Metro Line Research Articles

Research on Shield Tunneling across a River Using a Scale Model

This paper proposes a scale model test to simulate shield tunnel excavation over long distances. The test simulates the whole process of shield tunneling through the Weihe River on Xi’an Metro Line 1, where the tunneling length and diameter reach 100 m and 6 m, respectively. The dimensions of the test setup were 6.0 m × 1.0 m × 1.0 m, the diameter of the tunnel model was 160 mm, and the geometric similarity ratio was 1:40. Finite element analysis and field measurements were performed to complement the test results. By comparing the finite element simulation and field measurement, the scale model test was validated and verified to be reliable. The results show that the test effectively predicts riverbed deformation caused by shield construction. In addition, it can be applied to soil stability analysis and the impact evaluation of surface deformation in other shield-crossing rivers, complex strata, and superstructure groups, providing auxiliary guidance for shield constructions.

Characteristics of smoke movement in subway evacuation corridor under different blockage ratios

This study employed FLUENT to analyse smoke movement and temperature distribution in an evacuation corridor with varying blockage ratios, focusing on the subway tunnel section of Fuzhou Metro Line 4. The simulation results revealed that under natural ventilation condition, the smoke spread area in the evacuation corridor is significantly greater for the high blockage ratio tunnel than for the low blockage ratio tunnel in the tunnel’s length direction, and the entire temperature distribution in the tunnel’s height direction is also high. Following the introduction of longitudinal ventilation, smoke spread in the evacuation corridor and the tunnel ceiling upstream of the fire source are effectively controlled, with smoke suppression movement in the evacuation corridor being significantly faster than that near the tunnel ceiling. As ventilation time increases, the back-layering length of smoke in the evacuation corridor gradually shortens. Within 150 s of ventilation, the critical safety distance below the safety temperature for a low blockage ratio is shorter than that for a high blockage ratio tunnel. In conclusion, longitudinal ventilation increases the cooling rate of high-temperature smoke in a high blockage ratio tunnel, but the influence of high ventilation velocity on evacuation cannot be ignored. Practical application This study provides recommendations for the evacuation plan and procedures under longitudinal ventilation. It is advisable to consider lowering the height of the evacuation corridor in the tunnel from the rail surface, thereby creating a more extensive safety space for personnel evacuation. Additionally, the implementation of prominent marks and voice prompts in the upstream area of the fire outbreak is crucial. This ensures that personnel are directed to evacuate from the upstream section during emergency situations.

DEVELOPMENT OF ENERGY-EFFICIENT AIR DEDUSTING

Among the sources of internal pollution one can point to dust, breath products of passengers, various emissions from finishing materials of trains and metro stations, etc. This problem is usually solved in two ways: wet cleaning of tunnels and stations and using powerful tunnel vacuum cleaners. Both of these methods have common disadvantages. Firstly, dust removal can only be carried out at night, when there are no trains on the line. Secondly, the dust removal installations themselves are expensive and are effective only at low speeds of dust movement through the tunnel. All metros in the world have a problem with dust removal. Research methods include analytical and computational studies of air distribution in the metro ventilation network using mathematical modeling methods using graph theory and flow algorithms, as well as experimental studies of air flow parameters in natural conditions of the Almaty metro.This article proposes an innovative method for dust removal of tunnel air based on the use of piston action of trains and labyrinth filters installed in station ventilation joints. The parameters of the calculation model of the metro line are substantiated on the basis of a decomposition approach to the mathematical modeling of aerodynamic processes by moving from a linear model of the metro line to a periodic open-loop model. Computational aerodynamics methods were used to determine the patterns of changes in air speed through the ventilation vent and the available pressure drop depending on the speed and mode of trains passing through the station.

Stability analysis of shield tunnel face in sandy pebble strata considering the route slope angle

Unique physical characteristics of sandy pebble strata amplify disadvantages of the route slope angle for tunnel-face stability. This study uses Lanzhou Metro Line 1 as support project to investigate tunnel-face stability in sandy pebble strata. Using PFC 3D to simulate the tunnel-face failure mechanism of the horizontal tunnel and the longitudinal inclined tunnel. The results show that the slip line ahead of the tunnel face is like a logarithmic spiral, likewise, an ellipsoid failure region forms above the tunnel vault. Based on the above, the theoretical analysis model of tunnel-face stability considering the route slope angle is established. The logarithmic spiral-elliptical model comprises an upper elliptical loose region I and a logarithmic spiral slip region II. Moreover, the limit support pressure is derived by combining the upper bound theorem and associated flow rule. Finally, existing theoretical analysis models are compared with the proposed model, showing that the proposed model fits well with the tunnel-face failure mechanism in sandy pebble strata.

Resilience of metro tunnel structures: monitoring deformation due to surrounding engineering activities and effect of remediation treatment

Long term performance of urban metro tunnels requires that the tunnel structure maintains not only a sound structural state, i.e., free from significant damages, but also a minimal change in the physical shape. Over-deformation can cause structural damage but more importantly can affect the safe operation of the metro lines, therefore is a primary target of monitoring and intervention where it becomes necessary. This paper presents an overview of recent developments in field monitoring and assessment of metro tunnels in soft soil concerning over-deformation. In particular, the over-deformation of shield tunnel rings due to nearby construction activities, especially deep excavation, and its rectification using grout treatment is discussed on the basis of relevant field experiment and numerical modelling reported in recent publications. Key considerations in the development of a Material Point Method (MPM) based numerical modelling framework for simulating explicitly the grouting operations are highlighted, and the general performance of the numerical model is examined with reference to the field test data and characteristic parametric observations. Further research needs in terms of more rigorous assessment and design of grouting treatment, in conjunction with the continued development of numerical modelling capabilities, are discussed.

A novel method to solve the existed paradox of low-frequency vibration isolation and displacement attenuation in a nonlinear floating-slab on the wheel-rail loads

As we have known that it is impossible to attenuate the vibration displacement of the floating-slab depending on a strong stiffness and to improve the low-frequency vibration isolation performance of the floating-slab track (FST) depending on a soft stiffness simultaneously in engineering. In this paper, we propose a novel method to solve the paradox by introducing a “Hardening-First-Then-Softening” (HFTS) design based upon the energy distribution of wheel-rail loads to formulate a model of nonlinear floating-slab isolator. The average procedure is employed to analyze the vibration isolation ability of the isolator with parameters taken from a metro line load excitation. A simulation model of train-FST-tunnel with HFTS isolator is constructed to study the dynamic behaviors of the system. The numerical simulations show the significant suppression of displacement response of floating-slab and Z weighted acceleration vibration level of the tunnel. The results presented herein this paper provide a scheme to solve the strict requirements of displacement suppression and the vibration isolation which is of beneficial to steady and silent urban rail transit.

Energy consumption analysis of urban rail fast and slow train modes based on train running curve optimization

According to the operation characteristics of urban rail transit in fast and slow train modes, this paper studies the energy-saving problem of the two train modes from the perspective of optimization of the train running curve. A method based on the control parameters including control force and speed is proposed. Under the constraint of the interval running time, considering the station speed limit and curve speed limit, and with the goal of minimizing the energy consumption during operation, an optimization model of an urban rail transit train running curve under fast and slow train modes is established, and a solution method based on the simulated annealing algorithm and multi-parameter control strategy is designed. Using the line and operation data of Guangzhou Metro Line 21, the interval energy-saving running curves under two modes are obtained, and the data of the energy consumption and interval running time are analyzed, verifying the effectiveness of the energy-saving strategy. By comparing with the slow train, it is concluded that the energy consumption each kilometer of the fast train is reduced by 1.468 kW·h, saving 18.04%, and the energy consumption each hour is reduced by 36.213 kW·h, saving 6.76%, which provides support for energy-saving and cost reduction of the transportation sector under fast and slow train modes.

Assessment and Control of Metro-induced Vibration and Secondary Noise of TOD Buildings

Metro-induced vibration and structural secondary noise are becoming increasingly outstanding, which greatly restrict the further development of TOD (Transit-oriented development) project. To solve this problem, an evaluation methodology and dynamic model of vibration and secondary noise induced by metro train is developed firstly. Then the characteristic and distribution of vibration and secondary noise of the TOD subject to running train are studied. Finally, the control effect of steel-spring floating slab track (FST) on vibration and secondary noise of TOD project is evaluated. Results show that: when evaluating environmental problem caused by metro train, the standard of secondary noise is more strict than that of vibration. Main frequency of metro-induced vibration is concentrated in 40–63 Hz, and the second main frequency is concentrated in 6.3–16 Hz. The business building has the largest vibration due to its closest distance to the metro line. Secondary noises of most of the TOD buildings exceed the limit value, and the maximum exceeding value is 11.7 dB(A). FST is effective in controlling train-induced vibration and secondary noise of TOD buildings. FST cannot reduce vibrations in full frequency band, and vibration in some frequency bands are even amplified according to the stiffness of steel spring.

Node location of bi-level urban metro-based ground-underground logistics distribution

Metro-based underground logistics (M-ULS) can relieve the pressure of urban traffic and avert the road congestion through coordinating with ground logistics system. A bi-level node location model is proposed based on the ground-underground logistics distribution mode. The cost of delivery and pickup from the perspective of service companies and customers are minimized as the upper and lower objectives. Since the model is belonged to NP-hard problem, the simulated annealing algorithm (SA algorithm) whose new solution generation part was improved according to the characteristics of the model is used to solve the problem. In the case analysis part, the distribution nodes and customer points close to Nanjing Metro Line 3 were selected to verify the validity of the model and algorithm. The result shows that the improved SA algorithm outperformed in taking less iteration times and obtaining better solutions. The total transportation cost of the system can be reduced by 21.7 % with the optimized node location plan, and 63.6 % of the ground transportation distance can be replaced by the underground transportation, such results are also obtained when the cargo demand increases by 1.5 times and 2 times, which verifies the advantages of M-ULS node location in reducing truck emission and total delivery cost.

New metro and housing price and rent premiums: A natural experiment in China

Causal evidence of housing premiums of new metro lines is indispensable for financing and governing infrastructure investments. Previous studies have investigated the housing effects of urban rail transit with varying methods, while causality remains unsettled. This study used a natural experiment to estimate the causal effects of the new metro interventions on housing premiums in Shenzhen, China. We used metro planning knowledge, reasoning on pursuits in land finance and engineering efficiency to verify the as-if randomness of the treatment–control group assignment in the natural experiment to reinforce the power of causal inference. We applied hedonic difference-in-difference (DID) models to estimate the average treatment effects based on the longitudinal housing price and rent data. We found that housing rents increased significantly and consistently after the metro entered operation, but the price premium varied. In addition, the rent premiums around new metro lines showed a price gradient over the distance to stations. Our findings provide scientific evidence for designing value capture mechanisms (e.g. value-added property tax and rent revenue) to recover metro investment costs in China.

Two‐objective train operation optimization based on eco‐driving and timetabling

AbstractIn urban railway systems, the timetable guides the section operation of the single train and the arrangement of the train group to meet the dual needs of cost and passengers. This paper proposes a two‐objective train operation optimization based on eco‐driving and timetabling to restore a more realistic scene, including a method level and an objective level. For the method level, the speed curve optimization of the single train and the timetable optimization of the train group are adopted jointly. For the objective level, both the total energy consumption of the train group and the consuming time of passengers are considered. A hybrid solution strategy based on quadratic programming and improved artificial bee colony algorithm is proposed. A hardware‐in‐the‐loop platform is built to carry out validation experiments. Both the cases in general hours and special hours are verified based on the actual data from Beijing Metro Line 15. The results show that both the energy consumption and the passenger consuming time are reduced simultaneously. Correspondingly, the speed curve and the time distribution of the timetable are individually optimized based on the fluctuating passenger flow.

Twin tunnels critical underpass during Sofia metro line 3 extension

Twin tunnels critical underpass during Sofia metro line 3 extension

Method for Controlling Full-Frequency Band Environment Vibration by Coordinating Metro Vibration Sources and Propagation Paths

Floating slab tracks (FSTs) are used to reduce the impact of vibration on precision instruments and historical relics along metro lines; however, ground vibration is universally amplified at the natural frequency of the tracks. In this study, a full-frequency control method that considers frequency matching for environmental vibrations, in combination with metro vibration sources and propagation paths, was developed based on the bandgap theory of the periodic structure. The effectiveness of this method was analysed by establishing a three-dimensional metro train–FST coupled model and a finite element analysis model of track bed–tunnel–soil–row piles. The results show that ground vibration can be reduced by approximately 3–5 dB at the natural frequency of the FST by adjusting the bandgap range of the periodic piles to 7–9 Hz, eliminating the adverse effect of vibration amplification at the natural frequency of the FSTs. The proposed control method shows good vibration control effects and can effectively minimise ground vibration in the full-frequency range.

Festival timetable synchronization of metro trains and high-speed railway trains for late-night operations: an integrated bi-directional transfer optimization model

ABSTRACTThis paper focuses on synchronizing festival timetables between high-speed railway (HSR) and metro for late-night operations. A multi-objective model is proposed to optimize metro timetables of the last service period incorporating collaboration with HSR timetables. The model is designed to facilitate bi-directional transfers by maximizing spatial accessibility and temporal availability of metro service as well as minimizing transfer waiting times for HSR passengers. Our model can be efficiently solved using Gurobi, providing optimal solutions for large-scale metro networks within reasonable computational timeframes. A real-world case study is conducted to validate the effectiveness of our model. The results indicate that slight adjustments to metro timetables, without introducing additional trains, can yield significantly enhancements in late-night metro service for HSR passengers. Moreover, a smaller extension of service time across the entire metro network is proved to be more effective than a greater extension of service time on hub-connected metro lines.

Diffusion or Polarization in Intercity Property Markets after the Completion of Intercity Metro Line

Diffusion or Polarization in Intercity Property Markets after the Completion of Intercity Metro Line

In-Situ Dehydration Test of Shield Spoil in Mudstone and Pebble Soil Composite Stratum

When earth pressure balance (EPB) shield machine is driving in mudstone sand pebble composite stratum, it will produce a large amount of spoil with high water content. The high moisture content of spoil not only increases the difficulty and cost of transportation, but also easily leads to environmental pollution problems. In this paper, based on the shield tunnel project of Chengdu Metro Line 30, the hydraulic characteristic of shield spoil was tested, and on this basis, laboratory tests of shield spoil dehydration were carried out according to the designed precipitation scheme. The results show that: 1) The moisture content of the EPB shield spoil in the mudstone sand pebble composite stratum is as high as 55.2%, and its permeability coefficient is basically the same as that of silt, and the shield residue has the condition of in-situ dehydration. 2) The dehydration amount and residue moisture content of spoil in slope-type spoil pit showed a linear relationship with time, and the dehydration rate is slow and the total precipitation is less. In other schemes, the dehydration amount and water content of spoil increase rapidly in the first 24 hours and slowly in the later period. 3) Considering the total amount and speed of dehydration within 24 hours, the dehydration effect of spoil pit is ranked from high to low: 3D gravel cage wall spoil pit > 3D spoil pit with vacuum pumping > 3D permeable stone spoil pit > 3D spoil pit > Slope-type spoil pit. 4) 3D gravel cage wall spoil pit has high dewatering efficiency, and vacuum pumping can assist the discharge of water. It is recommended to use 3D gravel cage wall spoil pit and vacuum pumping scheme for on-site EPB tunnel spoil dewatering.

Service quality assessment of orange line metro train, Lahore, Pakistan

Service Quality increases the efficiency and effectiveness of a service leading to achieving the satisfaction of its users. A customer satisfaction score is considered one of the effective tools to achieve efficiency in any service. Service Quality and riders’ satisfaction with public transport is important for social, political, environmental, and economic outcomes. The research aims to assess service quality from the perspective of users of the Orange Line Metro Train OLMT, Lahore. The study was based on two types of surveys one was the observatory and the other was a questionnaire-based survey. The observatory surveys at stations were carried out to note down the status of facilities available. A questionnaire-based survey was conducted from passengers at different OLMT stations. The average ridership of OLMT is approx. 65,000 per month till the first quarter of 2022. The research used random sampling techniques for the selection of users riding from different stations of OLMT. The study used eight service quality variables; i.e. accessibility, safety and security, comfort and cleanliness, customer care, infrastructure, amenities, and fare satisfaction; and environmental conditions. The study concluded that the customer satisfaction score for the OLMT service is 65%. The riders were moderately satisfied with service quality at stations of OLMT. The absence of the park-and-ride facility is one of the most critical and challenging things. The majority of riders highlighted that the behavior of the staff working at stations was not cooperative. Observatory surveys and riders’ perceptions regarding various issues complement each other. The variables that need to be improved are particularly related to accessibility through the provision of park-and-ride facilities, comfort and convenience through the provision of additional facilities at the waiting area of stations. The findings of the study will help authorities and policymakers in improving factors that were identified during the surveys for the improvement of service quality.

Integrated optimization for passenger comfort-oriented train timetabling and passenger control strategy on an oversaturated metro line

The excessive travel demand in the metro system during peak hours may cause platform congestion and reduce the comfort of the passengers. Thus, this article proposes an approach for integrally optimizing the train timetable and passenger control on an oversaturated metro line, to improve the comfort of passengers on the platform. Specifically, taking the short-term impact of the boarding/alighting passengers into account, a novel quantitative assessment method of the perceived waiting time, considering the impact of the platform passengers’ density and passenger control strategy, named the generalized waiting time, is proposed. A mixed-integer nonlinear programming model is formulated to minimize the generalized waiting time, and a heuristic algorithm based on the adaptive simulated annealing genetic algorithm and the adaptive large neighbourhood search (ASAGA-ALNS) is designed to find high-quality solutions. The results of numerical experiments show that the method can alleviate platform congestion, while improving the comfort of waiting passengers.

Spatial Variation Law of Blasting Vibration in Layered Strata under Blasting Excavation of Subway Tunnel

Blasting vibration generated from blasting excavation of subway tunnel may endanger the adjacent structures buried in strata. To guarantee their safety and stability, it is crucial to understand the spatial variation law of blasting vibration in strata. In this paper, the blasting excavation of the large cross-sectional tunnel of Wuhan Metro Line 8 is studied. Three-dimensional finite element simulation is performed using the dynamic finite element program LS-DYNA, and its validity is verified by the field monitoring data. The spatial variation law of blasting vibration in layered strata is investigated through analyzed the distribution characteristic of blasting vibration in three directions, including the direction along the axis of the large cross-sectional tunnel, the direction perpendicular to the axis of the large cross-sectional tunnel, and the direction along the depth. A prediction model for blasting vibration velocity, which considers the impact of elevation differences, is established through dimensional analysis, enabling the prediction of blasting-induced vibrations at various depths in the layered strata.

Rail transit express and local train schedule optimization considering hybrid rolling stock composition

ABSTRACT This study adopts a hybrid rolling stock composition strategy and proposes a mixed-integer linear programming (MILP) model to optimize the rolling stock compositions together with the train timetable according to real-life passenger demand. The optimization objectives are to minimize the number of stranded passengers and rolling stocks. Two types of constraints are included: constraints related to timetabling and constraints related to passenger assignment. In addition, timetable optimization is used for mixed traffic, including local and express train services. Express trains overtake local trains at specific stations; therefore mapping constraints are built to match each train service to the corresponding train order at different stations to ensure a correct passenger assignment. Numerical examples based on the Shanghai Metro Line 16 are implemented to demonstrate the efficiency of the proposed model. The optimization results show that the proposed method can efficiently reduce the number of stranded passengers and the number of rolling stocks required.