Inside Tunnels Research Articles

Cracking Characteristics and Mechanism of Internal Components of Large-Span Shield Tunnel

With the ever-increasing number of large-span shield tunneling projects and the extended operational time, their distinctive internal component issues are becoming more pronounced and exhibiting unique characteristics. In order to reveal the cracking mechanism of concrete on the top of the middle partition wall, based on a large-span shield tunnel section of Nanjing Metro, the crack mode, distribution characteristics, and cracking process of concrete inside tunnel structure were studied by combined field investigation and extended finite element analysis. The results showed that: (1) there were 96 cracks of concrete on the top of the middle partition wall in the interval. Based on the propagation path, number, and shape of cracks, they could be divided into type I, II, III, Y, and Z, with type-Y and type-Z being subtypes of type-I. (2) The crack started at the opposite side of horizontal differential displacement of the flue plate. The development curves of the length and end width of type-I and type-II cracks showed the significant characteristics of three stages. The relationship between crack end width and length was nonlinear, showing that 250 and 225 mm, respectively, were the critical crack lengths growing with the rapid growth of the end width of type-I and type-II cracks. (3) In type-II cracks, the propagation curves of two cracks under the same working condition were consistent, and the spacing of plate joints greatly influenced the length and slope of each stage of the curve. For type-III cracks, the first crack propagation process was basically consistent with type-I and type-II cracks, and the propagation of the other two cracks had obvious brittle characteristics.

Experimental study on strain of SFRC tunnel lining segments using a comprehensive embedded optical fiber sensing system

In comparison to current techniques, optical fiber sensors (OFS) for structural health monitoring (SHM) of steel fibre reinforced concrete (SFRC) tunnel lining segments is an emerging technology that could enhance tunnel safety and reliability. However, the utilizing many measurement techniques in a single OFS technology has pros and cons, making it difficult to meet the demands for a comprehensive and reliable assessment for long-term monitoring inside tunnels. We present comprehensive OFS system for strain monitoring inside concrete tunnel lining segments. The system involves distributed optical fiber sensing (DOFS) cable, fiber Bragg grating (FBG) sensors, and chirped fiber Bragg grating (CFBG) sensors. The proposed system is particularly useful for high-risk or difficult-to-access locations, such as inside tunnel structures. We provide the deployment design after introducing the sensing principle of the system. To validate its effectiveness and reliability, we conduct a scaled-down laboratory experiment to evaluate the strain behavior. The proposed comprehensive OFS system accurately captures the strain evolution over time in various stages of tunnel lining segments, including casting, curing, loading, and even after failure. This system demonstrates high-resolution, and reliable monitoring of internal strain in tunnel lining segments, making it suitable for practical application in full-scale and long-term SHM during the construction and operation stages of shield tunnels with connection expansion for segments.

Cosmic muons as PMT and SiPM detector background signals

Photomultiplier tube (PMT) and Silicon Photo Multiplier (SiPM) are often used for detecting small number of photons or very weak radiations. A light guide usually connects these photodetectors to the test space. In this article, we investigate the effect of background signals caused by cosmic muons scintillation or interactions with PMT and SiPM, their light guide or input window materials. We study such interactions by making simulations using GATE software package and undertaking experiments using detector circuits developed as in [1]. The background cosmic muons can generate photons which will lead to errors in low radiation and single photon detection experiments especially if standard scintillators are not used. For such experiments, we conclude that the most useful method for cutting down the cosmic muons background should be by conducting the experiments deep underground or inside tunnels with several tens of meters of materials above it.

Numerical studies on a new strategy to mitigate pressure waves by accelerating trains through a long tunnel

The present work focused on exploring a strategy for mitigating the aerodynamic effects by accelerating through the tunnel. A three-dimensional, unsteady, compressible, and RNG k-ε turbulence model is adopted to simulate the pressure waves generated by high-speed trains passing through the tunnel at different speed modes. The findings demonstrated that trains cruising inside tunnels in an acceleration mode could effectively reduce the transient pressure on trains and tunnels while maintaining the efficiency of the passage. The acceleration method could alter the time at which the pressure maximum appeared at the head train surface, resulting in hysteresis that could effectively reduce the unexpected increase in the transient pressure due to the high-speed approach of the train into the tunnel. Throughout the pressure variation process, the acceleration mode could effectively improve the pressure variation at the train nose-point region compared to the uniform-speed mode. The acceleration modes with a lower acceleration (V325-375) and a higher acceleration (V300-400) reduced the pressure peaks by 15.37% and 5.63%, respectively. In addition, for most of the tunnel, the two acceleration modes could reduce various key pressure indicators on the tunnel walls as well. These results indicate that an accelerating train could be an alternative for higher-speed passing through tunnels to balance the passage efficiency and passenger safety and comfort.

Experimental study on vertical temperature distribution of the two-layer smoke flow in tunnel during construction

For a tunnel fire during construction, the formation of two-layer smoke flow underneath the ceiling accelerates the smoke descent threatening the personnel evacuation. As an important indicator of smoke diffusion, the gas temperature distribution inside tunnel is worthy of analysis in depth. However, the vertical temperature profiles within this kind of two-layer smoke flow inside tunnel have not been experimentally studied. To fill the gap, this paper conducts a series of fire experiments in a 1/20 reduced-scale tunnel model. Multi-variables including fire heat release rate, fire position, lifting-up height of fire source, inclined shaft slope, are considered. The visible flame shape, O2 volume fraction and gas temperature are recorded and measured. The burning of the propane gas persists steadily for 20 mins without the occurrence of self-extinction. The structural evolutions of the smoke layer are predicted by FDS simulation and traced by the laser sheet. The smoke descent process in the main tunnel is divided into three stages. The effects of fire source position, inclined shaft slope, fire heat release rate and lifting-up height on the gas temperature distributions inside tunnel are analyzed. The measured temperature rise and the perpendicular distance from the ceiling are normalized by ΔTmax and LT, respectively. At various longitudinal positions (1.82 ≤ │X-dm│/Hef ≤ 10.68), the normalized temperature distributions follow the same curve, independent of the values of Qm, dm and hm. The self-similarity of the vertical temperature distribution within the two-layer smoke flow are sufficiently proved. It is found that ΔT/ΔTmax with z/LT shows a two-regional variation. Based on over 1,740 temperature data from 36 experimental cases, an experimental equation is proposed to describe the gas temperature rise in the region between the fire source and the closed end. The proposed model shows good agreement with the measured data, which can help the researchers to better assess the smoke layer height inside tunnel.

Borehole cylindrical detector: A compact muon telescope for muon radiography applications

Muon Radiography (or muography) is a recent imaging methodology that uses cosmic muons to investigate the interior of large objects, such as volcanoes, mines or buildings. Some applications are intended to use muography to search for hidden cavities in the subsoil. In many cases the muon telescope needs to be installed underground, inside tunnels, excavated chambers or drilled holes. Usually places available to install the muon detector are difficult to access for people; we thus constructed a very compact cylindrical muon tracker to deal with this problem. Thanks to its shape the detector can be inserted in boreholes. It is 1 m high and has a 24 cm diameter; these dimensions are ideal to fit a realizable drilled well. It is composed of bar and arc-shaped plastic scintillators. The original geometry of sensitive elements allows to maximize the acceptance, minimizing the dead spaces. The new borehole cylindrical detector has been tested in laboratory and the result of a measurement of open sky muon flux is in good agreement with expectations. A first application on field is currently ongoing to validate the capability of the telescope to reveal the presence of underground voids.

Numerical investigation of the slipstream characteristics of a maglev train in a tunnel

High-speed maglev trains operate at higher speeds than conventional high-speed trains. This has implications on intensified aerodynamic issues, such as the transition between open air running and entering into a tunnel. In this paper, numerical simulation of a maglev train entering a tunnel is carried out using IDDES methods (based on SST k-omega model) to analyze the changing slipstream. The peaks and fluctuations of the slipstream are analyzed, together with the transient wake characteristics and TKE (turbulent kinetic energy) distributions. The influence of train nose length on the slipstream and its associated characteristics inside tunnels is also investigated in this paper. It was found that as the maglev train enters the tunnel, the wake slipstream at measuring points close to tunnel entrance increases significantly then decreases slightly with the increase of distance to tunnel entrance. Overall, the fluctuation and magnitude of slipstream inside tunnel is larger than that on open line, more specifically, the maximum TKE generated inside tunnel is. 7.62% larger than that on the open line at contour X = 3 H behind the train tail. Besides it takes longer time for the slipstream inside tunnel to return to the initial condition. These phenomena could be explained by that the scale of vortex structure formed behind the train tail is larger, the developing distance of the wake vortices in the streamwise direction is longer and the TKE generated is more significant inside tunnel. It was also found that increasing the nose length could effectively decrease the spatial scale and TKE of the wake vortices, which resulted on reducing the peak and pulsation of wake slipstream. Comparing to that of 5.4 m, the peak of the wake slipstream of the maglev trains with the 7.4 m and 9.4 m nose lengths at Y = 0.235 m(0.385) is reduced by approximately 23.7%(58%) and 35.9%(82.2%) on open field, and by about 3.6%(4.7%) and 14%(18.5%) inside tunnel. Besides, the maximum TKE at contour X = 2H/3H/5H behind the train tail decreases about 14.4%/10.7%/11.3% and 51%/31.5%/18% as the nose length increase to 7.4 m and 9.4 m respectively.

Ground vibration induced by maglev trains running inside tunnel: Numerical modelling and experimental validation

Vibration induced by urban rail transit has been a growing public concern worldwide. In this context, medium-low speed maglev trains gradually stand out due to their environmentally-friendly advantages in vibration and noise control. However, few studies have investigated maglev train-induced vibration, and much uncertainty still exists about the environmental vibration caused by underground medium-low speed maglev trains. This paper presents a numerical study of train-induced vibration and proposes a hybrid prediction model based on vehicle-track spatially coupled dynamics in the 2.5D FE framework. This method could consider the nonlinear behaviour of the vehicle-track system in more detail, and the application of Green's function makes this method more efficient when dealing with multiple conditions. Moreover, field measurements are carried out on maglev train-track-embankment system, and measured data show good agreement with the prediction results in the time and frequency domain, verifying the accuracy of the proposed model. Numerical analysis is conducted for the vibration response of the vehicle-track-tunnel-soil system, which reveals the transmission behaviour of the maglev train-induced vibration in layered soils, along with the possible causes of vibration amplification phenomena disclosed. Finally, the vibration levels caused by the maglev and subway trains are compared to quantify their differences. Related results provide insights for unveiling the mechanism of impact brought by daily maglev trains on the neighbouring environment and the quality of residents living alongside.

Sharpening and Detection of Road Studs for Intelligent Vehicles at Nighttime

Intelligent vehicles need to survive against various environments on roads such as sunlit, unclear, showery, shadowy, and inside tunnel conditions. This research designs a robust approach for detecting road studs at nighttime, which is the combination of various statistical methods. This detection approach is a unique approach developed for the detection of road lanes instead of road-painted lanes. Therefore, we detect road studs (cat eyes) instead of the painted lanes on roads at nighttime as the road studs have higher intensities at nighttime. First, we utilized Butterworth low-pass filter in order to sharpen the images. Second, we converted the image to grayscale and extracted the corresponding region of interest (ROI) from it. Then, the Canny edge detection algorithm was applied to create boundary lines in images. Finally, the Hough transform was applied to detect the desired lanes in the images, which are the road studs, and hence we successfully detected the road studs in images. We have used our own dataset for the stud’s detection, which considered most of the limitations of the previous datasets. Also, the dataset was collected in naturalistic environments at nighttime. The experimental result presents that the designed approach is accurate and robust for road stud detection against nighttime.

Antibacterial Effects of Chlorine Dioxide Against Microbes Attached to Clothes Inside Tunnel Washer

Antibacterial Effects of Chlorine Dioxide Against Microbes Attached to Clothes Inside Tunnel Washer

Calculation of BLEVE energy and overpressures inside a tunnel using analytical and CFD methods

Nowadays, more and more road tunnels have been constructed to cope with the transportation demands due to population growth and rapid economic development. Meanwhile, increasingly more Boiling Liquid Expanding Vapour Explosions (BLEVE) accidents have been reported, some of which occurred inside tunnels. The effect of BLEVE on tunnel structures, which may lead to catastrophic tunnel structural failure, has been rarely investigated and is not explicitly considered in the design and construction of road tunnels. In the tunnel engineering industry, the equivalent-TNT method is commonly used to predict accidental explosion loads. However, such an empirical method may not give good predictions of explosion loads due to the lack of consideration of the BLEVE mechanism, which may lead to unsafe or uneconomic designs of tunnel structures against BLEVE load. In this study, the energy-based analytical method and Computational Fluid Dynamics (CFD) simulation are used for more accurate BLEVE pressure prediction, which makes the more reliable assessment of BLEVE effects on tunnel structures become possible. The detailed procedure of BLEVE pressure prediction is provided, which compensates for the incapacity of the ANN method proposed in a previous study for large-scale BLEVE pressure calculation inside a tunnel. The analytically determined tank rupture pressures are utilized as input data in CFD simulations. The explosion wave propagation and reflection inside tunnels are also modelled in explosion load calculation. Twelve BLEVE and tunnel conditions are considered in numerical simulations. Data consisting of 360 peak incident pressures, 360 reflected pressures, and 360 reflected pressure wave velocities are extracted from CFD simulations. Two correlations representing the best-fitted results are derived for the reflected pressure calculation on tunnel walls. The incorporated analytical and CFD methods suggested in this study provide tunnel engineers meaningful guidelines to calculate the initial BLEVE energies, tank rupture pressures, peak incident and reflected pressures on tunnel walls.

Evaluation of Various Surface Cleaning Techniques Inside Tunnels on Pavement Skid Resistance.

A request started a comprehensive investigation on the Skid Resistance (SR) inside a highway tunnel in Madrid, Spain, to determine methods that will improve or maintain the SR above the minimum required level (60), after the application of Hydroblasting, without the need of pavement surface rehabilitation. The right lane located on eight sections inside tunnel XC was used as a test section, in which three went thru the application of water pressure applied weekly, biweekly, and monthly. Three other sections for surface sweeping at the same frequencies and two untreated sections as control. Using the Microgriptester, weekly SR measurements taken before and after tracked the pavement response. Results showed that SR decreased weekly depending on the frequency of the treatment applied and for higher frequencies, SR was almost at the same level. Water pressure and sweeping applied weekly, biweekly, and monthly, during the two months testing period, maintained the SR level above the required value of 60 and the untreated sections showed that pavement surface must be treated to maintain the SR above 60.

A Fast Method for Estimating the Emission Factors of Air Pollutants from In-Use Vehicles Fleet

The real-world emission factors of gaseous and particulate air pollutants emitted from in-use vehicles, can be rapidly estimated using monitoring data of their concentration profiles from inside roadway tunnels using a mobile laboratory equipped with fast monitoring instruments. The concentrations of CO2 and particle-bound polycyclic aromatic hydrocarbons (PM-PAHs) and NOx, were observed to increase linearly with traveling distance inside two successive roadway tunnels: the Hongjimun Tunnel and the Jeongneung Tunnel on the Naebu Express Way in Seoul, Korea, except for a small region of decrease. In the decreasing regions, within a few hundred meters of the entrance and before the exit, outside background air with low concentrations of air pollutants was thought to have intruded. From the slopes of the linear regression between distance and concentrations, a fleet-averaged (light-, medium-, and heavy-duty vehicles with 54%, 36%, and 10%, respectively) emission factor of CO2, PM-PAHs, and NOx at an average speed of ~60 km h−1 could be calculated as 197 ± 38 g km−1, 4.2 ± 0.8 × 10−4 g km−1, and 0.530 ± 0.230 g km−1, respectively, which are within the ranges of values reported in the literature. For each tunnel, the emission factors of CO2, PM-PAHs, and NOx estimated on days with higher-than-normal fractions of heavy-duty vehicles, were higher than those on other days. From these results, the new fast method proposed in this study is considered useful for estimating real-world emission factors of air pollutants by using a mobile laboratory as a complementary tool to traditional tunnel studies. This method can be used to rapidly make emission maps at roadway tunnels in mega-cities like Seoul, Korea, for urban air-quality management.

Topological Navigation and Localization in Tunnels—Application to Autonomous Load-Haul-Dump Vehicles Operating in Underground Mines

Mobile robots are no longer used exclusively in research laboratories and indoor controlled environments, but are now also used in dynamic industrial environments, including outdoor sites. Mining is one industry where robots and autonomous vehicles are increasingly used to increase the safety of the workers, as well as to augment the productivity, efficiency, and predictability of the processes. Since autonomous vehicles navigate inside tunnels in underground mines, this kind of navigation has different precision requirements than navigating in an open environment. When driving inside tunnels, it is not relevant to have accurate self-localization, but it is necessary for autonomous vehicles to be able to move safely through the tunnel and to make appropriate decisions at its intersections and access points in the tunnel. To address these needs, a topological navigation system for mining vehicles operating in tunnels is proposed and validated in this paper. This system was specially designed to be used by Load-Haul-Dump (LHD) vehicles, also known as scoop trams, operating in underground mines. In addition, a localization system, specifically designed to be used with the topological navigation system and its associated topological map, is also proposed. The proposed topological navigation and localization systems were validated using a commercial LHD during several months at a copper sub-level stoping mine located in the Coquimbo Region in the northern part of Chile. An important aspect to be addressed when working with heavy-duty machinery, such as LHDs, is the way in which automation systems are developed and tested. For this reason, the development and testing methodology, which includes the use of simulators, scale-models of LHDs, validation, and testing using a commercial LHD in test-fields, and its final validation in a mine, are described.

Experimental investigation on ceiling flame extension subject to relative large area of liquid fuel in a channel-like structure with confined portals

This paper provides a quantitative model study for ceiling impinging flame extension behaviors subject to the relatively large area of liquid fuel in channel-like structure with confined portals (eg. tunnel), based on experimental results. The fire tests were conducted in a model tunnel [8 m (Length) × 0.8 m (Height) × 0.6 m (Width)]. Different portal-confined areas and liquid fuel areas were considered. Results show that the ceiling flame extension is non-monotonously varied with the portal-confined area, which can be mainly attributed to the combined influence of two action mechanisms of restricting external air inflow and reducing internal heat loss. And there is a critical confined area determined by fuel area, at which the ceiling flame extension length is maximized. Especially, when fuel area is relatively large, a fuel-rich area appears inside tunnel and the high-temperature combustion region moves towards the portals. This provides a prior condition for the flame overflow phenomenon. Based on the analysis of ceiling impinging flame extension behaviors and experimental observations, a global dimensionless factor is introduced to characterize flame extension. A new empirical correlation for ceiling impinging flame extension is proposed accordingly by considering the portal-confined boundary. This empirical correlation performs well in the prediction of ceiling impinging flame extension in channel-like structure fires.

Landmark Attribute Analysis for a High-Precision Landmark-Based Local Positioning System

GPS signals are not reliable in urban canyons or inside tunnels. In those situations, accurate local positioning is possible through local landmarks. This paper presents the potential accuracy of such a landmark-based local positioning system and the desired attributes of landmarks influencing positioning accuracy. The analysis of the achievable accuracy and the sensitivity of the factors for precise vehicle positioning is performed using LiDAR sensor measurements in a controlled environment and a generic positioning method. The landmark-based positioning can achieve better than 0.2 m accuracy. The diameter and geometric configuration of the landmarks are the most important factors for higher accuracy. The results presented can guide the design and construction of a local positioning system in urban areas.

Research on Present Situation and the New Technology About Reinforcement in Collapsible Loess Foundation Inside Tunnels

The tunnel foundations treatment is the key and difficult point of the research of the tunnel in collapsible loess areas. The characteristics and advantages of the common foundations treatment technology for tunnels of loess areas are summarized in this paper, at the same time, the characteristics of a new technology for the non-vibration compaction treatment technology developed by the Northwest Research Institute Co., Ltd. of China Railway Engineering Corporation are introduced, which is suitable for the foundation reinforcement treatment of the tunnel in collapsible loess areas. Through the field experiment of base treatment of high-speed railway tunnel of the Baoji–Lanzhou High-Speed Railway Passenger Dedicated Line, it is demonstrated that the new non-vibration compaction machine has the advantages of convenient movement, controllable treatment effect, miniaturization, low cost and so on. The advancement and maneuverability are verified from the soil compaction coefficient between piles and the change law of collapsibility of the soil between piles under the different pile spacing conditions. The research results can provide new techniques and methods for the foundation reinforcement treatment of the tunnel of small space, strictly controlling construction vibration in collapsible loess areas.

Utilization of Papain Extracted from Chaya and Papaya Stalks as Halal Beef Tenderiser

Papain is a proteolytic enzyme extracted from plant latex. The protease has widely used in the meat industry and culinary work for a pre-tenderization step prior to further meat processing. The objective of this research was to evaluate the bioactivity of papain extracted from Chaya and papaya. The different levels of papain, casein substrate, temperature, and pH were set up in vitro conditions. Then, the fresh papain was used to digest raw beef and the beef was dried under solar process. The sun-dried beef was further analyzed of yield, moisture content, water activity, and tensile force. It was found that proteolytic activity from both plants was accelerated by a high level of papain or casein up to 2.0 (w/v). The best optimal proteolytic activity was recorded at 60oC and pH5. Later, the tenderized beef at pH6.5 was dried by a solar dryer, where an inside tunnel temperature was approximately 40oC, 40% relative humidity, and 187 Btu/ft2. hr solar radiation. The sun-dried beef had a 75% yield, a 32% moisture content, and 0.90 Aw. Despite the fact that the drying temperature and pH of beef were not optimal as given from the previous results, the tensile force and the work of tension of papain-treated beef both moist and dried states were lower than the non-treated beef.

Ubiquitous Transportation Mode Detection Using Single Cell Tower Information

Detecting the transportation mode of a user has an overwhelming significance for a vast domain of applications. It has been addressed by several systems using ubiquitous mobile phones. These systems leverage multiple cell towers' information, GPS, and inertial sensors. However, these phone sensors are limited to a small subset of phones (e.g. high-end phones or phones that support neighboring cell towers information), have high energy consumption, cannot work in certain areas (e.g. inside tunnels for GPS), and/or work only from the user side. Furthermore, there are variations in the receiving capabilities of different cell phone devices according to their brand, quality of receiver and cost which raises the problem of device heterogeneity. In this paper, a transportation mode detection system, MonoSense, is presented that leverages the phone serving cell information only. The basic idea is that the phone speed can be correlated with features extracted directly from both the serving cell tower ID and the received signal strength (RSS) from it. To achieve high detection accuracy with this limited information MonoSense leverages diversity along multiple feature dimensions to synthesize novel features. Specifically, MonoSense exploits both the time and frequency information available from the serving cell tower over different sliding window sizes. Besides, it is shown that both the logarithmic and linear RSS scales provide useful information about the movement of a phone, further enriching the feature space and leading to higher accuracy. Moreover, to overcome the heterogeneity problem, a set of device-independent features is derived and added to the feature set. MonoSense has been evaluated using 500 hours of cellular traces covering 1500 km for more than sixteen months and collected by four users using different android phones. MonoSense achieved an average precision, recall and F-measure of 87.3%, 85.9%, and 86.4%, respectively, in discriminating between stationary, walking and driving modes using only the serving cell tower information, highlighting its ability to enable a wide set of intelligent transportation applications.

Numerical Investigation of Smoke Propagation in Road Tunnels Caused by a Burned Truck

Abstract The efficiency of smoke extraction for longitudinal and transverse tunnel ventilation systems was studied in this paper by conducting numerical simulations using computational fluid dynamics (CFD). The smoke was assumed to result from a fire initiated from a truck inside the tunnel. The most dangerous issue regarding the fire inside tunnels is smoke as it leads to low visibility and choking and may lead to death. The most important result of this paper refers to that the longitudinal ventilation design does not provide efficient smoke extraction compared to the transverse ventilation design as the air jets push the smoke in the downstream direction and then the smoke spreads randomly after the flow loses its momentum gradually. There is a big drop in the visibility for the longitudinal ventilation design that appeared many times and at many locations downstream the fire location. On the other hand, the transverse ventilation design provided more efficient smoke extraction as the jet fan upstream the fire is turned off while the supply fan downstream the fire is reversed to work as an exhaust fan. As a conclusion based on the findings of this paper, it may be said that the transverse ventilation design provided more safe conditions, lower contaminants concentrations, and higher visibility values compared to the longitudinal ventilation design. This work tends to add more information to minimize the research gap related to having a detailed comparison between the two ventilation strategies for a special case where the fire size is relatively large in a long tunnel.