Search Results (173)

Settlement control for tunnel–terminal co-construction projects remains undefined, despite the growing trend of integrating multiple transportation modes within large-scale transport hubs. This study investigates a large underground structure passing beneath an airport terminal, combining field investigations, statistical analyses, and finite element simulations to examine differential settlement behavior under non-uniform loading conditions. The key contribution of this work is the proposal of a differential settlement control standard, defined by the tangent of the rotation angle between adjacent column foundations, with a recommended value of 1/625. Case analysis at cross-section E–E shows that the measured maximum tangent rotation angle was 1/839, corresponding to base slab settlements of 40.5 mm and 33.1 mm for the high-speed railway and metro structures, respectively. Application of the proposed 1/625 criterion yields allowable maximum base slab settlements of 55.28 mm for the high-speed railway and 44.83 mm for the metro, with differential settlement limits of 7.5 mm and 3.13 mm. Numerical simulations confirm the validity of this standard, ensuring the structural integrity of co-constructed systems and providing practical guidance for future airport terminal–tunnel integration projects. Full article

With the development of subway transportation, how to excavate large-section tunnels and find more convenient and reliable support methods has become an issue that cannot be ignored. This paper addresses issues such as low construction efficiency of core rock columns during the construction of large-section subway tunnels in sandstone–mudstone interbedded geological conditions. It proposes an optimized support scheme that replaces traditional core rock columns with temporary steel supports (steel columns). Finite element analysis was used to compare the deformation of the surrounding rock when retaining the core rock columns, using temporary steel columns to replace the core rock columns, and not providing additional support. Five interlayer positions and four interlayer angles were analyzed to identify the most dangerous geological conditions. Based on this analysis, the reasonable spacing of the temporary steel columns was investigated. The results indicate that temporary steel columns and core rock columns can effectively reduce vertical deformation of the surrounding rock, with steel columns showing slightly better results. Replacing core rock columns with steel columns is feasible. To control tunnel rock mass deformation, this project should ensure that the spacing between temporary steel columns is maintained between 21.88 m and 56.80 m. However, in construction sections with good rock mass conditions, the spacing can be extended as long as safety is ensured. Full article

As an important traffic and transportation roadway, tunnel engineering is widely used in important fields such as highways, railways, water conservancy, subways and mining. It is limited by complex geological conditions, harsh construction environments and poor robustness of the monitoring system. If the construction process and monitoring method are not properly designed, it will often directly induce disasters such as tunnel deformation, collapse, leakage and rockburst. This seriously threatens the safety of tunnel construction and operation and the protection of the regional ecological environment. Therefore, based on distributed fiber optic sensing technology, the full–cycle spatiotemporally continuous sensing information of the tunnel structure is obtained in real time. Accordingly, the health status of the tunnel is dynamically grasped, which is of great significance to ensure the intrinsic safety of the whole life cycle for the tunnel project. Firstly, this manuscript systematically sorts out the development and evolution process of the theory and technology of structural health monitoring in tunnel engineering. The scope of application, advantages and disadvantages of mainstream tunnel engineering monitoring equipment and main optical fiber technology are compared and analyzed from the two dimensions of equipment and technology. This provides a new path for clarifying the key points and difficulties of tunnel engineering monitoring. Secondly, the mechanism of action of four typical optical fiber sensing technologies and their application in tunnel engineering are introduced in detail. On this basis, a spatiotemporal continuous perception method for tunnel engineering based on DFOS is proposed. It provides new ideas for safety monitoring and early warning of tunnel engineering structures throughout the life cycle. Finally, a high–speed rail tunnel in northern China is used as the research object to carry out tunnel structure health monitoring. The dynamic changes in the average strain of the tunnel section measurement points during the pouring and curing period and the backfilling period are compared. The force deformation characteristics of different positions of tunnels in different periods have been mastered. Accordingly, scientific guidance is provided for the dynamic adjustment of tunnel engineering construction plans and disaster emergency prevention and control. At the same time, in view of the development and upgrading of new sensors, large models and support processes, an innovative tunnel engineering monitoring method integrating “acoustic, optical and electromagnetic” model is proposed, combining with various machine learning algorithms to train the long–term monitoring data of tunnel engineering. Based on this, a risk assessment model for potential hazards in tunnel engineering is developed. Thus, the potential and disaster effects of future disasters in tunnel engineering are predicted, and the level of disaster prevention, mitigation and relief of tunnel engineering is continuously improved. Full article

The jet fan system is a widely adopted form of longitudinal ventilation due to its cost-effectiveness, operational flexibility, and high reliability. However, in large-section highway tunnels with a low height-to-span ratio, the limited clearance between the tunnel ceiling and surrounding structural boundaries imposes significant constraints on improving ventilation performance by adjusting the installation height or pitch angle of the jet fan. To address this limitation, this study proposes a deflector shield system to enhance the aerodynamic efficiency of jet fans. A total of thirteen test cases, including a control group, three deflector plate quantities, and four deflector pitch angles, were tested in a full-scale field test conducted in a large-section tunnel. The objective of this study was to evaluate the influence of the number and pitch angle of deflector plates on tunnel ventilation efficiency and to identify the optimal parameter combination for application in large-section tunnels. The results show that static pressure along the tunnel initially rises with distance from the fan, peaks, and then declines sharply. The pressure rise coefficient is significantly enhanced under several configurations, particularly with four deflector plates at 8° and 10° pitches, and with five plates at 4° to 10° pitches. When the number of deflector plates is five, a sharp drop in average wind speed is observed 15 m downstream of the fan, and extensive low-velocity regions appear further downstream. In contrast, the configurations with four deflector plates at 8° and 10° exhibit better wind speed uniformity in the downstream flow field. Considering both the pressure rise coefficient and wind speed uniformity, the optimal ventilation performance of the jet fan system is achieved with four deflector plates at a pitch angle of 8°. Full article

Nonlinear wind-induced vibrations and coupled static–dynamic instabilities pose significant challenges for long-span suspension bridges, especially under large-amplitude and high-angle-of-attack conditions. However, existing studies have yet to fully capture the mechanisms behind large-amplitude torsional flutter. To address this, wind tunnel experiments were performed on H-shaped bluff sections and closed box girders using a high-precision five-component piezoelectric balance combined with a custom support system. Complementing these experiments, a finite element time-domain simulation framework was developed, incorporating experimentally derived nonlinear flutter derivatives. Validation was achieved through aeroelastic testing of a 1:110-scale model of the original Tacoma Narrows Bridge and corresponding numerical simulations. The results revealed Hopf bifurcation phenomena in H-shaped bluff sections, indicated by amplitude-dependent flutter derivatives and equivalent damping coefficients. The simulation results showed less than a 10% deviation from experimental and historical wind speed–amplitude data, confirming the model’s accuracy. Failure analysis identified suspenders as the critical failure components in the Tacoma collapse. This work develops a comprehensive performance-based design framework that improves the safety, robustness, and resilience of long-span suspension bridges against complex nonlinear aerodynamic effects while enabling cost-effective, targeted reinforcement strategies to advance modern bridge engineering. Full article

The Qinghai–Xizang Plateau and its surrounding regions have experienced intense tectonic activity, resulting in complex geostress environments that cause frequent and distinctive rockburst disasters in plateau tunnel engineering. In this study, numerical simulations were conducted to investigate the distribution characteristics and patterns of tunnel rockbursts in high-altitude regions, using geostress orientation, lateral pressure coefficient, and tunnel depth as the primary independent variables. Secondary development of FLAC3D 7.00.126 was carried out using FISH language to enable the recording and visualization of tangential stress, the Russense rockburst criterion, and elastic strain energy. Based on this, the influence mechanisms of these key geostress parameters on the location, extent, and intensity of rockbursts within tunnel cross sections were analyzed. Results indicate that geostress orientation predominantly affects the location of rockbursts, with the surrounding rock in the direction of the minimum principal stress on the tunnel cross section being particularly prone to rockburst risks. The lateral pressure coefficient primarily influences the rockburst intensity and pit range within local stress concentration zones, with higher values leading to greater rockburst intensity. Notably, when structural stress is sufficiently large, rockbursts may occur even in tunnels with shallow burial depths. Tunnel depth determines the magnitude of geostress, mainly affecting the overall risk and potential extent of rockbursts within the cross section, with greater depths leading to higher rockburst intensities and a wider affected area. Full article

Rectangular box jacking is widely used in densely developed urban areas. However, when conducted with limited clear distance near existing metro tunnels, it introduces considerable structural safety risks. This study investigates a large-section rectangular box jacking project in Suzhou that crosses a double-line metro tunnel with minimal vertical clear distance. Integrated field monitoring and finite element simulations were conducted to analyze the tunnel’s deformation behavior during various jacking phases. The results show that the upline tunnel experienced greater uplift than the downline tunnel, with maximum vertical displacement occurring directly beneath the jacking axis. The affected zone extended approximately 20 m beyond the pipe gallery boundaries. Both the tunnel vault and ballast bed exhibited vertical uplift, while the hance displaced laterally toward the launching shaft. These deformations showed clear stage-dependent patterns strongly influenced by the relative position of the jacking machine. Numerical simulations demonstrated that doubling the pipe–tunnel clearance reduced the vault displacement by 58.87% (upline) and 51.95% (downline). Increasing the pipe–slurry friction coefficient from 0.1 to 0.3 caused the hance displacement difference to rise from 0.12 mm to 0.36 mm. Further sensitivity analysis reveals that when the jacking machine is positioned directly above the tunnel, grouting pressure is the greatest influence on the structural response and must be carefully controlled. The proposed methodology and findings offer valuable insights for future applications in similar tunnelling projects. Full article

With the rapid advancement of urban underground space development, shield tunnel construction has seen a significant increase. However, at the initial launching stage of shield tunnels in shallow-buried weak strata, engineering risks such as face instability and sudden surface settlement frequently occur. At present, there are relatively few studies on the reinforcement technology of the initial section of shield tunnel in shallow soft ground and the evolution law of ground disturbance. This study takes the launching section of the Guanggang New City depot access tunnel on Guangzhou Metro Line 10 as the engineering background. By applying MIDAS/GTS numerical simulation, settlement monitoring, and theoretical analysis, the reinforcement technology at the tunnel face, the spatiotemporal evolution of ground settlement, and the mechanism of soil disturbance transmission during the launching process in muddy soil layer are revealed. The results show that: (1) the reinforcement scheme combining replacement filling, high-pressure jet grouting piles, and soil overburden counterpressure significantly improves surface settlement control. The primary influence zone is concentrated directly above the shield machine and in the forward excavation area. (2) When the shield machine reaches the junction between the reinforced and unreinforced zones, a large settlement area forms, with the maximum ground settlement reaching −26.94 mm. During excavation in the unreinforced zone, ground deformation mainly occurs beneath the rear reinforced section, with subsidence at the crown and uplift at the invert. (3) The transverse settlement trough exhibits a typical Gaussian distribution and the discrepancy between the measured maximum settlement and the numerical and theoretical values is only 3.33% and 1.76%, respectively. (4) The longitudinal settlement follows a trend of initial increase, subsequent decrease, and gradual stabilization, reaching a maximum when the excavation passes directly beneath the monitoring point. The findings can provide theoretical reference and engineering guidance for similar projects. Full article

Icing on transmission lines in cold regions can cause asymmetry in the conductor cross-section. This asymmetry can lead to low-frequency, large-amplitude oscillations, posing a serious threat to the stability and safety of power transmission systems. In this study, the aerodynamic characteristics of crescent-shaped and sector-shaped iced eight-bundled conductors were systematically investigated over an angle of attack range from 0° to 180°. A combined approach involving wind tunnel tests and high-precision computational fluid dynamics (CFD) simulations was adopted. In the wind tunnel tests, static aerodynamic coefficients and dynamic time series data were obtained using a high-precision aerodynamic balance and a turbulence grid. In the CFD simulations, transient flow structures and vortex shedding mechanisms were analyzed based on the Reynolds-averaged Navier–Stokes (RANS) equations with the SST k-ω turbulence model. A comprehensive comparison between the two ice accretion geometries was conducted. The results revealed distinct aerodynamic instability mechanisms and frequency-domain characteristics. The analysis was supported by Fourier’s fourth-order harmonic decomposition and energy spectrum analysis. It was found that crescent-shaped ice, due to its streamlined leading edge, induced a dominant single vortex shedding. In this case, the first-order harmonic accounted for 67.7% of the total energy. In contrast, the prismatic shape of sector-shaped ice caused migration of the separation point and introduced broadband energy input. Stability thresholds were determined using the Den Hartog criterion. Sector-shaped iced conductors exhibited significant negative aerodynamic damping under ten distinct operating conditions. Compared to the crescent-shaped case, the instability risk range increased by 60%. The strong agreement between simulation and experimental results validated the reliability of the numerical approach. This study establishes a multiscale analytical framework for understanding galloping mechanisms of iced conductors. It also identifies early warning indicators in the frequency domain and provides essential guidance for the design of more effective anti-galloping control strategies in resilient power transmission systems. Full article

This study investigates the deformation characteristics and control measures for existing metro shield tunnels induced by large-section rectangular pipe jacking over-crossing, focusing on the Chengbei Road Comprehensive Utility Corridor project in Suzhou. A 9.1 m × 5.5 m pipe gallery was installed 73.6 m through clay strata over operational subway tunnels, with a minimum clearance of 4.356 m above the tunnel. Finite element simulations and field monitoring were employed to analyze the deformation of the existing tunnels, particularly the effectiveness of anti-uplift counterweights. The results revealed that excavation-induced unloading caused significant tunnel uplift, with maximum vertical displacements of 5.51 mm and 4.95 mm for the down line (DL) and up line (UL) tunnels, respectively. The addition of counterweights reduced these displacements by 30.3% and 37.1%, while also decreasing lateral displacements by up to 61.6% and bending moments by approximately 33%. The study demonstrates that counterweights, combined with slurry lubrication, real-time monitoring, and over-excavation control, effectively mitigate deformation and stress variations during large-section pipe jacking. The successful completion of the project without disrupting subway operations highlights the practical applicability of these measures. Full article

In long-distance, large-section rectangular pipe jacking operations, machine deviation is an inevitable factor that poses substantial challenges to the accurate prediction of frictional resistance. To address this issue, a novel methodology is proposed to analyze the dynamic interactions at the pipe–soil–slurry interfaces. This approach integrates real-time alignment monitoring with the Winkler elastic foundation theory to enhance predictive accuracy. A comprehensive predictive framework is developed for excavation profiles and pipeline deflection curves under varying thrust distances, enabling the quantification of complex contact states. By applying Newton’s law of friction and the Navier–Stokes fluid mechanics equations, calculation methods for the frictional resistance of pipe–soil contact and pipe–mud contact are systematically derived. Furthermore, a predictive model for the jacking force in long-distance rectangular pipe jacking, accounting for complex contact conditions, is successfully established. The jacking force monitoring data from the 233.6-m utility tunnel pipe jacking project case is utilized to validate the reliability of the proposed theoretical prediction method. Parametric analyses demonstrate that doubling the subgrade reaction coefficient enhances peak resistance by 80%, while deviation amplitude exerts a 70% greater influence on performance compared to cycle parameters. Slurry viscosity emerges as a critical factor governing pipe–slurry interaction resistance, with each doubling of viscosity causing up to a 56% increase in resistance. The developed methodology proves adaptable across five distinct operational phases—machine advancement, initial jacking, stable jacking, deviation accumulation, and final jacking—establishing a robust theoretical framework for the design and precision control of ultra-long pipe jacking projects. Full article

Deep-buried subsea tunnels are often under high water pressure conditions, and the influence of the seepage field on the tunnel cannot be ignored. Existing studies generally assume that the surrounding rock exhibits permeability isotropy; this study developed a model of deep-buried subsea tunnel that considers the permeability anisotropy of surrounding rock and investigated the effects of permeability differences between the surrounding rock and lining structure on tunnel seepage flow and plastic zone extent. By employing coordinate transformation and conformal mapping methods, the hydraulic head and the seepage discharge for each region are determined for each section of the tunnel. Based on the analytical solution of the seepage field, the seepage force is treated as a body force, and using the Mohr–Coulomb criterion, an elastoplastic analytical solution for the lining and surrounding rock under anisotropic seepage is derived. Using the Shenzhen MaWan Sea-Crossing Passage as a case study, numerical simulations are conducted using Abaqus2021, and the results are compared with the analytical solution to verify the accuracy of the study. The research shows that the permeability anisotropy of surrounding rock increases the seepage discharge, and this effect becomes more significant with increasing burial depth. If the anisotropy is 10 times greater than its previous value, the tunnel seepage volume will increase by 35.6%. When the surrounding rock permeability is sufficiently large, the impact of permeability anisotropy on the seepage discharge is relatively weak, with the seepage discharge primarily dominated by the permeability of the lining. In the tunnel stress field, due to the significant difference in stiffness between the lining and the surrounding rock, the hoop stress in the lining is much larger than that in the surrounding rock, and there is a stress discontinuity at their interface. When the permeability of the elastic zone of the surrounding rock is 100 times greater than that of the plastic zone, the plastic radius of the tunnel will increase by 2 to 3 times compared to the previous value. Reducing the permeability of the plastic zone in the surrounding rock effectively limits the seepage body force acting on the lining, thereby enhancing the stability of the lining structure and reducing the risk of damage to the tunnel. Full article

The rapid development of urban transportation renovation and transportation networks in China has driven the construction of an increasing number of large-span, large cross-section tunnels under sensitive environments, such as airport runways, critical infrastructure, and high-speed railways. These projects often require strict settlement control within a millimeter-level tolerance range, thus theoretical methods and key technologies for micro-settlement control have been developed. This study first derives a calculation formula for surface settlement associated with large cross-section tunnels and elucidates its correlations with factors such as pipe-roof stiffness, support system stiffness, pipe-roof construction procedures, and groundwater level changes. Theoretical approaches for controlling micro-settlement are introduced, including increasing pipe-roof stiffness, reinforcing the support system, mitigating group pipe effects, maintaining pressure and reducing resistance around the pipe, and controlling groundwater levels. A method is proposed for determining the appropriate stiffness of the pipe roof and support system. The stiffness should be selected from the transition segment between the steep decline and the gentle slope on the stiffness-settlement curves of the pipe roof and the support system. If the stiffness of the pipe roof and primary support combined with temporary support fails to meet the micro-settlement control requirements, an integrated support system with greater stiffness can be adopted. A reasonable pressure-regulating grouting technique for maintaining pressure and reducing resistance around the pipe is proposed. It is recommended that the spacing for simultaneous jacking of pipes be greater than half the width of the settlement trough. For over-consolidation-sensitive strata such as medium or coarse sands, water-blocking measures, including freezing, grouting, or a combination of both, are recommended. For over-consolidation-insensitive strata like gravels and cobbles with strong permeability, water-blocking treatments are generally unnecessary. The proposed theoretical approaches have been successfully implemented in projects such as the tunnel beneath Beijing Capital Airport runways and Taiyuan Railway Station, demonstrating their reliability. The research findings provide valuable insights into surface micro-settlement control for similar projects. Full article

Large reservoir-induced landslides pose a persistent threat to the safety of the Three Gorges Project and the Yangtze River shipping channel. A comprehensive multi-field monitoring system has been established to observe potential landslide areas within the Three Gorges Reservoir Area. The tasks of effectively utilizing these extensive datasets and exploring the underlying correlation among various monitoring objects have become critical for understanding landslide movement patterns, assessing stability, and informing disaster prevention measures. This study focuses on the No. 1 riverside sliding mass of the Huangtupo landslide, a representative large-scale landslide in the Three Gorges Area. We specifically analyze the deformation characteristics at multiple monitoring points on the landslide surface and within underground tunnels. The analysis reveals a progressive increase in deformation rates from the rear to the front and from west to east. Representative monitoring points were selected from the front, middle, and rear sections of the landslide, along with four hydrological factors, including two reservoir water factors and two rainfall factors. These datasets were classified using the K-means clustering algorithm, while the FP-Growth algorithm was employed to uncover correlations between landslide deformation and hydrological factors. The results indicate significant spatial variability in the impacts of reservoir water levels and rainfall on the sliding mass. Specifically, reservoir water levels influence the overall deformation of the landslide, with medium-to-low water levels (146.32 to 163.23 m) or drawdowns (−18.70 to −2.16 m/month) accelerating deformation, whereas high water levels (165.37 to 175.10 m) or rising water levels (4.45 to 17.33 m/month) tend to mitigate it. In contrast, rainfall has minimal effects on the front of the landslide but significantly impacts the middle and rear areas. Given that landslide deformation is primarily driven by periodic fluctuations in reservoir water levels at the front, the movement pattern of the landslide is identified as retrogressive. The association rules derived from this study were validated using field monitoring data, demonstrating that the data mining method, in contrast to traditional statistical methods, enables the faster and more intuitive identification of reservoir-induced landslide deformation patterns and underlying mechanisms within extensive datasets. Full article

In the current excavation of water diversion tunnels, significant challenges such as water inrush, rockburst, and large deformations continue to persist. Consequently, research on the stability of the surrounding rock after tunnel excavation is of great scientific importance. To address the impact of groundwater on tunnel-surrounding rock deformation under complex geological conditions, this study utilizes a combination of field monitoring and numerical simulation. Specifically, the research simulates the excavation process under both groundwater and non-groundwater conditions. Systematically, it analyzes the deformation patterns of tunnel-surrounding rock under groundwater conditions. The findings reveal the following: (1) Settlement and excavation mileage exhibit a clear trend of “steep decline, gradual decline, stable,” both stabilizing around 35 m after the excavation reaches the monitoring cross-section. Changes in groundwater levels, whether rising or falling, can either accelerate or delay the point at which settlement stability is achieved. (2) The numerical simulation settlement curves closely align with the field monitoring curves, with simulated settlement values slightly exceeding the monitored results. However, the error rate between the two remains below 20%, indicating the reliability of the method. (3) Groundwater significantly impacts water-sensitive strata such as loess and sandstone, with maximum settlement values at the tunnel vault and ground surface under groundwater conditions being 2 to 3 times those observed in the absence of groundwater. This study provides a scientific basis for optimizing tunnel design and construction processes. Future research should focus on refining the numerical simulation model, by incorporating additional monitoring data for validation and enhancing the safety of tunnel construction. Full article