Tunnel Portal Research Articles

Study on the mitigation effect of a new type of connected structure on micro-pressure waves around 400 km/h railway tunnel exit

This paper aims to study a new connected structure composed of parallel headings and cross passages, mitigating micro-pressure waves (MPWs) at the 400 km/h railway tunnel exit. The numerical method based on the sliding mesh method with the RNG k-ε turbulence model is utilized to simulate the relative motion of the train and tunnel, of which the accuracy of the method is verified by moving model tests. Then, the paper analyzes the effects of the distance of cross passage to tunnel entrance (l1), length of cross passage (l2), number of cross passages (n), spacing of cross passages (l3), and layout location on MPWs. For one cross passage, as the increase of l1, MPWs gradually decrease, reaching an optimal value at l1 = 25 m, but as the increase of l2, MPWs gradually increase. When l1 = 25 m, l2 = 10 m, MPWs are reduced by about 34.4%. For multiple cross passages, when n = 2, the reduction rate of MPWs reaches a stable level of about 40%. l3 does not significantly affect MPWs. The connected structure placed at the tunnel entrance is more effective in mitigating MPWs. In addition, we find that the combination of the connected structure and a hat oblique tunnel portal can reduce MPWs by 52%. This study makes reasonable use of the parallel heading left by the tunnel construction to significantly alleviate MPWs without increasing the construction cost.

Field Test and Numerical Investigation of Tunnel Aerodynamic Effect Induced by High-Speed Trains Running at Higher Speeds

After decades of research in the field of high-speed railway technique, technology of running high-speed trains at the velocity level of 350 km/h gradually become mature. It is of great importance to capture the variation regular of aerodynamic parameters in the situation that the high-speed train runs at a higher speed level. The present paper is motivated by this knowledge gap, both field tests and numerical simulations were conducted to help illustrate the basic characteristic of transient pressure loads, micro-pressure wave, as well as the wave propagation inside the tunnel regrading train’s passage and intersection. Results present the major findings as: (1) Transient pressure loads acting at tunnel surface and train body unevenly distributes along the longitudinal, transverse, and vertical directions. Pressure peak along the longitudinal direction occurs nearly at tunnel center and fast decreases from the radiated center to the remote positions. (2) Variation of pressure peak near the tunnel portal in the situation of train’s passage and intersection is limited while its value becomes doubled at the intersection location. Field measurements suggest the maximum pressure load acting at tunnel sidewall at xtin = 200 m and tunnel center being 4.29 and 5.63 kPa, respectively; (3) The maximum value of micro-pressure wave (namely MPW) detected in the field test is approximately 36.73 Pa. Amplitude of MPW at tunnel portal is inversely proportional to its attenuated distance. Through data fitting, an empirical prediction model was established. Outcomes of this paper is anticipated to improve the understanding of tunnel aerodynamic effect regarding higher speed level and its associated problems. Besides, findings of this paper are useful for the future tunnel design.

Road tunnel noise: monitoring, prediction and evaluation of noise-induced hearing loss.

Incessant increases in vehicles and massive road networks lead to traffic-related problems and noise pollution. Road tunnels are considered a more feasible and effective solution for solving traffic problems. Compared to other traffic noise abatement strategies, road tunnels also offer enormous benefits to urban mass transit systems. However, the road tunnels that are non-complying with the design and safety standards negatively impact commuters' health of being exposed to the high noise level inside the tunnel, particularly for road tunnels above 500 m in length. The study aims to evaluate the applicability of the ASJ RTN-Model 2013 by validating predicted data with the measurement data at the tunnel portal. The study also investigates the acoustic characteristics of noise inside the tunnel by analysing octave frequencies to inspect the correlation of noise spectrum for noise-induced hearing loss (NIHL) and discussed the possible health effect on the pedestrian and vehicle riders passing through the tunnel. The result shows that people are exposed to a high noise level inside the tunnel. The equivalent sound pressure levels at different locations inside the tunnel along the length observed between 78.9 to 86.5 dB(A), which exceeded the CPCB, recommended permissible limits for road traffic noise. The locations L1, L5, L6 and L7 found higher sound pressure levels at 4 kHz and relates to NIHL. The observed average difference between the measurement and predicted LAeq value at the tunnel portal was 2.8 dB(A) which is highly acceptable and confirms the ASJ RTN-2013 prediction model applicability for predicting tunnel portal noise in the Indian road conditions. The study recommends complete restriction of honking inside the tunnel. Considering the commuter's safety perspective, the road tunnels above 500 m must have separate walk sides for pedestrians with a barrier.

A novel vented tunnel hood with decreasing open ratio to mitigate micro-pressure wave emitted at high-speed maglev tunnel exit

The significant increase in train speed contributes to stronger vehicle/tunnel coupling aerodynamic effect, especially on the intensity of the micro-pressure wave (MPW) emitted at high-speed maglev tunnel exit. Hence when the train speed reaches 600 km/h and more, how to effectively mitigate the MPW becomes a challenge for aerodynamic researchers. In this study, a novel vented tunnel hood with the decreasing open ratio along the enlarged cross-section wall was proposed, while one consistent and two inconsistent layouts of the hoods applied at the tunnel portals were attempted to obtain a better hood combination for the mitigation of MPW. In addition, the sliding mesh technique was used to simulate the train passing through the single-track high-speed maglev tunnel. The validation of the methodology has been carried out to compare with the previous moving model test results. The peak variations of pressure wave and MPW were analysed in combination with the grid-independence study and numerical validation. The new hoods installed consistently at the tunnel portals (entrance and exit), can reduce the maximums of MPWs at required locations, i.e., 20m and 50m from the tunnel exit, by 66.9% and 40.9% respectively, when compared to the existing unvented tunnel hood; however, when the new hood at the tunnel exit is replaced by the existing tunnel hood without vents, the maximums of MPWs at the corresponding 20m and 50m are significantly increased by 79.1% and 71.0%. After changing the set-up of the inconsistent hoods, i.e., the tunnel entrance hood is unvented and this novel hood is installed at the tunnel exit, the corresponding MPW peaks can be reduced by 84.0% and 71.1%. Therefore, the hoods at both of tunnel entrance and exit can affect the variations of MPWs, and a reasonable arrangement of the hood openings at tunnel portals can effectively mitigate the MPW emitted at the high-speed maglev tunnel exit.

Cover Picture: Geomechanics and Tunnelling 3/2023

AbstractThe 27 km long second track between Divača and Koper is one of Slovenia's most important infrastructure projects and includes eight tunnels with a total length of approx. 20.5 km. At the portal of the service tunnel in Mlinarji, slopes and embankments needed reinforcement. To do that, DSI Underground supplied galvanized DSI Hollow Bar Anchors R32‐280 and R32‐400 in lengths of 6, 9, and 12 m. (photo: DSI Underground)

<b>Reducing Micro-pressure Waves Using Train Nose Optimization Based on Linear Acoustic Theory</b>

The shapes of train noses have been optimized for several decades to reduce the peak values of the micro-pressure waves radiating from tunnel portals of high-speed railways. This study optimized the shapes of multistep noses using three transfer functions based on the theory of compact Green's function (WT ), experimental results (WE ), and the average value of WT and WE (WM ). Model experiments were performed to measure the maximum pressure gradients of compression waves generated by each train nose entering a tunnel for offset running. For optimized train noses based on WT or WE , the values of the maximum pressure gradient could not be sufficiently reduced, and the pressure gradient waveforms were not trapezoidal. Although the optimized noses based on WM reduced the maximum pressure gradients considerably, the maximum pressure gradient values were larger than those for the optimized noses based on the computational fluid dynamics.

Analysis of Loose Surrounding Rock Deformation and Slope Stability at Shallow Double-Track Tunnel Portal: A Case Study

A low-clearance tunnel portal in the shallow-buried, joint-developed, broken, and loose surrounding rock slope deposit may cause safety issues during construction. In this study, the Guanyin Mountain Tunnel of the Chong-Ai expressway was taken as a case study, and the characteristics of the loose and broken surrounding rocks, their low clearance, and shallow buried bias were comprehensively studied. The three-dimensional numerical model of the Guanyin Mountain tunnel portal section was constructed by the Rhino, AutoCAD, and FLAC 3D software, and the whole construction process of the tunnel portal was simulated. Under the conditions of loose and broken surrounding rocks, the surrounding rock deformation, surface settlement, and slope stability at the portal of the shallow buried tunnel with a small clear distance during the construction of the center diaphragm (CD) method and circular reserved core soil method were studied. The following conclusions are drawn. During the simulated excavation of the tunnel, the maximum surface settlement is 10.74 mm, which meets the requirement of the specification. When the left tunnel is excavated, the surrounding rock deformation of the right arch shoulder should be carefully considered. The maximum deformation value can reach 14.314 mm. After excavation, the deformation rate of the right tunnel is large, and initial support should be installed in time. Since the stratum rock at the portal of the tunnel is strongly weathered, the uplift value of the arch bottom is large and gradually decreases along the axial direction. The tunnel arch bottom and arch foot are plastic areas prone to tensile damage. Therefore, it is imperative to strengthen the inverted arch support of the tunnel in the strongly weathered rock stratum. The excavation sequence of the tunnel portal section adopts the method of excavating the left tunnel first and then excavating the right tunnel, which is more conducive to ensuring the slope stability.

Understanding traffic bottlenecks of long freeway tunnels based on a novel location-dependent lighting-related car-following model

To understand the formation of lighting-related traffic bottlenecks along the long freeway tunnels in the daytime, this study develops an intelligent driver model incorporating the location-dependent lighting-related desired speed (IDM-LLDS). This car-following model associates desired speed variations with the lighting-transition-incurred visual adaptation in the portal areas and low illumination in the interior zone of the tunnel, such that how the impact of location-heterogeneous lighting conditions on driver’s car-following behavior propagates through car platoons is described. The model is validated, and numerical examples are presented to illustrate the traffic patterns related to tunnel lighting and daylight. The results demonstrate that periodic oscillations in traffic patterns are presented under visual adaptation occurrence if traffic flow density is not significantly high. Adaptive tunnel lighting and implementation of sunscreens at tunnel portals can both improve the traffic conditions in strong daylight. The former performs better in improving traffic efficiency, while the latter excels in smoothing visual-adaptation-based traffic oscillation. With the objective of minimizing the magnitude of traffic oscillation, the tunnel lighting strategies adaptive to daylight are recommended under different traffic volumes and travel speeds where majority of cars can avoid obvious trajectory oscillation traversing the tunnel.

Determination of seismic response of reinforced tunnel portal slope using shaking table tests

The tunnel portal is a seismically weak part of the tunnel. To improve the seismic performance of the tunnel portal, reliable portal slope reinforcement measures were investigated, and a series of shaking table tests of the tunnel portal and slope which were reinforced by micropiles were conducted. The test equipment, similarity relation, material, test process, and loading conditions were introduced in detail. Two types of earthquake waves (Kobe and Wenchuan waves), whose peak accelerations were modified to 0.125 g, 0.25 g, 0.375 g, 0.5 g, and 0.7 g, were input in the transverse direction. Through the application of the Pearson correlation coefficient, 2-norm deviation, fast Fourier transform, frequency transfer function, Hilbert-Huang transform, and other means, an in-depth analysis of the data was conducted; the results indicated that the micropiles can effectively reduce the effect of the portal slope on the amplification of acceleration, lower the acceleration response of surrounding rock, improve the predominant frequency of surrounding rock, slow down the damage of the tunnel portal slope due to vibration, and decrease the internal force of the lining.

Study on Denoising Method of Vibration Signal Induced by Tunnel Portal Blasting Based on WOA-VMD Algorithm

Because of the impact of the complex environment of tunnel portals, the measured blasting vibration signals in a tunnel portal contains a lot of high-frequency noise. To achieve effective noise reduction, a novel method of noise reduction for blasting vibration signals based on the whale optimization algorithm (WOA) optimized with the variational mode decomposition (VMD) algorithm was proposed. The WOA algorithm is used to optimize globally for the mode number K and penalty factor α of VMD for measured signals and to determine the optimal parameters of [K, α], and to obtain the intrinsic mode function (IMF). Multi-scale permutation entropy (MPE) was used to identify and remove noise components in IMF, and then the reserved IMF was reconstructed to achieve a denoised signal. The method is applied to the blasting vibration analysis of the Xiali tunnel of the Jixin expressway in the Henan Province. Results indicate that the novel method can acquire the optimal decomposition mode number and identify the high frequency noise. Its denoising effect is better than the conventional VMD algorithm and the complete ensemble empirical mode decomposition with adaptive ability (CEEMDAN), which verifies the self-adaptivity and effectiveness of the WOA-VMD denoising method.

Seismic response and damage mechanism of tunnel lining in sensitive environment of soft rock stratum

Abstract In order to investigate the dynamic response characteristics and damage mechanism of the tunnel lining at the tunnel portal in the bridge–tunnel overlapping section in soft rock strata, a physical model with the scale ratio of 1:50 was made based on the similarity theory for shaking table tests. The acceleration and strain results of the tunnel lining under EL Centro seismic waves with different acceleration peak values were studied. Test results show that most of the acceleration values have significant amplification effects compared to input seismic waves, which increased significantly with greater peak values and elevations. Tensile deformations appear along the longitudinal and the circumferential directions of the tunnel lining. The tunnel spandrel and tunnel vault are the maximum deformation parts, respectively, at the standard section and the enlarged section of the tunnel lining. Therefore, it is suggested that the longitudinal anti-tensile design of the tunnel lining at the tunnel portal in such sensitive environments should be strengthened. And the anti-seismic design standard and durability requirement of the standard section of the tunnel lining adjacent to the enlarged section should be improved, so as to meet the requirements for stress deformation and overall stability when subjected to severe earthquakes.

Experimental Study of Scale Effect in Tunnel Fires at Different Sealing Ratios

Fully or partially sealing the openings of tunnels to accelerate the self-extinction of fires provides a promising firefighting tactic to beat large fires in a long tunnel. So far, most experimental studies on the characteristics of fire with different sealing ratios have been conducted in reduced-scale tunnels. However, whether the findings in a reduced-scale tunnel can be converted to its full-scale prototype tunnel based on scaling laws has not yet been adequately studied. A series of experiments with heat-release rates of 15.8, 31.6 and 63.2 kW were conducted with sealing ratios ranging from 0% to 100% in a prototype tunnel measuring 20 m long, 0.9 m wide and 0.46 m high. The experimental results were compared with those from a 1/2 reduced-scale tunnel measuring 10 m long, 0.45 m wide and 0.23 m high. It showed that temperature rise along the tunnel in the 1/2 reduced-tunnel could be significantly underestimated. The differences in temperature rise increased monotonously with distance away from the fire seat, and they were as high as 70% at the tunnel portals, irrespective of the heat-release rates and sealing ratios. The study showed that the scale effect of fires was not sensitive to the Reynolds number of flows in tunnels. The minimal sealing ratio for the self-extinction of fires in the prototype tunnel was 85%, whilst it was 75% in the 1/2 reduced-scale tunnel, and the study revealed that the fires were much easier to extinguish in the 1/2 reduced-scale tunnel than those in the prototype tunnel, where the fires can sustain in a lower oxygen concentration. The study demonstrated that scaling laws could be invalid for tunnel fires with different sealing ratios and that results observed in reduced-scale tunnels should be further verified when applied to full-scale prototypes.

Comparison of aerodynamic performance of moving train model at bridge–tunnel section in wind tunnel with or without tunnel portal

The moving train model test for wind tunnels is an advanced and effective research method for studying the aerodynamic effect of trains passing through tunnel portals in crosswind environments. However, the modelling of tunnel portal structures is cumbersome, and its influence on test results remains unclear. Here, the influence law of the presence and absence of a tunnel portal on the aerodynamic performance of a train was investigated via a wind tunnel test and an improved delayed eddy simulation turbulence model with “mosaic” mesh technology. First, the difference between train locomotion on the windward and leeward side lines with and without a portal was compared from the perspectives of aerodynamic load amplitude, power spectral density (PSD), and standard deviation. Second, the influence of vehicle speed on the amplitude of the train’s aerodynamic load was studied, and the recommended critical speed was determined. Finally, the applicability of the moving model test results under different scale ratios (Reynolds numbers) was explored. Key results show that the aerodynamic load amplitude, PSD peak and standard deviation of the train on the leeward side line are generally higher than those on the windward side line. As indicated by the lift force in the ‘EX’ process without the tunnel portal, the amplitude on the leeward side line is 1.73 time the corresponding values on the windward side line. At speeds of 6, 12 and 18 m/s, when the moving train model speed reaches 12 m/s, the influence of the tunnel portal on the aerodynamic load amplitude can be ignored. The results imply a serious distortion of the aerodynamic load amplitude for the 1:20 model scale, whereas it appears to be appropriate at the 1:16.8 and 1:10 scales. The model test with a Reynolds number of 2.67 × 105 offers an ideal reference value for real trains.

Modelling and Mitigating Secondary Crash Risk for Serial Tunnels on Freeway via Lighting-Related Microscopic Traffic Model with Inter-Lane Dependency.

This paper models and mitigates the secondary crash (SC) risk for serial tunnels on the freeway which is incurred by traffic turbulence after primary crash (PC) occurrence and location-heterogeneous lighting conditions along serial tunnels. A traffic conflict approach is developed where SC risk is quantified using a surrogate safety measure based on the simulated vehicle trajectories after PC occurs from a lighting-related microscopic traffic model with inter-lane dependency. Numerical examples are presented to validate the model, illustrate SC risk pattern over time, and evaluate the countermeasures for SC, including adaptive tunnel lighting control (ATLC) and advanced speed and lane-changing guidance (ASLG) for connected vehicles (CVs). The results demonstrate that the tail of the stretching queue on the PC occurrence lane, the adjacent lane of the PC-incurred queue, and areas near tunnel portals are high-risk locations. In serial tunnels, creating a good lighting condition for drivers is more effective than advanced warnings in CVs to mitigate SC risk. Combined ATLC and ASLG is promising since ASLG informs CVs of an immediate response to traffic turbulence on the lane where PC occurs and ATLC alleviates SC risks on adjacent lanes via smoothing the lighting condition variations and reducing inter-lane dependency.

Prediction Method of Tunnel Natural Wind Based on Open-Source Meteorological Parameters

The rational use of natural wind in extra-long tunnels for feedforward operation ventilation control can dramatically reduce tunnel operation costs. However, traditional tunnel natural wind calculation theory lacks a prediction function. This paper proposes a three-stage tunnel natural wind prediction method relying on the Yanglin Tunnel in Yunnan, China based on the massive meteorological parameters provided by the open-source national meteorological stations around the tunnel, which make up for the partial deficiency of the meteorological parameters of the tunnel portal. The multi-layer perceptron model (MLP) was used to predict the real-time meteorological parameters of the tunnel portal using the data from four national meteorological stations. The nonlinear autoregressive network model (NARX) was used to predict the meteorological parameters of the tunnel portal in the next period based on the predicted and measured real-time data. The natural wind speed in the tunnel was obtained by a theoretical calculation method using the predicted meteorological parameters. The final tunnel natural wind prediction results are in good agreement with the field measured data, which indicates that the research results of this paper can play a guiding role in the feedforward regulation of tunnel operation fans.

Seismic Response Characteristics of a Tunnel Portal Subjected to Topographical and Geological Asymmetsric Loading

The tunnel portal is the most seismically vulnerable section of the tunnel against earthquakes. Due to the combined effects of topographic and geological asymmetric loading, the mechanical characteristics of this type of portal are very complex. In this study, a three-dimensional numerical model was developed and calculated to investigate the seismic response characteristics of a tunnel portal subjected to topographic and geological asymmetric loading. The results show that the seismic weakness of the tunnel support structure is located at the tunnel arch shoulders and sidewalls; the time to reach the peak displacement around the tunnel is slightly delayed compared to the slope, and the time to reach the peak displacement shows a phased pattern. Compared to the tunnel structure, the slopes are more prone to landslides and other disasters due to terrain and geological factors under earthquake action. Therefore, more attention should be paid to the seismic and anti-seismic design of tunnel slopes.

Rock Mass Characterizations and Kinematic Analysis for Construction Design Method of Diversion Tunnel of Dolok Dam, Central Java

Investigation of slope stability in the design of the tunnel portal is important to minimize slope failure. This research aims to describe the rock mass characterizations and classifications using Geological Strength Index (GSI) and Rock Mass Rating (RMR), along with the kinematic analysis and Slope Mass Rating (SMR) to define the risk of slope failure and the recommended support at the tunnel portal. Geological mapping and core evaluation were conducted to analyse the slope stability. The results show that the rock masses consist of intercalated rudstone with mudstone, typically have disintegrated, moderately disturbed, and blocky structures with slightly to highly weathered. The discontinuities have 3 – 4 sets consisting of bedding and joint, have medium to high persistence, close spacing, and dominantly have no infillings. These rock masses are classified as poor-fair rock in the upper part of the sequence, and good rock in the bottom part of the sequence. The kinematic analysis predicts the risk of toppling failure both in the inlet and outlet portal. The recommended support in the inlet portal is the combination of shotcrete, beams, and bolts, whilst in the outlet portal is the combination of surface drainage, shotcrete, dental concrete, beams, and bolts.

Dynamic damage identification of tunnel portal and verification via shaking table test

Tunnel portals are seismically weak. Large-scale shaking-table tests of a tunnel portal were conducted. A method based on the Hilbert-Huang transform (HHT) for dynamic damage identification of tunnel portals was studied using the test results. The test preparation process and basic principles of the HHT are briefly described. The intrinsic-mode functions (IMFs) after empirical mode decomposition (EMD) were evaluated using multiple indicators, including the coefficient of determination (R2), root-mean-square error (Rmse), variance contribution rate (Mi), and energy moment (E). The time histories of the IMFs, marginal Hilbert spectrum, and Hilbert instantaneous energy spectrum were analysed. The results show that the damage development process of the lining and slope can be characterised by the marginal Hilbert spectrum and Hilbert Instantaneous energy spectrum. The slope had an obvious acceleration amplification effect with elevation and surface-trend amplification effect. Damage to the tunnel-portal slope is mainly caused by the development of tension cracks at the top of the slope, falling of scattered particles on the slope shoulder, development of cracks on the slope surface, and instability and collapse of the surrounding rock near the tunnel portal. Slope surface damage developed faster and to a greater extent than the interior of the slope. The lining of the portal section was dominated by longitudinal cracks, with some diagonal cracks. Damage to the invert at the tunnel portal occurs earlier than that of the crown, and the degree of injury is greater than that of the crown. The degree of damage and development speed of the tunnel portal were also greater than those of the tunnel body. The proposed method can serve as a guide for identifying the dynamic tunnel-portal damage.

Dynamic discrimination method of seismic damage in tunnel portal based on improved wavelet packet transform coupled with Hilbert-Huang transform

An improved wavelet packet transformation (IWPT) combined with Hilbert-Huang transformation (HHT) is proposed as a dynamic discrimination method (DDM) for seismic damage in tunnel portals. The similarities and differences between the method proposed in this paper and the conventional response analysis method (CRAM) are compared and analyzed by using an extensive shaking table test as the data source. To begin, a realistic wavelet basis function and decomposition order suitable for shaking table tets data are explained, a new threshold function is proposed, and noise robustness analysis are performed for the IWPT. The results reveal that the proposed damage discrimination method is accurate in determining macroscopic damage to the tunnel lining and slope when compared to conventional analysis method. The method proposed in this research also permits for the position and time orientation of damage to the slope and lining, allowing for greater understanding of the dynamic damage process.

A study on airflows induced by vehicle movement in road tunnels by the analysis of bulk data from tunnel sensors

A novel analytical formula is introduced for calculation the average longitudinal airflow velocity in tunnels as a result of the piston effect. Existing correlations were analyzed and reworked to better represent the piston effect of vehicles travelling in bulk, which allows relating the airflow velocity to not only average vehicle velocity, but also the traffic intensity and the traffic structure. The approach was validated using the recorded bulk data for an urban road tunnel located in Gdańsk (Poland). Air velocity, weather conditions, wind parameters at tunnel portals, traffic intensity and structure as well as average traffic speed by lane were recorded at 1 s intervals, and analyzed in form of 10 s and 5 min averages. Since ambient conditions may affect the flows inside the tunnel, their impact on flow measurements was studied with a numerical model of the tunnel portals. Despite its simplicity, the proposed model accurately predicted the air velocity due to vehicle movement. The significance of this approach is related to the ease of achieving the initial data, which allows for easy implementation in tunnel ventilation design, risk assessment methods, determination of initial conditions for fire related CFD analyses, continuous tunnel management or estimation of the potential of energy recuperation from airflow within the tunnel. The mean absolute error (MAE) of calculated air velocity to measurements was 0.28–0.38 m/s, with mean average percentage error (MAPE) of 7.8–10.9 %. The determination coefficient for the relation with the measured data was significantly over 0.9.