Metro Track Research Articles

Field measurement of track vibration induced by full-load and empty-load condition in curve section of underground metro line

In order to compare the differences in vibration before and after wheel re-profiling and assess the vibration impact of train under full-load and empty-load condition, the field vibration measurement was conducted on an underground metro track components (including rail, sleeper, and track-bed) by using a specific testing car. The results indicate that wheel re-profiling is effective in reducing track vibration, within the frequency range of 31.5–1250 Hz, the vibration acceleration levels of the track after wheel re-profiling were notably lower than those prior to re-profiling and the vibration acceleration levels of the rail, sleeper, and track-bed decrease by 4.7 dB, 6.6 dB, and 6.7 dB, respectively. In the frequency domain, the characteristic peak frequencies of the three track components, whether under full load or empty load, align closely with the frequencies associated with track irregularities. Full-load condition primarily affects the vibration acceleration at lower frequencies, with minor influence on higher frequencies. The vibration acceleration levels of all three track components are higher under full load than empty load. Additionally, under full-load condition, the transmission loss from the rail to the sleeper increases, while the transmission loss from the sleeper to the ballast remains nearly constant. The results of vibration acceleration levels obtained from routine vehicle operations validate the limited impact of axle load on track components vibration.

Metro Monolithic Track Bed Vibration Characterization

With the rapid development of cities, metro transportation has also developed rapidly to solve the congestion problems caused by urban development. However, with the continuous development of metro transportation, the vibration problems caused by it have become increasingly obvious. Based on the phonon crystal theory, this paper investigates the vibration characteristics of the metro track structure. It analyzes the influence of the track structure parameters on the band gap characteristics to regulate the metro vibration band gap range. To study the band gap characteristics of metro monolithic bed track structure, establish the double-layer Euler beam model and use the plane wave expansion method (PWE) to calculate its energy band structure; use the finite element method (FEM) to calculate to get its band structure, frequency response function, and time domain analysis. The calculation of PWE shows that there is a band gap in the range of 0–300[Formula: see text]Hz for the metro monolithic track bed, which is 0–194.5[Formula: see text]Hz; the calculation of FEM shows that the range of band gap is 0–193.7[Formula: see text]Hz. Fastening spacing, stiffness, and sub-slab support stiffness will have an impact on the band gap, so appropriate fastening and spacing need to be selected for effective vibration damping of the track structure. The results show that the band gap characteristics of the metro monolithic track bed can be calculated effectively and accurately by using the phononic crystal theory.

Unified Model Based on Reinforced Feature Reconstruction for Metro Track Anomaly Detection

Unified Model Based on Reinforced Feature Reconstruction for Metro Track Anomaly Detection

Metro track geometry car routing problem with periodic demands: a case study in Beijing, China

Because of their curvature, age, track type and maintenance history, metro tracks should be inspected periodically during the planning horizon. Metro companies operate track geometry cars to periodically collect measurement data from the tracks by crossing the urban rail transit network. Optimizing the schedule for the track geometry car is a challenge: in addition to minimizing travelling distance, the inspection time interval of the same line should be arranged as equally as possible within the planning horizon. This article proposes a mathematical model for the track geometry car routing problem with periodic demands (TGCRP-PD). To effectively address this problem, a memetic algorithm-based metaheuristic is adopted. The proposed solution approach is applied to a real-world case. The numerical results show that the proposed method could save a dead mileage of 295.016 km (accounting for 48.882%) and greatly improve the level of service intervals.

Short-pitch corrugation formation on resilient fastener metro tracks explained using rail-bending vibrations within the bogie wheelbase

Short-pitch corrugation is a serious problem on resilient fastened railway track for many metro lines, causing severe noise and vibration that shortens the life of the vehicle and track components. To address this problem, the formation mechanism of this kind of corrugation is investigated in this study. The corrugation characteristics and natural frequency of the resilient fastener track are determined by field investigations. Then, ‘frequency sweeping’ and long-term rail-roughness prediction models are developed to reveal the crucial role of the interactions between two wheelsets in the corrugation formation and to estimate the effects of speed variations and bogie wheelbase on corrugation growth. The spectral analysis results indicate that the spatial frequency spectrum exhibits several peaks at equal intervals due to the short-pitch corrugation of a resilient fastener metro track, which are related to the third-order rail-bending vibration within the bogie wheelbase at about 775 Hz. In addition, large and small speed variations affect the wavelength and depth growth of the corrugation, respectively. The growth of corrugation depth is amplified when the resonance frequency associated with the corrugation formation is an integer-multiple of the wheel-passing frequency. The wheelbase is also an important factor in determining the corrugation wavelength because of its influence on the resonance frequency.

Metro Track Geometry Defect Identification Model Based on Car-Body Vibration Data and Differentiable Architecture Search

Efficient and low-cost modes for detecting metro track geometry defects (TGDs) are essential for condition-prediction-based preventive maintenance, which can help improve the safety of metro operations and reduce the maintenance cost of metro tracks. Compared with the traditional TGD detection method that utilizes the track geometry car, the method that uses a portable detector to acquire the car-body vibration data (CVD) can be used on an ordinary in-service train without occupying the metro schedule line, thereby improving efficiency and reducing the cost. A convolutional neural network-based identification model for TGD, built on a differentiable architecture search, is proposed in this study to employ only the CVD acquired by a portable detector for integrated identification of the type and severity level of TGDs. Second, the random oversampling method is introduced, and a strategy for applying this method is proposed to improve the poor training effect of the model caused by the natural class-imbalance problem arising from the TGD dataset. Subsequently, a comprehensive performance-evaluation metric (track geometry defect F-score) is designed by considering the actual management needs of the metro infrastructure. Finally, a case study is conducted using actual field data collected from Beijing Subway to validate the proposed model.

A tailored branch-and-bound algorithm for routing a metro track inspection vehicle

The track geometry data provide an important basis on which engineers can evaluate the status of a metro track. The manual routing process for inspection vehicles usually takes a long time, and the solution quality may be unsatisfactory. Considering both energy efficiency and the convenience of engineers, this article studies the routing problem for an inspection vehicle to collect the metro track geometry data with minimum total cost under complicated constraints according to industry practice. This work differs from previous studies in that the characteristics of the metro network and convenience for data-processing engineers are specifically considered. As this routing problem is an NP-hard problem, a novel graph transformation method and a tailored branch-and-bound algorithm with reference lower bounds are designed. Finally, a numerical case is studied in Beijing’s metro network. The numerical results show that the designed algorithm can solve the problem effectively, and it outperforms the genetic algorithm.

Local-Ideal-Points based Autonomous Space Decomposition framework for the Multi-objective Periodic Generalized Directed Rural Postman problem under Length Restrictions with Intermediate Facilities

This paper introduces a Multi-objective Periodic Generalized Directed Rural Postman Problem under Length Restrictions with Intermediate Facilities (MO-PGDRPPLRIF) applied in the metro track inspection routing problem, which is a variant of the Arc Routing Problem (ARP). In the MO-PGDRPPLRIF, arcs are partitioned into given clusters, and each cluster is associated with a service frequency. As the vehicle has limited working hours per day, several trips may be necessary to complete all tasks. The vehicle must stop at an intermediate facility after each trip such that the parking location where the vehicle ends one day is the same as the position where the vehicle starts the next day. The following objectives are considered in the problem: (i) minimizing the total distance; (ii) making time intervals between two adjacent services for clusters with multiple service frequencies as consistent as possible; and (iii) minimizing the number of trips. In this paper, a novel multi-objective evolutionary algorithm, namely Local-Ideal-Points based Autonomous Space Decomposition (LIP-ASD), is developed to address the proposed problem. LIP-ASD employs a space-decomposition scheme to narrow the search space and exclude inferior solutions. The Discrete Particle Swarm Optimization (DPSO) is embedded to find a satisfactory solution in each decomposed space. The proposed approach is tested through the modified Capacitated ARP (CARP) benchmark instances and a real-world application in Beijing Metro Corporation. Computational results confirm that our solution approach can solve the problem effectively and outperforms the other three state-of-the-art multi-objective evolutionary algorithms.

Evaluating Water Table Rising Under Eastern Cairo (Metro Line)

The booming increase in population in last decades led to poor environmental condition in some areas in the capital city of Egypt. The main two tackled environmental impacts from the increased population, in this research, are the heavy traffic densities jam and groundwater rise in many areas in the city. The massive population causes traffic congestion in the capital due to the increased poor planned urban expansion. The groundwater rise is resulted from leakage from over loeaded and poorly maintained drinking and sanitary water networks. More than 40% of the capacity of these networks leaked to ground, moving, with the topographic gradient sub-surfable to the lower areas; transporting all pollutants and dissolved salts from soil to the aquifer. This, also, threatens the buildings stability and prevent the usability of these buildings. The government is currently exerting massive efforts and increasing the investments tremendously on solving the traffic congestions and implementing new roads. Zooming into the study area, replacing the non-working old metro track into a road to link between Mansheyet El-Bakry and El-Demrdash is faced with the high groundwater table occurring in the area. The main objective of the current research is, to evaluate the proposed alternatives for solving the traffic problem through implementing new road, taking into consideration conducting a suitable solution for the high groundwater table. Moreover, investigating the main causes of the groundwater rise and assess environmentally the impact on the study area. Several proposed alternatives were evaluated for solving the concerned issues through extensive field and hydrogeological investigations, pumping tests, and numerical model (GMS- modflow) to simulate the hydrogeological conditions of the study area and test the proposed solutions. The alternatives were, also, assessed through a designed weighted impact assessment to analyze the best solution. the weighting assessment factors include efficiency, initial and operational costs, extracted water volume, lower groundwater rise, building stability, construction feasibility. The comprehensive investigation and assessment indicated that the most effective solution. Nevertheless, prevention at source is also urgently needed through rehabilitation of drinking and sanitary water networks in the capital to minimize the seepage and losses percentage of the transported water. Keywords: Groundwater Rise, Cairo, traffic congestions, dewatering system, groundwater modeling, groundwater quality DOI: 10.7176/CER/14-6-03 Publication date: October 31 st 2022

Influence of Metro Track Irregularities on Pantograph Vibration and Its Interaction with Catenary

The problem of excessive wear of pantograph strips frequently occurs on China’s Z City Metro Line 1. After on-site investigation and analysis by the metro operating company, it was speculated that the problem was related to abnormal track irregularities. Therefore, taking Z City Metro Line 1 as the main research object, the measured track irregularity of the whole line was analyzed and compared with other typical track spectra, and a track-vehicle-pantograph-catenary coupling dynamics model was established to analyze the relationship between the pantograph-catenary dynamic characteristics and the track irregularity. The two frequency ranges of the track irregularity that have a significant impact on the pantograph-catenary contact were found. Finally, after numerical calculation and analysis, it is recommended to focus on the irregularities with the two wavelength ranges of 9~16 m and 3~4 m in the maintenance.

Development of metro track geometry fault diagnosis convolutional neural network model based on car-body vibration data

Traditional track geometry fault diagnosis methods, such as track geometry car, track detection trolley and manual measurement, suffer from low detection frequency. Therefore, using vibration data from in-service metro vehicles to diagnose metro track geometry faults can improve the efficiency of metro track condition detection. Hence, a metro track geometry fault diagnosis model using car-body vibration was established in this study based on a convolutional neural network model, and the effects of the structural hyperparameters on the model performance were analysed. First, the problem of car-body vibration data collection was addressed, and a mileage-locating model without the global navigation satellite system was developed. Then, the metro track geometry fault diagnosis model was derived using a convolutional neural network whose architecture is determined by four hyperparameters. Finally, a case study was performed using the Beijing Subway 1 track geometry car detection data and car-body vibration data. The results demonstrated the effectiveness of the proposed model.

Analysis and Research on Common Electrical Safety Problems of Metro Track

Analysis and Research on Common Electrical Safety Problems of Metro Track

Experimental and numerical investigation into development mechanism of wheel polygonalization

The polygonal wear is a significant concern in railway engineering, and the mechanism behind it remains elusive. In this study, the polygonal wear on a specific metro line in China is analyzed. The 7th-order and 8th-order wheel polygonal wear are commonly measured on the metro, in which corresponding excitation frequency is located in the 44.3–58.9 Hz interval at the operating speeds of 60–70 km/h. Meanwhile, an obvious natural resonance at 50.7 Hz is found by analyzing the acceleration of axle box, which is verified by the eigen analysis of the corresponding metro track. Moreover, the vehicle-track coupling model with polygonal wheel is established to analyze the vertical wheel/rail forces induced by polygonal wear. The result indicates that the P2 resonance is the main contributor to the high amplitude vertical wheel/rail forces, which is also the main factor for development of polygonal wear after formation.

Research on Vibration Reduction Characteristics of Straight Section of Metro Track with Damping Wheel

Research on Vibration Reduction Characteristics of Straight Section of Metro Track with Damping Wheel

Study on the effect of the fastener support structure on rail corrugation in metros based on the friction-induce vibration

Rail corrugation is very serious in Cologne egg fastener track; effective control measures are still lacking. The cause of the corrugation wear on a curved metro track is analyzed based on the friction-induced vibration theory. A finite element model is established to study the frequency domain and time domain features of the friction-induced oscillation of this system. The influences of the fastener spacing and the fastener support length on the corrugation wear are investigated to develop countermeasures. The simulation results show that the friction-induced vibration of the wheel-track system is the wavelength-fixed mechanism of the corrugation wear of rail of the curved Cologne egg fastener track. There are two reasons why the low rail corrugation wear is more serious. The contact resultant force between the low rail and the wheel is obviously bigger than that between the wheel and the high rail, resulting in a higher wear rate of the low rail. The contact force fluctuation of the low rail caused by the friction-induced vibration is more severe, resulting in a higher corrugation wear evolution speed on the low rail. The friction-induced oscillation cannot be eliminated only by adjusting the fastener support length and spacing. However, the long-wavelength corrugation wear instead of the more harmful short-wavelength corrugation wear can be produced by adjusting the fastener support length and the fastener spacing to alleviate the influence of corrugation wear on the vehicle-track system.

Assessment of Noise Pollution of Kolkata Metro Railway System and Its Impact on Urban Receptors A Case Study

An assessment of noise quality was conducted at underground and overground metro stations, within the metro rakes (AC and Non-AC) and at an institutional building near elevated metro corridor to assess the exposure of Kolkata Metro Railway System. The present study was conducted in different hours (peak and non-peak hour) for different types of rake (AC and Non-AC) movement. Different noise descriptors including A-weighted equivalent noise (Leq), statistical noise (L10,L50,L90), noise climate (NC), traffic noise index (TNI), two hour noise dose (%ND) and corresponding time-weighted average (TWA) were calculated under the purview of the present study. Pearson’s correlation was performed between all noise descriptors to investigate the relation between them. Scatter plot analysis was conducted between L10 and %ND. In case of all study duration, all noise descriptors mostly exceeded FTA prescribed noise standard, along with 2-hr TWA which exceeded the OSHA guidelines of 100 dB for both AC and Non-AC rakes. On the other hand, at underground and overground metro stations, within metro rakes (except at day peak hour within AC coach) and at school building, mean value of traffic noise index (TNI) exceeded 74 dB (A), the threshold of over criterion. The study results indicate that Non-AC rakes are more annoying than AC-rakes. In all the study units, Leq was influenced by L10, which originates from pressure honking. There is very strong relationship observed between L10 and % ND. This study proposes that noise barrier should be installed at underground and overground metro stations, along the stretches of overground metro track, within metro rakes for developing the acoustic quality of Kolkata Metro Railway System and the areas of its immediate vicinity.

A New On‐line Monitoring Method for Stray Current of DC Metro System

In order to solve the problem that the metro stray current cannot be directly numerically measured by the existing methods, and the data acquisition distortion caused by the special operating environment of the metro system, a new on‐line monitoring method for stray current was put forward in this paper. First, the stray current distribution function at different positions of metro trains was derived. Then, the equivalent circuit of stray current was built according to the field measured environment, and the numerical calculation formula of stray current was deduced. On the basis of the formula, the metro stray current could be calculated by the real‐time monitoring data, and the calculated data can be filtered and fitted with the stray current distribution function. In order to identify the distorted data, the potential energy function was introduced to judge the deviation degree of data point from the fitting function, so the erroneous data can be effectively eliminated. Thus, the accurate distribution value of stray current along the metro track was obtained. Taking a metro station in a certain city as the prototype, the CDEGS simulation model was built to verify the proposed method. The simulation results showed that even under the condition of sampling data distortion, the method could directly calculate the stray current value in real time, which had strong fault tolerance. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Experimental Investigation on the Bond Behavior of Deformed Bars in a Class of Structural Expanded Polystyrene (EPS) Concrete

The structural expanded polystyrene (EPS) concrete (above 35 MPa) has the potential to be used as metro track bed to reduce and isolate vibration, but its bond behavior is still unclear. This inhibits its application because it is often used in combination with reinforcing bar. In this paper, a class of structural EPS concrete (above 35 MPa) was developed. Based on this, a series of pull-out tests were conducted and the bond behavior of deformed bars in these structural EPS concretes was investigated. In addition, effects of rebar bond length and rebar diameter were analyzed in detail. Experimental results indicate that the structural EPS concrete suffers splitting failure more easily than the conventional concrete (CC). Increase of EPS replacement, rebar bond length or rebar diameter tends to cause the splitting failure of structural EPS concrete. Moreover, with increase of EPS replacement, the failure process is less explosive and more gradual. The stress-slip relationships of the most specimens show three stages, namely linear ascending, non-linear progression, and descending stages. The bond strength of structural EPS concrete is found depended linearly on the power function of its compressive strength, relative cover thickness (c/d) and relative rebar bond length (L/d), respectively. Accordingly, a bond strength prediction model was formulated, and it can precisely predict the bond strength of deformed bars in structural EPS concrete, specimens failing in splitting or splitting-pull out modes, and no fiber added. The results can provide reference for the design of structural EPS concrete.

Ground-Based Radar Interferometry for Monitoring the Dynamic Performance of a Multitrack Steel Truss High-Speed Railway Bridge

With the continuous expansion of the high-speed railway network in China, long-span railway bridges carrying multiple tracks demand reliable and fast testing procedures and techniques. Bridge dynamic behavior analysis is a critical process in ensuring safe operation of structures. In this study, we present some experimental results of the vibration monitoring of a four-track high-speed railway bridge with a metro–track on each side: the Nanjing–Dashengguan high-speed railway bridge (NDHRB). The results were obtained using a terrestrial microwave radar interferometer named IBIS-S. The radar measurements were interpreted with the support of lidar point clouds. The results of the bridge dynamic response under different loading conditions, including high-speed trains, metro and wind were compared with the existing bridge structure health monitoring (SHM) system, underlining the high spatial (0.5 m) and temporal resolutions (50 Hz–200 Hz) of this technique for railway bridge dynamic monitoring. The detailed results can help engineers capturing the maximum train-induced bridge displacement. The bridge was also monitored by the radar from a lateral position with respect to the bridge longitudinal direction. This allowed us to have a more exhaustive description of the bridge dynamic behavior. The different effects induced by the passage of trains through different tracks and directions were distinguished. In addition, the space deformation map of the wide bridge deck under the eccentric load of trains, especially along the lateral direction (30 m), can help evaluating the running stability of high-speed trains.

Foreign Object Intrusion Detection on Metro Track Using Commodity WiFi Devices with the Fast Phase Calibration Algorithm.

With continuous development in the scales of cities, the role of the metro in urban transportation is becoming more and more important. When running at a high speed, the safety of the train in the tunnel is significantly affected by any foreign objects. To address this problem, we propose a foreign object intrusion detection method based on WiFi technology, which uses radio frequency (RF) signals to sense environmental changes and is suitable for lightless tunnel environments. Firstly, based on extensive experiments, the abnormal phase offset between the RF chains of the WiFi network card and its offset law was observed. Based on this observation, a fast phase calibration method is proposed. This method only needs the azimuth information between the transmitter and the receiver to calibrate the the phase offset rapidly through the compensation of the channel state information (CSI) data. The time complexity of the algorithm is lower than the existing algorithm. Secondly, a method combining the MUSIC algorithm and static clutter suppression is proposed. This method utilizes the incoherence of the dynamic reflection signal to improve the efficiency of foreign object detection and localization in the tunnel with a strong multipath effect. Finally, experiments were conducted using Intel 5300 NIC in the indoor environment that was close to the tunnel environment. The performance of the detection probability and localization accuracy of the proposed method is tested.