Model Testing of Two-Layer Railway Track Ballast

Railway track ballast requires regular attention to maintain line and level. A recently developed maintenance method, known as pneumatic ballast injection (PBI) or stoneblowing, re-levels and realigns the track by lifting the sleepers and track and blowing smaller size gravel between the ballast and the base of the sleeper. This creates a two-layer ballast bed. Series of large-scale model tests have been carried out to gain a better understanding of the behavior of such a bed under repeated loading. The results confirm that stoneblowing is a better form of track maintenance than the commonly used ballast tamping method, but the size and type of stone and the thickness of the injected layer are of critical importance in determining the postmaintenance behavior.     

Response of Multilayer Foundation System beneath Railway Track under Cyclic Loading

For an efficient and economical design of a railway track system, it is necessary to understand the behavior of each track component with special reference to ballast and subgrade, which play a pivotal role in distributing the large, cyclic wheel loads longitudinally, laterally, and vertically away from the wheel contact area on the rail surface to the underlying soil strata. This paper presents an analytical model of a track-ballast-subgrade system with different formation soils such as dense uniform sand, stiff clay, loose sand, and soft clay modeled by using a mass-spring dashpot system with two degrees of freedom. This represents the varying energy distribution through ballast and subgrade in the vertical direction. Results are presented in the form of time-displacement response profiles for both the ballast and subgrade layers. In addition, the magnification factors for displacements with variation in subgrade soils for cyclic loading frequencies are reported. It is observed that the results obtained from the present analysis follow the experimentally observed trends already available in the literature.     

Two Approaches of Finite-Element Modeling of Ballasted Railway Track

Use of a ballast is still popular in railway engineering due to its resilience, relatively low noise, and convenience in construction and maintenance. The ballast layer was modeled with two modeling approaches in this study–continuous elastic solid and spring-connected elements. Two-dimensional finite element models were built. The parameters of ballast layers were correlated between two models to assure comparability. Three levels of vehicle moving speed were analyzed with the models. Significant differences of rail deflection and ballast were found in all speed levels. Vibration spectra were also compared to reveal the characteristics of different finite element models. It was found that the model with spring-connected discrete elements had higher characteristic frequency than the simple ballast model. Increasing speed may significantly increase rail deflections and ballast vibration levels and result in particles movements in the ballast layer. A thorough understanding of model characteristics and engineering problems is crucial to choose the most appropriate model.     

Dynamic Stress Analysis of a Ballasted Railway Track Bed during Train Passage

Scientific design of a railway track formation requires an understanding of the subgrade behavior and the factors affecting it. These include the effective resilient stiffness during train passage, which is likely to depend on the stress history and the stress state of the ground, and the stress path followed during loading. This study investigates the last of these, by means of a two-dimensional dynamic finite-element analysis. The effects of train speed, acceleration/braking, geometric variation in rail head level, and a single unsupported sleeper are considered. Results indicate that dynamic effects start to become apparent when the train speed is greater than 10% of the Rayleigh wave speed, vc, of the subgrade. At a train speed of 0.5vc, the shear stresses will be underestimated by 30% in a static analysis, and at train speeds greater than vc the stresses due to dynamic effects increase dramatically. Train acceleration/braking may increase shear stresses and horizontal displacements in the soil, and hence the requirement for track maintenance at locations where trains routinely brake or accelerate. For heavy haul freight trains, long wavelength variations in rail head level may lead to significantly increased stresses at passing frequencies (defined as the train speed divided by the wavelength of the variation in level) greater than 15, and short wavelength variations at passing frequencies of 60–70. Stress increases adjacent to an unsupported sleeper occur in the ballast and subballast layers, but rapidly become insignificant with increasing depth.     

Experimental and Numerical Study of Railway Ballast Behavior under Cyclic Loading

This paper presents the results of the influence of frequency on the permanent deformation and degradation behavior of ballast during cyclic loading. The behavior of ballast under numerous cycles was investigated through a series of large-scale cyclic triaxial tests. The tests were conducted at frequencies ranging from 10–40 Hz, which is equivalent to a train traveling from 73 km/h to 291 km/h over standard gauge tracks in Australia. The results showed that permanent deformation and degradation of ballast increased with the frequency of loading and number of cycles. Much of breakage occurs during the initial cycle; however, there exists a frequency zone of 20?Hz ? f ? 30?Hz where cyclic densification takes place without much additional breakage. An empirical relationship among axial strain, frequency and number of cycles has been proposed based on the experimental data. In addition, discrete-element method (DEM) simulations were carried out using PFC2D on an assembly of irregular shaped particles. A novel approach was used to model a two-dimensional (2D) projection of real ballast particles. Clusters of bonded circular particles were used to model a 2D projection of angular ballast particles. Degradation of the bonds within a cluster was considered to represent particle breakage. The results of DEM simulations captured the ballast behavior under cyclic loading in accordance with the experimental observations. Moreover, the evolution of micromechanical parameters such as a distribution of the contact force and bond force developed during cyclic loading was presented to explain the mechanism of particle breakage. It has been revealed that particle breakage is mainly due to the tensile stress developed during cyclic loading and is located mainly in the direction of the movement of ballast particles.     

435m^2烧结机台车跑偏现象的分析与纠正

武钢烧结厂一烧结车间烧结机自投产后,实际运行过程中故障停机率较高,台车跑偏现象较为严重,经多次调整后效果仍不明显。一烧结车间年修期间,对烧结机平面轨道、回车道、头、尾弯道进行了更换,对尾部星轮齿板不同步现象进行了调整,有效地解决了烧结机台车跑偏问题,提高了设备作业率,降低了烧结机漏风率,确保了烧结机的正常运行。     

Estimation of Maximum Liquid Depth in Layered Drainage Blankets over Landfill Barriers

Based on an extended form of the Dupuit assumption, this technical note proposes a computational solution for calculating the maximum liquid depth (Dmax) in layered porous media (e.g., geosynthetic and/or soil drainage blankets of landfills) under free discharge condition. The liquid profile and the location of Dmax for either homogeneous media or layered media can be provided from the approach presented in this technical note. In comparison with the results obtained by application of other methods, the presented approach is verified. Most approaches other than the presented method may lead to considerable error, especially when applied to the drainage system, which consists of a drainage geocomposite overlain by a sand layer with low hydraulic conductivity. The variations of Dmax in two-layered drainage media with varying geometrical parameters and varying hydraulic properties are studied by a parametric analysis. The results demonstrate for a medium consisting of two sand layers, if the hydraulic conductivity of the upper layer is smaller than that of the lower layer and the maximum liquid thickness above the barrier exceeds the thickness of the lower layer, Dmax is very sensitive to the hydraulic conductivity of the upper layer. For a medium consisting of a drainage geocomposite overlain by a sand layer, Dmax is significantly influenced by inflow rate, transmissivity of the geocomposite, and the hydraulic conductivity of the sand when they are not extraordinarily low, and Dmax is much more sensitive to the slope of the drainage layer compared with the system consisting of two sand layers. It is of great advantage to increase the inclination when geocomposites are applied as drainage material.     

基于声发射概率密度函数固废胶结充填体损伤分析

固废胶结充填体是保障矿山安全回采的关键承载结构,为探究其实际承载损伤破坏过程,在RMT-150C岩石力学测试系统上对不同粗骨料含量的4组胶结充填体试样进行了单轴压缩与循环载荷下的声发射试验。结果表明：循环载荷下,4组试样均具有显著的Kaiser效应,且含块石的3组试样声发射事件数更丰富,峰值应力前达到了纯尾砂试样的152%、225%和300%。同时,利用声发射概率密度与承载应力水平间的关联性,得到了4组不同块石含量胶结充填体的声发射概率密度方程,通过声发射概率密度函数实现了声发射参数量化分析胶结充填体承载损伤过程。对比损伤变量-应力水平曲线可以看出,块石的加入能够有效减缓并抑制前期损伤,当块石含量为20%时,效果最好。     

铝电解多功能天车轨道接头磨损的机理分析

分析铝电解多功能天车轨道接头的受力情况、轮轨磨损机理和现场采集的数据照片,指出轨道经过碾压后的硬度变化以及氧化铝灰对天车轨道接头磨损的影响,提出相应措施.     

Mechanical Stabilization of Cemented Soil–Fly Ash Mixtures with Recycled Plastic Strips

An experimental investigation was undertaken to evaluate the mechanical behavior of a soil–cement–fly ash composite, reinforced with recycled plastic strips (high-density polyethylene) that were obtained from postconsumer milk and water containers. The primary motivation for the study was to investigate the innovative reuse of several candidate waste materials in geotechnical and pavement applications. The specific objectives of the research were: (1) to evaluate the compressive, split tensile, and flexural strength characteristics of the material, and (2) to determine the effectiveness of recycled plastic strips in enhancing the toughness characteristics of the composite. Since cement-stabilized materials are weak in tension, the main focus of the experimental program was to conduct a series of specially instrumented split tensile and flexural tests on mixes containing various amounts of cement, fly ash, and plastic strips. For a meaningful comparison of test results, all specimens were prepared at a constant dry density. The standard ASTM C496 procedure for split tensile test was slightly modified by attaching two horizontal linear variable differential transformers (LVDTs) to measure the diametral deformation of the specimen due to compressive loading in an orthogonal direction. This modification enabled the evaluation of the postpeak toughness behavior of the composite. For some specimens, a strain gauge was attached to the middle of the face perpendicular to the loading plane in order to correlate the results with the one found using the LVDTs. All tests were performed with a 90 kN universal testing machine with deformation control. Experimental data show that the soil–cement matrix stabilized with 4% to 10% by weight of fly ash and reinforced with 0.25% to 0.5% (by weight) plastic strips (having lengths of 19 mm or 38 mm) can achieve a maximum compressive strength of 7000 kPa, a split tensile strength of 1000 kPa, and a flexural strength of 1200 kPa. These ranges in strength values are suitable for a high-quality stabilized base course for a highway pavement. To quantify the reinforcing effects in the postpeak region, a dimensionless toughness index is proposed. It is found that the use of fiber reinforcement significantly increases the postpeak load carrying capacity of the mix and thus the fracture energy. It is concluded that the lean cementitious mix containing recycled materials offer a lot of promise as an alternative material for civil engineering construction.     

Fatigue Life Evaluation of Concrete Bridge Deck Slabs Reinforced with Glass FRP Composite Bars

Since bridge deck slabs directly sustain repeated moving wheel loads, they are one of the most bridge elements susceptible to fatigue failure. Recently, glass fiber-reinforced polymer (FRP) composites have been widely used as internal reinforcement for concrete bridge deck slabs as they are less expensive compared to the other kinds of FRPs (carbon and aramid). However, there is still a lack of information on the performance of FRP–reinforced concrete elements subjected to cyclic fatigue loading. This research is designed to investigate the fatigue behavior and fatigue life of concrete bridge deck slabs reinforced with glass FRP bars. A total of five full-scale deck slabs were constructed and tested under concentrated cyclic loading until failure. Different reinforcement types (steel and glass FRP), ratios, and configurations were used. Different schemes of cyclic loading (accelerated variable amplitude fatigue loading) were applied. Results are presented in terms of deflections, strains in concrete and FRP bars, and crack widths at different levels of cyclic loading. The results showed the superior fatigue performance and longer fatigue life of concrete bridge deck slabs reinforced with glass FRP composite bars.     

Interphase Strain Gradients in Multilayered Steel Composite from Microdiffraction

Multilayered steel composites consisting of alternating martensite and austenite layers and exhibiting a combination of high strength and ductility were successfully fabricated. To understand the microplasticity mechanisms responsible for such exceptional mechanical behavior, 3D X-ray microscopy with a submicron beam size was employed to probe the stress/strain distribution within the top two layers during incremental tensile loading. The 3D depth-dependent strain gradients were monitored in situ near the martensite/austenite interfaces as a function of the load level. It was observed that the strain gradients redistributed during loading. Specifically, large compressive strains developed in the top martensite layer transverse to the loading direction, while small tensile strains were found across the layer interface into the underneath austenite layer.     

Behavior of Railroad Ballast under Monotonic and Cyclic Loading

A relatively new method for mechanized maintenance of railroad ballast (stoneblowing) puts a layer of single size stone between the ballast and each tie creating a two-layer gravel support. To get a better understanding of the behavior of this arrangement series of large diameter, triaxial tests have been carried out on single size and layered specimens. A new method of quantifying particle breakage during testing has been developed, and a conceptual model used to explain the combined effects of shearing and breakage on observed specimen behavior.     

Experimental Dynamic Response of a Short-Span Composite Bridge to Military Vehicles

A continued desire for increased mobility in the aftermath of natural disasters or on the battlefield has lead to the need for improved lightweight bridging solutions. Currently, within the U.S. military, there is a need for a lightweight bridging system for crossing short-span gaps up to 4 m (13.1 ft) in length. This paper describes the field testing of a newly developed lightweight fiber-reinforced polymer bridging system to meet the U.S. militaries needs. The study investigates dynamic impact loads of track and wheel vehicles at different crossing speeds to increase understanding of appropriate impact factors used in design. It was found that the impact loads for the bridge treadways were most sensitive to vehicle crossing speed and vehicle type (wheel versus track and axle spacing) with observed impact factors as high as 1.71.     

块石对充填体强度特性及损伤演化的影响

块石胶结充填体中块石含量是决定承载能力的关键因素,在RMT-150C材料试验机上进行不同块石含量的尾砂胶结充填体单轴压缩试验,研究块石对充填体不同承载阶段变化规律的影响。对比应力-应变关系曲线,发现块石的加入有利于提高充填体抗压强度,延迟应力峰值出现。利用试验测试结果得到损伤本构模型表达式和损伤演化方程表达式。分析损伤变量-应变关系曲线可知,块石的加入有利于减缓损伤变量的增长速率,并对提高残余承载能力具有显著效果。     

铁水罐低成本罐底垫补料的研制与应用

选择用后铝碳化硅滑板再生料为主要原材料,通过原料的合理选择与配方优化试验,研制了铁水罐维护用低成本罐底垫补料。通过实际生产应用,在仅进行2次垫补的条件下,取得了罐底工作衬与脱硫铁水罐其他部位使用寿命匹配的目标,从而减少了脱硫铁水罐的维护工作量,降低了维护成本。     

Behavior of Reinforced Concrete Bridge Decks on Skewed Steel Superstructure under Truck Wheel Loads

This paper focuses on the behavior of skewed concrete bridge decks on steel superstructure subjected to truck wheel loads. It was initiated to meet the need for investigating the role of truck loads in observed skewed deck cracking, which may interest bridge owners and engineers. Finite-element analysis was performed for typical skewed concrete decks, verified using in?situ deck strain measurement during load testing of a bridge skewed at 49.1°. The analysis results show that service truck loads induce low strains/stresses in the decks, unlikely to initiate concrete cracking alone. Nevertheless, repeated truck wheel load application may cause cracks to become wider, longer, and more visible. The local effect of wheel load significantly contributes to the total strain/stress response, and the global effect may be negligible or significant, depending on the location. The current design approach estimates the local effect but ignores the global effect. It therefore does not model the situation satisfactorily. In addition, total strain/stress effects due to truck load increase slightly because of skew angle.     

电解多功能起重机车轮的疲劳计算

本文针对目前铝电解多功能起重机使用的车轮进行计算分析,建立了车轮踏面最大接触应力与车轮直径、轨道曲率半径及轮压分布等因素的关系,并确定考虑机构工作级别和车轮材料性能的车轮踏面的疲劳极限许用应力,进一步完善了车轮踏面的疲劳计算。同时,对其它类型起重机车轮的疲劳计算也具有指导意义。     

180m~2烧结机台车跑偏调整实践

唐钢公司炼铁厂180 m2烧结机台车存在跑偏问题,分析原因是星轮两侧齿板不同步,机尾移动摆架配重重量不足,滑道、轨道、弯道磨损严重造成的,通过调整、更换弯道、滑道和轨道保证烧结机安装基准以及调整烧结机配重重量,有效解决了台车跑偏问题。     

Behavioral effects of environmental enrichment in randomly bred mice.

Reared 212 randomly bred mice from birth in an enriched environment or in a standard control environment. Ss were tested for open-field activity and defecation, running wheel activity, exploration, and hoarding. After the hoarding tests all Ss were sacrificed and adrenal glands were removed and weighed. Significant main effects due to treatment were found on gross body weight at 38 days of age, open-field activity and defecation, running wheel activity measures, and exploration. Correlational analyses revealed that open-field activity was positively associated with exploratory behavior, and that the 2 activity measures were positively associated. In the control Ss, the running wheel measures were positively associated with hoarding performance. Results are discussed and compared with previous studies of environmental enrichment and mouse behavior. It is concluded that the effects of early enrichment upon open-field activity, running wheel activity, and exploration are well established. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)