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This paper proposes a simplified analytical solution for longitudinal seismic responses of a circular tunnel crossing a fault zone under longitudinally propagating shear waves. The transmissions and reflections of shear waves at two geological interfaces between the fault zone and intact rock are considered when calculating the free‐field displacement. An improved elastic foundation beam model considering different tangential contact conditions at the tunnel‒rock interface is also adopted. According to the continuous conditions at the two geological interfaces, explicit expressions for the tunnel displacement, bending moment, and shearing force are given. The effectiveness of the proposed analytical solution is validated via numerical simulations, and the importance of accounting for tangential contact conditions at the tunnel‒rock interface is emphasized. Moreover, parametric studies are performed to investigate the effects of the fault zone width, rock conditions, tunnel lining stiffness, tangential contact conditions, and earthquake frequency on the deformation and internal forces of tunnels subjected to seismic waves. This novel analytical solution can be utilized to quickly estimate the longitudinal seismic responses of circular tunnels crossing fault zones subjected to longitudinally propagating shear waves, particularly in the preliminary engineering design, and can be extended to geological conditions with multiple interfaces. [ABSTRACT FROM AUTHOR]

Similar to the deep-buried tunnel, the lining of the cut-and-cover tunnel (CCT) exhibits varying degrees of cracking failure during ultrahigh backfill. To explore the whole progressive failure process of a high-filled cut-and-cover tunnel lining structure from the mesodamage to the macrolocal failure and then to the overall instability during backfill, based on the discrete-element program PFC2D, we simulated the mechanical behavior and fracture characteristics of the CCTs with rectangular, circular, and arch lining section features with the backfill height. Two load-reduction measures—load-reduction material (LRM) and the interaction of LRM and concrete walls—were then further proposed, and the impact of load-reduction measures on the progressive failure of CCT lining was analyzed. The simulation results show that the various lining section features indicate differences in the distribution and value of lining stress and fracture. But the CCT lining with features of the three sections exhibits a progressive failure process from cracking to local collapse and falling and finally to overall instability as the backfill height increases. Furthermore, the LRM and concrete walls can effectively reduce the vertical stress of the lining vault and the horizontal stress of the haunch, respectively, to ensure the stability and integrity of the CCT. [ABSTRACT FROM AUTHOR]

During the assembly of concrete segments into a tunnel lining, small geometric imperfections are unavoidable. In the longitudinal joints, they lead to contact deficiencies, which affect the eccentricities of the forces transferred through them. This influences the development of internal forces along the lining's circumference. However, it is often not realistically considered in structural calculations. In this paper, the effects of longitudinal joints assembly imperfections on the lining's internal forces were investigated by employing finite element models for various lining configurations. The results show that assembly imperfections have an unfavorable effect on the internal forces in most cases. Depending on the loading situation, this can lead to more required reinforcement and higher utilization ratios in the segments field and joints compared to perfectly assembled linings. Stiffer and less deformable configurations are at higher risk of experiencing more severe effects. In systems at risk, an individual assessment is recommendable. Therefore, a simplified method is introduced that requires a significantly reduced modeling effort and calculation time and lower software capabilities. [ABSTRACT FROM AUTHOR]

This study aims to investigate the influence of the tiny soil arch effect generated by the soil between the steel tubes in the ring direction of the tunnel overrun tube shed on the force deformation of the steel tubes during the working period. By assuming the arch effect axis between the steel tubes is circular and intercepting any three adjacent steel tubes on the tunnel contour line to establish a vertical coordinate system, the equation of the arch axis and the coordinates of the arch top were derived. Referring to the calculation theory of the peripheral rock pressure of the Taishaki tunnel, the peripheral rock pressure borne by the steel tubes of the pipe shed under the consideration of the micro‐arch effect was derived. Assuming the pipe shed acts as a semi‐infinite long beam on Pasternak's two‐parameter elastic foundation, the pipe shed was divided into four sections axially based on the initial support application status and the tunneling position of the working surface. The controlling equations for each section were analyzed and solved. The theoretical deflection curves of the pipe shed were obtained using actual engineering construction parameters and were validated by monitoring the settlement values of the soil layer above the tunnel using multipoint displacement meters. The study shows that the initial support application status and the tunneling position of the working surface significantly affect the functioning mechanism of the pipe shed, causing it to play different roles at different stages. When the working surface advances to the target section, the pipe shed exerts a beam arch effect; when the working surface tunnels beyond the target section, the pipe shed exerts a combined beam effect. The deflection change trend of the pipe shed with the advancement of the working surface is characterized by rapidly increasing, rapidly decreasing, and slowly decreasing stages, with the maximum deflection change occurring above the working surface position. Considering the micro‐arch effect, the theoretical deflection changes are larger and closer to the actual engineering situation compared to the existing theory that does not consider the micro‐arch effect. The results provide theoretical references for the design and implementation of tunnel overrun pipe sheds, moving beyond mere engineering experience and validating new methods for monitoring the deformation of surrounding rock during tunnel construction, effectively ensuring construction safety during tunnel excavation. [ABSTRACT FROM AUTHOR]

The accurate detection of tunnel lining cracks and prompt identification of their primary causes are critical for maintaining tunnel availability. The advancement of deep learning, particularly in the domain of convolutional neural network (CNN) for image segmentation, has made tunnel lining crack detection more feasible. However, the CNN-based technique for tunnel lining crack detection commonly prioritizes increasing algorithmic complexity to enhance detection accuracy, posing a challenge in balancing the accuracy of detection and the efficiency of the algorithm. Motivated by the superior performance of Unet in image segmentation, this paper proposes a lightweight tunnel lining crack detection model named Mini-Unet, which refined the Unet architecture and utilized depthwise separable convolutions (DSConv) to replace some standard convolution layers. In the optimization of the proposed model parameters, applying a hybrid loss function that integrated dice loss and cross-entropy loss effectively tackled the imbalance between crack and background categories. Several models were set up to contrast with Mini-Unet and the experimental results were analyzed. Mini-Unet achieves a mean intersection over union (MIoU) of 60.76%, a mean precision of 84.18%, and a frame per second (FPS) of 5.635, respectively. Mini-Unet outperforms several mainstream models, enabling rapid detection while maintaining identified accuracy and facilitating the practical application of AI power for real-time tunnel lining crack detection. [ABSTRACT FROM AUTHOR]

Considering the effect of surrounding rock on lining in the design of tunnel lining within fractured rock masses is challenging, particularly in accurately predicting the reserved deformation of the tunnel. This study bases a rock mass classification method and the established Hoek–Brown (H-B) strength criterion to assess the deformation characteristics of the surrounding rock. It establishes a more scientifically rigorous theoretical calculation method for the reserved deformation of tunnel linings that accounts for the rock–lining interaction. An optimization design approach for the lining structure, based on the synergistic effect and considering the stress safety of the concrete lining and the rock's displacement release rate, is proposed. Case analysis is utilized to validate the safety of the lining design in the study section through computational verification. The recommended optimized lining parameters are identified: the support time is initiated when the tunnel wall's surrounding rock deforms by 9 mm, and the lining thickness is optimized to 47 cm, which is approximately 36.5% less than the pre-optimization thickness. This precise optimization of support timing and lining thickness enhances both the safety and economic efficiency of the Wufengshan Tunnel. The method allows for the calculation of the optimal combination of support time and lining thickness tailored to different surrounding rock conditions, offering significant reference value for tunnel lining optimization. [ABSTRACT FROM AUTHOR]

Existing concrete specifications limit the crack width in order to fulfill the limits of serviceability and durability. The crack width calculation results differ depending on the influences of the variability of the used materials, the geometry, the actions and the uncertainty of the used calculation model itself. In this contribution, the influence of the variability of the input parameters on the calculated crack width is investigated using probabilistic methods in a real case study of a highly loaded tunnel lining cross‐section. The primary objective of this study is a sensitivity analysis to identify the geometric and material‐related input parameters with the most significant influence, which must be particularly controlled during execution for quality control purposes. The study in this article is based on the Eurocode deterministic model for calculating crack width for a stabilized cracking stage in late concrete age. [ABSTRACT FROM AUTHOR]

The paper introduces a new model of compressive membrane action (CMA) for a conical fan failure mechanism around a patch load in a reinforced concrete plate with in-plane restraint. The new model is based on a concept of 3-dimensional wedging and it is fundamentally different from conventional arching models of CMA. The new model accounts for the effects of CMA on the bending resistance at yield lines and the complementary wedging effect of compressive membrane forces at the yield lines, considering the interaction between the radial and tangential forces acting on the wedgelike segments in a restrained fan. The model was developed in the context of an investigation of the strength of fiber reinforced shotcrete (FRS) tunnel linings, but it is readily adaptable for conventional reinforced concrete plates and slabs. The paper compares the wedging model results (predicted load-deflection curves) with field test results for FRS tunnel linings. It is shown that the wedging model provides a good approximation to the available test results. [ABSTRACT FROM AUTHOR]

Water seepage in tunnel lining cracks considerably influences the structural safety of a tunnel. In this study, chitosan was introduced in the enzyme-induced carbonate precipitation (EICP) to repair the cracks in in-service tunnel linings. The influence of chitosan incorporation on the Ca2+ precipitation ratio during EICP was analyzed by aqueous solution experiments, and the optimal content of added chitosan was obtained. Moreover, in terms of specimen scale and field tests, the determination of permeability characteristics, and mass loss, scanning electron microscopy and ground penetrating radar technology were used to analyze the changes in permeability coefficient and mass loss of cracked concrete repaired by chitosan-combined EICP under normal temperature (25°C±2°C) and freeze–thaw (FT) cycling conditions. The effect, feasibility, and action mechanism of chitosan-combined EICP for tunnel crack repair in extreme environments were explored. The results showed that the incorporation of an appropriate amount of chitosan in traditional EICP could accelerate Ca2+ precipitation, provide nucleation sites for the precipitation of CaCO3 , promote the existence of the deposited CaCO3 crystals in the form of calcite with higher strength, and reduce mass loss in extreme circumstances. The combination of hydrogel and CaCO3 makes the impermeable layer more compact and reduces the permeability coefficient of repair concrete. The permeability coefficient descends exponentially with the decrease of mass loss under FT conditions. Chitosan-combined EICP represents an environmentally friendly and feasible method for crack repair in in-service tunnel linings. [ABSTRACT FROM AUTHOR]

Shield tunneling adjacent to existing piles is common occurrence in subway construction. This study proposes a novel tunnel model capable of simultaneously simulating ground loss, unloading effects, and void grouting under in-flight conditions. Several three-dimensional (3D) centrifugal scale model tests are implemented in a silty-silty clay composite to investigate the response of a single pile (Test SP) and pile group (Test GP) with a sinking low cap subject to adjacent tunneling. The results indicate a critical influence area, i.e., 0.75D in front and 0.25D behind the centerline of the existing piles, is observed for the pile head settlement, in each test, and the induced bending moment in the piles above the tunnel spring line is more sensitive to tunneling than that below it. A decreasing trend in axial force along the pile shaft is observed in Test SP, whereas Test GP shows the opposite behavior. The maximum variations in axial force and bending moment occur near the tunnel invert and crown in Test SP, respectively, however, they all appear near the tunnel spring line in Test GP. There is a law of load transfer for downward migration in Test SP. In Test GP, however, the load on the upper part of pile P1 decreases and shifts to the lower section of pile P1 and the whole pile P2. Subsequently, the load on the upper part of pile P2 reduces and transfers to the lower part of pile P2 and the whole pile P1. A significant increment in the earth pressure near the pile toe is observed. The pore water pressure increases slightly at first and then dissipates. Digital image correlation (DIC) has been preliminarily demonstrated as a valuable tool for visually capturing the progressive behavior of pile-soil interactions during in-flight tunneling, proving advantageous for analyzing tunnel-soil-pile interaction issues under centrifugation conditions. [ABSTRACT FROM AUTHOR]

The study investigates the application of shotcrete as a temporary support during tunnel excavation, emphasizing its role in stabilizing rock fragments by understanding the load-transfer mechanism. Current research problems include a lack of standardized methodologies for designing primary shotcrete linings and insufficient understanding of shotcrete behavior under varying stress conditions, particularly in squeezing ground conditions. The proposed method utilizes the convergence-confinement method and support capacity plots to design shotcrete linings. This approach is demonstrated through a non-linear, finite element analysis of four tunnel sections of the Atal tunnel, India. Initially, empirical approaches were used to analyze the squeezing effects using geological data, followed by 2D plane strain and axisymmetric analysis to establish ground reaction curves (GRC) and longitudinal deformation profiles (LDP). Subsequently, analytical solutions were used to construct support characteristic curve (SCC), and rock-support interaction curves were generated using these three components (GRC, LDP, and SCC). Further, the study examined the effects of parameters such as age, grade, thickness of the shotcrete, disturbance factor, and anisotropic stress on axial force, bending moment, and shear forces in the shotcrete. Additionally, the shear capacity and bending capacity plots were constructed to evaluate shotcrete stability. Findings indicate that C40 shotcrete with a thickness of 0.35 m provides adequate structural resilience against shearing and bending forces. However, this design is deemed unsafe for both shearing and bending when disturbance factors and anisotropic stress ratios were considered. Specifically, increasing the disturbance factor from 0 to 1 result in a substantial increase in axial force by 64.4%. Under the isotropic stress conditions (ko = 1), shotcrete exhibits uniform axial force distribution; however, when ko = 0.5, axial forces at the springline increase by 6%, and when ko = 1.5, axial forces at the crown and invert increases by 67%. These findings underscore the importance of selecting appropriate shotcrete grade and thickness to ensure the safety and stability of tunnel linings under various stress conditions. This comprehensive analysis offers a novel approach by integrating empirical, analytical, and numerical methods to evaluate shotcrete performance, providing valuable insights for engineers dealing with similar geological conditions. The study offers a realistic and practical method for shotcrete lining design in circular excavations subjected to anisotropic stresses and disturbances in squeezing ground conditions. [ABSTRACT FROM AUTHOR]

Hydraulic tunnels are prone to pass through faults and high-intensity earthquake areas, which will cause serious damage under fault dislocation and earthquake action. Fault dislocation and seismic excitation are often considered separately in previous studies. For tectonic earthquakes with higher frequency in seismic phenomena, fault dislocation and ground motion are often associated, and fault dislocation is usually the cause of earthquake occurrence, so it is limiting to consider the two separately. Moreover, strong earthquake records show that there will be significant differences in the mainland vibration within 50 m. The uniform ground motion inputs in previous studies are not suitable for long hydraulic tunnels. This paper begins with the simulation of non-uniform stochastic seismic excitations that consider spatial correlation. Based on stochastic vibration theory, multiple multi-point acceleration time-history curves that can reflect traveling wave effects, coherence effects, attenuation effects, and non-stationary characteristics are synthesized. Furthermore, a fault velocity function is introduced to account for the velocity effect of fault dislocation. Finally, numerical analyses of the response patterns of the tunnel lining under four different conditions are conducted based on an actual engineering project. The results indicate the following: (a) the maximum lining response values occur under the combined effects of fault dislocation and non-uniform seismic excitation, indicating its importance in the seismic resistance of the tunnel. (b) Compared to uniform seismic excitation, the peak displacement of the tunnel under non-uniform seismic excitation increases by up to 6.42%, and the peak maximum principal stress increases by up to 28%. Additionally, longer tunnels exhibit a noticeable delay effect in axial deformation during an earthquake. (c) Under non-uniform seismic excitation, the larger the fault dislocation magnitude, the greater the peak displacement and peak maximum principal stress at the monitoring points of the lining. The simulation results show that the extreme response values primarily occur at the crown and haunches of the tunnel, which require special attention. The research can provide valuable references for the seismic design of cross-fault tunnels. [ABSTRACT FROM AUTHOR]

The prefabricated assembled cover arch reinforcement method offers rapid construction and high quality, effectively addressing the challenges of cast-in-place cover arch reinforcement used in tunnel linings in mountainous areas of China. This study investigated the mechanical performance of prefabricated assembled arches in tunnels through model tests and numerical simulations. The results indicate that joint opening and deflection, as well as their change rates, increase with eccentric distance. There is a roughly linear relationship between joint opening and deflection with increasing load. At an eccentric distance of + 0.2 m, the peak stress appears on the outside of the joint, with a valley on the inside, and stress concentration at bolt holes. The application of bolt preloading enhances the joint's stress performance. Furthermore, the stiffness of the lining and soil significantly impacts the mechanical response of the cover arch, with peak stress mainly observed at the foot of the cover arch and the handhole of the joint. [ABSTRACT FROM AUTHOR]

Reinforcement corrosion in shield tunnel segments has an important impact on the structure's bearing capacity and failure mode. Generally, a shield tunnel structure is under small eccentric compression, but if the reinforcement corrosion develops sufficiently, then a transition occurs from small to large eccentric load state, thereby lowering the structural bearing capacity and endangering the safety of tunnel operation. In the study reported here, based on the compressive bending load characteristics of the shield lining structure, corrosion test columns with small eccentric loading were designed to simulate the actual force state of the tunnel lining, and the whole evolution process of their mid‐span strain, ultimate bearing capacity, and cracks under different corrosion degrees was analyzed. With increasing corrosion, the bearing capacity, concrete strain, and depth of the compressive zone of a test column decrease more and more rapidly, and at the maximum corrosion degree of 68.32%, the maximum reduction of bearing capacity is 53.23%. The tests show that the failure mode of a test column with high corrosion degree (≥46.25%) is transformed from small to large eccentric failure. Based on theoretical analysis of the normal section bearing capacity of reinforced concrete flexural members, a theoretical method is proposed for calculating the critical corrosion degree for the tunnel lining structure to transform from small to large eccentric failure. The theoretical calculation method is verified against finite‐element calculations, and the present research results offer theoretical support for the durability design and safety evaluation of shield tunnel lining structures. [ABSTRACT FROM AUTHOR]

Voids behind tunnel linings can be formed either during or after the construction phase, occurring due to inadequate backfilling, substandard workmanship, water erosion, or gravitational forces. Investigations into numerous tunnels in which collapses occurred while in operation have indicated that voids behind the liner constitute the primary contributors to these failures. Consequently, it is imperative to devise lining reinforcement strategies tailored to the specific conditions encountered in the field. Fiber-reinforced plastic (FRP) represents a viable alternative construction material that has been widely utilized in the reinforcement of concrete structures. It is essential to quantitatively assess the reinforcing effect of FRP grids when they are employed in the restoration of deteriorated tunnel linings, thereby facilitating the development of effective maintenance designs. In this study, we aimed to enhance the sensitivity analysis of the reinforcement method by evaluating the impact of voids through the analysis of bending moments and axial forces within the tunnel lining. The effects of voids based on the different locations in which they occur were explored numerically through an Elastoplast finite element analysis. The study involved simulating tunnel linings that had been reinforced with FRP grids and assessing the effects of such reinforcement in tunnels afflicted with various structural problems. Based on the outcomes of these simulations, the internal forces within the lining are scrutinized, and the efficacy of the reinforcement is appraised. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-parameter strain/displacement safety monitoring technology for railway tunnel lining structures. An integrated monitoring system with FBG (Fiber Bragg grating) and VDM (video displacement meter) components was used to monitor both the strain and deformation of the tunnel cross-section. Initially, a comprehensive experimental study was carried out using FBG strain sensors with temperature-compensated grating. The temperature-compensated grating was used to further improve the monitoring accuracy. The data show that the stability and accuracy were better than the traditional electronic strain sensor. Secondly, high-precision and multipoint monitoring of railway tunnel lining deformation was achieved by using VDM technology. Three months of case study results taken from the Gansu Railway Tunnel in China demonstrated a tunnel cross-section strain accuracy for microstrain and crown deformation at the submillimeter level, respectively. The technology provides a new high-precision way to monitor the condition of tunnel lining structures. [ABSTRACT FROM AUTHOR]

In order to study the dynamic damage evolution law of tunnel‐lining concrete with non‐through crack under single‐side sulfate attack, a 420‐day sulfate attack concrete test was conducted and the uniaxial compression and acoustic emission (AE) tests were carried out on each corrosion time. The test results showed that the compressive strength of each group can be divided into rising stage and falling stage, and the existence of non‐through crack reduced the compressive strength of concrete specimens and accelerated the corrosion of concrete specimens by sulfate. AE ringing count can be divided into compaction stage, elastic stage, yield stage, and post‐peak stage; the variation patterns of AE varied at different stages. Sulfate attack caused the yield point of concrete to advance. With the increase of corrosion time, microcracks increased gradually, cement mortar was consumed continuously, concrete spalling occurred, the proportion of AE cumulative ringing count Stage II decreased gradually, and the proportion of Stage III increased. Non‐through crack changed the energy storage of Stages II and III and reduced the AE activity of concrete after corrosion. The deeper the crack was, the smaller the average cumulative ringing count was and the lower the AE activity was. AE cumulative ringing counts can be used to characterize the damage evolution of corroded concrete. [ABSTRACT FROM AUTHOR]

• The internal force analytical solution of lining structure under P-ware action was obtained by using the analytical method. • The influence of the hardness of surrounding rock and peak acceleration on the analytical solution were analyzed. • Through the engineering, the reasons for the large error between numerical solution and analytical solution was analyzed. • The most unfavorable position of lining structure under P-wave seismic load was proposed. In an earthquake, the strong interaction between the surrounding rock and the lining structure causes the lining structure susceptible to extrusion or shear damage, and predicting the internal force distribution trend of the lining structure by the analytical method was advantageous for the preliminary design of the tunnel structure. In this work, the quasi-static method was used to approximate the displacement and deformation caused by the P-wave seismic load as far-field compressive stress. The analytical solution of the internal force for the lining structure was obtained by the analytical method, and the reliability of the analytical method was further verified. The dynamic response law of the lining structure was analyzed using numerical solutions in conjunction with engineering examples. The results show that the analytical method can be used to predict the trend of internal force distribution in the lining structure under seismic action, which has important theoretical guiding significance for the preliminary design of the tunnel structure. With the decrease in the hardness of the loess surrounding, the relative deviation of the theoretical, numerical, and literature results gradually decreases. With the increase of ground motion intensity, the interaction between the loess surrounding and the lining structure becomes more intense, and the internal force of the lining structure gradually increases. The numerical results were greater than the analytical results due to the consideration of the influence of initial stress. Under the action of the P-wave earthquake, the extreme values of the internal force with the lining structure mainly occurred at the location of the vault, arch waist, and inverted, and the most unfavorable positions of circular loess tunnel lining structures under P-wave seismic load was proposed. [ABSTRACT FROM AUTHOR]

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[Objective] Gabion is widely used in slope stabilization, revetment engineering, subgrade reinforcement, and other applications. However, its use in tunnel lining remains underexplored. Owing to its unique multiporosity, which provides excellent deformation capacity and notable bearing strength, gabion shows promising potential for managing the notable deformations and high ground stresses encountered in tunnel surrounding rock. Therefore, studying the static mechanical behavior of tunnel lining components made with gabion is of practical importance. [Methods] This paper presents a simplified molding technique for gabion components and a custom-designed test loading apparatus. Additionally, a numerical modeling methodology specifically tailored for gabion components in tunnel lining is introduced based on discrete element calculations. Next, a comparative analysis is conducted to examine the influence of two key parameters--the strength of the gabion mesh and the effective modulus of the stone filling--on the variation in static mechanical characteristics of tunnel lining components constructed with gabion. This study provides valuable insights into the performance of gabion-based tunnel linings. [Results] 1) The failure of the gabion component in tunnel lining mainly occurs through instability, with only minor cases of wire breakage and stone-filling fracture. Throughout the loading process, the load-displacement curve of the component exhibits notable fluctuations driven by the ongoing interaction between the internal stone filling and the gabion mesh. The overall load-displacement curve increases and then decreases. Despite considerable deformation, the component maintains a high bearing capacity at the end of loading. 2) The tensile strength of the gabion mesh has little effect on the deformation modulus during the initial deformation stage under static load but has more impact on the peak load. The higher the tensile strength of the gabion mesh, the greater the displacement and peak strength at peak load. Under varying tensile strength conditions, the differences in peak load displacement and peak strength reached 28.9% and 25.2%, respectively, because when the tensile strength of the gabion mesh is higher, the component is more resistant to failure, allowing a more effective interaction between the stone filling and the gabion mesh. 3) Compared with the tensile strength of the gabion mesh, the effective modulus of stone filling has a pronounced impact on the component performance. As the effective modulus of the stone filling increases, the postpeak decline in the load-displacement curve becomes more prominent. During the loading process, the energy consumption of the component, peak loading strength, and effective modulus of the stone filling exhibit a distinct piecewise relationship, characterized by an initial increase followed by stabilization. [Conclusions] This experiment provides clear guidance for students conducting static loading mechanical model tests on gabion-constructed tunnel lining components, enhancing the effectiveness of experimental teaching. [ABSTRACT FROM AUTHOR]

In this study, we propose the use of a fiber-reinforced plastic grid with polymer-cement-mortar (FRP Grid-PCM) to reinforce segment joints in tunnel shield linings. These joints play a crucial role in determining bearing capacity but are vulnerable to deterioration during operation. To investigate how to enhance the flexural performance of longitudinal shield lining joints, we built eccentric short column specimens by bolting two half-corbel columns together and tested them in the laboratory. The test program comprised two control specimens and three strengthened specimens with FRP grid applied on one side, away from the axial load. The tests varied two main parameters: loading eccentricity and the number of FRP grid layers. We conducted a detailed analysis of the failure process, bearing capacity, and bending stiffness of longitudinal joints under different conditions. Furthermore, we developed an analytical model to predict the flexural bearing capacity of longitudinal joints upgraded with the FRP Grid-PCM method and validated it through experimental results. The research demonstrates that the FRP grid effectively reduces joint opening and rotation angles while enhancing the bearing capacity of the short column, particularly with concurrent increases in loading eccentricity and the number of FRP grid layers. Overall, our findings offer a novel alternative for improving the flexural performance of longitudinal joints in shield tunnels. [ABSTRACT FROM AUTHOR]

In the design of tunnel linings in water-rich mountainous areas, the limited drainage method has been increasingly recognized for balancing the structural safety of the tunnels and the protection of surrounding environment. Currently, composite lining structures with waterproof boards and blind drainage systems are commonly used. However, there is still a lack of simple and practical methods for calculating the water pressure on the secondary lining, similar to the methods used for calculating surrounding rock pressure. By regarding the secondary lining and waterproof boards as water-blocking layers, and surrounding rock-grouting ring-shotcrete-blind drain as the drainage path, this paper derives that the total head drop along the drainage path is proportional to the limited drainage flow, based on the seepage theory of monolithic lining. The water pressure on the secondary lining and waterproof board was found to be the difference between the total head and the total head drop, eliminating the need to convert the drainage system flow into an assumed permeability coefficient for the secondary lining. A simple and feasible analytical method was put forward for calculating the water pressure on the secondary lining of composite-lining tunnels. This method allows for direct structural calculation of the secondary lining and surrounding rock reinforcement design based on the permissible drainage volume or secondary lining water pressure during the design stage, enabling proactive control of groundwater and ensuring the safety of the lining structure. [ABSTRACT FROM AUTHOR]

Based on the lining structure of an operational tunnel, the AHP and Fuzzy mathematical models were used to determine the weight of the evaluation index and solve the membership matrix. The weighted-average Fuzzy comprehensive function was used to combine the two, and the Fuzzy–AHP evaluation model was built and programmed. According to the self-developed Fuzzy–AHP evaluation-programmed model, a visualized structure safety evaluation system for operational tunnels was developed by using MATLAB. The system's functional design, program development, and computational visualized interface were implemented, and key codes were provided. The system can be divided into four modules: data management, fuzzy computation, predictive analysis and key disease indexes to focus on. In addition, the system can easily edit and modify the evaluation function, which includes not only the Fuzzy evaluation but also other types of evaluation functions applicable to other practical engineering projects, improving the applicability of the system. After that, the system was applied to the structure safety evaluation of a mountain tunnel, which provided the evaluation results and key indexes to focus on in the tunnel. Finally, the rationality of the system design was verified by constructing the corresponding BP–RBF combined neural network. This study provides a reference for the establishment of an intelligent structure safety warning system for operational tunnels. [ABSTRACT FROM AUTHOR]

The current active control waterproof and drainage system was difficult to achieve dynamic control of water inflows and pressure, which could lead to tunnel cracking and leakage, a pressure valve was installed at the circumferential drainage blind pipe in order to control the water inflow and water pressure. Additionally, the formula for calculating the tunnel water inflow was derived. Using the conformal transformation, the seepage field formula of the surrounding rock was derived from the basic differential equation of the stable seepage field. The tunnel seepage calculation model was further established, incorporating the parameters of circumferential drainage blind pipe spacing and discharge pressure. The calculation formula of tunnel drainage volume and external water pressure of the external water pressure of secondary lining and tunnel water inflow calculation formula was obtained. The decomposition and numerical simulation techniques confirmed the analytical solution's reasonableness. This served as the foundation for the establishment of a tunnel drainage design solution with a pressure valve. The findings indicated that the water pressure and flow rate were significantly impacted by the geotextile permeability coefficient and the spacing between drainage pipes. It was recommended to select a geotextile which permeability coefficient of at least 500 μm/s, and the spacing between drainage blind pipes could be adjusted based on the drainage pressure. The grouting ring thickness could be decreased by adding a pressure valve in comparison to the current active control waterproof and drainage. [ABSTRACT FROM AUTHOR]

In order to investigate the stress and strain state of the surrounding rock and the effect of supporting structure of the deep buried tunnel through the fault zone in mountainous area, taking Lianfeng Mountain Tunnel Project as the research background, based on ABAQUS large-scale finite element numerical computation program, the mechanics calculation model of the construction of the deep buried tunnel through the fault zone was established, and the change rule of the structural stress state and the horizontal and vertical settlement rule of the mountain after the tunnel excavation and lining were studied. The results showed that the settlement in the fault zone during tunnel excavation was much larger than that in the normal rock body; the stress difference between the surrounding rock and the peripheral mountain body at the fault zone was larger, and the stress difference at the junction with the normal mountain body was larger; the settlement caused by tunnel excavation affected the range of 50 m, and the settlement at the center of the twin tunnels increased with the increase of vertical height; the excavation of the second tunnel in the construction of the twin tunnels caused the increase of the strain of the first tunnel. [ABSTRACT FROM AUTHOR]

By simulating the high-temperature service environment of tunnel lining concrete, this study investigates the compressive and impermeable properties of tunnel lining concrete at 20, 60, and ambient temperature of 80 ℃ for 3, 7, and 28 d, and analyzes the changes in compressive and impermeable properties of tunnel lining concrete under high-temperature environmental conditions, in order to provide theoretical support and empirical reference for the construction of tunnel lining concrete under high-temperature environmental conditions. The results indicate that a high-temperature curing environment can improve the compressive strength of tunnel lining concrete at 3 and 7 d, but an 80 ℃ high-temperature curing environment can reduce the compressive strength of tunnel lining concrete at 28 d；With the increase of ultrafine powder content, the compressive strength of tunnel lining concrete first increases and then decreases. When the content is 30%, the compressive strength of concrete is the highest；With the increase of temperature and the addition of ultrafine powder, the electrical flux of tunnel lining concrete generally shows a downward trend. In the same mix, the modal chord length of concrete specimens does not show a significant change with the increase of curing temperature, but the average chord length decreases with the increase of curing temperature. [ABSTRACT FROM AUTHOR]

Bifurcated tunnels have many lines that significantly improve the utilization of underground space. However, the pressure waves (PWs) generated by a metro train in a tunnel may cause irreversible damage to the tunnel, particularly the more complex wave system generated by a train in a variable cross section bifurcated tunnel. Overset grid technology was adopted to simulate trains operating in tunnels; the differences between train operation in single-line and bifurcated tunnels were analyzed, and the PW characteristics of trains operating on three different lines in a bifurcated tunnel were compared. The numerical method was verified experimentally, and the pressure change trend fitted well. The results show the following: The bifurcated tunnel will increase the train surface PWs. The maximum pressure (pmax) of the surface of the train is reduced by more than 60% on average, and the minimum pressure (pmin) is basically the same. The peak-to-peak pressure (Δp) increases by more than 50% on average, but the distribution trend does not change. The influence of the bifurcated tunnel on the tunnel wall pmax, pmin, and Δp is bounded by the bifurcation area. The difference in surface pressure of trains operating on different lines in the bifurcated tunnel is mainly caused by the bifurcated area. The distribution trend of the pmax, pmin, and Δp of trains operating on different lines is the same. However, the pmax, pmin, and Δp of the wall of the train operating line are greater than those of the non-operating line. These findings can provide a reference for the design of bifurcated tunnels and route planning of metro trains. [ABSTRACT FROM AUTHOR]

A reverse calculation method termed soil and lining physics‐informed neural network (SL‐PINN) is proposed for the estimation of load for tunnel lining in elastic soil based on radial displacement measurements of the tunnel lining. To achieve efficient and accurate calculations, the framework of SL‐PINN is specially designed to consider the respective displacement characteristics of surrounding soil and tunnel lining. A multistep training method based on the meshless characteristics of SL‐PINN is established to promote calculation efficiency. The multistep training method involves increasing the number of collocation points in each calculation step while decreasing the learning rate after scaling of SL‐PINN. The feasibility of SL‐PINN is verified by numerical simulation data and field data. Compared to other inverse calculation methods, SL‐PINN has lower precision requirements for the measurement instrument with the same level of calculation accuracy. [ABSTRACT FROM AUTHOR]

The influence evaluation of the additive fibre on concrete structures is a concerned problem especially in strengthening and repairing engineering. Current theoretical studies on the damage mechanisms of tunnel lining are generally based on the tensile and compressive characteristics of the ordinary concrete. Little attention is paid to the toughness and damage development of the fibre reinforced concrete, as well as the influences of high-speed train dynamic loading. In this paper, both tensile and compressive experiments of fibre reinforced concrete with different lengths and volume contents are carried out considering three types of the glass, PVA (polyvinyl alcohol) and hybrid fibres. Afterwards, the damage evolution of fibre reinforced concrete is explored by application of the digital image correlation (DIC) technique. The hypothesis of strain equivalence and damage theory of Najar are employed to determine the damage parameters of the fibre reinforced concrete so as to establish three-dimensional finite element model of surrounding rock-tunnel. Finally, the parameters that affect damage development of concrete tunnel lining incorporated fibre under train loading, including the vehicle speed, fibre type, fibre length, and volume content, are performed. The results show that adding fibre into concrete can effectively enhance the damage resistance capacity of concrete and significantly improve the developing trend of multistep damage of ordinary concrete under train excitation loading. Moreover, fibre reinforced concrete can reduce the final damage values of tunnel lining subjected train loading. The paper contributes to the understanding of damage behaviours of fibre reinforced concrete lining for high-speed trains loading as a potential risk in the course of the operation. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a novel Forkshape nanosheet Inductive Tunnel Field-Effect Transistor (FS-iTFET) featuring a Gate-All-Around structure and a full-line tunneling heterojunction channel. The overlapping gate and source contact regions create a strong and uniform electric field in the channel. Furthermore, the metal–semiconductor Schottky junction in the intrinsic source region induces the required carriers without the need for doping. This innovative design achieves both a steeper subthreshold swing (SS) and a higher ON-state current (ION). Using calibration-based simulations with Sentaurus TCAD, we compare the performance of three newly designed device structures: the conventional Nanosheet Tunnel Field-Effect Transistor (NS-TFET), the Nanosheet Line-tunneling TFET (NS-LTFET), and the proposed FS-iTFET. Simulation results show that, compared to the traditional NS-TFET, the NS-LTFET with its full line-tunneling structure improves the average subthreshold swing (SSAVG) by 19.2%. More significantly, the FS-iTFET, utilizing the Schottky-inductive source, further improves the SSAVG by 49% and achieves a superior ION/IOFF ratio. Additionally, we explore the impact of Trap-Assisted Tunneling on the performance of the three different integrations. The FS-iTFET consistently demonstrates superior performance across various metrics, highlighting its potential in advancing tunnel field-effect transistor technology. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Architecture & Civil Engineering is the property of Chang'an Daxue Zazhishe 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.)

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]

The interaction between the surrounding rock and the support structure in a circular water conveyance tunnel with lining comprises two main aspects: internal and external hydraulic pressures, and the contact load between the post-excavation lining and the surrounding rock. There is currently no reasonable calculation method to consider both factors simultaneously. Therefore, by utilizing the assumption of smooth contact between the surrounding rock and the lining, an analytical model for a circular water conveyance tunnel with lining is developed through the complex function method. Smooth contact indicates continuity of radial contact stress, coordination of radial displacement, and the absence of shear stress transmission. Considering the inner and outer boundary stress conditions of the lining, two sets of undetermined analytical functions are established, corresponding to internal and external water pressure, as well as the contact stress between the surrounding rock and the lining. Ultimately, the stress and displacement components at any point within the surrounding rock and lining can be derived under the conditions outlined in this study. The analytical model elucidates the mechanism of load transfer within the circular water conveyance tunnel with lining, considering the combined effects of internal and external water pressure and excavation loads. Of particular note, it quantifies the restrictive impact of external water pressure on lining hydrofracturing when subjected to high internal water pressure. Additionally, the model offers a theoretical foundation for designing and assessing support structures for use in long-distance water conveyance projects. [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.)

Shield tunnels' structural stability is challenged due to the fact that they are often built under rivers, lakes, and oceans. It is crucial to execute the structural deformation perception of the shield tunnel. Fiber Bragg grating (FBG) sensing technology is sensitive to deformation information, making it one of the greatest options for shield tunnels to perceive structural deformation. In this study, a 1:20 scale model test was carried out to investigate the deformation perception of the shield tunnel structure under three different layouts of surface-mounted FBG sensors. The deformation law of the tunnel is discussed, under the condition of two-factor cross fusion and especially under the condition of constant water pressure and soil pressure change. The results indicate that, under the combined action of water and soil pressure, the uniform water pressure of 0.33 MPa has a stabilizing effect on the segment strain under the vertical load of 0.4 MPa. The traditional four-point layout and the 18° uniform layout are more effective in detecting changes in local tunnel curvature and strain, respectively, compared to the 36° uniform layout mode. It is advised that the traditional four-point layout be used to collect information for other sections' monitoring and that the 18° uniform layout is for harsh terrain conditions. [ABSTRACT FROM AUTHOR]

With the development of large-diameter shield tunnels, how to realize effective security and stability control of shield tunnel lining has become a significant research topic. This paper investigates the deformation and failure mechanism of lining large diameter shield tunnels in depth and discusses the deformation characteristics and influencing factors of the lining of the shield tunnel with various diameters through the software of finite element analysis ABACUS. A set of models with varying diameters is built under identical stress conditions in order to maintain control over the variable. The utilization of the elastic–plastic model is observed in the application of bolts and rebar. The utilization of the Concrete Damage Plasticity model has been taken into account for the concrete lining. For the sake of comparison, the crown displacement of the shield tunnel, strain in tension and compressive zones, bolt stress and strain, deformation and intemal force distribution around the shield tunnel, and cracks in the tension zone, are carefully studied. An in-depth analysis is conducted to elucidate the variations in damage evolution mechanisms across linings of different sizes, within the framework of plastic hinge theory. The results indicate that the convergence deformation of large-diameter tunnel lining increases significantly during loading compared with that of small-diameter tunnel. Moreover, the probability of brittle failure is higher in big-diameter shield tunnels compared to small-diameter tunnels, indicating that these larger tunnel structures are more prone to suffering geometric instability. [ABSTRACT FROM AUTHOR]

To address the problems of the lining cracking and spalling in tunnel structures in coastal areas under the influence of special geological conditions, environmental loading, and the coupling effect of chemical erosion, hybrid fibers were introduced to fly ash concrete in this study. The working performance, compressive strength, split tensile strength, and flexural strength of the hybrid fiber fly ash concrete were tested. A chloride diffusion coefficient under steady-state conditions and a durability test for resistance to sulfate corrosion were carried out. Thus, in-depth analyses of the comprehensive performance of the hybrid fiber fly ash concrete used for the tunnel lining were carried out and the damage mechanism was explored. The results showed that the hybrid fiber fly ash concrete exhibited higher strength compared to the concrete in the control group. However, when the fibers exceeded a certain dosage, the reduction in the working properties of the concrete structure led to the creation of larger pores in the matrix structure, which in turn affected the mechanical properties of the concrete. The most significant reduction in the chloride diffusion coefficient was observed when both steel fibers and coconut fibers were added at a 1.0% volumetric parameter, compared to the control group. The apparent state and compressive strength after sulfate corrosion were also minimally affected. This study ensured that the mechanical properties of the concrete were improved and the corrosion resistance of the matrix also substantially improved, providing a scientific basis for improving the performance of tunnel lining concrete, and confirming that steel–coconut hybrid fiber fly ash concrete has a great potential to improve the structural load-bearing capacity and durability, which may provide theoretical support for its continued use in tunneling projects and construction processes. [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.)

The capacity of the circumferential joint of the precast concrete segmental tunnel lining (PCTL) structure in terms of shear performance principally includes the dowel action by connector/bolt as well as friction force, and it is a vital parameter to assess the mechanical response of the circumferential joint. Further, as there was no analytical model available for precise estimation of a circumferential joint in terms of the shear‐bearing capacity considering the dowel action of the bolt in the presence of axial/normal force, therefore in this investigation, an analytical model has been proposed to estimate the shear‐bearing capacity of the circumferential joint. Furthermore, the analytical model's precision and accuracy were validated via large‐scale experimental investigation on a circumferential joint of PCTL. Upon comparing analytical model outcomes with experimental results, absolute error varied between +5% and −9%, with an average value of the coefficient of friction at the yield point of the bolt. Moreover, the formation of hinges on the side of the bolt within the segment was considered a failure of the circumferential joint. Additionally, the parametric investigation revealed that with just a 1% change in axial force, the diameter, pre‐tightening, and yield strength of the bolt and concrete strength improved by 2.85%, 1%, 0.27%, 0.26% and 0.17% shear‐bearing capacity of the circumferential joint respectively. Axial force variation greatly influences the shear‐bearing capacity of circumferential joint followed by diameter, pre‐tightening, yield strength of the bolt, and concrete strength. Conclusively, with analysis of axial force distribution around the ring for the tunnel, the proposed model has been applied to a full ring to estimate shear bearing capacity. [ABSTRACT FROM AUTHOR]

In this study, the segment joint and ring joint of the lining of the straight‐jointed tunnel are simplified as an equivalent open cylindrical shell with a small central angle and an equivalent closed cylindrical shell with a small width, and the lining of the straight‐jointed tunnel is thus simplified as an equivalent continuous periodic shell (ECPS) described by the cylindrical shell theory. Since the ECPS lining is periodic along the longitudinal direction, the tunnel‐soil system can thus be treated as a periodic system, which is referred to as the periodic tunnel‐soil system (PTSS) in this study. Based on the proposed ECPS lining model, an analytical method for the tunnel with the ECPS lining (ECPS tunnel) under seismic waves is established in this study. By employing the periodicity condition for the PTSS as well as the wave function expansion method, the representation for the wave field in the soil is established. With the aforementioned cylindrical shell theory and Fourier series expansion method, the convolution type constitutive relation for the ECPS lining and the Fourier space equations of motion are derived. By using the soil‐lining continuity condition and aforementioned formulations for the ECPS lining and soil, the coupled Fourier space equations of motion for the PTSS are established, with which the response of the ECPS lining and scattered waves in the soil can be determined. [ABSTRACT FROM AUTHOR]

The construction of tunnels excavated by the conventional method in densely populated urban environments requires an adequate characterization of the loads acting on the primary lining during the excavation process, to ensure that the ground is deformed and stresses around the tunnel are relieved, simultaneously complying with the failure and serviceability limits of international standards while minimizing damage to nearby structures. In this paper, common lining design criteria are revisited, through the numerical simulation of an instrumented tunnel section which is part of a 4.5 km long metro line currently under construction in Mexico City. Key needs for improvement in current design approaches are identified. The tunnel was instrumented with load cells, extensometers, and topographical references for convergences and divergences. A three-dimensional finite difference model of the instrumented section was developed, and the load transfer mechanisms between the excavated soil and the primary lining were analyzed. Then, the numerical simulation of the contribution of the secondary lining in the overall stability for sustained load was established, along with the expected ground settlements, which can significantly affect nearby structures. Results gathered from this research are key for updating lining design criteria for urban tunnels built in stiff brittle soils. [ABSTRACT FROM AUTHOR]

Featured Application: This paper examines the water pressure distribution and tunnel lining deformation in a water-rich tunnel crossing a fault zone, utilizing field tests and numerical simulations. The findings are applicable to the development of tunnels under similar geological conditions. This study investigates the water pressure distribution and deformation patterns in tunnel linings within water-rich tunnels traversing fault zones, focusing on the Gudou Mountain Tunnel. The study utilized field tests and numerical simulations to assess the water pressure distribution around test sections. Following the confirmation of consistent water pressure distribution patterns from field tests and simulations, we analyzed the deformation patterns of tunnel linings at various water levels. The results showed that water pressure is highest at the tunnel's inverted arch and arch foot, moderately high at the vault and spandrel, and lowest at the arch waist. The sections RK51 + 590 and LK51 + 640, located on opposite sides of a fault crush zone, experience high fragmentation of surrounding rock. This allows rainfall and reservoir water to seep through fractures, causing increased water pressure and significant deformation at the inverted arch of these sections. With rising groundwater levels, deformation intensifies at the inverted arch, arch foot, and vault. The appearance of macro-cracks in these critical areas leads to groundwater seepage through the cracks, severely impacting tunnel operations. Consequently, reinforcing the inverted arch, arch foot, and vault is crucial to reduce the risk of water leakage in the tunnel. [ABSTRACT FROM AUTHOR]

Segmental tunnel linings have a complex structural behavior that is difficult to predict. Full-scale in situ structural monitoring allows us to gain access to these structures, observe the acting mechanisms, and better understand the actual structural behavior under realistic boundary conditions. In a recent structural monitoring project in Frankfurt, Germany, strains, deformations, and temperatures were measured at the segmental lining of a twin-tube tunnel boring machine (TBM) tunnel. Hereby, internal forces were back-calculated from the strain measurements. The results of the monitoring are presented and discussed in this paper. The measurements began immediately after the assembly of the segments and have been performed continuously over several years. Because of that, it was possible to observe that the internal forces differ significantly between the construction stage and the final state. During the construction stage, the internal forces develop quickly within hours after ring assembly, showing a distribution along the lining's circumference that is hard to predict. Almost all radial deformations occur during this period and remain unchanged afterward. After this first early phase, a period of stress redistribution follows, including significant changes in the internal forces. At its end, the stable, final state is reached. In this state, the internal forces match better with expectations. In the monitored areas, the stresses during the construction stage slightly exceeded those of the final state, which should be avoided for economic reasons. Additional investigations regard the temperature development within the lining, the influence of the second tube construction on the already built tube, and the development of longitudinal ring interaction over time. The latter significantly influences the structural behavior, but its development is often subject to uncertainties. In this case, it was observed that the longitudinal interaction decreases considerably over time. Practical Applications: In the structural design of segmental tunnel linings, structural or geotechnical engineers have various options regarding the available calculation methods and modeling strategies. All of these options are part of the state of the art, and the selection is up to the engineer. However, the results can be quite different depending on the chosen option. Consequently, uncertainties remain regarding the real linings' internal forces and structural reliability. The actual mechanisms can be identified by investigating the real structural behavior of segmental tunnel linings with in situ structural monitoring. Then, with back-analyses, on the one hand, it can be tested to determine how well different calculation methods and modeling strategies correspond to reality. On the other hand, the monitoring data can contribute to improving existing calculation methods, developing new modeling approaches, and establishing more detailed recommendations or optimizations regarding the design and construction of segmental tunnel linings. This paper presents findings derived from a structural monitoring project on a segmental lining. Different mechanisms and aspects, sometimes uncertain or debatable in tunnel design, are discussed regarding their real in situ appearance. The gained data will also be used for further back-analyses and investigations. [ABSTRACT FROM AUTHOR]

Purpose: Multilayer composite liner structures are the primary structural form of hydraulic tunnels. However, the bearing mechanism of multilayer composite liners has not been investigated thoroughly. Many existing design schemes do not properly achieve a balance between structural safety, anti-seepage capacity, and cost effectiveness. Thus, a new composite liner structure type and its theoretical model was proposed. Design/methodology/approach: A novel hydraulic tunnel composite liner structure with a polyurea spray coating interlayer was proposed in this study. A theoretical model based on the state-space method was developed and verified using FEM models and existing theoretical models. Parametric analysis was conducted based on the theoretical model to investigate the influence of various variables, including interfacial shear stiffness, inner liner thickness, and outer liner elastic modulus. Findings: It was concluded that the proposed theoretical model can be used successfully to calculate multilayer composite liner structures with high calculation efficiency. The overall deformation stiffness of the composite liner system increased with the interfacial shear stiffness. The sprayed coating interlayer significantly affects the residual force distribution between the outer and inner liners, which can also be affected by the adjustment of the thickness of the outer and inner liners. Thus, attention should be paid to these factors in the rational design of the proposed composite liner system. Originality/value: With the development of China's water conservancy projects, complex geological conditions, high surrounding rock stress, high internal and external water pressures, and other unique application scenarios have gradually increased. This places higher requirements on the bearing performance and impermeability of hydraulic tunnel lining structures. On the other hand, conventional hydraulic tunnel lining structures can hardly achieve a satisfactory balance between economy, structural safety, and impermeability. Thus, the proposed structure has the potential to be used in a wide range of applications. [ABSTRACT FROM AUTHOR]

• An effective method is proposed to analyse the longitudinal mechanical response of shield tunnel during its construction. • The influence of the shearing dislocation of circumferential joints on the uplift of shield tunnel is fully considered. • A coefficient is introduced to accurately calculate the dynamic buoyancy generated by the synchronous grouting. • The effect of the equivalent shear stiffness of shield tunnel on the lining uplift is quantitatively analysed. During shield tunnelling, longitudinal deformation occurs in the shield tunnel structure owing to the buoyancy generated by the synchronous slurry, which has adverse effects on the assembly quality and even the structural integrity of the segmental ring structure. However, the current longitudinal beam-like model for analysing the uplift response during shield tunnel construction adopts the Euler–Bernoulli beam to describe the shield tunnel. This model does not consider the shearing dislocation effect, causing errors in the structural longitudinal deformation analysis. In this context, this study proposes a shield tunnelling uplift model based on the Timoshenko beam theory, which can effectively consider the shearing dislocation effect, aiming to evaluate the longitudinal response of shield tunnels more accurately. A Pasternak two-parameter foundation with springs reflecting the resistance of the overburden with different thicknesses was adopted to simulate the supporting effects of the synchronous grouting layer and surrounding soil layer composite on the tunnel, considering the influences of both the shearing effect of the foundation and tunnel buried depth on the shield tunnel uplift. The dynamic buoyancy coefficient, determined through an inverse analysis of the field measurement data, was introduced to accurately calculate the magnitude of the dynamic buoyancy generated by the flow of synchronous slurry. The proposed model was validated by comparing its results with actual measurements. The uplift characteristics of the shield tunnel during construction were obtained by using the proposed model in an actual project. It was found that the longitudinal analysis model for shield tunnel uplift based on the Euler–Bernoulli beam theory underestimates the uplift and overestimates the internal forces generated during shield tunnelling. [ABSTRACT FROM AUTHOR]

High-speed railway tunnel lining fragments can cause collisions with trains and track blockages, severely affecting train operation. When a train passes through a tunnel where lining fragment is likely to occur, the train wind effect may significantly affect the trajectory of the lining fragment, making the location where the lining fragment is difficult to predict. For safety purpose, this study aims to analyze the impact of the initial circumferential position and shape of irregular-shaped lining fragments on their aerodynamic performance. Using on-site scanning and mathematical statistical methods, the shape characteristics and probability distribution of actual lining fragments in the tunnel are obtained. The aerodynamic behavior of irregular-shaped lining fragments with different initial positions and three typical aspect ratios (ARs) are investigated based on the overset grid method and the dynamic fluid–body interaction model framework as a high-speed train passes. The study found that the most representative lining fragments with an AR of three have a mass of 1.5 kg and are located 2.5 m from the tunnel centerline. The flight behavior of lining fragments shows distinct three-dimensional features, with both translation and rotation significantly affected by the aerodynamic effects of the train and the geometric shape of the fragments. The longitudinal and lateral translational distances of lining fragments at the top of the train decrease as their initial position moves further from the tunnel's centerline. With an increase in AR, both the longitudinal and lateral flight distances and average flight velocities of the fragments increase. The macroscopic flow field within the tunnel directly influences the motion characteristics of the lining fragments. Complex flow separation and circulation phenomena near the fragments result in uneven pressure differences acting on the smooth and rough surfaces of the lining fragments, causing irregular motion. The conclusions of this study provide a theoretical basis for assessing and preventing the impact of lining fragments on the operational safety of trains. [ABSTRACT FROM AUTHOR]