竖向耦合系统,通过简化轮轨相互作用关系,建立列车-轨道系统竖向耦合振动方程,轨道及其下部结构在受力分析后通过矩阵的"对号入座"法则建立有砟轨道-路基的振动方程,最后得到列车-有砟轨道-路基竖向耦合系统的振动方程。基于MATLAB编程软件,采用Newmark-β逐步积分法求解振动方程。最后得到在列车荷载作用下,列车本身、钢轨、轨枕、道床层、路基层的动力响应以及轮轨力,分析计算得到的结果与相应的限定值进行比较,验证了所建立模型的正确性。     

超高无面板式土工格栅加筋路堤现场试验研究

结合在建宜巴高速公路50 m高的加筋填土断面进行现场试验,对超高无面板式土工格栅加筋路堤的格栅变形、垂直土压力、水平土压力、分层沉降以及深层水平位移等内容进行了近2 a的测试,研究超高无面板式土工格栅加筋土路堤的受力、变形规律,分析了其作用机理。结果表明：不同层位土工格栅的最大拉应变出现在离返包面约4~6 m处,格栅应变沿筋长呈双峰值分布,施工期土工格栅应变具有明显的滞后性,且工后1.5 a格栅出现明显的收缩回弹;土工格栅的存在对土压力分布具有明显的调整作用,格栅末端附近实测垂直土压力值略超过理论值,中间和近坡面部位实测土压力值小于理论值;水平土压力沿路堤高度呈非线性形式分布,路堤中部的水平土压力值略大于顶部,其值小于主动土压力;分层沉降量在施工期存在较大波动,在垂直高度上,上部和底部偏小,中下部偏大;深层水平位移随着深度的增加逐渐减小,填土结束后深层水平位移仍有一定程度增大。     

Laboratory and field investigation of the effect of geogrid-reinforced ballast on railway track lateral resistance

Continuous welded rail (CWR) tracks have particular advantages over common tracks with jointed rails such as increased ride comfort, reduced noise and vibration and decreased maintenance costs due to the removal of joints in rail connections. Alternatively, some complications associated with CWR tracks, for instance increased lateral forces, are the main reason of track buckling and its subsequent lateral deformation. These problems are usually more severe in curved tracks. In order to overcome the large lateral forces caused by temperature deviations of CWR tracks which results in railway vehicle instability, the ballasted track lateral resistance should be improved. Among the various methods proposed in this area, no specific study has been carried out on the effect of geogrid reinforcement on ballasted track lateral resistance. Thus, the present research was allocated to investigating the effect of geogrid on the lateral resistances of both single tie and track panel via laboratory and field tests. In this regard, at the first stage, the ballast layer was reinforced with various number of geogrid layers, the effect of which was investigated by conducting the single tie push test (STPT) in the lab environment to assess the optimum number of geogrid layers and their installation levels along the ballast layer thickness. Afterwards, a test track was executed in the field including various sections which were reinforced in the same way as the lab tests. Consequently, many STPTs and track panel displacement tests (TPDTs) were accomplished. As a result, the STPTs in the lab and field confirmed more than 31% and 42% increase in single tie lateral resistance for ballast layers reinforced respectively with one and two geogrid layers, while these values were reached to 29% and 40% in the case of TPDT.     

Effectiveness of geogrid reinforcement in improvement of mechanical behavior of sand-contaminated ballast

Vertical stiffness and shear strength of ballasts are significantly degraded when contaminated with sands. There is a lack of solutions/studies related to strengthening ballast against sand contamination. Addressing this limitation, a comprehensive laboratory investigation was made on effectiveness of geogrid reinforcement for improvement of mechanical properties of sand-contaminated ballast. To this end, large-scale direct shear tests as well as plate load tests were conducted on geogrid-reinforced ballast samples prepared with different levels of sand contamination. The obtained results indicate that geogrid reinforcement considerably improves shear strength and vertical stiffness of contaminated ballast. A bandwidth was obtained for contamination levels in which ballast reinforcement is effective. Through examining geogrid with different aperture sizes and locations in the ballast layer, the best performance conditions of geogrid reinforcement were derived. The results were used to propose an effective method of ballast reinforcement and an efficient ballast maintenance approach in sandy areas.     

格栅条带式加筋胎面挡土墙变形性能数值计算

采用土工格栅加筋的方法提高废旧轮胎挡墙的承载性能,促进废旧轮胎挡墙的推广应用,通过数值计算方法分析了不同墙顶荷载下有无土工格栅加筋的废旧轮胎挡墙的水平变形与竖向沉降反应特征,得出铺设土工格栅加筋的方法可显著减小墙体的水平变形和竖向沉降,提高废旧轮胎挡墙结构的承载能力,随着外荷载的增加,墙体变形模式依次呈凹凸微小变化型、“弯弓”型、“似弯弓”型和“鼓腮”型和直线型。考虑土工格栅的加筋长度、竖向加筋间距以及格栅加筋刚度3种因素对废旧轮胎+土工格栅加筋土挡墙的水平变形的影响,得出在废旧轮胎加筋土挡墙设计中,建议土工格栅的加筋长度选取范围为0.5H～0.7H,土工格栅竖向间距的选取范围为0.4 m~0.7 m,格栅刚度不宜大于5 000 kN/m。     

Use of cellular confinement for improved railway performance on soft subgrades

Due to extensive right-of-way, railroads are inevitably subject to poor subgrade conditions and interrupted service for significant maintenance due to excessive deformations and loss of track geometry. Geocell confinement presents itself as a possible solution for improving performance of ballasted railroad embankments over weak subgrade. To investigate the efficacy of geocell confinement on ballasted railway embankments, a set of well-instrumented, large-scale cyclic plate loading tests and numerical simulations were performed on geocell-confined ballast overlaying a weak subgrade material. The agreement of results from tests and simulations served as a basis for simulating practical track geometry and performance for various geocell configurations and subgrades using three-dimensional (3D) finite element (FE) analyses. The study showed that geocell reinforcement significantly decreased track settlement, decreased subgrade deformations with lower and uniform distribution of vertical stresses on subgrade and inhibited lateral deformation and serviceability under cyclic loading. These results demonstrate that geocell confinement can be an effective alternative to subsurface improvement or shorter maintenance cycles, particularly on weak subgrades.     

Behavior of geogrid-reinforced ballast under various levels of fouling

This paper presents a study of how the interface between ballast and geogrid copes with fouling by coal fines. The stress-displacement behavior of fresh and fouled ballast, and geogrid reinforced ballast was investigated through a series of large-scale direct shear tests where the levels of fouling ranged from 0% to 95% Void Contamination Index (VCI), at relatively low normal stresses varying from 15 kPa to 75 kPa. The results indicated that geogrid increases the shear strength and apparent angle of shearing resistance, while only slightly reducing the vertical displacement of the composite geogrid-ballast system. However, when ballast was fouled by coal fines, the benefits of geogrid reinforcement decreased in proportion to the increasing level of fouling. A conceptual normalized shear strength model was proposed to predict this decrease in peak shear stress and peak angle of shearing resistance caused by coal fines at a given normal stress.     

Behavior evaluation of geogrid-reinforced ballast-subballast interface under shear condition

The effective functioning of a railway track under operating conditions depends largely on the performance of various rail track interfaces (e.g. ballast-subballast interface, subballast-subgrade interface). In this context, a series of large-scale direct shear tests were conducted to investigate the shear behavior of unreinforced and geogrid-reinforced ballast-subballast interfaces at different normal stresses (σ_n) and rates of shearing (S_r). Fresh granite ballast and subballast having average particle size (D₅₀) of 42?mm and 3.5?mm respectively, and five geogrids with different aperture shapes and sizes were used in this study. Tests were performed at different normal stresses (σ_n) ranging from 20 to 100?kPa and shearing rates (S_r) ranging from 2.5 to 10.0?mm/min. The laboratory test results confirmed that the shear strength of ballast-subballast interface was highly influenced by the applied normal stress (σ_n) and rate of shearing (S_r). The friction angle (φ) of unreinforced ballast-subballast interface was found to decrease from 63.24° to 47.82° and dilation angle (ψ) from 14.56° to 5.23° as the values of σ_n and S_r increased from 20 to 100?kPa and 2.5–10.0?mm/min, respectively. Further, the breakage of ballast (B_g) was found to increase from 2.84 to 6.69%. However, geogrid inclusions enhanced the shear strength of the ballast-subballast interface and also reduced the extent of B_g. The results indicate that it is possible to establish a relationship between the friction angle (φ) and breakage of ballast (B_g), wherein the friction angle (φ) of both unreinforced and geogrid-reinforced interfaces reduces with the increase in breakage (B_g). The interface efficiency factor, defined as the ratio of the shear strength of the geogrid-reinforced ballast-subballast interface to the original shear strength of ballast-subballast interface varies from 1.04 to 1.22. Moreover, the current study revealed that the shear behavior of ballast-subballast interface was influenced by geogrid aperture size (A).     

Study of the behavior of mechanically stabilized earth (MSE) walls subjected to differential settlements

The limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE walls can be limited to an acceptable range by ensuring sufficient factors of safety (FOSs) for both external and internal stabilities. However, unexpected ground movements, such as movements induced by excavations, volume changes of expansive soils, collapse of sinkholes, and consolidations of underlying soils, can induce excessive differential settlements that may influence both the stability and the serviceability of MSE walls. In this study, a numerical model, which was calibrated by triaxial tests and further by a specially-designed MSE wall tests, investigated the behavior of an MSE wall as well as the influence of various factors on the performance of the MSE wall when the wall facing settled relatively to the reinforced zone. The numerical results showed that the differential settlement would cause substantial vertical and horizontal movements for the MSE wall, as well as an increase in lateral earth pressure and geosynthetic reinforcement strain. The maximum horizontal movement and increase of the lateral earth pressure occurred at about 1.0 m above the toe. The differential settlement resulted in a critical plane that coincided with the plane of 45°+?/2. The maximum increase of the strain for each geogrid layer occurred in that plane, and the bottom layer had the greatest strain increase among all layers of reinforcement. The study further indicated that the surcharge, backfill friction angle, tensile stiffness of geogrid, reinforcement length and MSE wall height had noticeable influences on horizontal and vertical movements, and strain in geosynthetics. According to the results, the MSE wall that had a higher factor of safety would have less movements and geosynthetic strain increase. In contrast, only the friction angle, tensile stiffness and MSE wall height showed some degree of influence on the lateral earth pressure due to differential settlements.     

Influence of the ballasted track on the dynamic properties of a truss railway bridge

This article presents numerical and experimental analyses of a steel truss railway bridge. The main feature of this work is that dynamic experiments have been performed before and after the ballasted track was placed on the bridge. Consequently, it has been possible to quantify the effect of the ballast and the rails on the dynamic properties of the bridge. For that, two finite element models, with and without the ballasted track, have been implemented and calibrated using the experimental results. It appears that the ballast gives an additional stiffness of about 25–30% for the lowest three eigenmodes. This additional stiffness can be only partly explained by the stiffness of the ballast. In fact, it seems that this additional stiffness is also due to a change in the support conditions.     

土工合成材料大型直剪界面作用宏细观研究

利用大型直剪模型试验设备，在不同竖向压力下进行一系列的土工合成材料直剪试验，应用数码可视化跟踪技术，结合土体变形无标点量测技术来研究双向土工格栅与砂土直剪界面作用的宏细观特性，同时分析界面附近土压力分布规律，并研究界面颗粒运动变化规律和细观组构演化特征与宏观特性的关联。分析结果表明，直剪筋土界面附近竖向压力分布从前端依次向后端减少；直剪界面位移达25 mm时，形成了稳定的剪应变集中带；在筋土界面（6～8）D₅₀粒径厚度范围内，界面颗粒以旋转和平动方式同时位移，该范围外颗粒以平动方式沿剪切方向位移，且位移较小；在剪切过程中，界面颗粒发生旋转，土体发生剪胀，孔隙率增大，平均接触数减小，颗粒重新被压密，孔隙率减小，平均接触数增多，颗粒长轴排列趋于水平方向，各细观组构处于相对稳定状态。     

An experimental evaluation of the behavior of footings on geosynthetic-reinforced sand

This research was performed to investigate the behavior of geosynthetic-reinforced sandy soil foundations and to study the effect of different parameters contributing to their performance using laboratory model tests. The parameters investigated in this study included top layer spacing, number of reinforcement layers, vertical spacing between layers, tensile modulus and type of geosynthetic reinforcement, embedment depth, and shape of footing. The effect of geosynthetic reinforcement on the vertical stress distribution in the sand and the strain distribution along the reinforcement were also investigated. The test results demonstrated the potential benefit of using geosynthetic-reinforced sand foundations. The test results also showed that the reinforcement configuration/layout has a very significant effect on the behavior of reinforced sand foundation. With two or more layers of reinforcement, the settlement can be reduced by 20% at all footing pressure levels. Sand reinforced by the composite of geogrid and geotextile performed better than those reinforced by geogrid or geotextile alone. The inclusion of reinforcement can redistribute the applied footing load to a more uniform pattern, hence reducing the stress concentration, which will result reduced settlement. Finally, the results of model tests were compared with the analytical solution developed by the authors in previous studies; and the analytical solution gave a good predication of the experimental results of footing on geosynthetic reinforced sand.