Tunnel Safety Research Articles

Study on spilled liquid from a continuous leakage in sloped tunnels

The study focuses on the behaviors of spilled liquid from a continuously leaked tank in sloped tunnels. Spillage width and area, which impact the potential heat release rates in case of fire, are investigated under different tunnel slopes and leakage flow rates by numerical simulations using interFoam based on the VOF method in the OpenFOAM toolbox following the validation. The simulation results show that the spillage width initially decreases rapidly and then slowly as the tunnel slope increases. Other parameters, including road surface roughness, physical properties of liquid and leakage source height, are also considered. Empirical models for predicting the spillage width and area are established considering both tunnel slope and leakage flow rate. The results may provide guidance for tunnel safety design and drainage system design affiliated with a tank leakage inside a tunnel.

Small Pilot Tunnel Advance and Step Reverse Expansion in Super-Large-Section Tunnel Excavation

Collapse of the vault and numerous other safety accidents often occur during the construction process of large-section tunnels. The utilization of a small pilot tunnel and a step reverse expansion construction methodology is proposed based on conventional construction methods to explore safe construction technology. First, a theoretical analysis combined with on-site monitoring parameters was conducted. It showed that the maximum displacement of the tunnel surrounding rock was 0.027 m during the elastic stage and increased to 0.031 m during the strength limit stage. The overall surrounding rock deformation does not have a noticeable impact on tunnel safety. A numerical simulation model of the small pilot tunnel advancement and step reverse expansion method was established. Simulation results showed that the first two excavation steps caused 89.6% of the total overlining strata subsidence, and the use of a small pilot tunnel advancement and step reverse expansion method can enhance the tunnel support. The tunnel surrounding rock was adequately stabilized after using this excavation method and provides the in-situ conditions for expanding the pilot tunnel to the large-section tunnel. The proposed method was adopted in an actual engineering project. It protected the subsequent construction of the main tunnel and decreased construction time, saving construction costs while ensuring safety, reducing construction risks, and improving production efficiency. This research can guide similar tunneling projects.

DEM simulation of rock creep in tunnels using Rate Process Theory

The time-dependent (creep) behaviour of rocks affects the safety and stability of tunnels excavated in weak rocks and at great depths. Several theories have been proposed to simulate the creep deformation in rock; i.e., the progressive time-dependent damage that rocks (or other materials) exhibit under constant stress. However, most of these theories do not capture the accelerating strains associated to tertiary creep and leading to rock failure. In this research, the Rate Process Theory (RPT), combined with the Discrete Element Method (DEM), are used to simulate rock creep deformation in deep tunnels. To do that, two-dimensional (2D) DEM tunnel models are built using particles, with their interactions being simulated by a hybrid mixture of the linear and flat joint contact models. The RPT is incorporated into such models by a user-defined Visual C++ script that modifies their friction coefficients during the DEM simulation, depending on the relative velocity between particles. Numerical results show, for the first time, that the joint RPT-DEM approach is able to reproduce all stages of tunnel convergences associated to rock creep, including tertiary creep; and that it can reproduce the rock damage associated to such creep strains.

Influence of blasting disturbance on dynamic response and safety of deep tunnels

Influence of blasting disturbance on dynamic response and safety of deep tunnels

Safety evaluation of urban underground utility tunnel with the grey clustering method based on the whole life cycle theory

ABSTRACT The construction of urban underground utility tunnel is a complicated process. With the rapid development of urbanization in China, the safety problem of utility tunnel is becoming more and more prominent. To evaluate the safety of utility tunnel, this study proposed an evaluation model based on the whole life cycle theory. Firstly, combining with the characteristics of utility tunnel, the construction period was divided into four phases: preliminary planning, design, construction and operation and maintenance. Through literature analysis and expert investigation method, 26 evaluation indices were selected, and the whole life cycle safety evaluation index system of urban underground utility tunnel was established; Secondly, the entropy weight method was used to determine the weight of each index; Thirdly, in order to evaluate the security of the utility tunnel in the whole life cycle, a grey clustering evaluation model was constructed. Finally, a case study was conducted to explain the application of the proposed model and to verify the validity of the model, the results indicated that the model could provide a new way to evaluate the safety state of the utility tunnel project.

Experimental and numerical research on the influence of steel arch frame corrosion on security of supporting system in subsea tunnel

Subjected to high chloride ion content in subsea, underwater structure will be corroded in different degree in the service environment, which will shorten the durability of the structure. Subsea tunnels are often constructed by drilling and blasting method, and microcracks are inevitable in primary support due to blasting impact. The cracks provide channels for chloride ion, sulfate ion in seawater and oxygen in air, which leads to steel arch frame corrosion in primary support. Corrosion will reduce the bond strength and bearing capacity of the supporting system, thus reducing the service time of the subsea tunnel. Based on Xiang'an subsea tunnel, the effect of steel arch frame corrosion on the supporting system was studied. First, the accelerated corrosion test and push-out test were carried out, the bond-slip degradation constitutive model between corroded I-shaped steel and concrete was proposed based on damage variables. Then, the degradation constitutive model was introduced into ANSYS to simulate the influence of corroded I-shaped steel on the overall mechanical behavior and safety of the subsea tunnel. Results of model indicated that with the increase of corrosion ratio, the internal stress of the I-shaped steel, sprayed concrete and secondary lining increased, and the corresponding safety factors all decreased.

Full-scale testing and numerical modelling of segmental-joint performance with corroded bolt

Water leakage through segmental joints often occurs for shield tunnels built under groundwater. Chloride ions in groundwater can cause the corrosion of steel bolts in segmental joints, reducing the rigidity of the tunnel lining and endanger the operation safety of tunnels. In this paper, the impact of the corrosion of the steel bolt on the structural performance of segmental joint was investigated using six full-scale segmental joint tests and a series of numerical simulation. Both the experimental and numerical results indicate that the segmental-joint performance can be divided into three stages under different loading and corrosion states. The bolt corrosion can reduce the waterproof ability, bending stiffness, and ultimate bearing capacity of the segmental joint. The impact of the bolt corrosion is most significant in the second stage. Furthermore, the bolt corrosion has a larger impact on segmental-joint performance under a positive bending moment than under a negative bending moment, owing to the configuration of the joint. The impact of the bolt corrosion is strongly dependent on the loading state of the tunnel joint and the corrosion ratio of the bolt.

RISK PREDICTION AND DIAGNOSIS OF WATER SEEPAGE IN OPERATIONAL SHIELD TUNNELS BASED ON RANDOM FOREST

Water seepage (WS) is a paramount defect during tunnel operation and directly affects the operational safety of tunnels. Effectively predicting and diagnosing WS are problems that urgently need to be solved. This paper presents a standard and an evaluation index system for WS grades and constructs a sample dataset from monitoring recoreds for demonstration purposes. First, we use bootstrap resampling to build a random forest (RF) seepage risk prediction model. Second, the optimal branch and parameters are selected by the 5-fold cross-validation method to establish the RF prediction training model. Additionally, to illustrate the effectiveness of the method, the operational stage of Wuhan Metro Line 3 in China is taken as a case study. The results conclude that the segment spalling area, crack width, and loss rate of the rebar cross-section have a strong influence on WS. Finally, the test data are predicted, and the prediction result error index is calculated. Compared with the predictions of some traditional machine learning methods, such as support vector machines and artificial neural networks, RF prediction has the highest accuracy and is the closest to the true value, which demonstrates the accuracy of the model and its application potential.

Численное моделирование пожара в автодорожном тоннеле. Выбор расчетной сетки

Рассматривается вопрос выбора расчетной сетки при моделировании пожара в тоннеле с помощью полевого метода и проводится оценка возможного влияния размеров ячеек сетки, а также граничного условия постоянства давления на результаты расчета. Выполнено моделирование пожара для четырех размеров расчетной сетки. Обоснована возможность применения наиболее грубой из используемых сеток с точки зрения инженерных расчетов, в том числе с оговоркой относительно постановки граничного условия. The issue of fire safety of road tunnels is currently an urgent task. Road tunnels are usually not standard typical facilities, but the unique structures. Therefore, it is necessary to study the influence of various parameters on the development of fire in order to take into account the characteristics of a particular object and make decisions on its effective fire protection. Implementation of field tests in this case is expensive and time-consuming. In this regard, numerical modeling is one of the most effective methods of such research. Field models are the most common and currently used for numerical calculations. These models are based on the numerical solution of the system of conservation equations for small control volumes of the calculation grid. This paper examines the issues of selection the calculation grid when modeling a fire in tunnels using the field method is considered and the possible influence of the size of the grid cells is estimated. The mathematical model used in this work is based on a set of differential equations of hydrodynamics, heat transfer, as well as the equation of conservation of the masses of components. Four computational grids were selected for a horizontal (without slope) model tunnel to determine the optimal cell size. As a result of conducted calculations it was established the following: the size of calculated grid is not fundamental for the initial stage of the fire; the use of smaller grid may be preferable at further development of fire, accompanied by increase of combustion capacity to the maximum; the maximum temperature values, especially in the far sections, are obtained on the coarsest grid. The use of such a grid for estimated engineering calculations can be allowed.

Influence of tectonic stress on the structural safety of mountain tunnel under the strike-slip faulting

The distribution of tectonic stress around the fault is very complicated, which may affect tunnel behavior under the dislocation of fault. Therefore, this paper aims to investigate the influence of tectonic stress on the structural safety of mountain tunnel under the strike-slip faulting. Variable lateral stress coefficients from 0.3 to 3.0 are considered via a series of three-dimensional finite element models. Safety assessment indices based on the overall lining damage in compression/tension and the ovalization of the tunnel cross-section are used to evaluate the damage of tunnel structure subjected to fault movement quantitatively. The results show that the cross-sectional damage and ovalization of tunnel lining mainly distribute around the fault plane, and the tectonic stress plays a crucial role in the tunnel’s response to strike-slip faulting. With the increasing lateral pressure coefficient, both the value and distribution scope of the cross-sectional compressive damage in the longitudinal direction increase; while the value and distribution of cross-sectional tensile damage decrease when the coefficient is larger than 1.0, and its damage is slighter than compressive damage. The cross-sectional ovalization of the tunnel is also significantly affected by the lateral pressure coefficient, especially when the coefficient is larger than 1.0.

Virtual simulation technology for the design of the interior environment in an ultralong tunnel

Long-term driving and monotonous internal environment increase the safety hazard of driving in ultralong tunnels. Therefore, methods to alleviate the driving fatigue caused by long-term driving are of great significance to promote the safety of ultralong tunnel driving. Firstly, the environmental factors influencing driving fatigue of ultralong tunnel were analyzed, which can be divided into light environment and interior environment. Then, a driving fatigue detection system based on virtual reality technology was built which can integrate different hardware and software. Finally, based on Laoying ultralong tunnel in Yunnan Province, tunnel models under different environments were established, fatigue relief zone was set up and simulation tests were carried out. The experimental results show that setting a fatigue relief zone in the middle of the long tunnel, in the form of the combination of a “blue sky and white clouds” pattern on the inner wall and a high-color-temperature light source, can make drivers more attentive and effectively alleviate driving fatigue. This paper proposes a virtual simulation technology for fatigue relief zone settings; this technology can be adopted for other similar projects.

Investigations of variations in physical and mechanical properties of granite, sandstone, and marble after temperature and acid solution treatments

Natural rock is a very common building material, and its stability plays an important role in the safety and durability of tunnels, rock slopes, and other projects. However, tunnels and other underground projects often face the threat of disasters such as fires, and during their service, the surrounding rocks are also subject to erosion by acidic groundwater. Therefore, it is of great engineering significance to study the damage of the surrounding rocks under the threat of fire and acid groundwater. In this study, the variations in chromatic aberration, mass, P-wave velocity, porosity, thermal conductivity, and tensile strength of granite, sandstone, and marble induced by high temperature and chemical erosion are investigated from room temperature to 1000 °C. The results show that the rock materials exhibit different degrees of variation in physical and mechanical properties under the effect of high temperatures and acidic solution corrosion. Then, according to the variation of physical and mechanical properties, the formation mechanism of damage is discussed and the damage process verified by the deterioration of mechanical properties. For rocks heated to different temperatures and eroded by acid solution, the main reason for damage is the increase of cracks which destroy the structure and weaken the bonding between particles.

Investigating the Importance of Tunnel Lighting and its Role in Reducing Traffic Accidents

Traffic safety is a major concern worldwide. Road accidents are the ninth leading cause of death in the world. Tunnel accidents are less common than road accidents. However, the severity of the accidents is more severe. One of the key factors in preventing accidents in road tunnels is proper lighting system. Failure to pay attention to this issue causes the phenomenon of black hole when approaching the tunnel, visual mismatch inside the tunnel and the phenomenon of glowing hole when leaving the tunnel. The creation of these factors has increased the risk potential at the entrance and exit of the tunnel up to 4 times the middle area of the tunnel. At the entrance to the tunnel, the reflection of sunlight from the surroundings and the lack of sufficient light usually cause some vision problems. It may lead to drivers' eyes not adapting to changing the brightness level at the tunnel entrance, thus increasing the risk of road accidents in this area. The aim of this study was to evaluate the lighting safety in very long road tunnels based on the visual adaptation of drivers in the tunnels. In this paper, first, generalities about tunnel safety are stated and using the CIE88-2004 standard, the required luminosity in the threshold, transition, interior and exit areas of the tunnel is designed. Finally, solutions are proposed to increase the safety of tunnels.

Computer safety analysis and research of electrified subway deep foundation pit excavation

Lanzhou Metro Line 1 is the first Metro Line in Gansu Province. Before the construction of buildings along the line, it is necessary to analyze the safety of the subway tunnel to ensure the safe operation of the subway. The new project, No.23 and No.24 plots of the old plant reconstruction project of Lanshi group (Lanshi ⋅ hobska n District), is close to the Shizi tunnel between the west railway station and the West Railway Station of Lanzhou Urban Rail Transit Line 1 phase I project, The excavation and supporting construction of foundation pit may have an impact on the structural safety of Shizi tunnel between West Railway Station and West Railway Station in the first phase of Rail Transit Line 1. It is particularly important to analyze and study the structural safety of subway tunnel before the construction of this project.

An optical-electrical co-sensing tape for cross-sectional deformation monitoring of shield tunnels

Cross-sectional deformation is a crucial index for evaluating the stability and safety of shield tunnels. Monitoring the cross-sectional deformation has been an important content in assessing the health condition of tunnels. For this reason, an optical-electrical co-sensing tape (OECST) by embedding distributed optical fiber sensor (DOFS) and coaxial cable F-P interferometer sensors (CCFPI) into a high elastic polyurethane tape has been proposed in this paper. It can simultaneously measure the low-strain area of structure with high accuracy by DOFS and large-strain area with relatively lower accuracy by CCFPI. The conceptual and geometric design, fabrication method, and sensing mechanism have been discussed. A laboratory test has also been conducted to validate that the OECST can provide reliable strain measurement. Subsequently, an algorithm has been proposed to measure the cross-sectional deformation of shield tunnels by using OECST strain measurements. The cross-sectional deformation has discontinuous features with large deformation of joints (dislocation, opening, closing, etc.) and small deformation of segments. The former can be obtained by performing geometrical analysis on rough strain measurements of the CCFPI in OECST. The latter can be derived by implementing the strain–displacement conversion on the accurate distributed strain measured by the DOFS-S in OECST. The method has been investigated experimentally. The findings from the study have demonstrated that the proposed OECST can measure the cross-sectional deformation of shield tunnels with a satisfactory accuracy, which can be used to assess the health condition of tunnels.

Critical velocity for preventing thermal backlayering flow in tunnel fire using longitudinal ventilation system: Effect of floor-fire separation distance

To design a reliable longitudinal ventilation system in a roadway tunnel, it is crucial to know the optimum value of the forced airflow velocity which must be applied to minimize hazards to users trapped in the building during a fire. This optimal value known as the critical longitudinal ventilation velocity, is a crucial criterion for tunnel safety when designing ventilation systems. Analysis of the influence of the fire development location from the tunnel floor on the critical velocity has rarely been studied, although this situation really exists due to the difference in vehicle sizes in practice. CFD simulations were performed in this paper to study this scenario and to estimate the critical velocity for a fire developing in different locations relative to the tunnel floor. The results indicate that as the elevation of the fire location increases from the tunnel floor, the critical velocity decreases. A new model involving the separation distance of the fire location on the tunnel floor and relating the critical velocity to the fire heat release rate is proposed. Furthermore, under critical conditions of ventilation velocity, the results show that the elevation of the fire source location from the floor has a significant effect on the maximum smoke temperature rise below the tunnel ceiling.

Study on the Influence of LED Spectrum on the Visual and Nonvisual Effects in the Interior Zone of Tunnels

Judicious use of lamps is of profound significance to improve the internal traffic safety of tunnels. This study evaluated the biological effects of spectrum on human visual and nonvisual under mesopic vision category. According to the difference of human eyes’ response to the visual and nonvisual biological effects of different wavelengths of light radiation, a method of applying the mesopic visual spectral luminous efficiency curve to the assessment of nonvisual biological effects and blue light hazards is proposed. The results show that, in theory, under mesopic vision category, the spectrum with high correlation color temperature (CCT) and high color rendering index (CRI) has higher blue light content Z-value and has greater impact on human nonvisual effects and blue light radiation damage, but it can also provide higher human perception luminance. The visual effect detection experiment of driving in the interior zones of the tunnel is simulated in the laboratory, and the critical flicker frequency and reaction time are taken as physiological indexes. The results show that the spectrum with high CCT and high CRI corresponds to lower critical flicker frequency drop value and faster reaction time, which has a positive effect on improving driving safety. Therefore, this paper suggests that the LED with high CCT and high CRI (CCT = 6500 K, CRI2012 = 95) should be used in the interior zones of the tunnel with relatively short lighting section, and the CCT and CRI should be appropriately reduced in other road environments with long lighting section to reduce the impact of spectrum on nonvisual photobiology, so as to improve road traffic safety.

The Application of the Strength Reduction Shortest Path Method to the Stability Analysis of Shallow Buried Tunnel

To improve the theoretical analysis of surrounding rock stability of shallow buried tunnels. The strength reduction shortest path theory is applied to the stability analysis of shallow buried tunnel surrounding rock, combined with the ultimate equilibrium strength reduction theory. We discussed the influence of the depth and span ratio of tunnel, cohesion, and internal friction angle on the shortest path of the strength reduction, and studied the effects of various factors on shallow buried tunnel safety relationship by using strength reduction factor of safety and the shortest path of the shallow buried tunnel surrounding rock and the grey relational analysis theory. The results show that: in the analysis of shallow buried tunnel in strength reduction, the approximate distribution obeys parabolic between reduction path length and the reduction ratio. When the strength reduction of cohesion is the shortest path the reduction rate is greater than the internal friction angle. The internal friction angle and cohesive force have a great influence on the stability of shallow tunnels under the method of shortest path of strength reduction. Finally, the comprehensive safety factor of shallow buried tunnels calculated by the finite element strength reduction shortest path method is greater than that calculated by the limit equilibrium method.

Modeling of speed in vehicles entering two-way suburban tunnels by Adaptive Neuro Fuzzy Inference System

The behavior of drivers on the roads is elicited from the state of the surrounding environment. The author's research shows that the vehicle starts to decelerate at a certain distance from the tunnel when it is observed, and they have the lowest speed when reaching the beginning of the tunnel. As soon as the tunnel is passed, the vehicle increases speed again in a certain length. The main purpose of this study is to model the speed of vehicles entering suburban tunnels based on the speed changes before entering the tunnel using the neuro-fuzzy network. Then, to validate the designed model, the data of 30 different drivers were used who travel in the same conditions by a Renault Logan vehicle with a manual transmission system. Using the Pearson correlation analysis method, the relationship between the variables of the speed of entrance to tunnel and changes in vehicle speed was investigated. The value of the correlation coefficient is equal to -0.7, which means the strong negative correlation between the two variables. The results show that the neuro-fuzzy network method has the ability to predict speed changes with a high accuracy based on the initial speed of entrance to the tunnel. The results of this study are used to analyze the behavior of drivers in suburban tunnels. Due to the importance of abrupt speed changes in an unusual way, especially on two-way routes, the safety of tunnels can be increased by reducing the stressors in drivers.

Study on the Progressive Deterioration of Tunnel Lining Structures in Cold Regions Experiencing Freeze–Thaw Cycles

The linings of tunnels in cold regions with long service lives usually have cracks, with parts of the structure peeling and falling off, which seriously threatens the tunnel safety and operation. The unsaturated freeze–thaw cycle of concrete, which is the main cause of structural deterioration, has not received much research attention. During the service life of tunnels in cold regions, unsaturated freeze–thaw cycles deteriorate the quality of the concrete, and its degree presents a gradual distribution in the circumferential and longitudinal directions. An experiment system was adopted to simulate the distribution of the progressive deterioration of tunnel lining concrete. The test results of the temperature field of the model show the distribution law of freeze–thaw cycles, and the gradual deterioration of the lining concrete was realized. Then, the bearing capacity of the model was tested after the progressive deterioration. The results show that the ultimate load of the model decreases with an increase in the number of freeze–thaw cycles. Finally, a numerical simulation was carried out to discuss the influence of the gradual deterioration of the lining. The gradual deterioration of lining concrete will encourage the gradual development of cracks, leading to serious cracking of the lining structure and even block spalling. Through this study, we hope to provide useful information for the prevention and control of tunnel frost damage in cold regions.