Effect of sand-fouled ballast on train-induced vibration

One of the most important issues in desert areas is ballast layer solidification due to windy sand accumulation. This phenomenon increases track modulus which leads to serious damage in railway track components. On the other hand, one of the side effects of this problem is the increase in ground-borne vibration during train passing. Therefore, this research is devoted to the investigating effect of sand-fouled ballast on train-induced vibration by means of experimental and numerical methods. For this purpose, five sections of ballasted railway track in central desert of Iran were monitored for 6 months, and many field measurements were conducted for obtaining track stiffness and ballast fouling percentage. Then, the field measured track stiffness values were implemented in finite element model, and the environmental vibrations due to train passing were assessed in the form of acceleration and displacement time histories for adjacent points of the railway track. The results indicated that, due to the increase in ballast fouling percentage from 0 to 62.7%, maximum acceleration increased by approximately 43% and maximum displacement decreased by approximately 68%.     

脏污对道床剪切性能影响及评估指标的离散元分析

对国内外典型的道床脏污评估指标进行了综合分析。基于已有研究成果,提出了新的道床评估指标PFI。采用离散元法建立了基于精细道砟仿真单元的直剪数值模型,对不同脏污程度道床的剪切性能及PFI的合理性进行了研究,研究结果表明:脏污会显著降低道床的抗剪性能,其下降幅度与道床的脏污程度有关;脏污材料的粒径对道床剪切性能影响明显,且在材质相同的情况下,小粒径的脏污会引起道床剪切性能的进一步降低;相比于已有评估指标VCI,PFI能够考虑脏污材料粒径的影响,从而更准确的评估道床脏污情况。     

Effect of particle size distribution and subgrade condition on degradation of railway ballast under impact loads

Ballasted rail tracks are generally exposed to impact loads generated from abnormal wheel-rail interface as well as sudden variations in support rigidity. These induced impact loads can lead to railway ballast degradation by attrition of the angular edges of the aggregate and breakage of single particle into finer fragments. In the present study, the degradation of ballast particles under impact loads is investigated by considering various fouling and breakage indices. For this purpose, impact test is conducted on ballast aggregates obtained from different quarries (rock types of basalt, marl, dolomite and trachyte) by varying the gradation of ballast aggregates, impact energy and subgrade type. According to the obtained results, the degradation of ballast specimens under impact loading is less for more broadly-graded ballast. In addition, providing a flexible subgrade as support condition leads to reduction in ballast degradation resulted from diminishing impact energy. Furthermore, the axial strain of ballast specimens reduces with decrease in degradation of aggregates under repeated impact loads.     

Time-Frequency Approach for Ground Penetrating Radar Data Analysis to Assess Railroad Ballast Condition

Railroad ballast plays an important role in supporting heavy rail loading, preventing the deformation of track, and providing drainage of water from the track structure. However, over time, ballast is fouled by the breakdown of ballast aggregate and/or the infiltration of fines, which undermine ballast functions. This may result in damage to the rail system, such as track settlement. Ground penetrating radar (GPR), a nondestructive method, can be used to rapidly, effectively, and continuously assess railroad track substructure conditions. Ballast under various fouling conditions generates various electromagnetic (EM) scattering patterns. In this study, air-coupled 2 GHz antenna was found to be sensitive to the scattering pattern change. Appropriate data processing was used to remove the effects of ties and rails to obtain clear GPR images of the subsurface layers. Then, the amplitude envelope and time-frequency approaches were implemented to characterize the signal in time and frequency domains simultaneously. Using these techniques, non-fouled ballast thickness can be assessed and trapped water can be detected, along the track.     

Discrete element modelling of scaled railway ballast under triaxial conditions

The aim of this study is to demonstrate the use of tetrahedral clumps to model scaled railway ballast using the discrete element method (DEM). In experimental triaxial tests, the peak friction angles for scaled ballast are less sensitive to the confining pressure when compared to full-sized ballast. This is presumed to be due to the size effect on particle strength, whereby smaller particles are statistically stronger and exhibit less abrasion. To investigate this in DEM, the ballast is modelled using clumps with breakable asperities to produce the correct volumetric deformation. The effects of the quantity and properties of these asperities are investigated, and it is shown that the strength affects the macroscopic shear strength at both high and low confining pressures, while the effects of the number of asperities diminishes with increasing confining pressure due to asperity breakage. It is also shown that changing the number of asperities only affects the peak friction angle but not the ultimate friction angle by comparing the angles of repose of samples with different numbers of asperities.     

An experimental investigation on the durability of railway ballast material by magnesium sulfate soundness

In this study, the durability of railway ballast material is investigated by magnesium sulfate soundness tests. Two types of ballast aggregates, which are produced from basaltic rocks and currently used as railway ballast in such high speed railway routes in Turkey, are investigated regarding their resistance against freezing–thawing (FT) and traffic loads. Firstly, the mineralogical and physico-mechanical properties of rocks are determined. Then the degradation of investigated ballast aggregates is determined by magnesium sulfate soundness and Los Angeles abrasion (LAA) tests. The natural FT effects are simulated by magnesium sulfate soundness tests up to 40 cycles, whereas the traffic loads are represented by LAA tests up to 3000 revolutions. The ballast fouling that leads to such problems are also investigated within the scope in the present study. The degree of ballast fouling is quantified as fouling index (FI) which is determined using the crushed particles generated after LAA tests. It is concluded from laboratory studies that rock properties considered are considerably influenced by simulated FT cycles. It is also achieved from the laboratory studies that magnesium sulfate soundness and Los Angeles abrasion tests are good indicators to clarify the fragmentation mechanism of the ballast aggregate in laboratory scale. In conclusion several empirical formulas are developed to predict LAA and FI for each rock type. The proposed empirical formulas could be utilized as a pre-design tool for new railway routes in design stage provided that the investigated ballast aggregates are considered.     

研究浓差极化和膜污染过程的方法与策略

简要综述了浓差极化和膜污染的研究方法和策略．利用超滤法处理印钞擦版废液实验说明研究思路和各种分析方法的应用．通过膜阻力模型实验,分析出各污染途径产生的阻力大小,讨论了应注意的问题．采用EDX,ICP,TOC,SEM,FTIR和MC对膜污染物、酸洗和碱洗液、清洗前后膜表面形貌分析鉴定,发现主要无机污染物是钙离子,主要有机污染物是磺化蓖麻油．模拟实验结果与上述结果一致,并引导出四步清洗方法,可对污染膜进行有效清洗;并发现对于严重污染的膜,采用三个以上清洗周期才能使膜通量得到完全恢复．最后提出一个浓差极化和膜污染的研究方法和策略框架图．     

Discrete element modelling of railway ballast

The discrete element method has been used to simulate the behaviour of railway ballast under different test conditions. Single particle crushing tests have been simulated using agglomerates of bonded balls, and the distribution of strengths correctly follows the Weibull distribution, and the size effect on average strength is also consistent with that measured in the laboratory. Realistic fast fracture can be obtained if non-viscous damping is reduced. Oedometer tests on aggregates of crushable ballast particles have also been simulated and compared with the results from laboratory tests. Finally, box tests which simulate traffic loading have been simulated using both spherical balls and 8-ball clumps. It is found that the 8-ball clumps give much more realistic behaviour due to particle interlocking.     

The impact of fouling on the performance of filter–evaporator combinations

This paper presents results of experiments performed on different combinations of five types of filters of varying efficiencies (MERV4, 6, 8, 11, and 14) and four types of evaporator coils with depths and fin geometries under clean and fouled conditions. The fouled conditions were obtained after injection of 600 g (1612 g/m² of coil face area) of dust upstream of the filter–coil combination, which was meant to simulate a year of operation in the field. The air-side pressure drops of the coils and filters and air-side effective heat transfer coefficients of the coils were determined from the measurements under the clean and fouled conditions. Depending upon the filter and coil, the coil pressure drops increased in the range of 6–30% for an air velocity of 2.54 m/s. The impact was significantly greater for tests performed without an upstream filter (the coil pressure drops increased from 43% to 200%). The largest relative effect of fouling on pressure drop occurs for coils with fewer rows, primarily due to higher fin densities. The impact of fouling on air-side effective heat transfer coefficients was found to be relatively small, which ranged from −14% to 4%. In some cases, heat transfer was actually enhanced due to additional turbulence caused by the presence of dust. However, with large dust deposits, heat transfer is degraded because the dust also acts as insulation and creates an uneven air velocity.     

Sensitive and Versatile Detection of the Fouling Process and Fouling Propensity of Proteins on Polyvinylidene Fluoride Membranes via Surface-Enhanced Raman Spectroscopy

Membrane fouling is the major drawback of membrane-based technologies because it will lead to severe flux declines and the need to clean or replace the fouled membrane. A technique capable of early diagnosis, process monitoring, and evaluation of the role of different foulants playing in the fouling process is crucial for the fouling control. We develop surface-enhanced Raman spectroscopy (SERS) as a new and versatile tool to investigate the fouling process of protein on PVDF (polyvinylidene fluoride) membranes as well as the fouling propensity of three different proteins. We optimized the aggregation level and volume of SERS-active Ag sol and the spectra acquisition method combined with a statistical analysis method to ensure a high detection sensitivity, signal uniformity, and stability. We then used SERS for the early diagnosis of the fouling process and determining when the membrane pores would be blocked. The fouled area was visualized by a combination of the silver staining and Raman mapping. The fouling propensity of different proteins was studied by comparing the relative SERS band intensities of different proteins on a glass slide and after membrane filtration. Compared with fluorescence-based techniques, the narrow, well-resolved Raman band, especially the use of the same excitation line and laser power, endows SERS the ability to compare the fouling propensity in a very simple way.     

Comparison of two different types of railway ballast in compression and direct shear tests: experimental results and DEM model validation

Railway ballast is an angular and coarse material, which demands careful DEM modelling and validation. Particle shape is often modelled in high accuracy, thus leading to computational expensive DEM models. Whether this effort will increase the DEM model’s overall prediction quality will also vitally depend on the used contact law and the validation process. In general, a DEM model validated using different types of principal experiments can be considered more trustworthy in simulating other load cases. Here, two types of railway ballast are compared and DEM model validation is conducted. Calcite and Kieselkalk are investigated under compression and direct shear test. All experimental data will be made openly accessible to promote further research on this topic. In the experiments, the behaviour of Calcite and Kieselkalk is surprisingly similar in the direct shear test, while clear differences can be seen in the stiffnesses in the compression test. In DEM modelling, simple particle shapes are combined with the Conical Damage Model contact law. For each type of ballast, one set of parameters is found, such that simulation and experimental results are in good accordance. A comparison with the simplified Hertz-Mindlin contact law shows several drawbacks of this model. First, the model cannot be calibrated to meet both compression and shear test results. Second, the similar behaviour in shear testing but differences in compression cannot be reproduced using the Hertz-Mindlin model. For these reasons, the CDM model is considered the better choice for the simulation of railway ballast, if simple particle shapes are used.     

The impact of evaporator fouling and filtration on the performance of packaged air conditioners

The goal of the study presented in this paper was to evaluate the impact of different filter types on the performance of three typical packaged air conditioners under both clean and fouled conditions. In a companion paper, combinations of six different levels of filtration and four different coils were tested under clean and fouled conditions. From the tests, it was found that fouling has a relatively small impact on air-side effective heat transfer coefficient, but can have a large impact on coil pressure drop. Data from the experimental study were used in developing simulation models for the three packaged air conditioners. Simulations show that the equipment cooling capacity is reduced with fouling primarily because of a decrease in air flow due to the increased pressure drop. In most cases, EER (energy efficiency ratio) was reduced with fouling primarily due to increased fan power. However, the changes in EER were relatively small, in the range of 1–10%. Equipment having low efficiency filters had higher EER after fouling than equipment with high efficiency filters, because high efficiency filters result in significantly higher pressure drops than low efficiency filters. The impact of the evaporator side fan efficiency was found to be significant. The energy penalty associated with high efficiency filters was reduced greatly when fan efficiency increased. Although high efficiency filters cause higher energy penalties they provide considerably better air quality. The quantity of dust passing through the coil with an MERV14 filter was approximately 30 times less than the dust passing the coil with an MERV4 filter. This difference was doubled when the MERV14 filter was compared to a case with no filter in place.     

The application of Weibull statistics to the strength of railway ballast

The tensile strengths of six types of ballast for various size fractions were investigated and quantified using Weibull statistics. For a given ballast and a given size fraction, the strengths follow the Weibull distribution reasonably well. However, it was found the size effect on strength implied by Weibull statistics for bulk failure of particles, is not consistent with measured values. Various possible reasons for this are explored, namely that the grinding process at the quarry may offer a proof test for ballast, that some ballasts may not be homogeneous or isotropic, and finally that surface fracture rather than bulk fracture may dominate.The authors would like to thank Lafarge Aggregates Ltd and Groundwork Hertfordshire for their financial and technical support for this project, which was funded though the Landfill Tax Credit Scheme.     

Pre- and post-cyclic behaviour of an unsaturated clayey soil contaminated with crude oil

Besides adverse impacts on the environment, pollution with hydrocarbon compounds such as crude oil affects the geotechnical parameters like deformation modulus and shear strength. The present research involves evaluation of clayey soil properties changes in an unsaturated state due to application of cyclic loads before and after contamination with crude oil. A series of constant water content (CW) static and dynamic triaxial tests were conducted on samples that were compacted to the same dry density but different degrees of saturation and net confining pressures. The soil studied was provided from a place near an oil refinery located in Iran’s capital city and was artificially polluted with 3%, 6% and 9% crude oil. Deformation modulus reduction due to cyclic loads application was considerably more than reduction of shear strength. Also, these parameters increased due to increasing net confining pressure and initial matric suction. Several chemical tests and techniques were employed to investigate the chemical variations in soil structure and the role of different chemical components of crude oil on quantitative variations of soil characteristics.     

水泥砂浆固化粉质黏土分离式Hopkinson压杆试验与分析

为研究掺砂量（与干土的质量比）对水泥粉质黏土冲击压缩强度及能量吸收特征的影响,采用Φ 50 mm分离式Hopkinson压杆（Split Hopkinson pressure bar,SHPB）试验装置对不同掺砂量的水泥粉质黏土进行了0.4 MPa冲击气压下的冲击压缩试验。结果表明：普通水泥粉质黏土（未掺砂）动态应力-应变曲线大致分为弹性阶段、屈服硬化阶段及破坏阶段,而随着掺砂量的逐渐增加,水泥砂浆固化粉质黏土动态应力-应变曲线中屈服阶段愈加不明显,出现了理想的塑性阶段;水泥砂浆固化粉质黏土的冲击压缩强度随掺砂量的增大而先增大后减小,在掺砂量为10%时达到最大平均动强度9.56 MPa,较普通水泥土强度提高9.79%;水泥砂浆固化粉质黏土的吸收能随冲击压缩强度的增大而增大,两者具有较好的指数关系。     

轨枕空吊对有砟道床动力特性影响的离散元分析

为研究轨枕空吊对有砟道床动力特性的影响,建立有砟轨道的离散元分析模型。通过缩小与枕底相接触的道砟颗粒的粒径实现了轨枕空吊的模拟,研究了轨枕空吊状态下有砟道床的动力响应,分析了轨枕空吊形式和空吊数量对有砟道床动力响应的影响。结果表明:轨枕空吊会使得道床中道砟颗粒接触力发生重分布,空吊轨枕所在道砟箱中强力键的个数会减少,两侧相邻道砟箱中强力键的个数会增多,轨枕非完全空吊时在列车荷载作用下会对道床产生冲击作用而增大部分道砟颗粒受力;空吊轨枕会失去对其下方道砟颗粒的约束作用而导致道砟颗粒振动的离散性增加,同时会增大轨枕盒中道砟颗粒的振动并显著提高两侧相邻轨枕下方道砟颗粒的振动水平;轨枕空吊会增大轨枕侧面与道砟颗粒之间的摩擦耗能,引起道砟出现"泛白"现象,同时还会增大两侧相邻轨枕下方道砟颗粒之间的摩擦耗能;3根轨枕连续完全空吊对道床动力响应的影响大于1根轨枕完全空吊的影响。     

铁路道床振动的理论模拟与试验研究

铁路道床的振动是引起轨道几何变形和养护维修费用增长的关键因素．国内外有关连续散粒体道床的振动分析方法与测量方法至今未得到很好解决。作者在前人研究基础上．基于道床锥体受荷假设，并引人道床剪切刚度和剪切阻尼的概念，建立了分析道床振动的五参数模型；在铁路线路上对道床振动进行了现场实测，试验结果与理论分析结果相吻合，从而验证了道床振动分析模型的正确有效性。     

Experimental development of clay liners for waste containment in arid and semi arid regions

ABSTRACT

The leachate from municipal solid waste, during or after rainfall, through desiccation cracks may contaminate underground aquifers in arid and semiarid regions. This experimental study proposes modified clay liners to control leachate contamination from waste. The test specimens of clay liners were prepared using a mixture of locally available clay, sand, cement and polyethylene chips to reduce the shrinkage potential. Microstructural analysis was also conducted by using Energy Dispersive X-Ray and X-Ray Diffraction. Scanning Electronic Microscopy tests were conducted to find chemical composition and microstructure of unmodified and modified soil specimens. These tests confirmed the presence of montmorillonite clay minerals that have high potential for swelling and thus volumetric shrinkage. The study proposes a combination of 15% sand, 4% cement and 0.5% polyethylene chips to reduce shrinkage potential from 17% to less than 4%. However, the effect of modification on hydraulic conductivity with water and leachate was not very significant. Based on statistical analysis, fair correlations were found between mixture composition and volumetric shrinkage.     

Effect of aggregate gradations on properties of porous friction course mixes

This paper presents the study on effect of aggregate gradation on the mix design and performance properties of porous friction course (PFC) mixes. Six aggregate gradations were tested with due consideration to gradations specified for PFC or similar mixes by different agencies around the world. The PFC mixes were characterized for volumetric properties, permeability, unaged and aged abrasion loss, moisture susceptibility, and rutting resistance. The results were statistically analysed to identify the factors that significantly influence the properties of PFC mixes. Findings of the study clearly indicate that the gradations specified by various agencies will have significant effect on the design properties of PFC mixes, thus they are different. It also, helps in framing the Master aggregate gradation band for PFC mixes. Generally, permeability property is considered to be an optional parameter in the design. However, the findings of the present study recommended considering the permeability as one of the prime parameters in the design of PFC mixes.     

Single-stage high-power-factor electronic ballast with complex frequency modulation for hid lamps

A single-stage, complex frequency-modulated (CFM), high-frequency-driven electronic ballast for high-intensity-discharging (HID) lamps is proposed. The presented ballast combines a power-factor-correction (PFC) converter with a half-bridge series-resonant parallel-loaded inverter as well as a CFM controller. The switching frequency of the integrated inverter is non-periodically modulated by the CFM signal that integrates DC-bus voltage ripples with an additional high-frequency sine-wave signal. Compared with constant-frequency and frequency-modulated (FM) control, the presented ballast offers a widely continuous power spectrum of lamp current with decreased amplitude in order to effectively expand the lamp power as well as reducing sideband frequencies and allowing for a much lower energy level of the eigen frequency that supplies the lamp. Because of its CFM operation, no acoustic resonance occurs; additionally, the obtained results include a 13 dBm reduction of power spectrum at the centre switching frequency compared with FM control, and a 22 dBm reduction compared with constant-frequency control. The ballast offers high power factor (0.99), high efficiency (90%), cost-effectiveness and a simple, easy-to-implement controller. A prototype ballast utilising the CFM control method with 110 V utility-line input voltage has been built, and experimental results were carried out on three different brands of 70 W metal-halide-type HID lamps