Tunnel Safety Research Articles

Precise Positioning Method of Moving Laser Point Cloud in Shield Tunnel Based on Bolt Hole Extraction

Mobile laser scanning technology used for deformation detection of shield tunnel is usually two-dimensional, which is expanded into three-dimensional (3D) through mileage, resulting in low positioning accuracy. This study proposes a 3D laser point cloud positioning method that is divided into rings in the mileage direction and blocks in the ring direction to improve the positional accuracy for shield tunnels. First, the cylindrical tunnel wall is expanded into a plane and the bolt holes are extracted using the self-adaptive parameter adjustment cloth simulation filter (CSF) algorithm combined with a density-based spatial clustering of applications with noise (DBSCAN) algorithm. Second, the mean-shift algorithm is used to obtain the center point of the bolt hole, and a model is designed to recognize the center point of different splicing blocks. Finally, the center point is combined with the standard straight-line equation to fit the straight-line positioning seam, achieving an accurate ring and block segmentation of a shield tunnel as a 3D laser point cloud. The proposed method is compared with existing methods to verify its feasibility and high accuracy using the seams located by the measured tunnel point cloud data and in the measured point cloud. The average differences between the circumferential seams positioned using the proposed method and those in the point cloud at the left waist, vault, and right waist were 3, 4, and 5 mm, respectively, and the average difference between the longitudinal seams was 3.4 mm The proposed research method provides important technical and theoretical support for tunnel safety monitoring and detection.

Traffic Safety Optimization Strategy of Mountainous Highway Tunnel Based on GA-SVR Visual Load Model

Improving the driving safety of mountainous highway tunnels has become an urgent problem in China, while the existing literature pays more attention to the safety of urban tunnels. From the perspective of visual load, this paper built a GA-SVR model to analyze the influences of speed, design brightness, measured brightness, and position in the Gaogu long tunnel. The results show the following: firstly, the changes of MTPA in the long mountainous highway tunnels can be divided into five stages, which is different from the three-stage division of urban tunnels; secondly, the influencing degree of factors was varied in different stages: the position factor mattered most in stages 1, 2, 4, and 5, while the design brightness had the greatest impact in stage 3; thirdly, the driver’s psychological pressure was greatest on the entrance and exit section of the tunnel; lastly, the increased length of mountainous highway tunnels and the long-term enclosed driving environment made the psychological load of drivers intensified. Therefore, it was necessary for the mountainous highway tunnels to consider more accurate gradual lighting design in the 200-m sections after the entrance and before the exit, meanwhile enhancing traffic safety management and protections in the middle of the tunnel.

An Analysis of Internet of Things Computer Network Security and Remote Control Technology

In order to solve the problem of the specific application of Internet of Things computer network security monitoring technology in infrastructure construction, a method of remote network monitoring system design is proposed, taking tunnel security construction as an example. According to the characteristics of construction tunnel safety monitoring, this method provides theoretical guidance from several aspects, such as computer remote monitoring, data decision analysis, safety control, personnel positioning, and data management. Through experiments, it is found that in the safety detection experiment, when the data is extracted within 2 minutes for detection, the detection accuracy is higher than 80%, and if it is 4 minutes, the detection accuracy is higher than 90%; in the response time test, the local control response time is generally less than 1 s. In the remote control response time test, the response time can generally be within 3 s, and it may be greater than 5 s. The designed construction tunnel monitoring system transmits the collected data to the monitoring terminal remotely. Then, the sensor data is analyzed for timing decision-making. This method can effectively calculate the safety status of each monitoring unit of the current tunnel according to a certain algorithm and formulate corresponding emergency measures according to the safety status.

Correction of Point Load Strength on Irregular Carbonaceous Slate in the Luang Prabang Suture Zone and the Prediction of Uniaxial Compressive Strength

Uniaxial compressive strength (UCS) testing requires high-quality core samples, which is a difficult task for weak, highly fractured, thinly bedded, foliated, and weathered rocks. In addition, it is time-consuming and expensive. Because of the good relationship between rock point load strength (PLS) and UCS, the PLS could be used to estimate rock UCS quickly. The lump structure and layer structure of carbonaceous slate are revealed in the tunnels of the China–Laos Railway in the Laos Luang Prabang Suture Zone as one of the important factors leading to tunnel squeezing deformation and support structures. To reveal the relationship between the PLS and UCS of carbonaceous slate in the Luang Prabang Suture Zone, PLS tests and UCS tests of lump-structure carbonaceous slate (lamina plane inconspicuous) and layer-structure carbonaceous slate (lamina plane conspicuous) were performed. Results show that the Is(50) of lump-structure carbonaceous slate ranged from 0.06 MPa to 0.30 Mpa, the Is(50) of layer-structure carbonaceous slates which were loaded perpendicular to the lamina plane ranged from 0.64 MPa to 1.25 MPa, the Is(50) of layer-structure carbonaceous slates which were loaded parallel to the lamina plane ranged from 0.49 MPa to 0.71 MPa, and the correction power index m ranged from 0.42 to 0.51 with an average value of 0.47. Four correlation expressions of carbonaceous slate relationships between PLS and UCS were fitted by zero-intercept linear expression, nonzero intercept linear expression, power expression, and logarithmic expression, and the calculation results were compared with results calculated by the International Society of Rock Mechanics (ISRM) correlation equation. It is concluded that the correlation equation between UCS and PLS recommended by ISRM specifications easily causes soft rock strength overestimation, which affects the correct evaluation of the surrounding rock property and the structural design safety of tunnels and underground projects. The zero-intercept linear equation UCS = 18.45Is(50) has better goodness of fit and higher accuracy in predicting the UCS of the carbonaceous slate in the Luang Prabang Suture Zone.

Experimental study on Inter-ring joint shearing characteristics of gas transmission shield tunnel with bent bolt and tenon

When a gas transmission shield tunnel passes through an underwater stratum under high water pressure for a long distance, structural damage due to segment joint dislocation notably affects the tunnel safety during service. Thus, the shearing characteristics of inter-ring joints constitute a critical research topic for the structural mechanical response of a segment. Considering the structure of an inter-ring joint, this study uses positive and negative shearing tests to investigate joint dislocation, shear stiffness, and the mechanism of the shear failure of segment joints. The main findings are as followings. The stress states of a bent bolt and tenon are critical factors affecting the shear performance of the inter-ring joint. Vulnerable areas appear at different positions according to the shear stress mode of the bolt and tenon. The failure process can be classified into the following three stages owing to the stress state. 1) Friction at the contact surface of the joints counteracts the shearing force, 2) the groove and convex tenons contact each other and the bolt begins to bear the force, and 3) visible cracks and collapse appear in the segment structure. Finally, the damage evolution of concrete occurs earlier than that of the bolt. Moreover, until the concrete fails, the bent bolt is close to yielding but is still not damaged. These findings can improve the design and theoretical analysis of oil and gas transmission shield tunnels.

How does the mural decoration of the long tunnel sidewall affect the driver's speed control ability?

Since a tunnel is dark and driving conditions are monotonous, drivers are prone to optical illusions, affecting driving safety in tunnels. Tunnel sidewall decorations can provide visual stimulation to prevent or reduce traffic crashes. Driving simulation experiments with a driving simulator and speed perception experiments with E-Prime software are performed to evaluate the influence of tunnel sidewall murals on the speed control of drivers in a long tunnel. Three mural designs (A2: 1.93 Hz, A3: 1.27 Hz, A4: 0.95 Hz) with different frequencies and a control group (no mural, A1) are evaluated. Four indicators of the driver’s speed control (speed, acceleration, stimulation of subjectively equal speed (SSES), and reaction time) are selected. The results show that the driver’s speed is significantly reduced in the middle of the tunnel and near the tunnel exit, and the driver's speed control is significantly enhanced by the murals. It is recommended to install murals in the middle and near the exit of the tunnel for optimal speed control. The SSES shows that tunnel murals affect drivers’ speed perception and alertness. As the frequency of the mural decreases, speed overestimation changes to underestimation, the degree of speed illusion increases, and the reaction time decreases. A difference is observed between the perceived and actual speed, and this difference depends on the mural’s frequency. Thus, choosing an appropriate mural frequency improves the mural’s effect. The results provide a basis for mural design on the sidewalls of long tunnels to improve tunnel safety, as well as a novel approach for speed reduction.

Stress wave propagation and incompatible deformation mechanisms in rock discontinuity interfaces in deep‐buried tunnels

AbstractComplex weak structural planes and fault zones induce significant heterogeneity, discontinuity, and nonlinear characteristics of a rock mass. When an earthquake occurs, these characteristics lead to extremely complex seismic wave propagation and vibrational behaviors and thus pose a huge threat to the safety and stability of deep buried tunnels. To investigate the wave propagation in a rock mass with different structural planes and fault zones, this study first introduced the theory of elastic wave propagation and elastodynamic principles and used the Zoeppritz equation to describe wave field decomposition and develop a seismic wave response model accordingly. Then, a physical wave propagation model was constructed to investigate seismic waves passing through a fault, and dynamic damage was analyzed by using shaking table tests. Finally, stress wave attenuation and dynamic incompatible deformation mechanisms in a rock mass with fault zones were explored. The results indicate that under the action of weak structural planes, stress waves appear as a complex wave field decomposition phenomenon. When a stress wave spreads to a weak structural plane, its scattering may transform into a tensile wave, generating tensile stress and destabilizing the rock mass; wave dynamic energy is absorbed by a low‐strength rock through wave scattering, which significantly weakens the seismic load. Wave propagation accelerates the initiation and expansion of internal defects in the rock mass and leads to a dynamic incompatible deformation. This is one of the main causes for large deformation and even instability within rock masses. These findings provide an important reference and guide with respect to stability analysis of rock mass with weak structural planes and fault zones.

Automatic Tunnel Crack Inspection Using an Efficient Mobile Imaging Module and a Lightweight CNN

Cracks in tunnel linings are the most common tunnel defects. As early indicators of structural deterioration, cracks represent critical problems for the safety of tunnels. Several mobile tunnel inspection systems (MTISs) have been developed for tunnel crack inspection. However, due to the weak signals of cracks, these MTISs require considerable exposure time to capture high-quality tunnel images, necessitating a low travel speed. Meanwhile, traditional crack detection methods encounter difficulties in processing tunnel crack images because of their low contrast and poor continuity. To overcome these challenges, this study presents a new MTIS for fast tunnel crack inspection that consists of a novel mobile imaging module and an automatic crack detection module. The imaging module is composed of an array of high-resolution charge-coupled device (CCD) cameras, a mobile laser scanner, and a lighting array. The core of the crack detection module is a novel lightweight convolutional neural network (CNN) designed for efficient tunnel crack detection, with an effective spatial constraint strategy to guarantee crack continuity. We collected a new tunnel crack dataset consisting of 1,218 images using our mobile imaging module at a driving speed of 80 km/h. Comprehensive experiments were conducted on this dataset to evaluate the performance of our proposed network. The results demonstrate that the presented CNN can effectively detect tunnel cracks with state-of-the-art performance, achieving an F1-score greater than 0.88 and an inference speed of 17 FPS with only 3.4M model parameters. The code and data are available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/urban-informatics/LinkCrack</uri> .

Study on the damage evolutional process of secondary tunnel lining under rheological effect of surrounding rock

Cracks are prone to occur in the secondary tunnel lining with the action of rheological deformation of surrounding rock, which will cause severely structural defects and adversely affect the long-term safety of tunnels. In this article, similar model tests and numerical simulations were conducted to investigate this issue. First, the overloading method was adopted as a simplified way to investigate the failure evolution process of lining in the model test. Then, the long-term safety of lining under the influence of geo-stress field, the amount and location of voids were revealed through numerical simulations. The results show that: (1) The variation of inner force with loading steps has two distinct stages that are similar to those for lining under the creep effect of rocks, which validates the availability of the overloading method preliminarily. (2) Sections of lining near the void bend outward, and the axial force in these sections is smaller than that of the other sections. (3) The failure process for lining with no void shows evidently progressive feature with the occurrence of two stress adjustment processes before its failure, while the existence of void accelerates the failure process of lining. (4) A crack near the void appears in the lining when the lining reaches its ultimate limit state of carrying capacity, and the crack occurs earliest compared to other cracks.

Resilient analysis on tunnel structural serviceability based on lifetime dynamic prediction model

In order to ensure tunnels safety and serviceability of under whole life cycle, it is indispensable to predict tunnel performance and appropriate maintenance time under multi-defects. In this study, the performance of tunnel system is regarded as the composition of long-term aging deterioration and a series of short-term events to define its development with time. With the subsequent events updating the residual performance, an innovative method for dynamic analysis of tunnel performance is proposed. According to failure mode and effects analysis (FMEA) method and hierarchical model, an initial life performance model is established. Divided into the failure, evolution and recovery stages, the system evaluates the performance variation of specific defect under short-term events. In the case study, an additional excavation event is put into consideration to analyze the performance loss and the new pattern of lifetime performance model. The key issues of the tunnel are extracted into longitudinal settlement, differential settlement and leakage. With the theory of key defects, the thresholds conditions are classified into four stages and the damage-recovery process are evaluated by the concept of resilience. The process of dynamic prediction model to tunnel system is employed to update the variation of maintenance schedule and the serviceable time among defects, meanwhile the new performance curve of tunnel system can be modified through the evaluation of structural equation. Finally, if all thresholds are not exceeded by short-term events, the original life-cycle service curve and short-term event are superimposed as the update of life cycle. The result implies that despite the short-term event only costs minor damage to the system, the consequence may cast a critical loss on the residual of operation time.

Tunnel Security Management Based on Association Rule Mining under Hadoop Platform

The problem of how to use large amounts of historical data for tunnel safety management has a greater practical application value. The association rule method in data mining technology can provide effective decision support for tunnel safety prevention by mining historical data. To address the problem of large data volume and sparse data items in tunnel safety management, an association rule method—Apriori algorithm—based on the Hadoop platform is proposed to improve the efficiency and accuracy of data mining in cloud environment. First, the parallel MapReduce implementation steps are analyzed on the basis of the distributed Hadoop framework. Then, the existing single-user data validation algorithm is improved by applying a multiuser parallel validation algorithm to Apriori in order to reduce the number of validations. Next, the traditional association rule Apriori algorithm is MapReduce optimized to generate a smaller set of useless candidate items. At the same time, Boolean ranking is used to optimize the way transactional data are stored in the database, reducing the number of redundant subsets and the number of times the database is connected, and shortening the task processing time. The experimental results show that the proposed method is able to mine the relationships between tunnel safety hazards and provide effective decision support for tunnel safety prevention. At the same time, the proposed method more efficiently operates than other association rule methods.

Safety Evaluation of Subway Tunnel Construction under Extreme Rainfall Weather Conditions Based on Combination Weighting–Set Pair Analysis Model

Regional extreme rainfall events have occurred frequently in China, and subway tunnel construction faces possible threats under extreme weather conditions. Thus, in this study, we used the set pair analysis (SPA) approach to the construction safety evaluation of subway tunnels and developed a construction safety evaluation model under extreme rainfall circumstances. Firstly, based on careful consideration of the complex construction environment of subway tunnels under extreme rainfall weather conditions, a construction safety evaluation system of subway tunnels was developed considering four aspects: rainfall, hydrogeology, construction design, and management. Moreover, the weighting analysis of each index factor was carried out using the improved analytic hierarchy process (IAHP) method, the entropy weight method (EWM), and the linear weighting method. Secondly, considering the uncertainty of subway tunnels’ construction safety evaluation system and the fuzzy nature of evaluation-level classification, a construction safety evaluation system of subway tunnels based on the multivariate linkage number and set pair analysis theory was established. Finally, we applied the model to a subway tunnel construction case. The results show that the evaluation results are consistent with the actual engineering survey results, which verifies the practicality and effectiveness of the model in evaluating subway tunnel safety. We also determined the primary factors and risk development trends that affect the safety of subway tunnel construction under extreme rainfall weather conditions to guide the safety risk management of subway tunnel construction.

Three-dimensional stress rotation and control mechanism of deep tunneling incorporating generalized Zhang–Zhu strength-based forward analysis

Deep rock tunneling exhibits a significant three-dimensional (3D) space effect. The complex stress path and extrusion deformation during excavation are the most significant and decisive factors in the stability and construction safety of a deep tunnel. 3D and forward numerical analyses based on generalized Zhang–Zhu (GZZ) strength criterion are performed to investigate the principal stress rotation behavior and active control mechanism during deep tunneling. The surrounding rock element experiences significant stress rotations because of the sharply increased shear stress (τry) near the tunnel face. A dimensionless stress index (τry/I1) is proposed to quantitatively evaluate the principal stress rotation during excavation. τry/I1 increases with increasing buried depth, and the deep tunnel presents significant principal stress rotation that reaches a large τry/I1 value. The mechanical behavior of the advanced core rock is primarily affected by the strengthening parameter, geological strength index (GSI). Strengthening of the core rock can greatly improve the stress conditions and mechanical behavior, increase the strength of the rock mass, and reduce the stress rotation. The pre-extrusion deformation of the core rock and pre-convergence of the surrounding rock are discovered to follow a consistency law, which suggests that the pre-convergence deformation and surrounding rock stability near the tunnel face depend on the extrusion deformation of the tunnel face. The GZZ strength-based 3D forward analysis and stress control method proposed in this study can enhance the design and construction of deep and ultra-deep tunnels by weakening the 3D space effect (e.g., tunnel face extrusion and stress rotation) and exerting the strength potential (self-bearing capacity) of a rock mass.

Numerical investigation on effect of air vent on air supply

An improper design of an air vent will not only cause waste of resources but also seriously threaten the safety of the spillway tunnel. The present study analyzes the effects of the area and position of the air vent on the air supply, using the volume of fluid method with the k–ε turbulence model. The air speed in the air vent will decrease with an increase in the area, but the quantity of air supplied will increase. When the area of air vents is equal to the tunnel residual, the air supply capacity of the air vent reaches the maximum. A relationship between the quantity of air supplied and the area of the air vent is put forward, and the error with the prototype observation result is about 10%. The distribution of negative pressure in the tunnel may be improved by arranging the air vent in a proper position; the quantity of air supplied also decreases as the distance between the air vent and the pressurized conduit increases. In general, it is more advantageous to position the air vent upstream. These results provide a reference for the air ventilation design in hydraulic engineering.

Pathological diagnosis of the seepage of a mountain tunnel

Seepage is one of the major defects that plague the operational safety of mountain tunnels. Because the mechanism is very complex and influenced by many factors, traditional diagnosis can only provide qualitative suggestions and cannot guide practical maintenance. Therefore, a pathological diagnosis method is proposed in this study for quantitatively sorting the influencing factors and conducting a risk analysis of the seepage of a mountain tunnel. A Weibull damage accumulation model, with its parameters structured as a function of influencing factors, is established to describe the statistical distribution of seepage. Accordingly, the importance of the influencing factors can be sorted in terms of the magnitudes of their coefficients in the function, and the failure risk of seepage can be predicted by the model. The proposed method was validated by a series of physical and statistical tests based on real data collected from a mountain tunnel in southern China. The illustrative example indicated that the order of importance of the influencing factors of seepage is as follows: existence of voids behind the secondary lining, rock mass grade of the surrounding rock, neighboring deformation joint, and operating time. The risk analysis predicted that more than 95% of the sections of the tunnel will exceed the waterproof requirements in the sixth year of operation. The benefits of the proposed method are that it (1) quantifies the contributions of different factors leading to the seepage of a mountain tunnel, providing suggestions for design, construction and maintenance; and (2) predicts the development of seepage in the future, which is of vital importance in the maintenance of tunnels.

Study on the variation rule of smoke back‐layering length of tunnel ceiling jet induced by strong fire plume

AbstractTunnel fire is a major research topic in tunnel safety. Because of the tunnel's narrow and enclosed structure, smoke movement plays an important role in the investigation of the tunnel fire. In this paper, the Froude similarity principle is used to study the variation rule of the smoke back‐layering length of tunnel ceiling jet induced by strong fire plume with different heat release rates, longitudinal ventilation velocities, and effective heights of fire source analyzed. It is found that the smoke back‐layering length of tunnel ceiling jet induced by strong fire plume increases with the increase of effective height of fire source and decreases with the increase of longitudinal ventilation velocity. When the heat release rate is relatively small (), the smoke back‐layering length of the tunnel ceiling jet induced by strong fire plume increases as the heat release rate increases. However, for the larger heat release rate (), the smoke back‐layering length of the tunnel ceiling jet induced by strong fire plume is mainly related to the longitudinal ventilation velocity. Based on Thomas's model and Li's model, by introducing the correction coefficient, correction formulas of the smoke back‐layering length of tunnel ceiling jet induced by strong fire plume changing with the effective height of fire source are proposed.

Dynamic Response of Pile-Soil Foundation with an Adjacent Tunnel under the High-Speed Train Loads: A Case Study

In order to study the dynamic response characteristics of a pile-soil foundation when an adjacent tunnel exists, both model tests and numerical simulations were performed in this study. Taking the peak vibration acceleration, peak vibration velocity, and peak vibration displacement as the evaluation indexes of the dynamic response, the dynamic response of the pile-soil foundation with an adjacent tunnel under high-speed train loads is studied. A method of dividing the affected zones of the dynamic response based on the safety threshold is provided in this paper, which can evaluate the safety of the adjacent tunnel under the action of train load. Additionally, the effect of train speed on dynamic response is further analyzed. The results show that the dynamic response index inside the foundation decays significantly with increasing distance from the surface when the train load is applied, regardless of the presence or absence of the adjacent tunnel. Compared with an ordinary pile-soil foundation, the dynamic response indexes inside the foundation increase significantly when there is an adjacent tunnel. With the increase in the horizontal distance from the pile foundation, the distribution characteristics of the horizontal transverse direction of each dynamic response index inside the foundation change from a “wavy” distribution to a monotonically decreasing distribution. According to the safety threshold of vibration velocity, the foundation is divided into the hazardous affected zone, strongly affected zone, and weakly affected zone, and then the corresponding vibration reduction measures are adopted. With the increase in train speed, the effect of tunnel structure on the attenuation of dynamic response in a pile-soil foundation becomes more obvious.

A Risk Analysis Method of Cable Fire in Utility Tunnel Based on a Bayesian Network

Recently, the fire safety of tunnels is attracting more and more attention with the utility tunnel springing up in major cities of China. Faced with challenges from fires in utility tunnels, fire risk analysis is critical and essential to discover the weaknesses of risk. It serves as the foundation of regulatory decision-making on whether to take appropriate measures to reduce risk. This study combines a Bayesian network (BN) model and a bow-tie (BT) method to propose a fire risk analysis method to predict the probability of cable fire in utility tunnels. First, cable fire risk factors and five potential accident scenarios are analyzed by BT method; Second, to avoid the influence of uncertain factors in BT, the optimized BN model is applied to the prediction analysis of cable fire probability, which can consider the actual development of cable fire in utility tunnel. This novel approach can better reveal the causal relationship between events and determine the critical basic events by sensitivity analysis. Finally, the probability of cable fire ignition occurrence and scenarios probabilities are periodically updated using the cumulative information collected during a time interval. The results show that this approach can assist in dealing with the uncertainty problem in utility tunnel and the optimized model is more in line with the reality by comparing the results before model optimization.

Impact of various multishaft combined ventilation modes on the removal of harmful gases released from mussel decay in a long-distance water conveyance tunnel

The harmful gases released from the decay of biologically invasive mussels are a major threat to the maintenance safety of long-distance water transfer projects in hot and humid climate areas. Setting up multiple working shafts along the long-distance underground water conveyance tunnel for maintenance ventilation can eliminate harmful gases and improve ventilation efficiency. The rational multishaft combined ventilation mode is an important guarantee for effective decontamination and maintenance safety in long-distance water conveyance tunnels. However, research on the release rule of harmful gases produced by rotten mussels and the multishaft combined ventilation modes of long-distance water conveyance tunnels has rarely been performed. In this study, a ventilation mathematical model considering the influence of harmful gases released by rotten mussels was implemented. The release rule of harmful gases was obtained by a mussel decay experiment, and the mathematical model was validated based on the data of a ventilation model test. Furthermore, the ventilation performance of multishaft combined ventilation modes was compared using a series of numerical simulations. The obtained results show that NH3 is the main component in harmful gases released by rotten mussels. The cumulative concentration of NH3 increases with the decay time of the mussel, reaching a peak value of 309.26 mg/m3. The maximum release rate of NH3 is 185.51 mg/(m3·d). In addition, the ventilation mode of alternately delivered and discharged airflow between adjacent working shafts is confirmed to be the best for long-distance tunnels with multiple working shafts according to the comparison of the airflow distribution and the removal effect of harmful gases under different modes of multishaft combined ventilation. This study provides useful guidance for the design and optimization of maintenance ventilation schemes in long-distance water transfer projects.

Tunnel safety: A pilot study investigating drivers’ fixation characteristics when approaching tunnel entrance at different driving speeds

This study presents the results of a driving experiment study on spatiotemporal characteristics of drivers’ fixation when entering a tunnel portal with different driving speeds. The study was performed during the daytime in a relatively long tunnel. Six experienced drivers were recruited to participate in the driving experiment. Experimental data of pupil area and fixation point position (from 200 m before the tunnel to the tunnel portal) were collected by non-intrusive eye-tracking equipment for three predetermined vehicle speeds (40 km/h, 60 km/h and 80 km/h). Fixation maps (color-coded maps showing distributed data) were created from fixation point position data to quantify visual behaviour changes. The results demonstrated that vehicle speed has a significant impact on pupil area and fixation zones. Fixation area and average pupil area had a significant negative correlation with vehicle speed during the daytime. Moreover, drivers concentrated more on the tunnel entrance portal, front road pavement and car control wheeling. The results revealed that the relationship between pupil area and vehicle speed fitted an exponential function. Limitations and future directions of the study are also discussed.