Tunnel Entrance Section Research Articles

Displacement prediction of tunnel entrance slope based on LSSVM and bacterial foraging optimization algorithm

In order to realize the effective prediction of landslide risk in the tunnel entrance area, an multivariate time series model is established on the basis of the traditional model, taking temperature and rainfall factors as additional input indicators. Bacterial foraging optimization algorithm (BFOA) is used to search the global optimal solution of the key parameters \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\gamma$$\\end{document} and \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma^{2}$$\\end{document} of least squares support vector machine (LSSVM) to improve its regression accuracy, and the evolved LSSVM is used to describe the aforementioned multivariate time series model. At the same time, a remote real-time internet of things (IoT) monitoring system for the tunnel entrance section, including monitoring indicators such as surface subsidence, temperature, and rainfall, has also been designed and implemented, providing a stable and accurate data source for the realization of this prediction model. Based on the engineering measurement data, the accuracy of the established model is checked and analyzed, the optimal value of historical data amount is determined to be 5 days, and the optimal value of prediction step is 1 day. The research results are applied in the construction of Wendong tunnel of Molin expressway, Yunnan, China. Practice shows that the prediction results of the multivariate time series model established in this study is accurate. This method can realize the prediction and early warning of slope risk, which provides a effective technical means for risk control of tunnel portal section.

A novel indicator for equivalent mean air temperature within the tunnel considering time-varying ventilation wind speeds: Calculation and application

The study examines the coupling effect between air temperature and time-varying ventilation wind speeds within the tunnel, abstracting their influence on tunnel coldness. This investigation introduces a novel indicator—the equivalent mean air temperature within the tunnel—derived through fluid dynamics and heat transfer theories based on the principle of equivalent convective heat transfer. Case studies using the Xinjiaodong Tunnel and BSLL Tunnel illustrate the indicator's applications, including optimal anti-freezing axis identification, insulation layer thickness design, and active-controlled ventilation implementation. The optimal anti-freezing axis orientation angle for the Xinjiaodong Tunnel entrance section is 133.3°, deviating significantly by 160.8° from the actual axis, indicating a lower level of equivalent mean annual air temperature (5.5 °C) at the entrance section. This underscores the necessity to reinforce anti-freezing measures specifically at the entrance section of the Xinjiaodong Tunnel. Determining a 10 cm-thick insulation layer requirement at the Xinjiaodong Tunnel entrance section based on the equivalent mean air temperature. Through on-site investigation and published findings, it was observed that a 5 cm-thick insulation layer failed to prevent freezing, resulting in water leakage and ice formation on the lining, thus validating the calculation results. The BSLL Tunnel requires an insulation layer thickness exceeding 10 cm based on the equivalent mean air temperature, necessitating the implementation of active-controlled ventilation. Calculation results reveal that, with active-controlled ventilation wind speeds increasing from 1 m/s to 4 m/s at a temperature threshold of 4 °C, the equivalent mean air temperature during cumulative negative temperature periods within the BSLL Tunnel rises sharply from 1.0 °C to 2.7 °C. These findings demonstrate that the equivalent mean air temperature not only guides the identification of optimal anti-freezing axis, the design of insulation layer thickness considering time-varying ventilation wind speeds, and the implementation of active-controlled ventilation but also provides new methods and technologies for anti-freezing design in cold-region tunnels.

The deformation and failure characteristics of tunnels in layered rock with gentle dip angles after freeze–thaw cycles: Physical model tests and numerical investigation

When a tunnel passes through layered rock with a gentle dip angle in cold regions, the occurrence of multiple freeze–thaw (F–T) cycles can easily cause fatigue damage to the rock bedding surfaces and seriously affect the rock stability. One of the engineering problems that needs to be solved is to determine the deformation and failure mechanisms of such surrounding rock under F–T cycles. Based on the similarity principle, the mechanical response of the tunnel lining structure and the progressive failure process of the surrounding rock under long-term F–T action were studied by performing physical model tests and numerical simulations. The results show that the model tunnel lining partially separates from the surrounding layered rock with a gentle dip angle under the action of F–T cycles. Moreover, the load bearing capacity of the model weakens after undergoing F–T cycles. Additionally, the bending moment and axial force evolution characteristics of the tunnel and surrounding rock model are consistent with the deformation characteristics, which agree with the actual mechanical and deformation characteristics of a real tunnel under F–T cycles. After establishing numerical calculation models for surrounding rock with three bedding angles (0°, 10°, and 20°) and verifying the numerical models based on the test results, the horizontal and vertical displacements of the surrounding rock in the tunnel entrance section under ground stress conditions at a depth of 400 m were calculated. The research results accurately reflect the long-term deformation characteristics of layered rock with gentle dip angles surrounding tunnels in cold regions and can provide theoretical guidance for the application of corresponding tunnel support measures in cold regions.

Calculation and optimization of slope reinforcement at tunnel entrances—taking manyanpo tunnel as an example

Slope reinforcement is a common method to solve the problem of slope instability, and reasonable optimization of the corresponding support parameters is crucial for practical engineering. In this paper, the slope support method of Manyanpo tunnel entrance section is taken as an example, and the theoretical calculation method is used to optimize the project cost. Combined with the orthogonal test, the sensitivity analysis of the influencing factors of the stability of the support system and the selection of the optimal parameter combination scheme are carried out. Then, based on flac3d software, the optimization scheme is compared with the original design scheme. The results show that the safety factor of the optimized scheme is increased from 1.32 to 1.43 compared with the actual project. The optimized support parameters have better control effect on the displacement of the slope, especially in the Z direction. The optimized parameters have better support effect. This study can provide reference for the optimization design of slope engineering support.

Analysis of Car-Following Behaviors under Different Conditions on the Entrance Section of Cross-River and Cross-Sea Tunnels: A Case Study of Shanghai Yangtze River Tunnel.

Compared to highway road tunnels, the entrance section of cross-river and cross-sea tunnels feature long and steep slopes. Along with a complicated traffic environment and harmful weather conditions, traffic congestion and rear-end crashes occur frequently during car-following in cross-river and cross-sea tunnels. It is necessary to examine the impact of traffic flow and weather conditions on car-following behavior at the entrance section of cross-river and cross-sea tunnels. To this end, this paper first extracted the vehicle speed data based surveillance video at the entrance of the Shanghai Yangtze River Tunnel. Moreover, the actual average speed under different traffic flow conditions was obtained through the clustering algorithm, which was used as the basis for setting the experimental parameters. Then, in the driving simulation experiment, three traffic flow conditions (free flow, congested flow, and jam flow) were set up in three weather conditions (sunny, rainy, and snowy), and a risk situation was set up in each condition. Distance headway, time headway, acceleration, lateral offset, and driver’s emergency response time were collected. Moreover, seven slopes of 2% to 5% were set, and the relationship of slope on longitudinal speed and lateral offset was analyzed. ANOVA and post-hoc analyses were applied. The result indicates that traffic flow conditions have a significant effect on the car-following behavior, while weather conditions mainly influence the time headway. Moreover, drivers tend to adopt more cautious driving behavior as the distance between the vehicle and the tunnel entrance decreases. The results also show that the slope of the cross-river and cross-sea tunnel entrance section has a major influence on vehicle speed.

Field test and numerical reconstitution of natural winds at the tunnel entrance section of high-speed railway

PurposeThe purpose of this paper is to understand the natural wind field characteristics of the tunnel entrance section and analyzing the aerodynamic performance of high-speed railway trains (HSRTs) under natural winds.Design/methodology/approachThree typical tunnel entrance section sites, namely, tunnel–bridge in a dry canyon (TBDC), tunnel–bridge in a river canyon (TBRC) and tunnel–flat ground (TF), are selected to conduct a continuous wind field measurement. Based on the measured wind characteristics, the natural winds of the TBDC and TF sites are reconstituted and imported into the two corresponding full-scale computational fluid dynamics models. The aerodynamic loads of the HSRT running on TBDC and TF with reconstituted winds are simply analyzed.FindingsThe von Kármán spectrum can be used to describe the wind field at the tunnel entrance section. In the reconstituted natural wind condition, a time-varying feature of wind speed distribution and leeward side vortex around the HSRT caused by the wind speed fluctuation is found. The fluctuating amplitude of aerodynamic loads at the TBDC infrastructure is up to 97.9% larger than that at the TF infrastructure.Originality/valueThe natural wind characteristics at tunnel entrance sections on the high-speed railway are first measured and analyzed. A numerical reconstitution scheme considering the temporal and spatial variation of natural wind speed is proposed and verified based on field measurement results. The aerodynamic performance of an HSRT under reconstituted natural winds is first investigated.

Combination Layout of Traffic Signs and Markings of Expressway Tunnel Entrance Sections: A Driving Simulator Study

To determine a better combination of signs and markings on expressway tunnel entrance sections, three types of typical signs and markings were compared and tested according to five indicators: speed, lane lateral offset, lane change behavior, fixation behavior, and operating load, using a driving simulator. The results identified that the obvious no overtaking and speed limit signs, combined with a layer of thin red pavement, had the most influence on drivers’ speed, and they led to the highest fixation frequency of static facilities, the longest average distance from the completion point of the lane change to the entrance, and the longest average lane change distance, which could help drivers to pass through tunnel entrance sections more smoothly. The location of the static facilities should be between 3 s before the tunnel entrance and 3 s after entering the tunnel, as this is the area where a driver’s relative viewpoint changes. The improper combination of warning signs and deceleration measures will affect a driver’s judgment, causing negative effects, such as premature lane changes and an increased operating load. The research results can provide a design basis and reference for the combination setting of safety signs and markings on tunnel entrance sections.

Investigation of the dynamic response of rock slopes at the entrance and exit section of a tunnel based on modal analysis

In the construction and operation of tunnel engineering in high intensity areas, the slope at a tunnel’s entrance and exit section has become a section prone to problems because of seismic load and tunnel excavation disturbance. To study the dynamic response characteristics of rock slopes at the tunnel entrance and exit section, considering the strong earthquake area in western China as the research area, a three-dimensional finite element (FE) model was established and the FE modal analysis of the slope at the tunnel entrance and exit section was conducted. The dynamic response characteristics of the slope body were investigated based on a frequency domain by analyzing the natural frequencies and corresponding vibration modes of different models. The results show that the tunnel excavation affects the slope’s dynamic response characteristics and natural frequency but has little effect on its vibration mode. The natural frequency ratio of slopes without and with a tunnel is 1.1:1.35 as a whole, under the same conditions. The slope gradient has a considerable effect on the natural frequency of the slope at the tunnel entrance and exit section. The natural frequency of the slope gradually increases with the gradient, and the changing trend is more obvious with an increase in the vibration mode order. The low-order vibration mode of the slope at the entrance of the tunnel is relatively simple, primarily demonstrating bending and torsional deformation. The vibration mode of the slopes with and without a tunnel is the same when the slope gradient is the same. The vibration modes of the two tunnel slope models with different gradients are also the same. This study investigated the dynamic response characteristics of the slope and tunnel structure based on the analysis of the inherent characteristics of the slopes at the tunnel entrance and exit section, which can provide a reference for the seismic design of the tunnel entrance section.

Study on the Soil Structure and Construction Technology of Large Span Double-Arch Tunnel Entrance

In the construction process of tunnel engineering, the construction of the entrance section is one of the crucial procedures. How to improve the construction efficiency and ensure the stability of the tunnel entrance section needs to be considered. Based on the project of a double-arch tunnel, this paper studies the construction techniques of the entrance of the urban double-arch tunnel with a large span. Based on the numerical simulation, it is proved that the construction of tunnel entrance by opening up a cross passage is feasible.

Stability analysis of full-section construction of staggered distance double-hole tunnel

In the staggered distance double-hole tunnel located on the slope of the mountain, the deformation of the surrounding rock and the supporting structure of the tunnel is complicated. The deformation stability of the tunnel entrance is one of the most difficult points of the tunnel. In order to clarify the deformation law of the full-section construction at the entrance of the staggered distance double-hole tunnel, the entrance section of the Georgia E60 Highway No. 3 tunnel under construction is used as the background, and the method of numerical simulation test is used to study the staggered distance double-hole tunnel, the influence of section construction on the deformation and stability of the side and front slopes of the tunnel entrance section and the support structure of the tunnel entrance section. The research results show that: For tunnels with full-section construction, excavation will cause certain deformations on the ground and the tunnel, and the stability of the left side support structure of the right line tunnel without rock column between the two tunnels is worse than that in other positions, on the whole, the construction plan is reasonable and feasible.

Cracking characteristics and mechanism of entrance section in asymmetrically-load tunnel with bedded rock mass: A case study of a highway tunnel in southwest China

Serious cracks of secondary lining appear at the entrance section of a highway tunnel in southwest China after excavation. The entrance section of the tunnel has geological characteristics of bedded rock mass with inclined structural plane, asymmetrically loaded terrain, shallow buried depth, and soft surrounding rock. This paper aims to explore the cracking mechanism of lining at the entrance section and propose reinforcement measures to prevent the structural damage accordingly. Site investigation was conducted to demonstrate the cracking characteristics (process, distribution, width, and depth) of tunnel lining. Cracks mainly appeared on the interior lining of left arch-haunch and right side-wall, as well as on the exterior lining of right arch-haunch. The deformation of secondary lining in cracking section was monitored and analyzed to explore the deformation characteristics after the appearance of cracking and installation of temporary supporting. Then, a three-dimensional finite difference numerical model based on the actual terrain was built to analyze the spatial mechanical characteristics of the entrance section. A deformation analysis model including four zones of the surrounding rock was used to analyze the cracking mechanism of asymmetrically-loaded tunnel with inclined weak structural plane. Finally, ground reinforcement measures and reversed loading to control deformation of bedded rock mass and tunnel structures are proposed. Investigating the cracking case of the tunnel has significance to the excavation of entrance section in relevant engineering.

Construction Stability Analysis of the Portal Section of Georgia’s E60 Highway Tunnel Based on Numerical Analysis

Combined with the construction of the No. 6 tunnel of the Khevi-Ubisa-Shorapani- Argveta section of Georgia’s E60 highway, the Midas GTSNX software was used to simulate the stability of the tunnel portal section during full-face construction. This paper analyzes the characteristics of displacement and stress variation of the tunnel portal slope during the whole section construction, the deformation law of surrounding rock during the whole section excavation, the deformation law of the initial support and final lining structure of the tunnel. The results based on the numerical simulation analysis show that when the entrance section of Georgia Tunnel No. 6 adopts full-face construction, the displacement of the supporting structure and the rock mass at the 5 m in front of the tunnel entrance changes greatly. Therefore, it is recommended to complete the invert construction of the tunnel before construction to ensure the safety of the tunnel entrance section; As for the entrance section as a whole, during the full-section construction process, the side slope of the entrance, the surrounding rock of the tunnel, and the supporting structure are all in a relatively stable state. Therefore, the full-section excavation of the No. 6 tunnel entrance section is safe and feasible.

Study on Stability of Surrounding Rock of Mechanized Construction in Tunnel Entrance Section

With the development of tunnel construction technology and mechanical equipment, the mechanized drilling and blasting construction of mountain tunnels has gradually developed, but there are still certain problems in the mechanized tunnel entry. Relying on a tunnel project in Yunnan, this article uses FLAC3D software to study the stability of surrounding rock under the condition of mechanized large-section construction of shallow buried section of the tunnel entrance. When the shallow buried section of the cave entrance is constructed by the micro-step method, the surrounding rock displacement and plastic zone changes of the surrounding rock before and after the use of different cyclic footage and the tunnel face reinforcement when the tunnel face is used are compared and analyzed. The results of the study show that when the tunnel face is not reinforced, in order to ensure the safety of construction, the mechanized excavation cycle footage of the tunnel entrance section should be controlled within 1.2m, and the overlap length of the leading pipe shed should be greater than 5m; if the circulation is to be increased for footage, the tunnel face must be reinforced. Under the condition that the tunnel face is reinforced with glass fiber anchors with a length of 10m and a pitch of 1.5m, the cycle footage can be increased to 1.8m at most.

Dynamic Response of the Entrance Structure of an Elliptical Mountain Tunnel under the Action of SH Waves

Generally, the surrounding rock at the entrance of a mountain tunnel is loose, and the entrance has more slopes due to topography, which causes the tunnel entrance section to be easily destroyed under an earthquake. Based on the established slope model with a single free surface, this paper adopted the elastic wave theory to derive the analytical solution of the strain at the entrance of the mountain tunnel when the SH wave is incident perpendicularly to the bottom of the tunnel; besides, the factors affecting strain were also analyzed. The tangential strain curve at each point of the entrance section takes the centre of the elliptical tunnel as the centre of symmetry, forming symmetry between the left and right sides and mirror symmetry between the top and bottom sides. Then, large‐scale shaking table model experiments were conducted to model the actual working conditions, and the correctness of the analytical solution was verified. The research can provide a theoretical reference for the seismic design of the entrance section of the high‐speed railway tunnel and greatly improve the understanding of its seismic response.

Dynamic characteristics of external luminance of highway tunnel in cold area

The external luminance of highway tunnels in cold areas is a key parameter for the lighting design of the tunnel entrance section. Due to the influence of the tunnel portal form, tunnel orientation, solar radiation intensity and solar irradiation angle, the external luminance of the tunnel varies with different seasons and different times. At present, there are relatively few studies on the time-varying characteristics of the external luminance of highway tunnels in cold areas. Relying on the Wunvfeng extra-long tunnel, combined with different tunnel opening orientations, the changes in the luminance of the tunnel exterior with time under several typical weather conditions are analyzed. The dynamic characteristics of the external luminance outside the tunnel in the cold area was obtained, which provide more detailed and reliable data for tunnel design. It has reference value for the lighting design and operation control of the entrance section of the tunnel and the design of light reduction outside the tunnel.

Analysis and Design Optimization of Collapse Characteristics of Taojiakuang Tunnel Entrance Section

As a key risk source for tunnel engineering, the entrance section of tunnel is extremely easy to collapse. By analyzing the collapse of the entrance section of Taojiakuang Tunnel, the deformation characteristics before the tunnel collapsed were obtained. From the aspects of construction method and advanced support, three kinds of working conditions were considered to optimize the original design. From the perspective of safety and economy, the original advanced support design is unreasonable, and the conversion of the center cross diagram method to the center diagram method is not appropriate. For construction of tunnel entrances in weak broken rock, it is necessary to use the appropriate excavation method. When changing construction method, it is necessary to carry out sufficient demonstration and then re-construction to prevent the initial deformation of the surrounding rock from being too large and causing the tunnel to collapse. When encountering a weak broken zone, especially a rock formation boundary, it is necessary to increase the length of the advance support. The study provides a technical reference for similar projects.

Analysis of Excavation Method and Transformation of Construction Method for Highway Tunnel

The geological conditions of tunnel entrance section are complex, and the hazards of landslide and collapse are easy to occur, which makes the selection of construction methods of tunnel entrance section particularly important before tunnel construction. Therefore, it is of great significance to study the transformation of construction methods between tunnel body section and tunnel entrance section for the safety construction of tunnel entrance section. Taking a tunnel of Meida Expressway as an example, the geological characteristics of the tunnel body and the tunnel entrance section of Meida Expressway are analyzed. Based on the comprehensive consideration of the construction period, safety and advantages and disadvantages of the construction method, the CD method is adopted to construct the tunnel outlet section. Through numerical simulation of tunnel body and outlet section, it is concluded that CD method is superior to bench method in tunnel body section, and can ensure construction safety; and the steps of conversion from bench method to CD method are summarized. Finally, through monitoring and measuring the surrounding rock and surface deformation near transition section, it is concluded that the maximum cumulative deformation at vault top is 78.6 mm, and the maximum cumulative deformation at surface is 94.6 mm, which meets the requirements of specifications and ensures the safety of the tunnel entrance. Therefore, reasonable transformation of tunnel construction method can ensure construction safety, at the same time, it can also speed up construction progress and save funds.

Experimental Study on the Ratio of Similar Materials in Weak Surrounding Rock Based on Orthogonal Design

In the aspect of stability analysis of tunneling engineering, geomechanical model test is an important research method. A similar material is the prerequisite for the success of geomechanical model test. In the field of major engineering applications, a variety of similar materials are prepared for different geological conditions of surrounding rock and applied in some major engineering. With the use of standard sand, fine sand, and silt clay as materials, similar materials for weak surrounding rock were developed. Based on the orthogonal design method, through the direct shear test, the range analysis and variance analysis of various factors affecting the physical and mechanical parameters of weak surrounding rock are carried out. The results show similar material can meet the requirements in weak surrounding rock. Standard sand is the key factor that influences the internal friction angle of similar materials, and silt clay is the key factor affecting the cohesion of similar materials. Similar materials can meet the elastic modulus and severe requirements of the weak surrounding rock and can be used for the weak surrounding rock engineering. The new type of similar material configuration is widely used in shallow buried tunnel entrance section and urban shallow buried excavation engineering, in addition to tunnel engineering in loess stratum, and the problems of engineering design and construction are solved through geomechanical model test.

Structural Safety Assessment of Existing Multiarch Tunnel: A Case Study

Structural health assessment is one of the key activities in maintaining the performance of a tunnel during its service life. Due to the development of modern detection technology, comprehensive structural health assessment system is being established for operating tunnels. To evaluate the actual operational state of Shitigou tunnel, overall detection of the liner crack, tunnel seepage, and liner void was conducted by employing the modern detection technology, such as crack width monitoring technology, concrete strength monitoring technology, and electromagnetic wave nondestructive monitoring technology. Through the statistical analysis of the detection results, the distribution characteristic, development law, and damage grade of structural defects were obtained. Tunnel liner cracks are mainly located on the middle wall; serious water leakage is encountered on the side wall, middle wall, and vault; the strength of foundation and liner structure of left tunnel does not meet the design requirement; the liner voids are mostly located at the tunnel entrance section, especially, on the tunnel vault; and the proportion of influence factors of structural defects should be considered. The research results presented for this study can serve as references for effective design and health assessment of existing multiarch tunnel projects.

Seismic Analysis of the Entrance Section of a Nuclear Power Intake Tunnel

For a nuclear power intake tunnel project, large-scale three-dimensional finite difference model is established by Flac3D to simulate the seismic response regularity of the entrance section of tunnel under the action of seismic waves schedule with the nonlinear dynamic analysis method. Through the input of the site seismic wave, the structure response characteristics of the tunnel entrance and slope are explored and duration curve of tunnel hole lining force under seismic waves action and tunnel lining figure can be obtained. The analysis results show that the anti-seismic weak parts of the tunnel entrance is at the location of tunnel spandrel and the sidewall. The analysis method and conclusions can be for reference in the seismic design of similar nuclear power intake tunnel project.