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Copyright of Transportation Science & Technolgy is the property of Transportation Science & Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The prevailing design methodology for foundation pit support structures conventionally treats the pit cross section as a two-dimensional plane, facilitating the computation of soil and water pressures acting upon the retaining structure. Regrettably, this conventional approach tends to overlook the critical corner effect, particularly when the foundation pit is in proximity to a subway tunnel, where the nuanced nature of this corner effect remains indeterminate. Consequently, this research is directed toward an in-depth investigation of a deep foundation pit contiguous to a subway tunnel. A systematic evaluation and optimization of the corner effect pertaining to the deep foundation pit are undertaken through a combination of comprehensive field monitoring and simulation methodologies. The results show that a substantial mitigation in the deformation of the supporting structure, settlements of the ground surface and adjacent buildings, as well as the displacement of the subway tunnel, were achieved through a consideration of the corner effect. Notably, the ameliorative impact of adjacent buildings on the corner effect is observed. Further scrutiny reveals that the supporting structure within a distance of 12 m from the pit corner is most susceptible to the corner effect, as evidenced by a plane strain ratio (PSR) falling below 0.8. Beyond a spatial threshold of 20 m, the PSR attains a value of 1.0, indicative of a negligible corner effect and the foundation pit section existing in a plane strain state. The adjustment of pile length or diameter based on the PSR emerges as a viable strategy that can realize the construction cost optimization on the premise of ensuring the stability of the foundation pit. The impact of pile diameter variation is paramount, corresponding to a reduction in the range of PSR values below 0.8 from 12 m to 9.8 m. The corner effect is significantly diminished. [ABSTRACT FROM AUTHOR]

High-precision and rapid detection of apparent defects in subway tunnel linings is crucial for ensuring the structural integrity of tunnels and the safety of train operations. However, current methods often do not adequately account for the spatial characteristics of these defects and perform poorly in detecting and extracting small-scale defects, which limits the accuracy of detection and geometric parameter extraction. To address these challenges, this paper proposes an efficient algorithm for detecting and extracting apparent defects in subway tunnels. Firstly, YOLOv8 was selected as the foundational architecture due to its comprehensive performance. The coordinate attention module and Bottleneck Transformer 3 were then integrated into the model's backbone to enhance the focus on defect-prone areas and improve the learning of feature relationships between defects and other infrastructure. Subsequently, a high-resolution detection layer was added to the model's head to further improve sensitivity to subtle defects. Additionally, a low-quality crack dataset was created using an open access dataset, and transfer learning combined with Real-ESRGAN was employed to enhance the detail and resolution of fine cracks. The results of the field experiments demonstrate that the proposed model significantly improves detection accuracy in high-incidence areas and for small-scale defects, achieving a mean average precision (mAP) of 87% in detecting cracks, leakage, exfoliation, and related infrastructure defects. Furthermore, the crack enhancement techniques substantially improve the representation of fine-crack details, increasing feature extraction accuracy by a factor of four. The findings of this paper could provide crucial technical support for the automated operation and maintenance of metro tunnels. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Entering the 21st century, with the acceleration of economic globalization, urban development is facing many challenges such as population growth, resource scarcity, and environmental pressure. Therefore, underground engineering construction has received widespread attention. The application of Wireless Sensing Network (WSN) technology in civil engineering structural monitoring meets the intelligent monitoring needs of tunnel construction and solves the problem of construction safety monitoring. This study combines statistical analysis, theoretical research, numerical simulation, BIM technology, and on-site verification methods to systematically explore the perception and visualization management of safety risks in subway construction. The application of wireless monitoring technology has verified the monitoring effect of wireless laser ranging and wireless inclination sensors during the construction period. The results show that under timely support conditions, the tunnel structure remains basically safe. For weak stratum tunnels, numerical simulation and backward advanced deep hole grouting pre reinforcement technology are studied to ensure the stability of the soil layer around the tunnel. At the same time, BIM technology is used to construct a tunnel model, visualize the construction process, and develop an intelligent sensing control system for real-time monitoring and risk warning. [ABSTRACT FROM AUTHOR]

The construction of new bridge piles adjacent to existing subway tunnels poses a significant threat to the safety of the tunnels. To accurately assess the impact of the construction of the steel casing of bridge piles on nearby subway tunnels, a simplified analytical method incorporating a mechanical model is developed in this study. Specifically, modified calculation formulas for the additional force are proposed, taking into consideration the characteristics of casing segmental construction and the soil-squeezing effect. The two-stage analysis method is employed to determine the additional stress and longitudinal vertical deformation of the tunnel. Subsequently, a series of calculations are performed to gain further insights into the effects of varying lengths and diameters of bridge piles, as well as the relative distance between the pile and tunnel on the tunnel–pile interactions. As the construction depth increases, the existing tunnel experiences a slight initial rise followed by progressively larger settlement that eventually levels off. The maximum settlement exhibits a linear increase with the increasing length and diameter of the bridge piles, while it exponentially increases with decreasing relative distance between the pile and tunnel. Moreover, impact zones of varying degrees of the bridge pile construction on the nearby tunnel are proposed. Based on the Response Surface Methodology, the relative distance is found to exert the greatest influence on the deformation of the existing tunnel, and an optimal relationship among the parameters is provided. The theoretical results are well validated with field-measured data from a representative engineering project and numerical simulation results. The proposed solution can be proved to offer reasonable theoretical support for risk assessment of tunnels under the influence of adjacent piles construction. [ABSTRACT FROM AUTHOR]

The deteriorating thermal environment of tunnels and the increase in energy consumption of environmental control systems has become highlights in the subway field. In existing research related to analysis of subway tunnel thermal environments and thermal accumulation; there is no predictive law that accounts for thermal accumulation or the long-term change in subway tunnel thermal environments. In this study, a combination of simulations and experiments is used. First, the long-term evolution of tunnel thermal environments with and without thermal interference are predicted and analyzed. Then, the changes in the tunnel thermal environment after the use of capillary heat exchangers are explored. The research results indicate that the model of the system has high accuracy and reliability. When there is a capillary heat exchanger installed in the subway tunnel, the anti-seasonal heat storage characteristics of the system result in the tunnel temperature increasing significantly in summer and decreasing significantly in winter, with a small decrease in the average annual temperature. This study provides a theoretical reference for environment-based subway tunnel construction and the comprehensive utilization of tunnel waste heat. [ABSTRACT FROM AUTHOR]

Monitoring and predicting ground settlement during tunnel construction is of paramount importance for ensuring the safety of tunnel construction and the stability of the surrounding environment. Existing studies on settlement prediction mainly rely on single settlement values and often overlook temporal characteristics, and that prediction models struggle to capture the nonlinear trends in actual settlements, leading to suboptimal predictive accuracy. In this study, based on the monitoring data of settlement deformation in a subway section of a certain city, a multi-factor-driven prediction method for surface settlement in subway tunnel excavation using the Informer model is proposed. The predictive accuracy is compared and analyzed with other models, including CNN-LSTM, LSTM, SARIMA, and Transformer. The results indicate that: (1) The Informer model outperforms CNN-LSTM, LSTM, SARIMA, and Transformer in terms of RMSE, MAE, and MAPE evaluation metrics, demonstrating that the Informer model exhibits smaller average prediction errors in forecasting surface settlement during subway construction. (2) Compared to LSTM, CNN-LSTM, Transformer, and other models, the Informer model can better capture the temporal characteristics and long-term forecasting ability of settlement data, while the SARIMA model fails to capture the temporal features in actual settlement data effectively. (3) Considering the influencing factors of temperature and soil pressure has a positive impact on the predictive performance of the Informer model, and the relationship between soil pressure information in the case study construction area and surface settlement is more closely associated. In summary, the Informer model, which takes into account temporal characteristics and multiple influencing factors, demonstrates good predictive ability for nonlinear settlement data. It provides a new method for analyzing settlement trends caused by subway tunnel excavation under complex environmental conditions, facilitating efficient and accurate assessment. It also offers objective data support for short-term bridge construction scheduling and long-term construction planning. [ABSTRACT FROM AUTHOR]

When river channels or foundation pits are excavated above the existing subway tunnels, ground soil unloading will have a disturbance effect on the safety of the existing tunnel structure. Based on a typical river-channel excavation project, this paper designs a total of 25 comparison schemes considering the influence of five major factors: the relative distance between the river channel and the existing tunnel, river-channel excavation width, tunnel's embedment depth, grouting reinforcement thickness and grouting reinforcement range. This paper conducts a numerical simulation study on the river-channel excavation above the existing subway tunnels under different working conditions, and carries out comparative analysis on disturbance effect laws of different working conditions on deformation of the ground soil and the existing tunnel structure. On this basis, this paper constructs sensitivity evaluation indexes for disturbance effect on the existing tunnels, identifies the influence sensitivity of the above five major factors, and provides engineering suggestions and measures. Finally, based on the numerical simulation results, we carried out a field verification test. The research work in this paper can provide some reference for design and risk prevention of excavation engineering adjacent to the existing subway tunnels. [ABSTRACT FROM AUTHOR]

Subway tunnel flooding is one of the typical scenarios in urban waterlogging. When the emergency decision-making is untimely and inaccurate, it can lead to serious casualties. However, it is expected that through some responsive monitoring methods, an intelligent system can be constructed to achieve the real-time perception of the underground flood situation and to predict the process and intensity of the disaster. This study is based on a scale model experiment of flooding in straight subway tunnels. Firstly, it classified the basic patterns of the flood process. Some fitting formulas were respectively established for water depth and kinematic parameters. A calculation method for quickly predicting the flood inundation process was constructed. Secondly, this paper proposed a mode for the monitoring and early warning system. Based on the flood patterns and characteristic variables in subway tunnel flooding, the system can quickly determine the flow rate and entry position of flood and deduce the flood trend in the future at a relatively low cost. The system workflow was divided into three phases, and the mechanism for each phase of the system was sorted out. It could help to provide scientific and reliable information for emergency decision-making and gain time for the emergency response. [ABSTRACT FROM AUTHOR]

Model-scale experimental tests and numerical simulations were conducted to investigate the characteristics of the smoke overflow at the lateral carriage doors and the smoke temperature below the tunnel ceiling of a carriage fire in a longitudinally ventilated tunnel. Results indicates that the smoke overflows from the carriage into the tunnel through the lateral doors downstream of the fire source under the impact of longitudinal ventilation. Depending on the fire location, the amount of the overflow smoke exhibited either an inverted V-shaped variation or a monotonical increase with the door position. Multiple peaks in the smoke temperature below the tunnel ceiling is attributed to the uneven distribution of the overflow smoke. A dimensional analysis revealed a quantifiable relationship between the heat flow of the overflow smoke and the peak temperatures below the tunnel ceiling. Consequently, an empirical model was developed to predict the maximum smoke temperature below the tunnel ceiling under different heat release rates and longitudinal ventilation velocities. These findings are excepted to enhance the understanding of carriage fires and provide a theoretical guidance for future ventilation and safety designs in subway systems. [ABSTRACT FROM AUTHOR]

With the wide application of cantilever roadheader in urban subway tunnel construction, accurate prediction of excavation performance of cantilever roadheader in rock stratum has become a research hotspot. Accurate prediction of tunneling performance of cantilever roadheader in rock stratum is the key to its successful application in tunnel engineering. Based on Guiyang Rail Transit Line 1 and Line 3, this paper conducts field investigation and statistical analysis of data on the construction performance and tunneling characteristics of roadheader, and establishes a prediction database of tunneling performance of hard rock cantilever roadheader. The principal component analysis (PCA) was introduced into the deep belief network (DBN) to optimize the input parameters of the DBN model, and the PCA–DBN model for the performance prediction of hard rock cantilever roadheader was proposed. The new model is trained and predicted based on the data of Guiyang Rail Transit Line 1, and the rationality and feasibility of the model are verified through the field data test and analysis of Guiyang Rail Transit Line 3. The results show that the performance prediction model of hard rock cantilever roadheader based on PCA–DBN can realize real-time and continuous prediction of tunneling performance of ground roadheader in front of tunnel face according to engineering measured data. The comparative analysis with the DBN model shows that the accuracy of the PCA–DBN prediction model is better than that of the DBN model, which can better adapt to complex and changeable geological conditions. The new model provides a new method and possibility for accurately predicting the tunneling performance of cantilever roadheader in hard rock. Highlights: A prediction database of hard rock cantilever roadheader tunneling performance was established. The performance prediction model of hard rock cantilever roadheader based on PCA–DBN was established. The performance prediction model realizes real-time and continuous prediction of tunneling performance of ground roadheader. The prediction accuracy of PCA–DBN is higher than DBN in predicting the performance of cantilever roadheader. [ABSTRACT FROM AUTHOR]

More complex geological conditions could be encountered with the construction of urban subway projects. At present, many subway tunnels have been built in composite strata with upper soft and lower hard layers, but the presence of a cavity in the strata increases the risk of collapse during construction. In this paper, a series of model experiments and discrete element methods were conducted to investigate the failure behavior of composite strata with a cavity caused by tunnel excavation disturbance. The influence of the distance between the cavity and vault (hd) and the distance between the soil–rock interface and vault (hr) on the collapse of the composite strata are analyzed. The research results indicate that tunnel collapse exhibits progressive failure because of the forming of a collapsed arch in the strata. If the hd is greater than the tunnel span (D), the arch can be stabilized without other disturbances. Additionally, the thickness of the tunnel rock layer affects the height of the collapsed arch significantly, as it is difficult to form a stable arch when the hr is less than 2/3 D. Finally, reasonable construction safety distances are proposed based on the possibility of forming a stable arch collapse in the tunnel and determining the range of the collapse. [ABSTRACT FROM AUTHOR]

With the rapid economic development and urbanization in China, subway systems have become the primary mode of urban rail transit. However, during subway operation, the tunnels may experience settlement and deformation due to various influencing factors. To guarantee safe operation of subway systems and eliminate potential safety hazards, tunnel settlement prediction has important significance. However, existing studies have seldom discussed the effects of weighting factors on subway tunnel settlement prediction. In addition, the optimization of support vector machine (SVM) using particle swarm optimization (PSO) often suffers from issues such as local optimization and premature convergence. To address these problems, grey relational analysis (GRA) and weighted particle swarm optimization (WPSO) SVM were combined, and a GRA-WPSO-SVM prediction model was constructed. This model was applied to predict subway tunnel settlement in the Sanyao Section of the Xi'an Exhibition Center in China. Prediction results from the GRAWPSO-SVM prediction model were compared with those from the PSO-SVM and SVM using root mean square error (RMSE), mean relative error (MRE), and correlation coefficient as evaluation metrics. Results demonstrate that, the RMSE and MRE of GRA-WPSO-SVM are 0.0008 m and 1.9707%, which are better than those of PSO-SVM and SVM. Moreover, prediction results of the GRA-WPSO-SVM exhibit a strong correlation with the measured data of tunnels, with a correlation coefficient of 0.93. Obviously, the GRA-WPSO-SVM is effective. The proposed method provides an important evidence for the prediction of subway tunnel settlement and deformation trends. [ABSTRACT FROM AUTHOR]

The subway operation generates a large amount of waste heat, which will lead to a disruption of the underground thermal balance. To remove the heat, a ground source heat pump system adopting capillary net as the front-end heat exchanger can be built in the tunnels to recycle the waste heat and use it for building heating. Different simulation method was used to analyze the heat transfer process in the tunnel and the surrounding rock. The existing simulation method usually takes a long time for calculation and can not be used for a real-time regulation of the system. Based on the concept of thermoelectric analogy, a resistance-capacitance (RC) model was proposed for rapid prediction and analysis on the heat transfer of the capillary net in subway tunnel. The annual thermal response in the tunnel was analyzed, and the influence of the tunnel air temperature and the capillary inlet water temperature was examined using this model. The maximum heat transfer flux of the capillary in summer (release heat) and in winter (extract heat) was 55.27 W/m 2 and 38.33 W/m 2, respectively. The effect of capillary inlet water temperature was more remarkable than that of the tunnel air temperature on the capillary heat exchange process. [ABSTRACT FROM AUTHOR]

With the long-term running of the subway, the soil layer around the tunnel takes on the thermal deposition effect, which can lead the air in the tunnel to heat up and pose a serious threat to the safety operation of trains. Through taking some subway tunnels from typical zones as an example, the influence of tunnel depth on the heat storage characteristics of the surrounding soil mass was analyzed in the paper. The results indicate that the temperature field of the surrounding soil mass was thermally disturbed by both the ground air temperature and the tunnel air temperature, and there was a significant coupling point 'O' located at the center of the tunnel overburden. With the extension of the heat-exchange time, the shape of the cooling ring around the tunnel gradually changed from a circle to an oval. For the analysis of cases, from the space aspect, when the tunnel depth was less than 30 m, the wall temperature increased gradually with the increase of tunnel depth. From the time aspect, over time, the wall temperature gradually rose and finally reached a fixed value. From the region aspect, the heat absorption capacity of different areas decreased gradually with the increase of tunnel depth. When the depth exceeded 45 m, the heat absorption capacity of certain cities became negative. In addition, three typical boundaries were discussed, and the optimal method for evaluating the heat absorption capacity of the tunnel soil was ultimately determined. This study has important reference value for temperature control and positioning problems in the process of tunnel construction and operation. [ABSTRACT FROM AUTHOR]

Based on a cross-river tunnel of Wuhan Metro Line 8, we present a two-dimensional discrete element model for shield attitude adjustment considering the effect of overbreak cutters. The shield shell mechanics under the influence of over-excavation rate, over-excavation orientations, and overburden load are simulated, and the tunneling mechanics law and the ultimate range during the adjustment of the shield attitude are investigated. The simulation results indicate the following: (1) The greater the over-excavation rate, the smaller the force exerted by the soil layer in the negative direction of the shield movement; therefore, increasing the over-excavation rate is helpful in expanding the range of shield attitude adjustment. (2) The shield is stressed symmetrically while conducting positive and negative horizontal adjustments in the soil layer, which has a symmetrical distribution, but vertical upward adjustment is more difficult than vertical downward adjustment. (3) With the increase in overburden load, the space of the shield attitude adjustment is gradually reduced at the same over-excavation rate. A good engineering application was achieved in this project using the simulation model. It is recommended to use the attitude adjustment method by controlling the tunneling parameters. In difficult situations such as high overlying loads, the over-excavation cutter can be used to assist in adjusting the shield attitude. [ABSTRACT FROM AUTHOR]

With the increase in urban rail transit construction, instances of tunnel disease are on the rise, and cracks have become the focus of tunnel maintenance and management. Therefore, it is essential to carry out crack detection in a timely and efficient manner to not only prolong the service life of the tunnel but also reduce the incidence of accidents. In this paper, the design and structure of a tunnel crack detection system are analyzed. On this basis, this paper proposes a new method for crack identification and feature detection using image processing technology. This method fully considers the characteristics of tunnel images and the combination of these characteristics with deep learning, while a deep convolutional network (Single-Shot MultiBox Detector (SSD)) is proposed based on deep learning for object detection in complex images. The experimental results show that the test set accuracy and training set accuracy of the support vector machine (SVM) in the classification comparison test are up to 88% and 87.8%, respectively; while the test accuracy of Alexnet's deep convolutional neural network-based classification and identification is up to 96.7%, and the training set accuracy is up to 97.5%. It can be seen that this deep convolutional network recognition algorithm based on deep learning and image processing is better and more suitable for the detection of cracks in subway tunnels. [ABSTRACT FROM AUTHOR]

Due to the limited space in urban area, subway tunnels have to be designed and constructed with marginal clearance between each other. In the construction of subway tunnels, the installation and dismantling of temporary lining prone to affect the existing subway and new subway. In this paper, based on the Nijiaqiao Station Project in Chengdu Metro, stress state and deformation of the existing subway and the new subway, induced by dismantling of temporary lining, are compared and analyzed. It is found that different installation sequence of lining and dismantling temporary lining will affect the deformation of the subway, especially in the floor. The deformation and stress conditions of the structure are the least affected when all secondary linings are constructed in the first place and then all temporary linings are dismantled; and condition II is the worst and leads to excessive deformation and stress. Based on the analysis of the construction efficiency and influence of dismantling temporary lining, it is suggested that the combination form of divisional lining and dismantling temporary lining (i.e., condition III) can be adopted for the construction of closely-undercrossing subway. Finally, it is found that the field monitoring results are basically consistent with the simulation results, which verifies the validity of the numerical simulation. The results obtained in this paper can provide some vital references for the design and construction of similar projects (i.e., closely-undercrossing cases) in the future. [ABSTRACT FROM AUTHOR]

To study the influence of shield excavation on the surrounding soil, and to control the influence of the shield excavation of the subway tunnel on the surface settlement and the deformation of the surrounding buildings, it is necessary to study the additional stress of the surrounding soil caused by the tunnel shield excavation and the law of surface settlement. Combined with a shield construction project of a subway tunnel, this article uses the Mindlin solution in elastic mechanics to obtain three-dimensional calculation formulas for the additional thrust on the shield cutter head surface and the additional stress and displacement field caused by the friction force between the shield shell and the soil contact interface on the surrounding soil. The Loganathan ground movement pattern is used to determine the soil movement mode. The source–sink method is used to study the formula for calculating the three-dimensional additional stress of the soil around the shield tunnel caused by ground loss. The results show that when the shield is digging, the ground goes through five stages, namely the uplift of the ground before the arrival of the shield cutter head, surface settlement when the shield reaches the surface subsides when the shield tail of the shield passes through, the passage of the shield tail of the shield, surface settlement when the lining is separated from the shield, and consolidation and settlement after the shield passes through. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the growing demand for efficient travel, tunnels are being lengthened and train speeds are being increased. High-speed subway brings new challenges to the flow environment of tunnel. Additionally, the emergence of express trains passing through stations without stopping has an enormous impact on the tunnel's and the station's flow field. This study focuses on a new type of station (NS) with overtaking and avoidance lines, allowing slow trains to stop for passengers to get on and off, while express trains pass through without stopping. The study analyzes pressure variation and wind speed when express trains pass through the NS without stopping. Different train speeds are taken into account. Based on this, the enhancement of station ventilation by utilizing the piston winds generated by express trains passing through NS is investigated. The air exchange effect and energy savings of the NS are explored. The results indicate that enhancing station air exchanges by fully utilizing piston wind saves about 190.68 kWh/day in mechanical ventilation energy consumption. This study contributes to the improvement of subway station construction and the advancement of subway train development. It can offer data assistance and theoretical direction for high-speed train operations. • A dynamic mesh model of the train passing through the new station is built. • The pressure variation and wind speed at the tunnel and station are investigated. • The effects of different influencing factors on the flow field are analyzed. • The effect of airflow and energy saving in the new stations is given. [ABSTRACT FROM AUTHOR]

• The DFO is applied to monitor the circumferential joint shear tests of segments with positioning tenons. • The circumferential shear failure patterns of segments with positioning tenons are presented. • The damage characteristics of the positioning tenon and its interaction with the segments are revealed. • The main crack shear coefficient is proposed for evaluating residual shear performance. Positioning tenons have been used in more and more subway projects to improve segment assembly performance and to limit the occurrence of common problems between segments. The joints are the weak parts of the segment connection and are often damaged during construction. However, there are limited studies on the joints of segments with positioning tenons, and their damage characteristics have yet to be investigated. In this study, circumferential joint shear damage in segments with positioning tenons is studied and the evolution of the distributed damage is monitored by distributed fiber optics. First of all, the shear performance of segments with positioning tenons is investigated under different axial forces. Particularly, the damage distribution and development of segments subjected to the extrusion of the positioning tenons are analyzed through the strain signals and the macroscopic cracks during the shearing process. Furthermore, the changes in the strain signals of the distributed fiber before shear failure are analyzed. Based on the above study, the failure patterns of the inner surfaces and circumferential joint surfaces of segments with grooves are revealed. The interaction between the positioning tenons and the segments is analyzed, and the damage characteristics of the tenons are obtained. Finally, the main crack shear coefficient is proposed to evaluate the residual shear performance of segments when the macroscopic main crack occurs on the inner surface. This study aims to reveal the interaction between positioning tenons and segments and to promote the application of positioning tenons in subways. Further, it lays the foundation for optimizing the flexible joints of segments in subways and contributes to the safe construction of subway tunnels. [ABSTRACT FROM AUTHOR]

When a moving subway train catches fire in tunnels, high-temperature smoke spreads rapidly, posing a threat to the personnel evacuation process. Rational design parameters for evacuation facilities can mitigate the impact of high-temperature smoke on personnel evacuation. This study utilizes both the N − S equation and the fully buoyant corrected Renormalization-group (RNG) k − ε turbulence model to build a smoke spread model. Additionally, the study employs two-dimensional cellular automata to develop a personnel evacuation model in interval tunnels. Then determining the smoke spread and the influence of evacuation facility parameters on personnel evacuations. Furthermore, optimization algorithms are employed to optimize evacuation facility parameters. The results can be summarized as follows: (1) High-temperature smoke spreads to the downstream area after the train stops due to piston wind, severely limiting personnel evacuation. The efficiency of the downstream evacuation process determines overall efficiency of the evacuation process. (2) The width of evacuation walkways and the spacing of connecting bypasses significantly influence the total evacuation time, while the impact of the evacuation safety door width is minimal. (3) The spacing of connecting bypasses and the width of evacuation safety doors significantly influence evacuation exit congestion time, while the impact of evacuation walkway widths is small. (4) Evacuation facility parameters were optimized to minimize both the total evacuation time and exit congestion time. The Pareto frontier was analyzed, and optimization results were obtained. (5) After optimization, total evacuation time decreased by 72 %, and congestion time decreased by 85 %. • Determined the process of smoke spread in subway tunnels under a moving train with fires. • A simulation model for personnel evacuation has been developed to analyze the characteristics of evacuation behavior. • Optimization of evacuation facility parameters with the objective of minimizing both evacuation time and congestion time. [ABSTRACT FROM AUTHOR]

The surge in terrorist attacks and regional conflicts in recent years underscores the compelling necessity to acknowledge the potential threat of bomb attacks on subway tunnels. Consequently, a meticulous assessment of the fragility of subway tunnels in the context of a bombing disaster becomes imperative. In pursuit of this objective, this study endeavors to introduce a comprehensive fragility assessment framework designed to evaluate the probability of damage to subway tunnels in the face of explosion hazards. First, we quantify the uncertainty in bomb explosion positions across three distinct guidance accuracies: Laser-guided, GPS-guided, and INS-guided. This quantitative analysis uses the rigorous Latin Hypercube Sampling (LHS) method. Subsequently, a sophisticated three-dimensional finite element model is formulated, considering the interaction between shockwaves and tunnel structure. Following this, a fragility function for tunnel explosions is meticulously developed, forming a logarithmic regression model that establishes a robust relationship between explosion intensity measures (IM) and tunnel damage measures (DM). Finally, this study employs tunnel explosion fragility functions to precisely quantify the probability of tunnel damage across various states of destruction. Additionally, a comprehensive analysis is conducted to discern the specific influence of distinct bomb guidance accuracies and weight of TNT (WTNT) on tunnel fragility. This research enhances the design and management of tunnels and underground transportation networks by incorporating an in-depth understanding of explosion risk. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Quickly and accurately identifying water leakage is one of the important components of the health monitoring of subway tunnels. A mobile vision measurement system consisting of several high-resolution, industrial, charge-coupled device (CCD) cameras is placed on trains to implement structural health monitoring in tunnels. Through the image processing technology proposed in this paper, water leakage areas in subway tunnels can be found and repaired in real time. A lightweight automatic segmentation approach to water leakage using hybrid-supervised-deep-learning technology is proposed. This approach consists of the weakly supervised learning Water Leakage-CAM and fully supervised learning WRDeepLabV3+. The Water Leakage-CAM is used for the automatic labeling of data. The WRDeepLabV3+ is used for the accurate identification of water leakage areas in subway tunnels. Compared with other end-to-end semantic segmentation networks, the hybrid-supervised learning approach can more completely segment the water leakage region when dealing with water leakage in complex environments. The hybrid-supervised-deep-learning approach proposed in this paper achieves the highest MIoU of 82.8% on the experimental dataset, which is 6.4% higher than the second. The efficiency is also 25% higher than the second and significantly outperforms other end-to-end deep learning approaches. [ABSTRACT FROM AUTHOR]

With the rapid development of the subway rail transit, tunnels are buried at an increasing depth, raising the requirements of bearing capacity and waterproofness for linings. Functionally graded materials are introduced into the design of linings to save costs, and concrete with different elastic moduli is equipped at different positions to reduce the waste of materials, compared to the homogeneous lining. The significance of this study includes that the functionally graded lining for the buried subway tunnel is under the non-uniform confining pressure and the calculation model of internal force and deformation for the functionally graded lining is established. The elastic modulus of the lining is set to vary with the angle in the form of a power function, and the function parameters are analyzed on the basis of this model. The results show that the radial displacement of the lining axis decreases with the increase in a and b, but the deformation mode remains the same, and the reduction in deformation is smaller and smaller. With the increase in a and b, the distribution trend of the moment remains the same. The lateral pressure coefficient λ has a great impact on the safety of the structure, which exceeds the influence of the function parameters on the safety of the structure. The displacement of the lining axis and the section moment change linearly with the increase in λ. With the increase in λ , the shape of the lining changes significantly, which shows that the side with larger pressure deforms to the inside and the side with smaller pressure expands to the outside. When the maximum deformation occurs at 0 ° , the parameter a should be larger than b. When the maximum deformation occurs at 90 ° , the parameter b should be larger than a, so as to minimize the cost of materials and reduce the structural deformation. Finally, the numerical simulation is conducted to verify the theoretical results, showing that the calculation model of internal force and deformation is suitable for the cylinder with t / R ≤ 0.2 , and there is a certain gap between the theoretical calculation and numerical simulation, but the largest gap of the displacement is within 8%. Compared with Function I, Function II has some advantages in reducing the maximum deformation of the structure, but the advantages are relatively low. The analysis results have significant reference value for designers and relevant scholars. [ABSTRACT FROM AUTHOR]

In order to study the impact of the blasting vibration of subway tunnels on adjacent buildings, taking the tunnel mining method construction of the section between Zhifang Street Station and Metro Town Station of Wuhan Metro Line 27 as the engineering background, the blasting scheme is optimized by reducing the maximum single section charge, multi-section and densifying the surrounding holes. The HHT method and wavelet analysis are used to evaluate the advantages and disadvantages of the optimization scheme from the perspective of energy. The results show that the peak velocity of the blasting vibration is significantly reduced and the frequency is significantly increased after the blasting scheme is optimized. After the blasting scheme is optimized, when the working face is directly below the external wall of the building, the peak vibration velocity is the largest; from the back of the working face to the front of the working face, the peak velocity of the surface particle vibration first increases and then decreases. The frequency band of the optimized blasting vibration signal energy distribution is wider and the energy is more dispersed. This study can provide some practical experience for the design and construction of similar projects. [ABSTRACT FROM AUTHOR]

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The dynamic interaction between the ground fissure and an oblique two-section horseshoe-shaped subway tunnel under the subway dynamic load was investigated based on a series of model tests in this study. The results indicated that the subway subway-induced vibration attenuated in different degrees when propagating in the directions in the soil layer, while the ground fissure had an attenuation effect on subway vibration. Furthermore, the vibration of the soil layer below the tunnel near the ground fissure was stronger than that of the upper soil layer, and the vibration response at the tunnel bottom was stronger than that of the arch waist and the tunnel crown. The additional contact pressure between the tunnel bottom and the soil was relatively large when the ground fissure was not active, while the additional strain at the top and bottom of the tunnel caused by the excitation was small. Moreover, when the hanging wall of the ground fissure descended, the additional contact pressure at the tunnel crown in the hanging wall and the tunnel bottom in the footwall significantly increased, and a negative additional stain was identified at those two positions. Meanwhile, a positive additional stain was identified at the tunnel crown in the footwall and the tunnel crown in the hanging wall, increasing with the descent of the hanging wall. [ABSTRACT FROM AUTHOR]

In this paper, a practical project of subway tunnel lining demolition via blasting for the construction of a subway station under the action of the blasting load and the weight of collapsed rock mass was proposed. The tunnel overbreak and underbreak quality, the failure mechanism of the tunnel lining structure, the particle peak velocity (PPV), and the stress evolution law of the surrounding rock caused by tunnel blasting were researched using LS-DYNA. Firstly, the results show that the blasting parameters presented in this paper can maintain the cross-section of a smooth outline of tunnel excavation and the overbreak or underbreak quality in control. Secondly, the tensile stress in the existing tunnel lining caused by blasting exceeded the concrete tensile strength, and the radius of the burst fracture was 0.86 m, which is greater than the thickness of the tunnel lining (0.7 m). Thirdly, the blasting stress in the surrounding rock peaked within 0.1 × 10−3 s after the blasting, and failure of the surrounding rock occurred. Moreover, the relationship between the PPV and the distance from the blasting center shows that the blasting parameters used in this paper can effectively control the PPV. Therefore, this study reveals that the expansion of existing tunnels into subway stations using this method can improve the efficiency of construction. [ABSTRACT FROM AUTHOR]

Thermal hazards of the surrounding rock of subway tunnels are becoming apparent, in which the heat transfer in the surrounding rock plays a crucial role. Due to the shallow buried depth, the subway tunnel encounters a more complicated heat exchange under the duplicate effects of periodic temperature fluctuation of ground atmosphere and periodic temperature variation of tunnel wind, but this issue has not been fully addressed. In this work, a transient heat transfer model of tunnel surrounding rock based on dual periodic temperature boundaries was established. A solver was developed to estimate the temperature rise and heat transfer of surrounding rock. The correctness of this model was then verified by comparing with previous empirical values and semi-empirical equations. The results show that the temperatures of the surrounding rock at different depths still fluctuate following the simple harmonic waves, and there are some regions that are heavily affected by the duplicate effects, such as the overlying strata of the tunnel. The surrounding rock generally exhibits heat storage in annual cycle, but the total heat storage decreases year by year until it tends to stabilize. Furthermore, the shallower the tunnel is buried, the greater the influence of ground temperature and the higher the temperature rise in the tunnel surrounding rock. This research provides an alternative approach to determine the heat storage of tunnel surrounding rock and evaluates the process of thermal disaster manifestation of subway. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Subway trains cannot stop immediately to extinguish fires and evacuate passengers if a fire accident occurs. The piston wind generated by train movement coupled with longitudinal ventilation, makes the process of high-temperature smoke spreading upstream and downstream of the fire source more complex and unpredictable. The evacuation process of personnel is affected by high-temperature smoke in tunnels, it is worthwhile to investigate personnel evacuation in interval tunnels under longitudinal ventilation during a train fire. This paper uses a three-dimensional compressible N-S\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$N - S$$\end{document} equation and a fully buoyant corrected Renormalization-group (RNG) k-ε\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$k - \varepsilon$$\end{document} turbulence model to build a fire smoke spread model. Additionally, a cellular automaton model is employed to construct a simulation model for the evacuation of personnel in interval tunnels. We used the models to investigate the influence of longitudinal ventilation speed on smoke spread and the evacuation behavior characteristics of personnel under a moving subway train with fire. Results show that smoke spreads downstream of the fire source, and the temperature of smoke in tunnels decreases as longitudinal ventilation speed increases. A prediction model between longitudinal ventilation and the peak value of smoke temperatures in tunnels was modified based on Li's prediction model. Meanwhile, the total evacuation time decreases as the longitudinal ventilation speed increases. A theoretical prediction model between the peak value of smoke temperatures and total evacuation time is developed. The model parameters are determined using a nonlinear fitting method. The influence of longitudinal ventilation on the average flow rate and arrival time at the exit upstream of the fire source is less. However, it has a significant effect downstream of the fire source. As the longitudinal ventilation speed increases, the average flow rate at the exit downstream of the fire source increases, leading to a decrease in total evacuation time. A notable consideration is that the elderly or minors are significantly affected by smoke in the late stages of evacuation process, leading to an increase in total evacuation time. [ABSTRACT FROM AUTHOR]

[Display omitted] Deep learning (DL) semantic segmentation of tunnel point cloud shows an efficient path for applications related to subway tunnel scenes, such as health inspection and building information modelling (BIM). Current methods for tunnel point cloud segmentation often suffer from a shortage of benchmarks. This paper proposed a large-scale, multi-modal dataset for semantic segmentation of subway tunnel point cloud called subway tunnel segmentation dataset (STSD). The STSD comprises point clouds and projected images annotated into 12 categories, encompassing three types of subway tunnels with a combined length exceeding 2700 m, totaling over 2.26 billion points. A novel approach for DL semantic segmentation of subway tunnel point clouds is proposed herein. This approach enables the direct utilization of image-based DL segmentation networks on subway tunnel point clouds. Furthermore, it incorporates a lossless coordinate transformation method capable of converting tunnel point clouds of any cross-section shape into images with minimal information loss. Further evaluation of several classic or state-of-the-art 2D and 3D DL semantic segmentation models shows the feasibility of the approach and dataset. The best 2D model achieves a mIoU of 86.26% and outperforms the best 3D model by almost 10%. This research provides a novel approach for DL semantic segmentation in subway tunnel point clouds, contributes a large-scale, multi-modal dataset for the tunnel semantic segmentation, and creates a benchmark for further evaluation of the corresponding algorithms. [ABSTRACT FROM AUTHOR]

The conventional method of urban subway tunnel excavation using a double-shield tunnel boring machine (DS-TBM) typically involves a two-stage backfilling process behind the segment wall using pea gravel and grouting. However, this method has inherent drawbacks such as uneven backfilling of pea gravel and delayed grouting, which can lead to structural issues such as segment dislocation, damage, and groundwater leakage during tunnel excavation. To address these problems, this study proposes a technical theory of synchronous backfilling self-compacting concrete backfilling material (SCCBM), considering the limitations of the conventional DS-TBM backfill method. This theory uses a specially designed wear-resistant seal plate suitable for a DS-TBM shield tail. The optimal proportion of SCCBM for backfilling the segment wall was determined based on Okamura's empirical method using anti-dispersion powder, fine stones (1–5 mm particle size), and coarse stones (5–10 mm particle size) as the basic materials. The SCCBM was designed and evaluated using various test methods, including the mini-slump, standard slump flow, standard L-box, and improved L-box tests. The engineering characteristics of the backfill material, such as initial setting time, blocking ability ratio, stone rate, and axial compressive strength, were considered during the evaluation. The results demonstrate that all indicators meet the standards for backfilling behind subway tunnel segment walls. Furthermore, an on-site synchronous backfilling SCCBM experiment was conducted to validate the feasibility and advantages of the new synchronous backfilling technology. The experiment involved observing the complete backfill process and monitoring the vertical displacement of the segment. Through these observations, the practicality and benefits of the proposed synchronous backfilling technology were confirmed. • A novel synchronous backfilling technology using self-compacting concrete in double-shield TBM tunnel was proposed. • The optimal proportion of self-compacting concrete backfilling material (SCCBM) using empirical methods was determined. • The feasibility and advantages of the proposed synchronous backfilling technology was confirmed by field data. [ABSTRACT FROM AUTHOR]

An important and typical scenario of radio propagation in a railway or subway tunnel environment is the cascaded straight and curved tunnel. In this paper, we propose a joint path loss model for cascaded tunnels at 3.5 GHz and 5.6 GHz frequency bands. By combining the waveguide mode theory and the method of shooting and bouncing ray (SBR), it is found that the curvature of tunnels introduces an extra loss in the far-field region, which can be modeled as a linear function of the propagation distance of the signal in the curved tunnel. The channel of the cascaded straight and curved tunnel is thus characterized using the extra loss coefficient (ELC). Based on the ray-tracing (RT) method, an empirical formula between ELC and the radius of the curvature is provided for 3.5 GHz and 5.6 GHz, respectively. Finally, the accuracy of the proposed model is verified by measurement and simulation results. It is shown that the proposed model can predict path loss in cascaded tunnels with desirable accuracy and low complexity. [ABSTRACT FROM AUTHOR]

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Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For the images of crack defects of subway tunnel, traditional image processing algorithms is hardly effective for dealing with problems existing in the image like uneven illumination or severe noise interference. Based on pixel-level processing, an improved crack detection algorithm is proposed using structural analysis for improving the quality of tunnel images. Firstly, image preprocessing transforms the raw images of tunnel surface into binary images containing crack pixels and noise pixels. To extract crack information from binary images, three kinds of interference components are removed by structural analysis. With few interference components remaining in the image, the width of crack can be calculated according to the mean and standard deviation of the local area of the crack. Based on the algorithm, a crack detection system is designed, and a tunnel inspection experiment is conducted in a subway tunnel to capture tunnel surface images. Compared with popular image processing method, the crack recognition rate of the proposed method is 91.15% which is approximately 10% higher than others, and the measurement result of crack width based on the proposed method is closer to the ground truth. The experiment result indicates that the proposed method shows a better performance in crack detection. [ABSTRACT FROM AUTHOR]

The statistical characteristics of structural defects of shield and cast-in-situ subway tunnels are of great significance for risk assessment, preventive maintenance, and reduction of safety accidents. In this study, the apparent defect indexes, statistical characteristics, probability models, and index correlations of different lining types of subway tunnels are studied. First, quantitative and objective statistical indicators suitable for modern subway tunnel detection technology are proposed. Then, the statistical characteristics of defect data from the two different tunnel lining types are analyzed. Using the maximum likelihood estimation method, a probability analysis of the defect indexes is carried out, and the quantile test method is used to verify the probability analysis results. Finally, the correlation between defect indexes is discussed through correlation and regression analysis. The results indicate that the influence of different lining types on the defect characteristics of subway tunnels is different, and the corresponding statistical characteristics are significantly different. The probability distribution models of the two tunnel types are obviously different due to different quantitative bases of defect index severity, and appropriate probability distribution models for some indexes cannot determined. There is a certain correlation between the defect indexes of shield tunnels, but this correlation is weak in cast-in-situ tunnels. The safety evaluation index of tunnel structures can be selected according to the index correlation, and type and weight of the index of different lining types should be treated differently. [ABSTRACT FROM AUTHOR]

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The interaction between subway tunnels is investigated by using a 2D analytic model of a twin tunnels system embedded in a homogenous half-space. The closed-form analytical solution for tunnel displacement response is derived through the wave function expansion method and the mirror method, and the correctness of the solution is verified through residuals convergence and comparison with the published results. The analysis focuses on the effects of tunnel relative stiffness on tunnel–soil–tunnel interaction. Tunnel relative stiffness has a great influence on tunnel displacement response. For small tunnel relative stiffness, tunnel displacement amplitude can be enlarged by 3.3 times that of single rigid tunnel model. The response of the tunnel–soil–tunnel interaction system depends not only on the distances between tunnels but also on the frequency of the incident wave and the incident angle. The strength of the interaction between the tunnels is highly related to the tunnel spacing distance. The smaller the distance between tunnels, the stronger the interaction between them. When the distance between tunnels reaches s/a = 20, the interaction between tunnels can be ignored. It is worth pointing out that the seismic design of underground tunnels should consider the interaction between tunnels when the tunnel distance is small. [ABSTRACT FROM AUTHOR]

The principal aim of this paper is to analyze the impact of rubber pad systems on levels of vibrations and values of stresses and deformations induced in the subway tunnel segments. Thus, the 3D model has been selected to be isotropically simulated in the ANSYS program to conduct a finite element analysis. Therefore, the proposed track system in the tunnel of line 4 of the Greater Cairo Metro has been selected as an analytical and simulation case study. The impact of using eight different values for the stiffness of the rubber pad system in the case of a single tunnel has been analyzed. The results showed that levels of vibrations are significantly affected and are in logarithmic correlation with the stiffness. Also, the impact of the stiffness on the deformations and stresses are determined as well as mathematical models connecting the different parameters have been introduced. [ABSTRACT FROM AUTHOR]

Summary: Automatic visual inspection of cracks on concrete surface has become increasingly important for the health diagnosis of subway tunnel structures to prevent catastrophic failures. This paper designs an on‐board image acquisition system using multiple line scan cameras to capture the full‐section images of tunnel surface and proposes a robust automatic crack detection method for noisy and complicated tunnel surface images. The detection method consists of three steps. The first step is a crack enhancing process by using morphological image processing and frequency‐domain enhancing algorithm. In the second step, a multistage fusion filtering algorithm is designed to filter out background noise and interference from images of water stain and various railway devices on the tunnel surface. The third step is to use an improved seed growth algorithm to segment real cracks from the noisy background. The detection system is tested in the Beijing Metro Line 1, and the results demonstrate that the proposed method outperforms existing methods that are only robust for images of small area with a simple background. [ABSTRACT FROM AUTHOR]

In order to efficiently control the severe dust pollution ahead of the driving face during drilling operation, this study combined the numerical simulation with field measurements to analyze the effect of installation position of the forced air duct on the airflow-dust migration behavior in a subway tunnel. Nine schemes of installation position of the forced air duct were chosen to in-depth investigate the dynamic variation of dust concentration in four personnel breathing zones, then the optimal installation position of the forced air duct with regard to the efficient dust suppression performance was determined. The numerical simulation results showed that from the perspective of the static excavation process, the optimal dust suppression performance was achieved when the forced air duct was installed in the bottom arch of 30 m from the driving face, and the average dust concentration in four personnel breathing zones was 31.78 mg/m3. While, from the perspective of 10 m dynamic excavation process, the optimal dust suppression performance was achieved when the forced air duct was installed in the bottom arch of 20 m from the driving face, and the average dust concentration in four personnel breathing zones was 33.21 mg/m3. Finally, the accuracy of the numerical simulation results was validated by field measurement. [Display omitted] • A full-scale physical model of subway tunnel was established. • The mass flow rate and particle size distribution of the dust produce from drilling operation were measured. • Airflow-dust migration behavior under different installation position of forced air duct was investigated using CFD. • The optimal installation position of forced air duct was in the bottom arch of 30 m from the driving face. [ABSTRACT FROM AUTHOR]