Subway Tunnel Research Articles

Enhanced Detection of Subway Insulator Defects Based on Improved YOLOv5

Insulators, pivotal to the integrity of railway catenaries, demand impeccable functioning to prevent system failures. Their consistent assessment is vital for railway safety. Current insulator evaluations in subways predominantly involve human intervention, a method fraught with inefficiencies, inaccuracies, and oversights, exacerbated by the complex backdrop of subway tunnels and minuscule defect dimensions. This study introduces an enhanced algorithm, anchored in the YOLOv5 framework, to refine insulator defect identification. Challenges in defect detection include limited, imbalanced data samples and adaptability. Addressing this, an accurate catenary model mirrors the subway line’s architecture, facilitating the creation of synthetic instances of both intact and impaired insulators. An atomization technique augments the dataset volume, fortifying the algorithm’s resilience in reduced visibility conditions, such as fog. Tackling sample equilibrium, the study introduces an equilibrium loss function, assigning disparate weights to various sample categories during training, thereby sharpening the algorithm’s focus on positive instances, particularly those that are challenging to discern, and rectifying the disproportion in sample categories. Incorporating lightweight structures like GhostNet and the Efficient Channel Attention Network (ECA-Net) channel attention scheme not only diminishes the network’s computational demands, thereby elevating the detection capabilities, but also minimizes superfluous data processing, enhancing the accuracy in identifying smaller targets. Empirical analyses indicate substantial model optimization: a size reduction to 60 pp of its original (from 15 MB to 9 MB), a near 1.4 pp increase in mean average precision (mAP) to 96.57%, and a tripling of the detection speed (from 30 to 90 FPS). Real-world image assessments further reveal a mAP improvement of approximately 2.5 pp (reaching 98.43%), confirming the model’s suitability for real-time applications.

Design and Evaluation of Virtual Reality Environments for Claustrophobia

Abstract Claustrophobia is a specific phobia characterized by fear of enclosed spaces (such as elevators, subway tunnels, etc.). While some individuals with claustrophobia might experience only mild anxiety and discomfort in enclosed spaces, others might suffer from panic attacks usually triggered by a fear of losing control or being unable to escape when needed. One of the most recent and successful treatment methods applied in specific phobias are virtual reality (VR)-based exposure therapy techniques. This feasibility study aimed to design and validate a set of immersive virtual environments (VEs) for exposure therapy in claustrophobia, with interactive scenarios enabling systematic, gradual, and controlled induction of claustrophobic fear. In total, eighteen individuals participated in the feasibility study. Participants were recruited from a general population and divided into two groups (phobic vs. control group). Each participant was asked to evaluate a set of various virtual environments. The study results indicate that the designed virtual environments have the potential to induce claustrophobic fear and are thus considered suitable for use in the exposure therapy of claustrophobia. These virtual environments also evoked a sense of presence, particularly the spatial presence component, while the reported cybersickness symptoms were none or minimal.

Efficiency Scoring for Subway Tunnel Construction Based on Shield-Focused Big Data and Gaussian Broad Learning System

Efficiency Scoring for Subway Tunnel Construction Based on Shield-Focused Big Data and Gaussian Broad Learning System

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.

Research on Lateral Deformation Control Criteria of Metro Shield Tunnels with Excessive Ellipticity

In recent years, excessive lateral deformation of subway shield tunnels has been observed due to adjacent engineering activities. This study examines the monitoring of excessive lateral deformation of the shield tunnel and the special steel plate reinforcement process to enhance the safety and stability of the operating subway tunnel structure. It uses a three-dimensional refined finite-element model of the shield tunnel for parametric structural loading simulation analysis to propose a structural deformation limit value suitable for the subway shield tunnel. This study’s findings indicated the following: (1) as observed from the engineering examples, a tunnel with significant elliptical deformation increases the likelihood of cracking and other structural issues in the adjacent subway shield tunnel segment; (2) as observed from the post-reinforcement monitoring data, the steel plate reinforcement method effectively enhances the load-bearing stability of the damaged tunnel structure; (3) based on the finite-element simulation results and the comprehensive review of practical conditions, the standard warning value for lateral deformation, using ellipticity evaluation of the subway shield tunnel, is established at 20‰, with a control value of 25‰. The outcomes of this research offer valuable insights into the operation, maintenance, and health monitoring of subway shield tunnels.

Deformation Control of Subway Tunnels Undercrossing Airport Facilities: A Case Study of the Xinzheng Airport Rail Transit Hub Project

The rapid expansion of urban areas due to China’s booming economy has led to a conflict between people and vehicular traffic. Consequently, rail transit, represented by subways, has become the primary mode of transportation for residents. However, the influence of soil damage on tunnel deformation is often overlooked in research on the safety of soft soil tunneling, leading to discrepancies between the results predicted by models and the actual settlement of tunnels. In this study, soil investigation and mechanical strength testing were carried out to analyze the impact of aircraft takeoff and landing activities on the Xinzheng Airport facilities. Damage variables are introduced into the Drucker‒Prager ideal elastic‒plastic criterion, and a soft soil tunneling model with soil deformation is established to investigate the spatial and temporal effects of the shield-cutting force, moving aircraft load, and tunnel deformation. Based on the synchronous grouting technique, a mechanical load-bearing system consisting of a concrete runway, solidified grout, and high-strength segments is formed to ensure the safety of flight activities.

Damage and deformation behavior of reinforced concrete pipes with varying joints under surface explosion

Reinforced concrete pipes (RCP) are the mainstay of urban water transmission networks. Urban development entails increased potential for blasting activities (such as subway tunneling, excavation, and demolition) as well as the risk of accidental explosions. This paper provides a detailed description of the damage evolution and deformation process of RCP under explosive loads using validated numerical simulation methods. A concise phenomenon-based method is introduced for RCP damage grading. Furthermore, a comparative analysis is conducted on the damage and deformation of RCP resulting from explosions at different locations and with varying weights. At last, this paper especially investigates and explains the impact of four commonly used joint types on the RCP’s response to explosions. The research results help to enhance the understanding of damage evolution and deformation behavior of RCP (or similar structures) induced by explosion, and are also references for protection, repairing and failure identification of segmented structures subjected to explosion.

Temperature prediction of Bragg grating sensing based on a one-dimensional convolutional neural network.

In this paper, we propose a new (to us) way of demodulating the grating sensing spectrum using a one-dimensional convolutional neural network (1DCNN) to overcome the limitation of the traditional fitting method of temperature demodulation for subway tunnel fires. This method constructs a one-dimensional convolutional neural network model and combines it with the experimental device of a fiber Bragg grating (FBG) temperature measurement. One thousand eight hundred spectra of experimental data are selected as sample data for training. Adam's random optimization algorithm is used in training to predict the temperature of multiple periods, with an accuracy of 99.95% and a root-mean-square deviation (RMSE) of 0.0832°C. The experiment shows that the algorithm in this paper is better than the GRU and LSTM algorithms, as traditional maximum peak methods, and can effectively improve the measurement accuracy. This article aims to provide a high-speed demodulation solution for FBG-based sensing systems to meet the practical needs of large-scale real-time monitoring.

Managing Extreme Rainfall and Flooding Events: A Case Study of the 20 July 2021 Zhengzhou Flood in China

On 20 July 2021, an extreme rainstorm battered Zhengzhou in China’s Henan Province, killing 302 people, including 14 individuals who drowned in a subway tunnel and 6 who drowned in a road tunnel. As the global climate warms, extreme weather events similar to the Zhengzhou flood will become more frequent, with increasingly catastrophic consequences for society. Taking a case study-based approach by focusing on the record-breaking Zhengzhou flood, this paper examines the governance capacity of inland cities in North China for managing extreme precipitation and flooding events from the perspective of the flood risk management process. Based on in-depth case analysis, our paper hypothesizes that inland cities in North China still have low risk perceptions of extreme weather events, which was manifested in insufficient pre-disaster preparation and prevention, poor risk communication, and slow emergency response. Accordingly, it is recommended that inland cities update their risk perceptions of extreme rainfall and flooding events, which are no longer low-probability, high-impact “black swans”, but turning into high-probability, high-impact “gray rhinos.” In particular, cities must make sufficient preparation for extreme weather events by revising contingency plans and strengthening their implementation, improving risk communication of meteorological warnings, and synchronizing emergency response with meteorological warnings.

Justification of an Energy-Efficient Air Purification System in Subways Based on Air Dust Content Studies

It is not uncommon that subways count as densely populated areas, so air quality standards, including fine dust concentration, have been established for them. As passengers and subway staff are exposed to potentially harmful airborne particles, addressing this issue is vital to ensuring a safe and healthy environment on the subway. To reduce the dust concentration in subway systems, the authors propose installing filters to capture dust in ventilation failures between subway tunnels near metro stations. A novel aspect of the proposed method is the fact that airflow will be moved through filters by using the piston action of trains passing through the tunnels. The result of this research provides empirical evidence regarding dust content and mass concentrations of PM2.5 and PM10 in subway environments. While some existing literature discusses air quality in subways, the inclusion of specific measurements and data from the experiment strengthens the understanding of the severity of dust-related air quality issues in such environments. The data for this study were collected in the Almaty subway (Republic of Kazakhstan) at four stations: Raiymbek Batyr, Almaty, Baikonur and Alatau. Measuring points were located on passenger platforms, in the halls and at the entrances to the station. The lab scale tests determined the percentage of particles by their diameters relative to the total volume of dust, the percentage of dust particles smaller than a certain diameter, the percentage of various metal oxides and the average dust density. A preliminary energy assessment has been done on the proposed method of air purification from dust. With a frequency of 24 pairs of trains per hour, the energy savings per ventilation failure will be 240.170 kWh.

Assessing potential building damage caused by leakage to urban tunnels

AbstractBuilding damage is a major risk for urban tunnelling. In areas with soft soil conditions, water ingress to bedrock tunnels can cause significant pore pressure reduction, consolidation settlements and damage to nearby buildings and infrastructure. In Norway, guidelines to determine leakage limits are based on a national database, containing data on water ingress, pore pressure reduction and influence zone. To support future projects, the database has been implemented into an ArcGIS tool and merged with the Ground Impact and Building Vulnerability method to assess potential building damage at early project stages. In this paper, the adopted methodology is presented and its application is shown for a new subway tunnel in Oslo, Norway.

Studying on the ability of application of gyrotheodolite to the tunnel orientating in constructing the subway tunnel by TBM technology in Vietnam

This paper briefly presents the operation principle, the ability of application of gyrotheodolite to the tunnel orientation. The paper also presents a comparison of the accuracy between the traverse established with traditional method, measuring angles and sides, and the traverse inside the tunnel with azimuth of measured sides determined by gyrotheodolite. From the comparison, the advantages, disadvantages and the ability of application of the gyrotheodolite in order to ensure and improve the accuracy of the tunnel orientation when constructing the subway tunnel by TBM technology (Tunnel Boring Machine) in Vietnam were analyzed and evaluated.

Safety Criterion for Hollow Pipe Piles Under Blasting Vibration Based on Wave Function Expansion Method

When the drilling and blasting method is used to excavate urban subway tunnels, the blasting seismic waves will inevitably produce vibration effects on the pile foundations under the surface buildings, which will seriously threaten the safety of surrounding buildings and the environment. Based on the transmission and reflection laws of stress waves at the interface between soil medium and pile medium and the displacement–stress continuous assumption, the wave function expansion method is used to analyze the whole process mechanism of vibration effect of hollow pipe piles under the action of incident [Formula: see text] waves. In addition, the theoretical model of safety criterion for hollow pipe piles under blasting vibration is proposed and the reliability of the model is verified. Furthermore, the impacts of the elastic modulus, density, and pile section parameters of soil and piles on the safety criterion for the blasting vibration effect of hollow pipe piles are analyzed. The results show that as the elastic modulus and density of the soil increase, the critical peak particle velocity (PPV) curves of hollow pipe piles move to the high-frequency and low-frequency bands, respectively, resulting in a decrease in the overall safety of piles. This indicates that hollow pipe piles should not be buried in soil layers with high elastic modulus and density. It is also shown that the larger the hollow area of hollow pipe piles, the lower their safety. Compared to solid circular piles, hollow pipe piles have a higher overall seismic safety reserve. The study results have guidance and reference value for effectively evaluating and controlling the harm of blasting vibration effects of hollow pipe piles.

Characteristics of shallow buried karst and its safety distance to tunnel in wuxi city, China

Subway tunneling construction in shallow buried karst region is a common challenge. Survey boreholes and cross-hole seismic CT data showed that 29 karst caves exist at elevation of −17 m to −37 m in Si–He section of the Wuxi Metro Line 4, which are consisted of 18 filled caves and 11 empty caves and constitute substantial dangers to the stability and quality of metro construction projects. Based on their size, position, and type of filling, we divided these shallow karst caves into four types. Aimed at exploring the instability of the tunnel after excavation, numerical analyses have been developed by using the Finite difference method. Both the effects of the distance between tunnel and karst caves and the effects of the filling of the cavities on the overall stability of the rock mass around the tunnel have been investigated. According to the design criteria, safety distance between tunnel and karst caves was determined. The monitoring data of tunnel during excavation proved the rationality and accuracy of the analysis results. The research results can provide technical reference for the design and construction of other proposed tunnels that are located in the regions of shallow buried karst in Jiangsu Province.

Comparative Analysis and Safety Evaluation of Shield Segment Structure Model under Surcharge Loading.

In shield tunneling projects, the selection of an accurate model to calculate the mechanical response of segment structure plays a crucial role in the design and cost of the project. The shell-spring and beam-spring models are two widely used methods for this purpose. However, it is still not clear how accurate and different these models are in calculation results under surcharge load. Therefore, to accurately calculate the internal forces and deformation of the segment structure and clarify the difference between the two models' results, the shell-spring and beam-spring models were established based on a subway shield tunnel project in Zhengzhou city. The reliability of the models was verified by comparing and analyzing the differences in deformation results between the models and field measurements. Furthermore, the safety of the segment structure was evaluated according to the ultimate bearing capacity of the normal section. The results declare that: (1) In the shell-spring model, the internal force gradually reduces from the edges towards the center of the segment width, and the shield segment exhibits a prominent non-plane strain state. (2) The internal force of the beam-spring model is larger than that of the shell-spring model. The axial force difference between the two models is relatively small; meanwhile, there is a larger disparity in the bending moment. However, with an increase in surcharge loading, the discrepancy in internal forces between the two models gradually decreases. (3) The calculation results of the shell-spring model are close to the field-measured values and the shield tunnel model test values, which verifies the accuracy and reliability of the shell-spring model. Therefore, it is more reasonable to use the shell-spring model to calculate the mechanical response of the segment structure. (4) With an increase in surcharge loading, the safety of the shield tunnel decreases gradually. Therefore, surcharge loading above the shield tunnel should be reasonably controlled to meet the requirements of the normal use of the shield segment. This manuscript aims to provide a reference for the future design and optimization of the shield tunnels' lining structure.

Determining the best depth of subway tunnel excavation considering ground type, support system characteristics, and tunneling cost: case study of Tabriz subway, Line 2

Determining the best depth of subway tunnel excavation considering ground type, support system characteristics, and tunneling cost: case study of Tabriz subway, Line 2

Estimating longitudinal maximum smoke temperature attenuation due to large-angle bifurcation in UTLT-like tunnels under longitudinal ventilation condition

Extensive studies have focused on single-straight tunnels or subway bifurcation tunnel fire. However, the effect of large angle bifurcation on longitudinal maximum temperature rise attenuation in Urban Traffic Link Tunnel（UTLT）needs to be further studied. In this study, based on the theoretical analysis, a double exponential prediction model for longitudinal temperature rise attenuation in bifurcation tunnels is established. To obtain the correlation coefficients, a series of full-scale numerical fire simulation experiments were carried out in an UTLT-like tunnels using Fire Dynamics Simulator. The results revealed that the bifurcation structure of the large-angle bifurcation angle tunnels impeded the longitudinal movement of the fire smoke and hot smoke diversion. Without longitudinal ventilation conditions, the longitudinal decay of the temperature rise in each region can be expressed as the sum of double exponential expressions with different coefficients. The law governing the effect of the bifurcation angle on the longitudinal decay of the temperature rise is the quadratic equation of the angle sin α. A prediction model for the longitudinal decay of the temperature rise in the tunnel downstream of the fire source under longitudinal ventilation is proposed. The findings of the numerical simulation corresponded to those of the model prediction.

Underwater noise prediction and control of a cross-river subway tunnel: an experimental and numerical study

Underwater noise prediction and control of a cross-river subway tunnel: an experimental and numerical study

Mechanical characterization of subway tunnel construction in urban shallow distributed karst stratums

To address the challenges posed by rapid urban and population growth, China has undertaken extensive urban subway construction. In order to explore the mechanical characteristics of subway tunnel construction in urban shallow karst environment, based on the first phase project of Guiyang rail transit line 3, the concept of “distributed Karst” is proposed according to the occurrence characteristics of karst in urban environment. The dry ice and model soil were used to characterize the karst strata, and the similar model test study on the influence of different volume karst rates on subway tunnel construction was carried out. The influence of tunnel excavation on surrounding rock disturbance, internal force of arch structure and ground settlement under distributed karst stratum condition is studied comprehensively. The following key findings emerged:(1) Karst presence causes an abrupt change in the release curve of surrounding rock earth pressure. Higher degrees of karst development result in smaller changes in earth pressure on the arch top and shoulder after tunnel excavation, with final earth pressure changes of 91.1 kPa, 83.5 kPa, and 74.8 kPa for volumetric karst rates of 5%, 10%, and 20%, respectively. (2) Distributed karst in the tunnel arch has a limited impact on the lateral excavation displacement of the arch girdle but significantly affects the vertical settlement of the tunnel vault. Increasing volumetric karst rates by twofold (from 5% to 10% and 20%) reduces arch settlement by 48.9% and 55.6%, respectively. (3) At volumetric karst rates of 5%, 10%, and 20%, the axial force values at the tunnel top are 58.2 kN, 52.8 kN, and 50.3 kN, while the corresponding bending moment values are 49.6 kN-m, 37.1 kN-m, and 26.0 kN-m, respectively, indicating a more significant difference in bending moment values than axial force values. (4) Karst presence leads to increased surface settlement, with a 48.8% increase in peak ground settlement observed as the volumetric karst rate rises from 5% to 20%.

On-site measurement and environmental impact of vibration caused by construction of double-shield TBM tunnel in urban subway

The vibration generated during the construction of subway tunnels with double-shield tunnel boring machine (TBM) has a significant impact on the environment, which has caused multiple complaints from residents. Taking a double-shield TBM tunnel project as the background, vibration measurements were conducted by installing vibration sensors on-site. By combining theoretical methods—such as normalization, polynomial fitting prediction, and gray correlation analysis—the vibration characteristics, impact range on the environment, and factors affecting the vibration of TBM construction were studied. The key research results included: (1) The amplified zone of X and Y vibration acceleration occurred on the left-hand side of the tunnel from 3.15 to 13.85 m, but rapidly decayed away from the amplification zone. (2) The impact range of TBM vibrations on residential areas at night and during the day was studied according to the official “Urban Regional Environmental Vibration Standard” and it was found to be larger at night than during the day. (3)The main factors affecting the TBM vibration level was studied—including the cutter-head torque, TBM thrust, cutter-head speed, penetration, field penetration index (FPI) and so on. In summary, when the double-shield TBM construction tunnel is adjacent to residential areas, the vibration generated exceeds the national standard limit. In order to reduce the impact of TBM vibration on residential areas, excavation parameters such as cutter head torque, TBM thrust, cutter head speed, and penetration should be appropriately reduced.