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Insufficient knowledge and control of the surrounding environmental risks in the process of subway tunnel construction will lead to different degrees of surface settlement during construction, and it is of practical significance to grasp the impact of environmental risks on surface settlement and make predictions on this basis. There is a close connection between the surrounding environment of subway tunnel construction and the settlement monitoring data, and the high precision prediction of surface settlement through the surrounding environment before subway tunnel construction can guarantee the safety of subway tunnel construction. Therefore, this paper proposes a surface settlement prediction model based on environmental risk zoning. Establish the integrated impact zoning of underground mining environmental risk through spatial superposition and risk quantification, and divide the construction environment into high‐risk, middle‐risk, and low‐risk region. Adopt four different noise reduction algorithms for data noise reduction on the raw data of the monitoring points at the intervals of different risk zones, and combine the time series prediction as well as the deep learning prediction method to get the prediction model for environmental risk zoning based on the environmental risk zoning. The monitoring data of Urumqi Metro Line 1 is analyzed as an example, and the suitable combination of prediction models for each region under the environmental risk zoning of the subway tunnel construction is obtained: high‐risk region (singular value decomposition (SVD) + long and short‐term memory (LSTM) neural network); middle‐risk region (wavelet transform/Kalman filter + back propagation neural network (BPNN)); and low‐risk region (mean filtering + autoregressive integrated moving average model (ARIMA)). [ABSTRACT FROM AUTHOR]

Existing tunnel detection methods include crack and water‐leakage segmentation networks. However, if the automated detection algorithm cannot process all defect cases, manual detection is required to eliminate potential risks. The existing intelligent detection methods lack a universal method that can accurately segment all types of defects, particularly when multiple defects are superimposed. To address this issue, a defect segmentation model is proposed based on Vision Transformer (ViT), which is completely different from the network structure of a convolutional neural network. The model proposes an adapter and a decoding head to improve the training effect of the transformer encoder, allowing it to be fitted to small‐scale datasets. In post‐processing, a method is proposed to quantify the threat level for the defects, with the aim of outputting qualitative results that simulate human observation. The model showed impressive results on a real‐world dataset containing 11,781 defect images collected from a real subway tunnel. The visualizing results proved that this method is effective and has uniform criteria for single, multiple, and comprehensive defects. Moreover, the tests proved that the proposed model has a significant advantage in the case of multiple‐defect superposition, and it achieved 93.77%, 88.36%, and 92.93% for mean accuracy (Acc), mean intersection over union, and mean F1‐score, respectively. With similar training parameters, the Acc of the proposed method is improved by more than 10% over the DeepLabv3+, Mask R‐convolutional neural network, and UPerNet‐R50 models and by more than 5% over the Swin Transformer and ViT‐Adapter. This study implemented a general method that can process all defect cases and output the threat evaluation results, thereby making more intelligent tunnel detection. [ABSTRACT FROM AUTHOR]

The release of ground stress brought on by overlying excavation poses a significant threat to regular tunnel operation, especially when the foundation pit intersects the tunnel inclination, and the torsional deformation of the tunnel also needs to be considered. Based on the foundation pit intersecting with the subway tunnel at an angle, the U-shaped soil reinforcing (USR) technique was introduced to limit the tunnel heave produced by overlying excavation. The Topcon MS05A automated monitoring system was used to track the following: (1) the evolution of the tunnel heave over time and space; (2) the convergent deformation of the cross section; and (3) the torsional deformation. The reinforcement efficiency of the USR method was assessed with numerical simulations, and the effect of intersection angles and reinforcement dimensions on the deformation of the underlying tunnel was further discussed. In addition, an optimal design was suggested for the USR method that considers cost. Tunnel deformation utilizing the USR method was reduced by 63.40%, and the maximum heave was observed to be merely 6.5 mm. The influence zone on the tunnel by overlying excavation was up to 2.5 times the excavation widths, and the tunnel always produced clockwise rotation. Backfilling generates significant and sharp distortion, so the backfilling speed must be carefully controlled. The foundation pit spanning the tunnel at a small angle caused a bigger heave and torsion of the tunnel, which should be avoided. The proposed optimization approach can determine the cost based on the tunnel deformation control criteria. This study provided a valuable reference for the protection of adjacent excavations of subway tunnels in deep sandy strata. [ABSTRACT FROM AUTHOR]

Accurate and robust simultaneous localization and mapping (SLAM) is essential for autonomous exploration, unmanned transportation, and emergency rescue operations in complex underground spaces. However, the demanding conditions of underground spaces, characterized by poor lighting, weak textures, and high dust levels, pose substantial challenges to SLAM. To address this issue, we propose a graph-based adaptive weighted fusion SLAM (AWF-SLAM) for autonomous robots to achieve accurate and robust SLAM in complex underground spaces. First, a contrast limited adaptive histogram equalization (CLAHE) that combined adaptive gamma correction with weighting distribution (AGCWD) in hue, saturation, and value (HSV) space is proposed to enhance the brightness and contrast of visual images in underground spaces. Then, the performance of each sensor is evaluated using a consistency check based on the Mahalanobis distance to select the optimal configuration for specific conditions. Subsequently, we elaborate an adaptive weighting function model, which leverages the residuals from point cloud matching and the inner point rate of image matching. This model fuses data from light detection and ranging (LiDAR), inertial measurement unit (IMU), and cameras dynamically, enhancing the flexibility of the fusion process. Finally, multiple primitive features are adaptively fused within the factor graph optimization, utilizing a sliding window approach. Extensive experiments were conducted to check the performance of AWF-SLAM using a self-designed mobile robot in underground parking lots, excavated subway tunnels, and complex underground coal mine spaces based on reference trajectories and reconstructions provided by state-of-the-art methods. Satisfactorily, the root mean square error (RMSE) of trajectory translation is only 0.17 m, and the mean relative robustness distance between the point cloud maps reconstructed by AWF-SLAM and the reference point cloud map is lower than 0.09 m. These results indicate a substantial improvement in the accuracy and robustness of SLAM in complex underground spaces. [ABSTRACT FROM AUTHOR]

Soft marine soil exhibits unique mechanical properties that can lead to significant deformation and instability in the surrounding rock of urban subway tunnels. This presents a critical challenge for tunnel engineering researchers and designers. This thesis investigates the stability characteristics of surrounding rock in marine soft soil tunnels under cyclic loading conditions. Focusing on the shield tunnel segment between Left Fortress Station and Taiziwan Station of Shenzhen Urban Rail Transit Line 12, a discrete–continuous coupled numerical analysis method is employed to examine the deformation characteristics of the surrounding rock. This analysis takes into account the effects of dynamic loads resulting from train operations on the arch bottom's surrounding rock. The findings indicate that damage to the surrounding rock occurs gradually, with the marine soft soil layer, particularly at higher water content, being prone to substantial plastic deformation. Additionally, under the influence of train vibration loads, the degree of vertical fluctuation in the internal marine soft soil diminishes with increasing depth from the bottom of the tunnel arch. This coupled numerical analysis approach offers valuable insights and methodologies for assessing the structural safety of tunnel projects throughout their operational periods. [ABSTRACT FROM AUTHOR]

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.)

As urbanization gathers pace, projects involving adjacent subway tunnels are increasing, thereby amplifying the need for robust tunnel protection measures. Currently, there exists a notable lack of precise analyses on the three‐dimensional (3D) deformation laws and mechanisms of tunnels affected by adjacent deep excavation. Moreover, the influence patterns of retaining wall stiffness and deep excavation depth on the 3D deformation of pit‐side tunnels remain unclear. The purpose of this research is to bridge the existing disparity by adopting the hypoplastic model, which effectively captures soil stiffness that is dependent on soil state, strain, and stress path, even at small strains, as well as soil strength, based on reported centrifuge model tests. This approach facilitates a comprehensive, precise numerical analysis of the interaction between deep excavation and preexisting tunnels located outside the retaining wall. The analysis sheds light on the deformation mechanisms and trends of pit‐side tunnels not solely confined to the longitudinal axis but extending to the transverse plane as well, while systematically examining the influence of varying excavation depths and retaining wall stiffness on key tunnel parameters, including longitudinal deformation, diameter changes, bending strains, and soil pressure distributions around the tunnels. The study reveals that if the tunnel situated outside the retaining structure lies beneath the foundation pit's base, deep excavation only slightly deforms the tunnel. However, when the tunnel outside the retaining structure is positioned above the pit's base, its deformation progressively intensifies with deeper excavation, but the growth rate has a decreasing trend. An enhancement in the stiffness of the retaining wall results in a notable decrease in the deformation exhibited by the adjacent tunnels. The findings contribute to a deeper understanding of the complex responses of pit‐side tunnels to excavation activities, ultimately facilitating the design and construction of safer and more resilient urban subway infrastructure. [ABSTRACT FROM AUTHOR]

For structures in the near field, the velocity spectrum is significant. The aim of this study is to examine, taking into account the soil–structure interaction (SSI), how metropolitan subway tunnels with a circular cross section in alluvial soils affect the ground surface velocity spectrum. The frequency of the soil–tunnel systems was altered by varying the parameters of the soil and the geometrical features of the tunnel, such as the radius, the lining's thickness, and the depth of burial. The maximum velocity was determined at several sites on the ground surface as well as the tunnel crown. Based on the soil–tunnel system's period, the spectrum velocity graph was produced by averaging and squaring the standard deviation of the highest velocity for every frequency. Ansys finite element software and Plaxis2D were used in this study. The findings demonstrate that the tunnel's presence reduces spectral velocity (SV) relative to free‐field (FF) circumstances during the examined period at the position that corresponds to the ground‐based image of the tunnel crown. The tunnel's existence lowers the ground‐level velocity range by 14.5 percent. By moving away from the image of the tunnel crown on the ground surface, the presence of the tunnel amplifies the SV at more points by 5.5% at long periods. In addition, the tunnel crown velocity spectrum was developed. The findings indicate that the velocity spectrum diagram's envelope for the tunnel crown is a nonlinear function of the soil–tunnel system's period. [ABSTRACT FROM AUTHOR]

Ground fissures, as a typical geohazard, pose potential georisks to the construction and maintenance of urban transportation infrastructure. Under the influence of ground fissures, the segmented tunnel structure used in subway systems complicates the propagation of subway train vibrations. In this study, the soil acceleration, earth pressure and contact pressure of a three-section subway tunnel under dynamic loading of a subway train in a ground fissure environment were observed and analyzed by physical modeling tests, and the effects of the presence and activity of the ground fissure and tunnel segmentation were discussed. The results show that the vibration generated by the subway traveling will have different degrees of attenuation when propagating in all directions in the soil layer, and the ground fissure has a damping effect on the subway vibration. The attenuation and enhancement of acceleration by ground fissure is affected by the activity and propagation direction of ground fissure. The distribution of additional earth pressure is affected by the ground fissure, soil contact state, which is related to the ground fissure activity state. The ground fissure activity on the contact additional pressure mainly focuses on the bottom and top of the tunnel and there are differences in the location of the hanging wall and footwall. Three-section tunnels have a stronger vibration response and vibration attenuation than monolithic tunnels due to the influence of segmentation. Based on the consideration of the effects of ground fissure and tunnel segmentation, the tunnel design mainly takes into account the amount of ground fissure activity and determines the structural measures, the tunnel structure at the location of the ground fissure is strengthened, in addition to the vibration attenuation measures for the segmented tunnels when crossing the ground fissure. The discussion of mechanical response and design measures in this study helps to reduce the georisk of ground fissures on urban underground transportation infrastructure. [ABSTRACT FROM AUTHOR]

The shield method is a commonly used construction technique in subway tunnel engineering. However, studies on greenhouse gas (GHG) emissions specifically in subway shield tunnel engineering are lacking. This study aims to investigate the GHG emission characteristics and GHG reduction pathways during the construction period of subway shield tunnels. Firstly, based on the life cycle assessment (LCA) method, a greenhouse gas (GHG) emission quantification model for the shield tunnel construction period was developed using a multi-level decomposition of construction. Then, the GHG emission level and intensity during the construction period of a case project are quantified, and its emission characteristics and GHG reduction potential points are assessed. Finally, a comprehensive path for GHG reduction in subway shield tunnel engineering is proposed. The research results indicate that constructing 1 km of subway shield tunnel can generate 19,294.28 t CO2eq. Among these, material production element dominates the emissions with a percentage of 89.05%, while transportation and mechanical construction elements contribute 1.81% and 9.14%, respectively. From the structure perspective, the main structure contributes 88.73% of total emissions, while the ancillary structure contributes 11.27%. Among them, the working shaft and tunnel segments are the main sources of emissions for the main structure, accounting for 23.65% and 65.08%, respectively. Connecting channel and end reinforcement are the main emission sources of the ancillary structures, accounting for 43.63% and 31.30%, respectively. These findings provide a scientific foundation for the environmentally friendly transformation of urban railway development regarding pursuing "carbon peaking and carbon neutrality" strategic goals. [ABSTRACT FROM AUTHOR]

Vibrations induced by hard rock tunnel boring machine (TBM) construction have become an important concern affecting the environmental quality, particularly in urban environments. Herein, the vibration mechanism of TBM construction is studied by synchronously evaluating the three-dimensional vibration acceleration at different positions (such as the TBM cutterhead, rock stratum, and ground surface) based on the TBM construction subway tunnel project in Qingdao, China. At the TBM cutterhead, the acceleration value in the X direction considerably exceeds those in the Y and Z directions. The effective acceleration values in the X, Y, and Z directions are 0.007, 0.005, and 0.004 m/s2, respectively. Because of the presence of structural cracks in rock mass, the vibration influence of strongly weathered rock strata exceeds that of slightly weathered rock strata. On the ground, the acceleration values in the X and Y directions are amplified at 8.5 m away from the tunnel axis and the vibration signals of different frequencies will rebound at different distances from the tunnel axis. Although the vibration induced by TBM construction does not exceed the national specification requirements, the noise exceeds the set limit, thus necessitating noise control measures. [ABSTRACT FROM AUTHOR]

The joint construction of subways and other public buildings is a relatively newer type of construction. There is little research experience in the vibration characteristics and track damping design for this type of structure. In this study, a field test was adopted to conduct site measurement analysis on the vibration response of the joint construction project consisting of a subway tunnel and a building with typical frame structures. Numerical simulation methods were also adopted to, respectively, assume the use of ordinary tracks and steel-spring floating slab tracks for the subway for the situation where the Cologne-egg high-elastic fasteners were used on the track for damping purposes. Comparisons were performed to analyze the difference in the system vibration response between three different types of track. The results showed that the high-elastic fastener track and floating slab track both have a certain degree of damping effect compared with an ordinary track. Specifically speaking, the former has a damping advantage for frequency bands below 20 Hz, while the latter has the advantage for frequency bands above 20 Hz under the impact of the structural vibration characteristics for this joint construction. For this jointly construction structure, affected by the natural vibration characteristics of the structure, the natural frequency of the floating slab track is within 4 ∼ 10 Hz, and the similar vibration reduction effect can be achieved. This indicates that the structural vibration characteristic of the jointly constructed structure is an important factor determining the appropriate natural frequency of the floating slab track. [ABSTRACT FROM AUTHOR]

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]

In a study conducted in a metro tunnel, acceleration and displacement sensors were strategically placed along steel rails, track beds, and tunnel walls to capture real-time dynamic responses during train operations. Data were analyzed in the time and frequency domains, focusing on vibration levels and one-third octave bands. The results indicated that peak vibration acceleration significantly decreases from steel rails to tunnel walls, with different vibration frequencies observed at various locations: steel rails (200 Hz–1400 Hz), track beds, and tunnel walls (70 Hz–400 Hz). Cracks notably increase peak acceleration, vibration levels, peak frequency, and steel rail displacement but do not alter the overall vibration trends. Tunnel wall responses show the highest sensitivity to cracks, with a 300% increase in peak frequency, followed by track beds (100%) and steel rails (70%). Vibration levels under one-third octave band processing increased by 12.4% for tunnel walls, 8.8% for track beds, and 2.2% for steel rails. Cracks also caused steel rails' vertical and lateral displacement to rise by 112% and 53%, respectively. These findings provide valuable insights for vibration reduction and crack repair in long-term subway operations. [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.)

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.)

Copyright of China Mining Magazine is the property of China Mining Magazine Co., Ltd. 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]

A novel coupled model integrating Elman-AdaBoost with adaptive mutation sparrow search algorithm (AM-SSA), called AMSSAElman-AdaBoost, is proposed for predicting the existing metro tunnel deformation induced by adjacent deep excavations in soft ground. The novelty is that the modified SSA proposes adaptive adjustment strategy to create a balance between the capacity of exploitation and exploration. In AM-SSA, firstly, the population is initialized by cat mapping chaotic sequences to improve the ergodicity and randomness of the individual sparrow, enhancing the global search ability. Then the individuals are adjusted by Tent chaotic disturbance and Cauchy mutation to avoid the population being too concentrated or scattered, expanding the local search ability. Finally, the adaptive producer-scrounger number adjustment formula is introduced to balance the ability to seek the global and local optimal. In addition, it leads to the improved algorithm achieving a better accuracy level and convergence speed compared with the original SSA. To demonstrate the effectiveness and reliability of AM-SSA, 23 classical benchmark functions and 25 IEEE Congress on Evolutionary Computation benchmark test functions (CEC2005), are employed as the numerical examples and investigated in comparison with some wellknown optimization algorithms. The statistical results indicate the promising performance of AM-SSA in a variety of optimization with constrained and unknown search spaces. By utilizing the AdaBoost algorithm, multiple sets of weak AMSSA-Elman predictor functions are restructured into one strong predictor by successive iterations for the tunnel deformation prediction output. Additionally, the on-site monitoring data acquired from a deep excavation project in Ningbo, China, were selected as the training and testing sample. Meanwhile, the predictive outcomes are compared with those of other different optimization and machine learning techniques. In the end, the obtained results in this real-world geotechnical engineering field reveal the feasibility of the proposed hybrid algorithm model, illustrating its power and superiority in terms of computational efficiency, accuracy, stability, and robustness. More critically, by observing data in real time on daily basis, the structural safety associated with metro tunnels could be supervised, which enables decision-makers to take concrete control and protection measures. [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 detection of corroded bolts is crucial for tunnel safety. However, the specific directionality and complex texture of corroded bolt defects make current YOLO series models unable to identify them accurately. This study proposes a spatial adaptive improved detection network (SAIDN), which integrates a spatial adaptive improvement module (SAIM) that adaptively emphasizes important features and reduces interference, enhancing detection accuracy. The SAIM performs a detailed analysis and transformation of features in the spatial and channel dimensions, enhancing the model's ability to recognize critical defect information. The use of depthwise separable convolutions and adaptive feature reweighting strategies improves detail processing capabilities and computational efficiency. Experimental results show that SAIDN significantly outperforms existing models in detection accuracy, achieving 94.4 % accuracy and 98.5 % recall, surpassing advanced models such as YOLOv9 and Cascade RCNN. These findings highlight the potential of SAIDN in enhancing subway tunnels' safety and maintenance efficiency. [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]

In complex underground conditions, the excavation of deep foundation pits has a significant impact on the deformation of retaining structures and nearby subway stations. To investigate the influence of deep excavation on the deformation of adjacent structures, a three-dimensional numerical model of the foundation pit, existing subway station, and tunnel structure was established using FLAC 3D software, based on the Shenzhen Bay Super Headquarters C Tower foundation pit project. The study analyzed the deformation characteristics of retaining structures, adjacent subway stations, and tunnels during different stages of deep excavation, and the accuracy of the numerical simulation results was validated through field monitoring data. The results indicate that during the excavation process of the foundation pit, the lateral horizontal displacement of the retaining structure is generally small, with a typical "concave inward" lateral deformation curve; the horizontal displacement value of the contiguous wall section is less than that of the interlocking pile section. The bending moments of the retaining structure show a distribution pattern with larger values in the middle and smaller values at the top and bottom of the pit, with a relatively uniform distribution of internal support forces. The maximum displacement of the nearby subway station is 8.75 mm, and the maximum displacement of the subway tunnel is 2.29 mm. The research findings can provide references for evaluating the impact of newly built foundation pits near subway stations and contribute to the rational design and safe construction of new projects. [ABSTRACT FROM AUTHOR]

The construction of a new generation of smart cities puts forward higher requirements for the digitization and intelligence of subway tunnel engineering. Digital twin technology has shown great potential in high-fidelity modeling, virtual–real mapping, and decision support based on data analysis, but its research is still in its infancy. To this end, this paper first discusses in depth the inherent complexity and safety risks of subway tunnel construction and emphasizes the significant advantages of digital twin technology compared with traditional technology. Then, by summarizing the existing concepts, this paper proposes a specific explanation of DT applicable to subway tunnel engineering. In order to deeply analyze the potential of digital twin technology in subway tunnel engineering, this paper first conducts a bibliometric analysis and organizes the relevant research directions in recent years based on a visual map. Then, the application of DT in the field of subway tunnel engineering is discussed, including the modeling method of the subway digital twin, intelligent management of the construction process, safety guarantee, operation and maintenance, and resource optimization of traffic facilities in subway stations. Finally, this paper discusses the prospects and gaps of digital twin technology in theoretical and practical applications, aiming to promote the practical application of this technology in subway tunnel engineering. Through the summary and prospect of the existing research, this paper provides a valuable reference for future research directions and practical applications. [ABSTRACT FROM AUTHOR]

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 P 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. [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]

The lateral impact loads induced by blasting excavation of subway tunnel are detrimental to adjacent structures with pile foundations. Physical model tests are carried out to study the dynamic behaviors and failure modes of pile foundations under blasting impact loads. Specifically, the acceleration and strain variation monitoring of friction pile foundations subjected to tunnel blasting is conducted. It is indicated that the bending moment, horizontal acceleration, and dominant frequency (DF) of the pile foundation gradually increase with the standoff distance decrease, while the vibration duration becomes shorter. In the case of pile foundations located in the far field of the explosion, an acceleration amplification effect is observed at the pile top due to the presence of Rayleigh waves (R waves) and the high-frequency filtering effect of the surrounding soil and rock mass. Consequently, the pile-superstructure system experiences resonance, leading to shear failure at the connection between the pile cap and pile top. With decreasing standoff distance, the high-magnitude blasting loads may result in either tensile failure at the pile-soil bond interface or bending failure at the connection. For the pile foundations situated in the near field of the explosion, tensile failure occurs at the pile-soil bond interface, resulting in a loss or failure of the pile's lateral frictional resistance. Alternatively, buckling failure may occur in the middle of the pile, and spalling, cracking failure of concrete occurs at the bottom of the pile. [ABSTRACT FROM AUTHOR]

In recent years, the pipe shed advanced support method has emerged as a new technique for excavating tunnels in weak surrounding rock. However, the necessity to maintain a certain inclination angle when constructing large pipe sheds unavoidably increases the excavation and lining quantities. Consequently, as the length of the pipe shed increases, construction errors also grow, resulting in larger excavations and backfilling works, thereby making it difficult to control the quality of pipe shed installations and limiting the development of the pipe shed method. Faced with the challenges presented by tunnel support construction as part of subway tunnel construction, this paper is based on the Songhuai Youyuan Station tunnel project involving Zhengzhou Metro Line 9. Field experiments were conducted, using high-torque horizontal drilling machines and pipe shed guiding technology to successfully complete the installation of a 208 m long pipe shed in a single operation (the longest in the world). Through case analysis and technological innovation, a feasible and effective drilling technology scheme was proposed. Compared with traditional methods, the key technology for installing super-long pipe sheds in a single operation reduced the construction time by 35% and construction costs by 25%, providing valuable insights for similar projects. [ABSTRACT FROM AUTHOR]

Ellipticity is an important indicator for measuring the deformation of subway shield tunnel segments. The key to ellipticity analysis is the points on the inner wall of the tunnel. Because there are rail beds and pipelines in the subway tunnel, there are many non-inner wall points in the tunnel point cloud with varying distances from the inner wall, which will affect the analysis of ellipticity. Currently, the commonly used method is to use a straight-through filter to process rail beds, but the effect is not good when there is a large clearance between the rails and the bed. For other attachments, the distance threshold method is used, but there is a difficulty in accurately determining the threshold in advance. This paper proposed a distance threshold elimination method for rail bed points and a grading weighting elimination algorithm for attachment points, based on the distribution characteristics of the shield tunnel point cloud. The method ensured that the points used in ellipticity calculation were all inner wall points, improving the accuracy of subway shield tunnel ellipticity analysis. Simulation data shows that the MAE of ellipticity obtained by the algorithm proposed in this paper is 0.085‰, which is better than the direct least squares method and RANSAC algorithm. Based on laser point clouds of 56 single-ring subway tunnels, the performance of the algorithm is tested, with the average MAE of ellipticity for each ring being 0.174‰ and the average standard deviation of ellipticity for each ring being 0.216‰, which is respectively 19.1% and 19.7% higher than the RANSAC algorithm. This demonstrates that the proposed method can effectively eliminate the influence of non-inner wall points in subway tunnel point clouds, and the ellipticity calculation results are robust. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the excavation method, excavation sequence, and optimum trailing distance between excavation stages of the tunnel face to control ground settlement caused by constructing the Tehran Subway Tunnel-Line 6 in the northern part. To this end, 3D numerical modeling is performed, and settlement data validate the obtained results. The results showed that among the sequential excavation methods, the ring-cut (RC) and central diaphragm (CD) have more appropriate control over the surface settlement. The maximum settlement resulting from the RC method and CD is within the permissible settlement range. Considering the better control of the RC method compared to the CD method in limiting the ground settlement, the RC method was chosen to determine the excavation sequence and optimum trailing distance between excavation stages of the tunnel face. Increasing the number of excavation sequences and excavation support core in the final stages of the face can play an effective role in limiting ground settlement. Also, the results showed that when the trailing distance between excavation stages is more than one-time the tunnel diameter, due to the less interference of the stress distribution zones, the settlement of the ground surface declines dramatically and falls within the permissible settlement range. [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]

This paper proposes a novel parameterized frequency‐domain modal parameter identification method, called direct modal variational mode decomposition (DMVMD), based on the multivariate variational mode decomposition (MVMD) framework and the principle of modal superposition. Under the constraint of normalized mode shapes, this paper theoretically derives the relationship between multivariate variational mode decomposition and the natural frequencies and mode shapes of structural systems. The aim is to extract K response modes and their corresponding mode shapes from the excited C‐dimensional vibration signals of the measured component's response. First, the measured multichannel vibration signals are decomposed into IMFs aligned with K‐order natural frequencies using multivariate variational mode decomposition (MVMD). Then, the Hilbert equations and mode shape normalization constraints are used to solve the structural natural frequencies and mode shapes. Furthermore, the proposed multimodal identification algorithm has been validated through numerical simulations and experimental examples, demonstrating its high accuracy and robustness in modal identification. Compared to the existing multimodal algorithms related to variational mode decomposition, the proposed method is more direct and elegant. This method has been successfully applied to the modal parameter identification of subway tunnel structures, enabling accurate determination of the location of tunnel damage through analysis of the identified modal parameters. [ABSTRACT FROM AUTHOR]

Tunnels for subways and railways are a vital part of urban transportation systems, where shield tunneling using assembled segmental linings is the predominant construction approach. With increasing operation time and varying geological conditions, shield tunnels usually develop defects that compromise both structural integrity and operational safety. One common issue is the separation of segment joints that may cause water/mud penetration and corrosion. Existing inspection strategies can only detect openings after their occurrence, which cannot provide early warnings for predictive maintenance. To address this issue, this work proposes a multi-point seam contact pressure monitoring method for joint opening identification. It first derived the theoretical correlation between contact pressure distribution and segment opening; then, a finite element model was established to explore the stress and deformation responses under combined axial and bending loads. Finally, multi-point piezoelectric film sensors were implemented on a scaled segment model to validate the theoretical and numerical analyses. Results indicate that the multi-point monitoring method can effectively identify opening amounts at the segment joints with an average error of 8.8%, confirming the method's feasibility. These findings support the use of this monitoring technique for early detection and assessment of joint openings in shield tunnels. [ABSTRACT FROM AUTHOR]

The issue of uneven ground settlement caused by the excavation of subway tunnels represents a significant challenge in the design and construction of subway projects. This paper examined the fractal characteristics of surface settlement caused by subway excavation, employing wavelet transform and fractal theory. Firstly, the noise reduction effects of different wavelet functions, decomposition levels, threshold functions, and threshold selection rules were evaluated using the SNR and RMSE. Subsequently, 291 data points were derived from 18 interpolation points through fractal interpolation, representing a utilization of only 18% of the original data, to enhance the original monitoring data information by a factor of 2.94. The average relative error between the fractal interpolation results and the monitoring data was approximately 13%, which was indicative of a high degree of accuracy. Finally, the fractal dimension of the monitoring curves under different monitoring frequencies was calculated using the box-counting method. The denoising effect of the dbN wavelet function was found to be superior to that of the symN wavelet function in the denoising process of subway construction surface deformation monitoring data. Furthermore, the hard threshold method was observed to be more effective than the soft threshold method. As the monitoring frequency decreased, the fractal dimension of the deformation curves showed an overall decreasing trend. This indicated that high-frequency monitoring could capture more details and complexity of the surface settlement, while low-frequency monitoring led to a gradual flattening of the curves and a decrease in details. [ABSTRACT FROM AUTHOR]

To address the constraints associated with conventional fitting techniques for temperature demodulation in the context of subway tunnel fires, a new method of demodulation grating sensing spectrum using long short‐term memory convolutional neural network (LSTM‐CNN) is proposed in this paper. Build the monitoring platform based on LSTM‐CNN ultra‐weak fiber grating temperature measurement system, predict its sensing signals by LSTM‐CNN algorithm, select 18000 spectra as sample data for training, use AdamW stochastic optimization algorithm for training, and carry out the temperature calibration and demodulation error analysis of the Fiber Bragg Grating within the temperature range of 25–75°C. Compared with GRU algorithm, LSTM algorithm and traditional maximum peak method, the algorithm of this paper is good and can effectively improve the measurement accuracy, the experimental results show that: the demodulation accuracy of temperature wavelength prediction in this paper can be up to 99.27%, and the root mean square deviation is 0.08528°C, through the experiments, it is verified that the method proposed in this paper has a certain reference and support in terms of theories and technology significance. It is suitable for the identification and monitoring of fire hazards in underground tunnels, and also has application value in the signal processing of grating array sensing demodulation system. [ABSTRACT FROM AUTHOR]

The objective of this research is to investigate the characteristics of the deformation response in adjacent subway tunnels caused by deep foundation excavation of reclaimed land. Focusing on a deep foundation excavation project situated in proximity to Line 11 of the subway in Shenzhen, this study employs theoretical analysis, numerical simulation, and on-site measurements to thoroughly investigate the deformation issues induced by the unloading of the excavation. The research results are as follows: using the energy method to calculate the uneven deformation of adjacent subway tunnels caused by the excavation can overcome the limitations of traditional algorithms, which treat the subway tunnel as a uniformly elastic foundation beam, resulting in more reasonable calculation results. Increasing the self-stiffness (EI)eq of the tunnel can effectively reduce the maximum displacement (wmax) of the tunnel, and as (EI)eq increases, its "weakening effect" on wmax gradually diminishes. Underground continuous walls can effectively control tunnel deformation, with tunnel displacement decreasing as the thickness and concrete strength of the continuous walls increase. "Long excavation" deep foundation excavations can impact the displacement and uplift range of the tunnel, with the maximum tunnel displacement showing a nonlinear decrease with increasing excavation depth. Tunnel displacement decreases as geotechnical parameters (elastic modulus E, internal friction angle φ, and cohesion C) increase, with the elastic modulus being the most sensitive parameter. The research findings can be applied to tunnel construction, maintenance, and safety evaluations, providing valuable references for similar engineering projects in the future. [ABSTRACT FROM AUTHOR]

In open-cut assembled subway tunnels, foundation pit enclosure piles are typically cast in place. However, this conventional approach limits the functionality of the piles to serving as retaining structures during excavation, resulting in resource inefficiency and the underutilization of prefabrication techniques. To address this issue, a fully prefabricated pile-wall composite scheme is proposed for cut-and-cover tunnels to optimize the retaining effect of the piles and leverage the benefits of prefabricated technology. In this scheme, the retaining pile and lining are both prefabricated. The pile is the temporary retaining structure during pit excavation and a part of the sidewall. This scheme was researched and applied in Jinan, China. Field monitoring and numerical simulation were used to investigate the load transfer within the fully prefabricated pile-wall composite structure (PPWS) and its mechanical response, respectively. The results show: (1) The development of lateral earth pressures on the PPWS experienced three stages. The lateral earth pressure distribution indicates that the PPWS can fully activate the retaining effect of precast piles. (2) Following the backfilling of the joints, the horizontal displacement at the bottom of the precast pile reduced by 0.39 mm. Numerical simulation results indicate the effectiveness of precast pile restraint in PPWS. (3) The PPWS exhibited uniform deformation transition at the joints. The joints play a crucial role in coordinating deformation between the precast piles and sidewalls, utilizing the restraining effect of the precast piles. [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]

The cumulative length of subways and tunnels in China has reached nearly 25 000 kilometers, bringing huge demand for underground construction. The monitoring for construction safety has become more significant, due to complicated environment and rapid-onset natural disasters, which raises the frequency of accidents in underground construction. The informatization engineering of monitoring and early-warning on natural disasters is built to achieve construction safety, through promoting integrated monitoring on multi-hazard and disaster chains, and practicing intelligent algorithms on comprehensive quick accurate perception and early-warning of construction hazards. The integrated network architecture for intelligent safety monitoring with edge-computing ability is established, realizing the visualization of monitoring data analysis through researches on AD hoc transmission based on directional antenna network bridge, development of IoT edge computing software and researches on accessing to IoT platform for multiple types of sensors, and development of the front-end and back-end of the monitoring system. The introduction of IoT and cloud computing sustains accessing to platform for huge amount of sensors and full exploiting of big-data mining, improving intelligent safety hazard identification, and reducing safety risks in construction. Based on the instant response of edge devices and interval data acquisition of sensors, and the capability for more than 100 000 sensors to access the system simultaneously, the complete monitoring system for underground constructions with second-level warning is established. [ABSTRACT FROM AUTHOR]

According to the design specifications, the construction of extended piles involves traversing the tunnel's upper region and extending to the underlying rock layer. To address this challenge, a subterranean transfer structure spanning multiple subway tunnels was proposed. Deliberating on the function of piles in the transfer structure as springs with axial and bending stiffness, and taking into account the force balance and deformation coordination conditions of beams and plates within the transfer structure, we established a simplified mechanical model that incorporates soil stratification by combining it with the Winkler elastic foundation beam model. The resolved established simplifiedmechanicalmodel employed finite difference technology and the Newton-Simpsonmethod, elucidating the mechanical mechanism of the transfer structure. The research findings suggest that the load carried by the upper structural columns can be transferred to the pile foundation beneath the beams through the transfer structure, subsequently reaching the deep soil layer and ensuring minimal impact on adjacent tunnels. The established simplified analysis method can be used for stress analysis of the transfer structure, concurrently considering soil stratification, pile foundation behavior, and plate action. The pile length, pile section size, and beam section size within the transfer structure should account for the characteristics of the upper load, ensuring an even distribution of the beam bending moment. [ABSTRACT FROM AUTHOR]

Primarily generated at the interface between the wheel and the rail, railroad vibrations then propagate through the supporting soil. If these vibrations reach nearby bridges and buildings, they amplify the vibration nuisance and cause ground noise, which has detrimental effects on nearby residents, sensitive equipment, and historic structures. By analyzing measured data from metro vibration field vibration experiments, this article attempts to contribute to the body of knowledge on environmental vibration propagation patterns by offering insightful conclusions. Before analyzing the deformation response of the metro jet system (MJS) vibration isolation piles to the structure and the ground, we investigated the effect of MJS vibration isolation piles in the ground of the existing subway tunnel structure on the control of vibration of the proximate structure and conducted dynamic tests on the vibration of bridges without vibration isolation measures caused by operating subway trains. The tests determined that the acceleration of the bridge's lateral vibration exceeded the code limit; one of the contributing factors was that the bridge's structure had already sustained damage. The utilization of MJS isolation piles was also discovered to safeguard the extant bridge pile foundations. The paper presents an innovation in the form of economically viable vibration mitigation strategies that were implemented subsequent to the identification that the lateral vibration acceleration of the preexisting bridge surpassed the prescribed code standards. Considerable insight is gained regarding the design and implementation of vibration control systems for structures situated near caverns, encompassing deep foundation works. [ABSTRACT FROM AUTHOR]

Deep excavations near subway tunnels can induce deformation, necessitating a comprehensive investigation into causal factors and mitigation strategies. Field measurements were conducted to assess both vertical and horizontal displacements of existing tunnels near a deep excavation in Shenzhen. Utilizing a validated three-dimensional finite element model that considers structure−strata interactions, this study analyzes tunnel displacements, ground movements, diaphragm wall impacts and the sensitivity of enclosure structure parameters. The results indicate that tunnel deformation correlates with enclosure structure deformation, particularly near the center of the pit. Moreover, shallow soil excavation significantly affects the vertical displacement of shallow-buried tunnels. However, the design parameters of the existing enclosure structures inadequately limit tunnel displacement. Therefore, it is crucial to intensify vertical displacement monitoring in shallow tunnels during early excavation stages and to enhance horizontal displacement monitoring during later phases. Implementing measures such as optimizing central support design or retaining soil at the pit bottom helps control maximum horizontal displacement. While support stiffness plays a greater role than retaining wall thickness, its impact on deep excavation projects is limited. [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]

It is a high-risk project in most cases for urban subway tunnels to pass through structures at close distances. In order to effectively control the stratum deformation and reduce the construction disturbance, it is extremely critical to select a practical tunnel construction method. Based on the Jing-Zhang high-speed rail shield tunnel under an extremely small interval of the subway section of Beijing Line 12 in China, a numerical simulation was conducted regarding the bench-cut method, the temporary inverted arch (TIA) method, the center diaphragm method, and the center cross diaphragm method. The key issues are discussed in detail, such as the laws of the stratum deformation, the surface subsidence pattern, the deformation of the shield segment, and the force characteristics of the supporting structure. The research results show that the maximum deformation of the shield segment caused by subway construction is within the range of ±15 m from the central section of the double interval. The TIA method not only reduces the stress caused by the bending moment of the initial support, but also takes full advantage of the locking effect of the anchor pipe, and the stratum deformation is well controlled. [ABSTRACT FROM AUTHOR]

The coastal areas are the most economically developed, and they need to build many infrastructures such as airports, ports, and subways. However, the complex geological conditions in the coastal areas pose risk issues to the construction. In response to the characteristics of the high risk of subway shield tunneling, we proposed a new method to evaluate the safety of subway shield tunneling by using the entropy weight method and the matter-element theory. In addition, we built a safety evaluation index system with 52 evaluation indexes, including workers, machinery, materials, technology, environment, etc. Accordingly, using the entropy value method, we calculated the weight of each index and built the classical domain with the matter-element theory. Then, combining the joint domain with the evaluation of the main factors, we calculated the risk correlation degree. Moreover, we established the safety assessment model. Taking the coastal tunnel between the Hujing Station and Wanshou Station of Fuzhou metro line 6 as an example, we validated the evaluation model and assessed the risk of the coastal tunnel. The result demonstrates that the total construction safety risk level is low. But the environmental factors are very crucial; the highest is the embankment collapse C523, and its proportion is 8.14%. It is necessary to measure deformation and reduce the environmental risks of construction. The case study can provide a very valid reference for some similar coastal projects. [ABSTRACT FROM AUTHOR]

The construction of deep foundation pits that are adjacent to an operating subway tunnel can cause significant disturbance to the surrounding soil and tunnel structure. Assessing the stability of the soil in the security area of the tunnel is key to controlling the displacement of the tunnel structure. Assuming that the soil behind the wall is in the elastic stage of small deformation, the unloading stress distribution law of the soil on the excavation surface of the side wall is inversely calculated using the horizontal displacement curve of the retaining structure. Based on the analytical solutions for the horizontal displacement and surface settlement of the soil behind the wall proposed in this paper, the spatial distribution characteristics of the deformation transfer of the soil in the security area are obtained. Considering the interaction between the soil in the security area and the tunnel structure, by simplifying the soil in the security area to a Pasternak foundation model, the tunnel displacement that is caused by deformation transfer can be obtained. The correctness of the theoretical model is verified by comparing it with the measured data for the soil displacement behind the wall and the tunnel structure in project cases of foundation pit excavation. [ABSTRACT FROM AUTHOR]

Stratum cavity collapse induced by water and sand leakage in a subway tunnel is a sudden urban geological disaster, which can cause serious casualties and economic losses. In response to the hazards of stratum cavity collapse induced by water and sand leakage around subway tunnels, a set of visual test devices with variable hole diameters were designed to simulate the stratum cavity collapse induced by water and sand leakage under comprehensive consideration of the size of the cavity diameter, clay thickness, clay strength, and so on. Based on pressure arch theory and unified strength theory, a critical calculation formula was established for stratum cavity collapse under two modes, of tensile shear and shear failure. Furthermore, the accuracy of the theoretical calculation formula was verified by experiment. The results show that the critical radius increases with the increase of clay strength and decreases with the increase of buried depth and friction angle. Clay soil is more prone to shear failure at the arch foot under the same conditions. The larger the soil sand mix ratio and the cavity diameter, the smaller the critical water pressure of soil collapse. The thicker the soil layer, the greater the critical water pressure. The theoretical analysis method has a clear physical meaning and the theoretical results agree well with the test results. The research results are of great significance for the warning of and prevention of such urban geological disasters. [ABSTRACT FROM AUTHOR]

An increasing number of studies have shown that the seismic response of shield tunnels differs from that of aboveground structures. While the seismic response of aboveground structures is mainly influenced by the peak acceleration and frequency of the earthquake, the seismic response of shield tunnels is more influenced by the ground displacement due to the surrounding soil layers. In this study, it is not appropriate to follow the seismic concept of aboveground structures. Dynamic time-history analysis is a powerful and effective method to study the seismic response of tunnels in the typical subway in this paper. The analysis results show that the overall levelling of the tunnel will not affect the tunnel too much, and the seismic response of the tunnel is mainly related to the relative displacement of the ground around the tunnel. The analysis results show that the internal force of the tunnel and the tunnel inclination have a good linear relationship, and the tunnel inclination can be used to measure the magnitude of the seismic response of the tunnel. In the seismic design of shield tunnels, the inclination of the tunnel can be taken into account to evaluate the change in the internal forces of the tunnel during earthquakes, which avoids the need for complex dynamic time-history analysis and greatly improves the efficiency of the seismic design of shield tunnels. [ABSTRACT FROM AUTHOR]

With the increase in the number of buildings along the subway, the impact of building construction on the adjacent subway tunnels has gradually come to the forefront and become an important problem to be solved in the engineering field. In particular, the excavation and unloading process of deep foundation pits will trigger an additional deformation of the subway structure, which may pose a serious threat to the safety and stability of subway tunnels. This article is based on a foundation pit project in the sub-center of Beijing, focusing on the form of a connected double foundation pit. Using the HSS constitutive model for soil materials, this study simulates the deformation response of adjacent existing subway tunnels under three excavation sequences: sequential excavation, simultaneous excavation, and the comprehensive excavation of the connected double foundation pits. The study shows that, from the point of view of the total displacement of the whole construction process, the impact of a synchronized excavation of double pits on the existing tunnel line is relatively large in the process, and the impact of sequential excavation is relatively small in the construction cycle. The result of the similarity of the excavation sequence is the similarity of the impact trend. The volume of excavated earth determines the value of displacement change for each excavation scenario in each working condition and is also responsible for the convergence of changes. The trend of total tunnel displacement is more consistent with that of vertical displacement, which is dominated by vertical displacement, with horizontal displacement having a relatively small influence. The maximum value of the total tunnel displacement occurs at the side of the tunnel near the excavation area, and the direction is inclined to the excavation area. The application of supporting structures, especially the center plate and the bottom plate, can suppress the vertical deformation of the tunnel bulge. [ABSTRACT FROM AUTHOR]