Tunnel Section Research Articles

Variable speed limit control strategy at the entrance and exit of freeway tunnel

In order to effectively reduce the accident rate of freeway tunnel section and improve the safety factor of tunnel section, variable speed limit control scheme at the entrance and exit of tunnel is presented from the perspective of safety. First, by considering the influence of tunnel section characteristics on vehicle operation, variable speed limit cells and variable length cells are added to improve the cell transmission model and establish a dynamic traffic flow model; Second, aimed at the minimum speed dispersion and the minimum change rate of tunnel illumination, and taken the fixed speed limit and the maximum speed difference as constraints, the variable speed limit control optimization model at the entrance and exit of the tunnel is established; Third, the genetic algorithm is employed to solve the control function with meeting the safety requirement of traffic operation. The results show that compared with the fixed speed limit mode, the implementation of variable speed control in tunnel group sections can significantly reduce the dispersion of running speed, which is conducive to traffic safety and operation efficiency.

Study on the effect of excavation sequence of three-hole shield tunnel on surface settlement and segment deformation

In order to study the influence of excavation sequence of three-hole parallel shield tunnel on surface settlement and segment convergence, an improved “three-stage analysis method” was proposed to calculate the surface settlement of three-hole parallel shield tunnel. Based on Peck's existing theory, this method deduced the ground settlement formula under the three-hole parallel condition, and can calculate the ground settlement more accurately. Based on the engineering background of a shield tunnel section in Jiangsu Province, a three-dimensional model of a three-hole parallel shield tunnel was established by using Flac3d software, and the three-hole parallel shield tunnel was simulated under four working conditions: right–center–left, right–left–center, right–left–right and right–center (reverse)–left. This paper analyzed the influence of tunnel excavation sequence on surface settlement, soil displacement and deformation of tunnel segments. The construction sequence was optimized based on the above influencing factors. It was found that Case 4, S-type sequential excavation, produced the least ground settlement. The surface settlement value caused by S-type excavation sequence was only 11.41 mm, and the convergence value of the segments generated by S-type excavation sequence was relatively small. Considering the economic factors such as construction efficiency and benefit, the S-shaped excavation sequence was better. The new calculation method of tunnel surface settlement and the optimal sequence of tunnel construction proposed in this paper can provide reference for actual construction.

Numerical investigation on the thermal performance of energy tunnels under groundwater flow and tunnel airflow

The integration of underground tunnels with ground heat exchangers (GHEs), also known as energy tunnels, is a promising technology that has gained attention in energy geotechnics research. This study investigates the coupled effects of groundwater and tunnel-air flows on the energy tunnel system via 3D thermo-hydraulic numerical modelling. It is found that the combination of groundwater flow parallel to the tunnel and limited airflow velocity results in reduced operational efficiency of ground source heat pump (GSHP) due to the strong thermal interference along the tunnel. The study also highlights the importance of real-scale modelling to evaluate the thermal yield of long energy tunnels, particularly when dealing with parallel groundwater flow in geothermal tunnel design.
 The use of shallow geothermal energy is a renewable solution towards net-zero carbon emissions. In recent years, a variety of conventional geotechnical structures, such as piles, retaining walls and tunnels, have been transformed into energy geostructures to also serve as GHEs to harness renewable energy for space heating and cooling purposes [7]. The thermal performance of energy tunnels is significantly affected by the presence of groundwater flow [1, 6] and the airflow in the tunnel [2, 4]. The groundwater flow and tunnel airflow can both be present in the field, however, their coupled effects on the energy tunnel system are hardly explored in the literature. This study aims to bridge this gap via real-scale numerical investigations.
 This study uses 3D thermo-hydraulic numerical modelling developed with the finite element package COMSOL Multiphysics [3]. The numerical model was successfully validated against an energy tunnel model-scale laboratory experiment [5]. Figure 1 shows the overall geometry and boundary conditions of the numerical model. A 48 m long tunnel section is thermally activated with the embedment of HDPE pipes (outer diameter of 25 mm and 2.3 mm thickness) placed in the lining segments at a spacing of 200 mm. A single tunnel ring consists of six segments with absorber pipes joined between them. Every four adjacent rings are connected in series to form a complete loop (with a single inlet and outlet), which is then connected in parallel to a flow and return header pipe(s). The entire thermally activated section comprises six loops, with identical fluid inlet temperature and flow rates, as they are fed by the same flow header pipe. The outlet fluid from each loop is mixed along the return header pipe to the GSHP. A constant 36 kW cooling thermal load is applied, and the simulation is run for ten years to allow the system to reach a steady state condition considering the minimum groundwater flow and airflow. The thermal properties of the ground are prescribed as 2 W/(m·K) and 1100 J/(kg∙K) for thermal conductivity and specific heat capacity, respectively.
 Figure 2 shows the entering water temperature (EWT, header outlet) and the coefficient of performance (COP) of the GSHP after 10 years of operation for different groundwater flow velocities and directions for tunnel air velocities = 0.05 m/s and 2 m/s.
 Results show that an increase in and leads to a decrease in EWT and an increase in COP. However, the effect of groundwater direction and velocity is more significant when airflow is limited ( = 0.05 m/s). The parallel groundwater flow leads to a higher EWT and lower COP than when the flow is inclined and perpendicular to the longitudinal tunnel axis. Consequently, the thermal performance of the system under parallel flow with a higher can be even worse than the perpendicular and inclined flow with a lower . When = 0.05 m/s, the EWT of parallel flow increases by 15% to 20% compared to the perpendicular flow, resulting in a maximum decrease of 15% in the COP. The effect of groundwater flow is much less significant when airflow is fast ( = 2 m/s): for increases from 0.05 to 2 m/d, EWT and COP change by no more than 13% and 5%, respectively, and the impact of groundwater flow direction is minor.

Evaluating construction parameters of HB and CD methods for super large section tunnel: a case study

The double sidewall guide pit and centre cross diagram (CRD) methods are often used for the construction of large-section tunnels through water-rich fault fracture zones due to their long construction time and high construction cost. To shorten the construction period and save costs, the top heading and benching method (HB) and centre diaphragm (CD) can be chosen for construction. The construction parameters of the step and CD methods are optimized to ensure the surrounding rock stability and tunnel safety. By relying on the Tongzi Tunnel, we simulate the excavation of different step heights in the construction of the top heading and benching method (HB) and CD methods through numerical simulation, the laws of tunnel vault settlement, and changes in the surrounding rock stress, initial support axial force, bending moment and safety factor. The study shows that as the height of the upper step increases, the settlement of the vault and the convergence of the periphery increase, the initial support safety factor decreases, and the plastic zone of the surrounding rock increases at 30 m from the target face. The step height for the top heading and benching method (HB) of construction is optimized as follows. The ratios of the upper, middle and lower step heights are 0.45H, 0.35H and 0.2H, respectively. The CD method construction step height is optimized to the left (right) upper and left (right) lower step height ratios of 0.5H and 0.5H, respectively.

Mechanical response of precast tunnel segments with steel and synthetic macro-fibers

Precast tunnel lining segments manufactured with synthetic macro-fibers and steel fibers as the primary reinforcement were tested under flexural and edge compression loading. Since steel fibers are usually prescribed as the primary reinforcement of tunnel sections, the dosage of synthetic fibers was determined by matching their residual flexural strength. The performance of tunnel segments was verified using the extensive data collected from instrumented deflection, crack growth, quantitative DIC, and strain gauge results and correlated with the load vs. deformation response. Results show that synthetic fibers can meet the design load requirements specified for the steel fibers reinforcement. Flexural test results indicate a 16% increase in macro-fiber content from 0.80% to 0.93% by weight resulting in a 32% increase in the residual strength of standard beam samples and a 41% increase in the residual strength of full sections. Compared to the steel fiber samples, samples with polymeric macro-fiber had a 6.5% higher average toughness. The full-scale load-deflection results were within 7% of the average values in each category of samples which is almost half the variation in the flexural ASTM C1609 results. The edge compression tests indicated that the mode of failure under concentrated jack forces is governed and dominated by the tensile lateral bursting stresses resulting from inefficient distribution of the load to the supporting edge.

Research on reasonable reserved deformation and height-span ratio of a large deformation tunnel section in high geo-stress soft rock near a fault zone: a case study

Research on reasonable reserved deformation and height-span ratio of a large deformation tunnel section in high geo-stress soft rock near a fault zone: a case study

An experimental study on the smoke spread in underground interconnected infrastructure with longitudinal ventilation

The underground interconnected infrastructures are under development in the metropolitan areas, and simultaneously, also raise many safety issues, especially with regards to the smoke control once a fire occurred. Owing to the interconnected structure, the smoke spread in underground interconnected infrastructures can be more complex than that in “normal” tunnels, where the smoke spread is commonly simplified as one-dimensional spreading. In this study, the properties of maximum temperature, temperature decay, and smoke spread in a longitudinally ventilated underground interconnected infrastructure were studied. Experiments were conducted in a reduced-scale model which was divided into the tunnel part A and part B, and the scenario of a fire occurring at the junction point was mainly considered. For such a scenario, it is found that the temperature decay depends on the ventilated velocities of both upstream and connected tunnel sections. The spreading of the smoke in the upstream tunnel section depends on the ventilated velocity of the upstream tunnel section and can be well described by previous back-layering correlation. Whereas for the spreading of smoke in the connected tunnel section, both the ventilated velocities in the upstream and connected tunnel sections show a distinct impact. The estimation of whether the smoke spreads to the connected tunnel is established by comparing the buoyance force of the smoke and the inertia force of the ventilated flow. It is indicated that the smoke flow will be less inclined to spread to the connected tunnel under the scenarios of weak buoyancy force and large ventilated velocity. The findings of this work may contribute to an improved understanding of thermal-driven smoke propagation in underground interconnected infrastructures.

Minimization of overbreak in different tunnel sections through predictive modeling and optimization of blasting parameters

Engineering projects are confronted with many problems resulting from overbreak in tunnel blasting, necessitating the optimization of design parameters to minimize overbreak. In this study, an AI-based model for overbreak prediction and optimization is proposed, aiming to mitigate the hazards associated with overbreak. Firstly, the Extreme Gradient Boosting (XGBoost) model is integrated with three distinct metaheuristic algorithms, namely Particle Swarm Optimization (PSO), Whale Optimization Algorithm (WOA), and Sparrow Search Algorithm (SSA), respectively. Consequently, the hyperparameters are optimized, and the performance of predictions is enhanced. Meanwhile, to overcome the limitations of a small dataset and enhance the generalization ability of the three developed models, a 5-fold cross-validation is employed. Then, the performance of the different models with five distinct swarm sizes is evaluated via four metrics, including coefficient of determination (R2), mean square error (MSE), mean absolute error (MAE), and variance accounted for (VAF). Subsequently, by comparing the aforementioned developed models, the optimal prediction model with the highest accuracy can be obtained, which is then used for parameter optimization research. Finally, individual studies are conducted to address the issue of overbreak caused by the adoption of identical blasting parameters due to geological variations, aiming to minimize overbreak in different sections of the tunnel. By comparing the optimization abilities of PSO, WOA, and SSA, the objective of finding the minimum value of overbreak within a short timeframe is achieved. The results indicate that the model developed in this study accurately predicts overbreak, and effectively optimizes blast parameters for different sections of the tunnel.

Experimental Flutter Analysis over Different Selected Wing Planforms by Varying the Wing Cross Section Geometry

Flutter is a phenomenon that occurs in structures which are subjected to aerodynamic forces. As the wing model flies at increasing speeds and increasing angle of attack the vibrations get increased and the frequency of these modes coincide with each other which leads to resonance, this is called Flutter and this may lead to catastrophic failures in the aircraft flight. An appropriate wing model design includes various parameters that need to be selected according to the wind-tunnel test conditions. The material used for skin is monocot, spars are made of aluminium, ribs are made of balsa wood. We follow an iterative approach in which angle of attack and true airspeed are constant per iteration. In the present note, parameters we are going to use are design lift coefficient and location of maximum camber, the flutter response of the wing models is detected experimentally with the help of accelerometers placed at the leading edge and trailing edge of the aero elastic models. The aero elastic models we use in the present experiment have two degrees of freedom, these wing models with accelerometer setup are placed in the test section of the wind tunnel where Arduino UNO gives the code to encrypt the flutter response to save the values from each iteration; by the observation of this iterative approach we can reach a conclusion. This experimental flutter analysis on aircraft wings ensures that flutter does not occur if we make sure the model strictly operates in its design limitations.

Study on the Effect of Large Cross-Section Quasi-Rectangular Pipe Jacking near Side Crossing Viaduct Piles in Soft Soil Areas

Due to its high section use rate and minimal environmental impact, pipe jacking technology is frequently utilized in the building of urban rail transit and other municipal projects. This paper develops a three-dimensional numerical model for the gradual construction of rectangular pipe jacking based on the quasi-rectangular pipe jacking metro station project on Shanghai Line 14 and examines the interaction between the subsequent construction of double line pipe jacking and pile foundation. To analyze the deformation pattern of the tunnel section and the ground surface during the construction period and to confirm the applicability and accuracy of the model, the simulation results are compared with the monitoring data. The findings demonstrate that although the bending moment of the pipe jacking section is distributed as a “butterfly” under the influence of the viaduct piles, the maximum positive and negative bending moments as well as the lateral and vertical radial deformations of the pipe section cross-section are all somewhat diminished. The ground surface settlement curve in the vicinity of the bearing platform exhibits a more pronounced non-uniform settlement when the two pipe jackings pass through the pile foundation in close proximity, one after the other. The largest horizontal displacement of the pile foundation is found inside the jacking pipe tunnel at a depth of roughly 17 m below ground, where pipe jacking II has a greater influence on the lateral displacement of the pile foundation than pipe jacking I. The study’s findings line up with the monitoring data, which can serve as a guide and aid in the development of initiatives of a similar nature.

Assessment and Control of Construction Risk for a Super-Sized Quasi-Rectangular Pipe-Jacking Tunnel Adjacently to High-Speed Railways: A Case Study

Constructing super-sized quasi-rectangular pipe-jacking tunnels beneath high-speed railways presents a significant risk to both the railways and the tunnels. This paper uses expert inquiry, numerical simulation, fuzzy comprehensive evaluation, and on-site monitoring to assess and control risks for constructing a super-sized quasi-rectangular pipe-jacking tunnel project beneath high-speed railways. An assessment system including 18 factors from 6 aspects is built by integrating existing literature, expert consultation, and causality analysis. As the insufficient number of projects, the Analytic Hierarchy Process (AHP), Fuzzy Comprehensive Evaluation Method (FCEM), Delphi method, and numerical simulation are employed to establish a risk assessment model. The pre-support roof construction (P-SRC) technology is proposed to control tunnel construction risks. The actual scenario on site examines the validity and practicality of the evaluation model and control measures. The results indicate that the super-sized quasi-rectangular pipe-jacking tunnel sections for planned and operational high-speed railways belong to the level I risk, requiring risk reduction measures. The artificial borehole piles + D-shaped beams scheme and pile-plate structure scheme decrease the construction risk from level I to IV, and the evaluated risk results and control effect are in good agreement with actual construction conditions. The proposed risk assessment method and control technology are reasonable and reliable, providing a scientific reference for similar projects.

Stability Analysis of Saka DAM Diversion Tunnel Portal

The Saka Dam has a channel in the form of a diversion tunnel. This paper presents the results of rock mass characterization using the Geological Strength Index (GSI) classification and evaluation of the stability of the tunnel portal slope with earthquake loads using numerical methods. Based on the GSI classification, the Saka Dam tunnel portal slope is composed of rock masses that are poor quality, fair, and good. The calculation results show the Saka Dam can experience earthquake loads with an acceleration value of 0.4g. Earthquake loads can cause a decrease in the safety value (SRF) of the tunnel portal slope based on the results of numerical analysis. SRF value of natural portal slope without earthquake effect is 10.23 (inlet) and 1.5 (outlet). SRF value of the design slope portal without earthquake effect is 6.64 (inlet) and 1.76 (outlet), whereas if the earthquake effect is taken into account the SRF value obtained is 20.31 (inlet) and 0.99 (outlet). This shows that the condition of the natural portal slope and the portal slope design planner section of the Saka Dam inlet diversion tunnel is in the safe category. Meanwhile, for the portal slope excavated from the outlet section, modification is needed to obtain a safe slope condition. The results of the modified geometry of the slopes at the outlet section resulted in an SRF value of 1.47 which indicates the slope is stable

Microseismic monitoring and experimental study on rockburst in water-rich area of tunnel

During the excavation of tunnels in the Hanjiang-to-Weihe River Diversion Project, many rockbursts occurred in water-rich (WR) areas. To study the mechanism of rockburst under such conditions, the features of microseismic events and rockbursts in WR tunnel sections excavated by both a tunnel boring machine (TBM) and “drilling and blasting” methods were statistically analysed and compared with those of adjacent water-poor (WP) areas. The results show that in both WR and WP areas, rockbursts are related to the classification of surrounding rock and are also affected by the excavation method. The rockbursts in most WP areas are more active than those in the nearby WR areas in sections excavated by TBM. However, the opposite is true under high in situ stress conditions. To explain the microseismic monitoring results, the mechanical behaviour of rock, including short- and long-term mechanical behaviour under different water and loading conditions, was also investigated, and the results show that under high stress conditions, water will accelerate the occurrence of rockburst. Therefore, the appropriate method to control rockburst is stress release, which can be achieved by advanced pilot tunnel excavation, hydraulic fracturing, and presplitting blasting, rather than high-pressure water spraying in the surrounding rock.

A method for evaluating the safety of freeway tunnel sections based on driving comfort - a naturalistic driving study

Objective Driving comfort is crucial for tunnel safety because tunnel sections on freeways often introduce significant environmental changes that can compromise comfort and increase the risk of traffic accidents. This study aimed to quantitatively evaluate the driving comfort in tunnel sections and its implications for safety management. Methods Four indicators were used to assess the driving comfort: heart rate growth rate (Hrgr), skin conductance response (SCR), speed, and acceleration. The CRITIC weighting method was employed to calculate a quantitative driving comfort score, and the presence and severity of discomfort were used to evaluate the safety of each tunnel area. In addition, the evaluation was based on a naturalistic test consisting of Hrgr, SCR, speed, and acceleration data. A total of 32 participants were recruited based on a web-based questionnaire screening process, after which they were tested while driving through 30 tunnel sections on the roadway. These 30 tunnels included 14 short (< 500 m), 12 medium (500–1,000 m), and 4 long (1,000–3,000 m) tunnels. Results The results revealed that the four selected indicators exhibited minimal multicollinearity and effectively captured the driving comfort. Among the indicators, SCR had the most significant contribution to the driving comfort score. Most drivers did not experience substantial discomfort while driving through tunnels. The area where drivers were most susceptible to discomfort was the middle zones of tunnels. However, drivers were more likely to experience strong discomfort in the outside exit, entrance, and middle zones of short, medium, and long tunnels, respectively. Conclusions This study provides a comprehensive set of safety evaluation methods for tunnel sections on freeways, with a focus on quantifying the driving comfort. The findings provide theoretical support for freeway management personnel in implementing personalized controls in different tunnel areas with the aim of enhancing tunnel safety and mitigating the occurrence of traffic accidents.

A Study on the Influence of Double Tunnel Excavations on the Settlement Deformation of Flood Control Dikes

This article combines numerical simulation and field monitoring methods to study the stability of the overlying Liuyang River embankment in the tunnel crossing between Huaqiao Station and Rice Museum Station of Changsha Metro’s Line 6. Using AutoCAD, 3Dmine, and COMSOL Multiphysics, a calculation model of the entire subway tunnel section crossing the flood control embankment under the coupling of fluids and solids was established. The process of tunnel-crossing the embankment and the variation in spatial displacement and plastic strain in different geological layers were analyzed from the perspective of time evolution and spatial distribution. The research results show that during the process of crossing the embankment, the deformation of the east bank is greater than that of the west bank, and crossing the west bank is the relatively riskier stage of the entire project. Moreover, during the process of crossing the embankment, the overlying soil layer will produce a plastic strain zone, and only a small amount of plastic strain is generated in the surrounding sandstone layer of the tunnel walls. In terms of the magnitude of plastic strain, the plastic strain area produced by the leading tunnel’s surrounding rocks is larger than that of the following tunnel. As the excavation progresses, a funnel-shaped settlement displacement gradually forms during the passage of the leading tunnel, and this settlement funnel gradually expands during the passage of the following tunnel, with the maximum settlement point transitioning from directly above the leading tunnel to the middle position between the two tunnels. Using the jitter filter algorithm and the adjacent average method to process the field monitoring data, the results show that the monitored deformation results well match the simulated settlement results.

Experimental and theoretical analysis of spalling in deep hard rock tunnels with different arch structures

To study the spalling characteristics and induction mechanism of tunnels with different arch structures, a series of true triaxial tests were conducted on three types of cubic granite specimens with a through-going arched hole and analytical stress solutions were obtained for the three arch sections. Test results show that the failure process of specimens includes four periods: a quiet period, a buckling deformation period, a gradual buckling and exfoliation period of rock fragments, and a V-shaped notch formation period. Specimens with different arch structures are listed in a descending order as the three-centered arch with f/B (arch rise/tunnel width) = 1/3 (II), three-centered arch with f/B = 1/4 (III), and semi-circular arch with f/B = 1/2 (I) according to the size of rock fragments. Before the spalling of arched tunnels, the acoustic emission (AE) count is low, while the AE count and cumulative AE count are high during spalling. Stress analysis results show that as the vertical stress rises, the arch feet of tunnels undergo initial failure at first due to stress concentration; spalling cracks appear in both side walls due to compressive stress concentration, which induce spalling failure; tensile cracks initiate in the vault and invert due to tensile stress concentration. The sequence of spalling in tunnels with different arch structures varies due to a change in section structure. Therefore, the quality of section structures can be evaluated according to the stress distribution characteristics of surrounding rocks. The vertical stress inducing the initial failure of tunnel surrounding rocks increases gradually in different arch structures from the II, III, to I; the failure severity of surrounding rocks decreases in different arch structures, also from II, III, to I. In addition, the stress analysis results also verify the accuracy of the test results. In practical engineering applications, to consider both the section utilization ratio and control of spalling in surrounding rocks, selecting tunnel sections with f/B = 1/4 is more economic and safer than that of f/B = 1/3.

Service reliability evaluation of highway tunnel based on digital image processing.

China is gradually transitioning from the "tunnel construction exploration era" to the "tunnel high-quality construction and operation era", and the maintenance demand of highway tunnels has increased sharply. Therefore, there is an urgent need for an evaluation method to evaluate the service reliability of highway tunnels, so as to provide reference for tunnel maintenance personnel to carry out maintenance work. Taking highway tunnels as the research object, this paper extracts three parameters, including length, maximum width and fractal dimension, from the binary image of highway tunnel lining cracks. The standard for dividing the length of the highway tunnel section is 500m as the tunnel section, and a section disease sample space including multiple highway tunnels is constructed. The EM clustering algorithm was used to determine the number of graded grades of disease, and the relative Euclidean distance was used as the evaluation index to divide the safety grade of the tunnel into five grades: normal, degraded, inferior, deteriorated and hazardous. The partial least squares method is used to establish the lining service reliability evaluation formula and verify the residual of each sample point in the sample space. The smaller the average value of the residual, the better fitting effect of the established evaluation formula. The service reliability evaluation method proposed in this paper is applied to engineering practice and compared with the expert scoring method and the national standard method, which proves that the evaluation method in this paper has the advantages of strong visibility, simple evaluation method, and is conducive to engineering practice.

Coupled FEM–DEM analysis of mountain tunnels subjected to explosion-induced landslide

In this study, the onset of a landslide induced by an explosion within a shallow buried mountain transit tunnel was simulated using a coupled finite-element–discrete-element method (FEM–DEM). Two cases of mountain tunnels were considered for the investigation: a continuous tunnel passing through the mountain body and the terminal end of the tunnel. The effect of the location of the explosion inside the tunnel and the angle of slope on the dynamic response of the tunnel and landslide mechanism were investigated. The initiation of landslide and the location of mobilisation of overlying soil varied as the location of the explosion was changed. Time of initiation increased when the explosive was positioned away from the mouth of the tunnel. Changing the location of the explosive also affected the tunnel's response. Highest displacement and acceleration were observed at the crown in the tunnel section where the explosive was positioned. However, regardless of the location of the explosive, substantially high displacement and acceleration were still observed at the mouth of the tunnel. Early triggering of a landslide occurred when the slope angle was increased for the same location of explosion. However, the effect of slope angle on the response of the tunnel was minimal.

Research on Operational Safety Risk Assessment Method for Long and Large Highway Tunnels Based on FAHP and SPA

Compared to the construction phase, the assessment of tunnel safety risks during the operational stage has not been thoroughly conducted, and the related research work is relatively lagging. To deepen the research and application of theoretical methods for assessing operational tunnel safety risks, and to improve the level of hazard investigation and prevention in long and large highway tunnels, this paper establishes a tunnel section assessment index system from four perspectives: tunnel condition, traffic characteristics, operational environment, and operational management. A combined qualitative and quantitative approach is employed, and a practical classification standard for the indicators is proposed. Based on the traditional Analytic Hierarchy Process (AHP) and fuzzy analysis theory, a new form of questionnaire survey, known as the expert system analysis method, is introduced to collect expert opinions. A novel approach for determining fuzzy numbers based on expert opinions is proposed. Consequently, a combined model for assessing operational tunnel safety risks in long and large highways is established by integrating the Fuzzy Analytic Hierarchy Process (FAHP) and the Set Pair Analysis (SPA). This model effectively combines subjective weighting with objective evaluation, thereby enhancing the accuracy of operational tunnel safety risk assessment for long and large highways. The safety risks of three long and large tunnels within the G1523 Yongguan Expressway were assessed using the evaluation method proposed in this paper. A comparative analysis was conducted between the results obtained using the proposed Fuzzy Analytic Hierarchy Process (FAHP) and Set Pair Analysis (SPA) method and the traditional Analytic Hierarchy Process (AHP) evaluation. The results indicate that the operational tunnel safety risk assessment method based on FAHP and SPA exhibits greater rationality and accuracy compared to the traditional AHP approach.

Numerical investigation on aerodynamic characteristics of a high-speed train travelling through a bridge–tunnel section under non-uniform airflows caused by mountain terrain effect

A thorough understanding of aerodynamic characteristics of a high-speed train in a bridge–tunnel section is of extremely importance to ensure the vehicle safety of driving. This study presents a numerical investigation on aerodynamic characteristics of a high-speed train travelling through a bridge–tunnel section under non-uniform airflows caused by mountain terrain effect. First, the wind field distribution of the section is obtained from a large-scale numerical simulation model of a mountain terrain. Second, a high-fidelity small-scale model is established to simulate the aerodynamic characteristics. It is validated by the wind tunnel test. Third, the influence of non-uniform wind speeds and wind attack angles airflows on the aerodynamic characteristics are investigated. Finally, a derived empirical equation is introduced to predict the aerodynamic coefficients of the vehicle under non-uniform airflows caused by the mountain terrain. The results demonstrate that due to the effect of mountain terrain, the trend of aerodynamic coefficients varies slowly when the vehicle travels in the bridge–tunnel section. Meanwhile, when the vehicle travels near the tunnel exit, the jumping property of the pressure along the vehicle longitudinal axis is reduced. Furthermore, the predictions of the overturning moment coefficients via the simple empirical equation are consistent with the numerical simulation results.