Tunnel Cross Section Research Articles

Saving lives in a road tunnel using transformable elements restricting the propagation of fire products

The paper considers various scenarios of fire development in road tunnels. The dynamics of combustion products propagation is studied by taking into account the fire strength, tunnel geometry and layout, and aerodynamics of the ventilation flow. The impact of strong fires on the sustainability and proper operation of ventilation systems is demonstrated, and different types of numerical models are considered with the FDS software environment. Theoretical and numerical experiments have demonstrated that strong fires in tunnels can induce dynamic pressures greater than the static pressures of the tunnel fans. The latter can change the direction of movement of ventilation flows in the tunnels with an inclination of 3% or more when the seat of fire is at a hypsometrical height lower than the air supply portal, thus drastically impairing the self-evacuation capability of people in the disaster zone. It was demonstrated that one of the most reliable ways to save lives in case of fire is to limit the spread of flue gases to prolong the time for evacuation. The paper proposes a transformable flexible system to save lives, which artificially increases the aerodynamic resistance of tunnels to prevent the propagation of harmful combustion products on the people’s evacuation route. By considering the fire development scenarios in horizontal and inclined tunnels, the dynamics of the spread of the fire damaging factors when ventilation system is no longer operable and the only solution is the use of the flexible system is examined. The results of modeling evidence that by closing 50% of the tunnel cross-section with a flexible system it is possible to obtain important positive results in reducing the spread of combustion products and saving lives. The use of the proposed system reduces the intensity of the spread of fire hazards and will definitely help the people in the disaster zone. The analysis carried out clearly shows its necessity and that the comprehensive study of fires and generalization of study results will be useful in adequate planning and implementing future measures to prevent and reduce their harmful effects. Following the above-mentioned, a detailed description, analysis and development of a clear algorithm of action of fire cases, and communicating the results to rescuers, tunnel service personnel and the general public are needed.

A review of research into aerodynamic concepts for high speed trains in tunnels and open air and the air-tightness requirements for passenger comfort

India will soon have its first line with trains operating at internationally defined standards of high speed (exceeding 250 km/h). On the MAHSR (Mumbai-Ahmedabad High Speed Railway) corridor modern high speed trains will routinely operate at speeds as high as 200 mph (320 km/h). At high speed, trains are capable of generating significant aerodynamic effects including wind gusts and air pressure changes, which makes it necessary to address HSTs’ aerodynamics during the planning stage of high-speed rail (HSR) lines. The dynamic pressure tightness in train cars is also an important factor in the design of future railway tunnels, together with the medical health criterion and pressure comfort criteria. With increasing speed, the requirements of pressure tightness increases, which are explained and illustrated in this study. The current study is based on prior work done in the field of aerodynamic effects of HSTs, international standards, and design practice followed in existing HSR projects. Effort has been made to bring various studies in one place for ready reference. Parameters such as pressure comfort, optimized distance between center of track, wayside structural design, and tunnel cross-section requirements are explained. Based on the study and established relation by different authors, the pressure difference calculation is done for the MAHSR project for different scenarios, and passenger comfort was deduced. In this study, three major aspects of the aerodynamic pressure effect on the rolling stock and surroundings are examined, and each aspect is discussed distinctly: (1) open-air considerations: pressure effect on wayside structures, (2) open-air considerations: two trains crossing in the open field, and (3) open-air considerations: tunnel phenomenon: pressure wave effects on trains inside tunnels. The present study and a substantial portion of the existing knowledge base can be extrapolated for use in the future guidelines in India. This study examine the resultant pressures on wayside structures, the resultant pressures on adjacent trains, and pressure wave effects in tunnels (associated analyses were performed to determine the appropriate cross-sectional area of the tunnels), respectively. It includes basic aerodynamic concepts, influencing factors, measurement and calculation of pressure between trains, known and potential impacts, mitigations, standards, conclusions, and recommendations.

Automatic extraction of tunnel centerline and cross-sections from 3D point clouds

The accurate extraction of tunnel centerline and tunnel cross-section plays a vital role in many tunnel deformation monitoring projects. To address this issue, An automatic data extraction method for a tunnel centerline and cross-section is proposed based on the three-dimensional laser scanning data. A k-dimensional tree index is first constructed based on the horizontal projection of the tunnel point clouds, and then a series of seed points is selected as the center of several neighborhood point sets with different radii; the difference set region, which will be used to calculate the tunnel horizontal centerline point based on the convex hull operation, is obtained. Then, according to the horizontal centerline, the cross-section of the tunnel point clouds is extracted and fitted to obtain the tunnel cross-section parameters and three-dimensional centerline. Based on the design values of the three-dimensional centerline and tunnel radius, the overall model of the tunnel can be constructed and applied to the visual analysis of tunnel deformation. The experimental results show that the proposed method can accurately obtain the tunnel centerline and cross-section parameters, with a minimal 0.011 cm error for the extraction of the horizontal centerline. The proposed tunnel model could simulate the undulation of the tunnel surface well and provide reference values for similar cases.

Investigation of the emplacement dry density of granulated bentonite mixtures using dielectric, mass-balance and actively heated fiber-optic distributed temperature sensing methods

Granulated bentonite mixture (GBM) is considered to be one of the key elements of the engineered barrier system in the Swiss concept for disposal of spent fuel/vitrified high-level waste. To demonstrate the full-scale emplacement of GBM using a prototype backfilling machine consisting of five screw feeders, an 8-m-long mock-up tunnel in a warehouse and a 50-m-long tunnel in the Mont Terri rock laboratory were backfilled. To ensure the successful emplacement of the GBM in these tests, attempts were made to quantify the dry density of the GBM using conventional mass-balance averaging as well as tools based on dielectric and heated fiber-optic methods. In the mock-up test, the dry density was measured using a set of dielectric tools installed through the tunnel wall. Heterogeneity over the tunnel cross-section was captured, with a general trend towards higher dry density near the screw feeders and lower values near the tunnel wall and crown areas. The in-situ tunnel backfilling in the Mont Terri rock laboratory was performed in twelve steps and the section-wise average dry densities along the tunnel showed a longitudinal variation. Nonetheless, both mock-up and in-situ backfilling tests showed that the overall average dry density exceeded the target value of 1,450 kg/m3. The fiber-optic method involved actively heating the fiber-optic cable installed near the GBM-shotcrete interface at the crown of the tunnel. The GBM dry density profile along the cable was estimated based on the temperature responses. The estimated dry density near the tunnel crown indicated longitudinal variations and was generally lower, which was consistent with the results of the mock-up test. The three methods provided the GBM dry density at different locations with different spatial resolutions. However, the combined results demonstrated that GBM backfilling met engineering and safety-relevant requirements.

Research on the Stability of Shallow-Buried Large Cross-Section Tunnel by Construction Method Conversion

The blind and random use of the combined construction method may have a great impact on tunnel stability. To determine the influence of construction method conversion on tunnel deformation and the reasonable conversion condition, a numerical model is established to simulate the construction method transforms from central diaphragm method to the benching tunneling method based on Jiaoweiqin Tunnel. The conversion condition is determined based on the results of tunnel geological prediction and in-site monitoring, and the temporary two-bench tunneling method is adopted to ensure the success of construction method conversion. Besides, the parameter analysis is done to analyze the influence of mechanical properties of surrounding rock mass and bench length on tunnel stability. Research results indicate that the construction safety should be evaluated before construction method conversion is carried out by analyzing the design blueprint, tunnel geological prediction results, geological survey reports, rock mass conditions in front of tunnel face, in-site monitoring data, and numerical simulation results. Meanwhile, the construction method conversion can be carried out in the order of central diaphragm method, two-bench tunneling method, and bench tunneling method. Parameter analysis results reveal that the deformation of primary support decreases in a negative exponential form with the increase in elasticity modulus and increases approximately linearly with the increase in bench length. For shallow buried and large cross-section tunnels, the tunnel deformation is in a small state when the elastic modulus of rock mass reaches a certain value. The construction method conversion can be carried out when the rock mass has a certain stability, and the length of construction method conversion should be small to ensure construction safety.

Influence of Foundation Pit Excavation on Tunnels at Different Locations

To evaluate the tunnel deformation law and soil stress distribution between foundation pit excavation and tunnel in different locations, numerical analyses using the hypoplastic model are conducted based on reported centrifuge model tests. Two cases are designed to investigate the effects of the foundation pit excavation on the deformation of existing tunnels. In case C, an existing tunnel is directly located underneath the foundation pit; in case S, the tunnel is located at one side of the foundation pit. Three-dimensional tunnel deformation mechanisms along the tunnel axis are observed through the variation of stresses change in the soil circumambient tunnel. It is found that compared with case C, there are minor Earth pressure changes in case S. The different Earth pressure changes around the tunnel lead to different modes of tunnel deformation. The maximum additional tunnel bending strain appears at the crown and invert, while the minimum value appears at the spring lines in case C. In case S, the maximum values appear in the right shoulder and left knee, while the minimum values appear on the left shoulder and right knee. The additional tunnel bending strain and stress reduction at different tunnel cross sections in case S is much smaller than those in case C. In case C, after the excavation, lateral Earth pressure coefficient changes ΔKxz and ΔKyz rise to 70% and 150%, respectively, of their initial value at shoulders, while little changes can be found at spring lines. However, in case S, the maximum absolute value of both ΔKxz/(Kxz)0 and (ΔKyz/(Kyz)0) is no more than 10%.

Lawsone and Indigo-Loaded Sepiolite Nanofibers for Hair Coloring with Sustained Release

Natural clay materials have been present in people’s lives for centuries, from pottery and house construction to food processing and cosmetics, proving their utility and safety for human use. Recent developments in tubule and fiber clay systems demonstrated their efficacy at carrying chemical loads in their inner tunnels of nanometer diameters. We exploited nanofibrous sepiolite possessing 0.4 × 1.1 nm cross-sectional tunnels for loading with dyes and drugs followed by their spontaneous assembly on human hair from an aqueous suspension to form a 1–2 μm-thick coating with a concentration near cuticle edges. This bio-friendly process avoids any chemical reactions on the hair and results in a simple and safe coating for coloring or topical medical treatment. It is especially valuable for the application of water-insoluble dyes, such as lawsone and indigo. We successfully loaded lawsone and indigo into the sepiolite and applied the composite onto hair, creating stable brown and blue coatings. Up to 80% of the initial hair color is preserved after six shampoo washes. Coatings of the dye-sepiolite composite on permed hair reduced the surface roughness, enhancing the hair volume and color performance. We also loaded sepiolite with drugs (e.g., antilice permethrin or ivermectin), which could be used for topical hair and scalp treatments with sustained release.

A New Design Method of Shield Tunnel Based on the Concept of Minimum Bending Moment

As the soil-resistance coefficient in a soft soil area is small, overlarge bending moment may cause exceeding transverse deformation for the shield tunnel and cause structural diseases and waterproof failure at the longitudinal segment joints. Hence, a new idea of cross-section design for a minimum bending moment shield tunnel was proposed. This article has first put forward the concept of a zero bending moment shield tunnel. Then, based on rational and feasible hypotheses, a structural mechanical model and an analytical expression of axis for the cross-section of the zero bending moment shield tunnel was obtained, and computational formulas of internal force and key geometry parameters were given. Based on the case of the metro shield tunnel constructed in the Shanghai soft soil area, the zero bending moment shield tunnel was designed, and its characteristics were analyzed. Considering only one cross-section of shield tunnel can be adopted in one metro line, the design method and procedure of the minimum bending moment shield tunnel were put forward. Finally, taking one of the Shanghai metro lines as an example, a cross-section of a minimum bending moment shield tunnel was designed, and its bending moment was compared with the bending moment of a circular section shield tunnel, which had the same horizontal diameter. The comparison revealed that the cross-section of the minimum bending moment can significantly reduce the bending moment of shield tunnel.

A Simplified Method for Predicting Tunneling-Induced Ground Movement considering Nonuniform Deformation Boundary

Stochastic medium (SM) theory is a practical method in ground settlement prediction, while its nonintegrable double integral form makes the solution process complicated. A simplified analytical solution based on the SM theory is developed to predict the ground movement in tunneling excavation. With the simplified solution, the ground movement for single tunnel and twin tunnels could be predicted based on the gap parameter G and influence angle β. A feasible approach is developed to estimate these two parameters using the maximum ground settlement Smax and tunnel design parameters, including tunnel depth H and diameter R. The proposed approach can be used to predict the ground movement curve for both circular and noncircular cross section tunnels. To validate its accuracy, the results predicted by the simplified procedure are compared with those obtained by the SM theory and measured in situ. The comparisons show that the current results agree well with those obtained by the SM theory and measured in situ. The comparison of five tunnels in literature illustrates that the simplified method can provide a more reasonable prediction for the ground movement induced by tunneling.

Dynamic Response Analysis of Super Shallow‐Buried Rectangular Tunnel

Relying on the project of the open‐cut municipal tunnel undercrossing Ankang Freight V yard, the train dynamic response and seismic response of ultrashallow‐buried rectangular tunnel of the lower interchange are studied, respectively, by combining the method of field measurement and numerical simulation. The results show that under the action of train vibration load, the dynamic stress response of the top plate midspan and the upper end of the side wall of the tunnel cross section directly below the rail is the most significant, and the dynamic stress response of the bottom plate is the smallest. Under the rare earthquake, the tunnel structure has large transverse deformation, in which the transverse displacement of the tunnel roof is the largest. At the same time, there is a large stress concentration at the variable section of the tunnel.

The First Japanese Stilling Basin Constructed in the form of Extremely Large Cross-Sectional Tunnel

The First Japanese Stilling Basin Constructed in the form of Extremely Large Cross-Sectional Tunnel

Method for shield tunnel cross-section curve reconstruction based on FBG sensors and neural network

To improve the accuracy of reconstructing morphology in shield tunnel monitoring by fiber-optic Bragg grating (FBG) sensors, a Transformer network-based optimized tunnel cross-sectional curve reconstruction method is proposed to solve the problem of low reconstruction accuracy due to the cumulative error of discrete curvature points. In this research, the optimization method uses all interpolation points as initial points to minimize the cumulative error in fitting the curve with discrete curvature points. Simulation model experiments of the shield tunnel were carried out to verify the accuracy of the optimization method in reconstructing the tunnel section curve. The results show that the shield tunnel simulation model experiments, more accurate tunnel section reconstruction curves were obtained using this optimization method, increasing reconstruction accuracy by 27.3424%.

Effect of Beam Angle of the Transmitting Antenna on Radio Wave Coverage in the Region Containing Tunnel Entrance

Radio wave coverage in open-confined mixed space along the railway is studied in this paper. The space along the railway can be classified into three kinds of spaces, that are, open space, confined space and the open-confined mixed space. The open-confined mixed space locates between the open space and confined space. In order to reveal the radio wave coverage mechanism in the open-confined mixed space and find out the important influence factors, the influence of antenna gain, antenna position, tunnel cross-section shape, and beam angle on the radio wave coverage in the open-confined mixed space are studied. Considering the complexity of environment, the radio wave coverage is modeled by finite difference time domain method. The simulation results show that the radio wave coverage is sensitive to the beam angle of transmitting antenna. And the variation law of radio wave coverage with the beam angle shows a certain correlation with the transmitting antenna position and tunnel cross-section shape.

Analysis of the Causes of the Collapse of a Deep-Buried Large Cross-Section of Loess Tunnel and Evaluation of Treatment Measures

To address the problem of the collapse of the roof of the Bailuyuan tunnel during construction, the causes of collapse were analyzed, targeted treatment measures were proposed, and the effects of the treatment measures were evaluated through on-site monitoring and three-dimensional numerical simulations. The results showed that the particular characteristics of loess and the synergy of groundwater were the internal causes of the tunnel’s collapse as well as, to a certain extent, atmospheric precipitation. Therefore, the combination of multiple factors contributed to the tunnel’s collapse. Untimely monitoring and measurement, as well as the low initial support parameters, reflect a lack of human understanding of the collapse. Based on the analysis of the causes of the collapse, comprehensive treatment measures for inside and outside the tunnel are proposed, which are shown to be effective and to be capable of preventing the occurrence of further collapses. After the collapse treatment, the measured maximum settlement of the tunnel vault was 65.1 mm, the maximum horizontal convergence was 25 mm, the maximum surrounding rock pressure was 0.56 MPa, and the maximum stress on the steel arch frame was 54.34 MPa. Compared with the original design plan, the vertical stress, horizontal stress, and shear stress of the surrounding rock obtained from numerical simulation after the collapse treatment were greatly reduced, the reduction rate at the vault reached 50%, and the safety factors of the initial support positions after treatment met the specification requirements. The research results can provide engineering guidance for the design and construction of large-section tunnels crossing deep-loess strata, and they are of important engineering significance.

Investigating the Deformation and Failure Mechanism of a Submarine Tunnel with Flexible Joints Subjected to Strike-Slip Faults

Knowledge from historical earthquake events indicates that a submarine tunnel crossing active strike-slip faults is prone to be damaged in an earthquake. Previous studies have demonstrated that the flexible joints are an effective measure for a submarine tunnel crossing a strike-slip fault. The background project of this paper is the second submarine tunnel of Jiaozhou bay. In this work, model tests and numerical simulations are conducted to investigate the deformation and failure mechanism of a submarine tunnel with flexible joints under a strike-slip fault dislocation. The influence of strike-slip faults on a tunnel with flexible joints has been investigated by examining the deformation of rock mass surface, analyzing lining stains, and crack propagation from model tests. Numerical simulations are conducted to study the effects of the design parameters of a tunnel with flexible joints on the mechanical response of the lining. The results showed that the ‘articulated design’ measure can improve the ability of the tunnel to resist the strike-slip faults. In terms of the mechanism of design parameters of a tunnel with flexible joints, this paper finds that increasing the lining thickness, decreasing the lining segment length, and decreasing the tunnel diameter to a reasonable extent could effectively improve the performance of this faulting resistance measure for a tunnel under the strike-slip fault zone dislocation. Compared with the horseshoe tunnel cross-section, the circular tunnel cross-section can improve the ability of the faulting resistance of a tunnel with flexible joints, while the optimal angle of the tunnel crossing the fault zone is 90º. It is concluded that the wider fault zone, smaller flexible joint width, and less stiffness of the flexible joint could make lining safer under a strike-slip fault dislocation. The above research results can serve as a necessary theoretical reference and technical support for the design of reinforcement measures for a submarine tunnel with flexible joints under strike-slip fault dislocation.

Face stability of EPB shield tunnels in multilayered ground with soft sand lying on hard rock considering dynamic excavation process: A DEM study

This paper aims at studying the face stability of earth pressure balanced (EPB) shield tunnels in multilayered ground with soft sand lying on hard rock considering dynamic excavation process. The analysis was performed using three dimensional discrete element method (DEM). The present work has two advantages: (1) it reveals the influence of soil disturbance induced by dynamic cutting process on tunnel stability in multilayered ground; (2) it reveals the influence of soil retaining provided by cutterhead panel on tunnel face stability in multilayered ground. Results show that tunnel face collapse undergoes two stages. The underlying hard rock restricts the movement of overlying soft soil, and face failure happens more abruptly with decreasing η (η = a/D. a = height of soft sand within tunnel cross section; D = tunnel diameter). The normalized limit support pressure pf/γD (pf = limit support pressure; γ = soil unit weight) obtained from this paper is larger than that of existing research, i.e. existing research underestimate the limit support pressure. The weakening effect of cutterhead dynamic cutting process on face stability is larger than the strengthening effect of cutterhead panel retaining on face stability. The difference generally increases with increasing C/D (C = tunnel cover depth) and η. Partial collapse occurs in multilayered ground with soft sand lying on hard rock. C/D mainly influences the shape of the failure zone, and η mainly determines the size of the failure zone.

Fire behaviors along timber linings affixed to tunnel walls in mines.

Timber linings are applied as primary supports in the tunnel fault and fracture zones of mines. These linings are essential to prevent broken rock from falling during the occurrence of exogenous fires. In this study, experiments and numerical simulations were carried out using a fire dynamics simulator to investigate the flame-spread rate, flame characteristics, smoke movement, and spread process of timber-lining fires under different wind speeds of 0, 0.25, 0.5, and 0.75 m/s. It was found that cross-section flame spreading follows the three-stage sidewall-ceiling-sidewall pattern. Moreover, the average flame-spread rate increases along the vertical flame-spreading direction and decreases when the flame reaches the timber-lining corners. Moreover, the flame lengths underneath the timber-lining ceiling in the x-direction are longer than those in the y-direction. As the wind speed increases, the normalized flame lengths R(f) in the two directions decrease, and the maximum temperature underneath the ceiling decreases. In addition, the maximum temperature in the three tunnel sections of interest is first recorded in the tunnel cross-section in the initial fire stage. Higher wind speeds correspond to farther distances of the maximum-temperature points of the three timber-lining sections from the fire source.

Analysis of deformation control mechanism of prestressed anchor on jointed soft rock in large cross-section tunnel

Analysis of deformation control mechanism of prestressed anchor on jointed soft rock in large cross-section tunnel

Modeling study of cumulative damage effects and safety criterion of surrounding rock under multiple full-face blasting of a large cross-section tunnel

A blast-induced damage model integrating the tensile damage model with the Drucker-Prager yield condition is established. Based on the excavation of a large cross-section tunnel in China, the damage process of surrounding rock under multiple full-face blasting is simulated by the established rock damage model embedded into the LS-DYNA computer code through its user subroutines and a cumulative damage formulation in the LS-DYNA. The simulation results are well verified against field test data. The results show that the maximum damage depth of surrounding rock is determined by the blasting of the excavated cross-sections closest to the surrounding rock. Both the maximum damage depth and the maximum peak particle velocity (PPV) occur in the middle of the tunnel invert. Based on the defined damage threshold D cr and the modeled maximum damage depth of surrounding rock, the influence of initiation sequence on the critical PPV for rock damage is studied, and a critical PPV associated with rock damage is proposed for tunnel blasting excavation.

Study on Mutual Feedback Mechanism and Stability Control of Toppling Slope and Tunnels with High Excavation Rate

During the construction of large-scale hydropower projects in deep mountain gorge areas of the Western China, the difficulties, such as uncontrollable large deformation, great deformation caused by small disturbance, are often encountered in the process of implementation. In particular, due to the limitation of topography, geological conditions and the layout of structures, the slope and dense tunnel group with large section need to be excavated simultaneously in the toppling rock mass. The feedback action mechanism between slope and tunnel excavation is complicated and the deformation control of toppling rock is difficult, which leads to great challenges to engineering construction. In MW hydropower project in west of China, the intake slope, the spillway channel slope, four headrace tunnels, and the sand flushing tunnel, as well as the construction traffic tunnel are arranged in Huishi Ridge on the left bank, where two high slopes and six lager cross-section tunnels are simultaneously excavated and the excavation rate in the toppling deformation rock mass is over 50%, moreover, the lateral coverage thickness of tunnel body is less than the diameter of the tunnel, which leads to the great difficulty of stability control. The excavation stability and safe of the thin mountain ridge is the vital issue to the success of the whole project. Based on the study of the physical and mechanical parameters of toppling rock mass of MW HPP, the mutual feedback mechanism of toppling slope and tunnel group is revealed, an excavation method involving horizontal partitioning, vertical layering, reserving rock plug and reasonable skipping warehouse is proposed. Monitoring results shows that the slope and surrounding rock of the tunnels are stable during the operation period. The research of this paper based on the MW HPP can provide reference for other similar projects.