Tunnel Surface Research Articles

Automatic crack detection for tunnel inspection using deep learning and heuristic image post-processing

In this paper, a crack detection mechanism for concrete tunnel surfaces is presented. The proposed methodology leverages deep Convolutional Neural Networks and domain-specific heuristic post-processing techniques to address a variety of challenges, including high accuracy requirements, low operational times and limited hardware resources, poor and variable lighting conditions, low textured lining surfaces, scarcity of training data, and abundance of noise. The proposed framework leverages the representational power of the convolutional layers of CNNs, which inherently selects effective features, thus obviating the need for the tedious task of handcrafted feature extraction. Additionally, the good performance rates attained by the proposed framework are acquired at a significantly lower execution time compared to other techniques. The presented mechanism was designed and developed as a core component of an autonomous robotic inspector deployed and validated in the tunnels of Egnatia Motorway in Metsovo, Greece. The obtained results denote the proposed approach’s superiority over a variety of methods and suggest a promising potential as a driver of autonomous concrete-lining tunnel-inspection robots.

Nascent Proteins Interact with Key Regions of the Outer Surface of the Ribosome

While in vitro protein folding is reasonably well understood, very little is known about how nascent chains achieve their native state in the complex cellular environment. The earliest stages of protein folding as nascent chains emerge out of the ribosome are still poorly characterized. Proteins and rRNA located within the ribosomal exit tunnel and outer surface, for instance, may interact with nascent proteins and affect their folding. Previous studies in the Cavagnero group showed that ribosome-bound nascent chains (RNCs) derived from the intrinsically disordered protein PIR and its highly negatively charged variants exhibit a significant spatial bias, consistent with the presence of non-covalent interactions between RNCs and the ribosomal surface. In this work, we probe RNC-ribosomal-protein contacts by a combination of chemical crosslinking and Western blotting, and show direct evidence for well-defined interactions between RNCs of PIR and specific ribosomal proteins. Surprisingly, the interacting ribosomal proteins are clustered only on one side of the ribosomal surface, relative to the exit tunnel. The observed interactions are particularly strong when about 15 amino acids have emerged outside of the ribosomal exit tunnel, and get weaker as the chain gets longer. This result suggests that the interactions are targeted towards the prevention of co-translational aggregation. This work corroborates an emerging view according to which the ribosome plays a fundamental role in protein biogenesis that extends well beyond the mere catalysis of peptide bond formation.

Closure of foramen ovale triggered by injury to tunnel surfaces of septum primum and secundum.

We investigated the feasibility to proactively stimulate subsequent closure of a patent foramen ovale (PFO) by injuring (mechanical trauma or radiofrequency [RF] energy) the opposing surfaces of the septum primum (SP) and septum secundum (SS). 1. Mechanical Injury: The interatrial septum of patients who underwent multiple left atrial (LA) ablations over 6years, where a PFO was used for LA access, were examined. Patients whose PFO was absent during a later procedure were identified. Eleven patients with LA accessed via a PFO also underwent subsequent LA procedures. 2. Ablation: Ten patients undergoing ablation for drug-resistant atrial fibrillation (AF), who also had a PFO, were studied. RF delivery was extended along the upper SP. Transthoracic echocardiogram (TTE) bubble study was repeated after 3months. 1. Mechanical Injury: Seven were male with a mean age of 58.3 ± 9.99. LA size was 42.73 ± 3.52mm. The mean left ventricular ejection fraction (EF) was 62 ± 7.4%. During the repeat procedure, in 4 patients, the PFO could not be visualized and the fossa ovalis (FO) was punctured. The fourth patient had three procedures. During the second procedure the PFO was accessed, but with difficulty. During the third procedure, it was no longer present. All four patients had subsequent TTE showing no PFO. 2. Ablation: Seven were male with a mean age of 61.1 ± 9.8years. The mean EF and LA diameters were 55 ± 5% and 4.4 ± 0.8cm respectively. The mean RF time was 5.4 ± 2.2min. At 3months, 9 patients out of 10 showed no interatrial communication. Injury of tunnel surfaces of the SP and SS by mechanical trauma or ablation can fuse the foramen ovale.

Probability analysis of shallow circular tunnels in homogeneous soil using the surface response methodology optimized by a genetic algorithm

In order to calculate the reliability index of a circular tunnel excavated in a soil mass, the first-order reliability method (FORM) is used. A 2D numerical model in a transversal section and a serviceability limit state (SLS) is considered in this analysis. This work focuses on the tunnel lining bending moment and surface settlement trough. Only the soil parameters are considered as random variables. The response surface methodology is utilized for the assessment of the Hasofer-Lind reliability index βHL and is optimized by the use of a genetic algorithm. Two assumptions (normal distribution or non-normal) were used for the random variables. The comparison between analysis using negatively correlated and uncorrelated variables (Young's modulus and Poisson's ratio) indicates that the results are conservative if a negative correlation is considered among the elastic parameters. The assumption of non-normal distribution for the random variables has an effect on the reliability index of the surface settlements and lining bending moments.

Study of the unsteady aerodynamic performance of an inter-city train passing through a station in a tunnel

Based on sliding mesh technology, this paper numerically investigates the aerodynamic performance of an 8-car inter-city train passing through a underground station at full speed. The effects of the gap between the car and the platform screen doors on the aerodynamic performance of the train passing through underground stations are analyzed. The curve of pressure variations at survey points on the train and the tunnel surface obtained from numerical simulation agree with those obtained from the moving model test. The asymmetrical internal structure of the station and the abrupt change in cross-section are the main factors contributing to the poor running stability of the inter-city train, with car 1 and car 8 showing the worst running stability. When the gap between the car and the platform screen doors increases from 130 mm to 425 mm, the maximum side force drops by 52.72% when car 1 passes the platform screen doors, and a linear relationship between the maximum side force and the gap between the car and the platform screen doors is observed.

Sweeping Jet Film Cooling on a Turbine Vane

The cooling performance of sweeping jet film cooling was studied on a turbine vane suction surface in a low-speed linear cascade wind tunnel. The sweeping jet holes consist of fluidic oscillators with an aspect ratio (AR) of unity and a hole spacing of Pd/D = 6. Infrared (IR) thermography was used to estimate the adiabatic film effectiveness at several blowing ratios and two different freestream turbulence levels (Tu = 0.3% and 6.1%). Convective heat transfer coefficient was measured by a transient IR technique, and the net heat flux benefit was calculated. The total pressure loss due to sweeping jet film cooling was characterized by traversing a total pressure probe at the exit plane of the cascade. Tests were performed with a baseline shaped hole (SH) (777-shaped hole) for comparison. The sweeping jet hole showed higher adiabatic film effectiveness than the 777-shaped hole in the near hole region. Although the unsteady sweeping action of the jet augments heat transfer, the net positive cooling benefit is higher for sweeping jet holes compared to 777 hole at particular flow conditions. The total pressure loss measurement showed a 12% increase in total pressure loss at a blowing ratio of M = 1.5 for sweeping jet hole, while 777-shaped hole showed a 8% total pressure loss increase at the corresponding blowing ratio.

Study on Face stability analysis of the aeolian sand tunnel

In view of the particularity of the geological environment of the surrounding rock of the aeolian sand, the tunnel will be destabilized due to its poor self-stability during tunnel excavation, which is worthy of attention. In this paper, the three-dimensional discrete element method is used to establish the discrete element numerical model of the excavation surface of the aeolian sand tunnel. The macroscopic mechanical response of the face is obtained and analysed, and the process of instability of the excavation surface is revealed from the macroscopic and microscopic mechanics. Based on this, the reasonable and safe support force of the excavation face is determined. Compared with the existing research, this paper uses the discrete element method to influence the dynamic construction of aeolian sand stratum on the stability of the face, which is closer to the engineering practice. The research results can provide reference for ensuring the stability of the tunnel face in the aeolian sand stratum.

Application of laser scanning for rock mass characterization and discrete fracture network generation in an underground limestone mine

Terrestrial laser scanning (TLS) is a useful technology for rock mass characterization. A laser scanner produces a massive point cloud of a scanned area, such as an exposed rock surface in an underground tunnel, with millimeter precision. The density of the point cloud depends on several parameters from both the TLS operational conditions and the specifications of the project, such as the resolution and the quality of the laser scan, the section of the tunnel, the distance between scanning stations, and the purpose of the scans. One purpose of the scan can be to characterize the rock mass and statistically analyze the discontinuities that compose it for further discontinuous modeling. In these instances, additional data processing and a detailed analysis should be performed on the point cloud to extract the parameters to define a discrete fracture network (DFN) for each discontinuity set. I-site studio is a point cloud processing software that allows users to edit and process laser scans. This software contains a set of geotechnical analysis tools that assist engineers during the structural mapping process, allowing for greater and more representative data regarding the structural information of the rock mass, which may be used for generating DFNs. This paper presents the procedures used during a laser scan for characterizing discontinuities in an underground limestone mine and the results of the scan as applied to the generation of DFNs for further discontinuous modeling.

Use of large-scale shake table tests to assess the seismic response of a tunnel embedded in compacted sand

Shield tunnels are widely used throughout the world. However, their seismic performance has not been well studied. This paper focuses on the seismic response of a large scale model tunnel in compacted sand. A9.3 m long, 3.7 m wide and 2.5 m high rigid box was filled with sand so as to simulate the sandy soil surrounding the tunnel. The setup was excited on a largescale shake table. The model tunnel used was a 1:8 scaled model with a cross-sectional diameter of 900 mm. The effective shock absorbing layer (SAL) on the seismic response of the model tunnel was also investigated. The thickness of the tunnel lining is 60 mm. The earthquake motion recorded from the Kobe earthquake waves was used. The ground motions were scaled to have the same peak accelerations. A total of three peak accelerations were considered (i.e., 0.1 g, 0.2 g and 0.4 g). During the tests, the strain, acceleration and soil pressure on the surface of the tunnel were measured. In order to investigate the effect of shock absorbing layer on the dynamic response of the sand- tunnel system, two tunnel models were set up, one with and one without the shock absorbing layer of foam board were used. The results shows the longitudinal direction acceleration of the model tunnel with a shock absorbing layer were lower than those of model tunnel without the shock absorbing layer, Which indicates that the shock absorbing layer has a beneficial effect on the acceleration reduction. In addition, the shock absorbing layer has influence on the hoop strain and earth pressure of the model tunnel, this the effect of shock absorbing layer to the model tunnel will be discussed in the paper.

Optimization Analysis of Construction Scheme for Large-Span Highway Tunnel Under Complex Conditions

AbstractThe construction process of the tunnel ground deformation regularity of surrounding rock, stability, deformation control of tunnel surface based on the requirements, combined with the characteristics of shallow tunnel with large-span. Used three-dimensional numerical simulation software, established a dynamic tunnel analysis program to simulate the construction process of center cross-diagram method and double sidewall drift method. Based on the stratum deformation, supporting force and analysis of plastic zone distribution, comparative analysis of engineering adaptability of different construction methods from the construction process and construction mechanics, get optimization tunnel construction scheme.

Gradient‐Enhancement of a Rock Model Applied to Numerical Simulations of Tunnel Advance

AbstractRock is classified as a frictional cohesive material characterized by nonlinear stress‐strain relations including softening leading to structural failure. To describe the mechanical behavior of rock comprising the accumulation of irreversible strains, strain hardening, and the degradation of stiffness and strength, an isotropic damage plasticity model for intact rock and rock mass was proposed in [1]. In the context of numerical simulations of tunneling, considering strain softening of rock allows to predict the formation of shear bands emanating from the tunnel surface due to the excavation process, which is crucial for engineers to forecast potentially dangerous situations related to failure. To ensure objective results in the softening regime upon mesh refinement, in the aforementioned rock model the concept of the crack band approach by Bažant and Oh was adopted. As a remedy of known deficiencies related to this regularization approach, the rock model is extended by the over‐nonlocal implicit gradient‐enhancement proposed in [2]. Accordingly, a nonlocal field of the damage‐driving variable, implicitly defined as the solution of a Helmholtz‐like partial differential equation, is introduced yielding a fully coupled system of second‐order PDEs. In the present contribution, the over‐nonlocal gradient enhancement of the rock model is presented and applied together with a linear‐elastic material model for shotcrete to finite element simulations of a deep tunnel constructed by the New Austrian Tunneling Method. Based on this real example, objectivity of the results with respect to the finite element discretization is discussed.

A smart unmanned aerial vehicle (UAV) based imaging system for inspection of deep hazardous tunnels

Abstract Inspection of deep tunnel networks is extremely challenging due to their inaccessibility, and them being an unknown and potentially hazardous environment. Unmanned aerial vehicles (UAVs) provide a viable alternative for access, and are unaffected by debris or sewer flow. However, commercial UAVs are designed for high altitude aerial imagery and are not appropriate for short-range detailed imaging of tunnel surfaces. In addition, autonomous flight is usually achieved using GPS, which is not available underground. This paper presents the design and development of a smart UAV platform, Surveyor with Intelligent Rotating Lens (SWIRL), customized for autonomous operation in tunnels. It can capture high resolution images for subsequent image processing, and defect detection and classification. An innovative rotating system enables undistorted imaging of the tunnel's inner circumference surface using a single camera. The proposed location method using limited data resulted in substantial unit weight and power consumption reductions, compared to existing systems, making more than 35 minutes of autonomous flight possible.

Study on heat transfer performance of metro tunnel capillary heat exchanger

The metro tunnel capillary heat exchanger, which is to lay the capillary along the wall surface of the subway tunnel, is a kind of front end heat exchanger of the air conditioning heat pump system. The numerical simulation is used to analyze the heat transfer characteristics of the metro tunnel capillary heat exchanger with different pipe spacings. Combined with the system regulation and operation, the optimal pipe spacing suitable for the metro tunnel capillary heat exchanger was obtained. Through experimental tests, we concluded the law of temperature distribution and the heat transfer characteristics of the sand with the capillary heat exchanger were buried, the correctness of the simulated value was verified.

Investigation of the excavation damaged zone around deep TBM tunnel using a Voronoi-element based explicit numerical manifold method

A Voronoi-element based explicit numerical manifold method is adopted to investigate the evolution process and failure characteristics of the excavation damaged zone around a deeply buried TBM tunnel. An explicit time integration scheme of numerical manifold method is adopted as the numerical platform, based on which a Voronoi polygon assemblage is generated to approximate the blocky structure of the surrounding rock mass resulting from discrete fracture networks. A new mathematical mesh generation method is developed to better adapt to the Voronoi polygons and an excavation algorithm including both in-situ stress equilibrium and TBM excavation modelling techniques is proposed to capture the mechanical response of the TBM tunnelling process. With the newly developed VE-ENMM approach, the progressive failure process of the surrounding rock mass in a headrace tunnel of Yindajihuang Project is simulated and the formation mechanism of the excavation damaged zone is explored. Simulation results show that a large extent of excavation damaged zone is easily formed in the highly fractured rock mass due to the high in-situ stress in deep grounds. Besides, relatively large convergence displacements are predicted around the tunnel surface, leading to a high risk of TBM shield jamming as in the practical situation. However, the development of damaged zone is effectively restrained and the convergence displacements are well controlled by an early installation of the tunnel lining segments, thus preventing the occurance of TBM shield jamming. Additional simulations are conducted to study the effects of the lateral in-situ stress ratio on the excavation damaged zone. It is inferred that the increase of lateral stress ratio facilitates the fracturing of the surrounding rock mass, which results in a larger extent of the damaged zone and more severe squeezing deformation compared with those under lower lateral stresses.

Theoretical study of the exhalation of radon from a circular tubular cover layer

Radium, which is naturally present in many rocks, decays to the radioactive gas radon, which is exhaled from the surface of underground tunnels and air-raid shelters and is a major source of human exposure to radioactivity. We developed a mathematical model for the migration of radon from a finite-thickness circular tubular emanation medium and a semi-infinite hollow cylindrical emanation medium based on the seepage–diffusion migration theory of radon in porous emanation media. We obtained an analytical solution for the distribution of radon concentration and a formula for the radon exhalation rate under steady-state conditions. When there was no seepage, the radon exhalation rate in the covering layer decreased as the thickness of the covering layer increased and tended toward zero. The radon exhalation rate from the covering layer increased as the radon diffusion coefficient increased. When seepage occurred, the difference in the radon exhalation rate between seepage and non-seepage decreased as the thickness of the covering layer increased. When v > 0, the radon exhalation rate in the covering layer increased as the seepage velocity increased. When v < 0, the radon exhalation rate in the covering layer decreased as the seepage velocity increased.

Building bridges: matching density functional theory with experiment

ABSTRACTWe will discuss the key concepts in density functional theory (DFT), how it can be used to model experimental data, and consider how the synergy between DFT and experiment can give significant insights. The discussion will centre on the scanning tunnelling microscope (STM) and surface problems, tracking the author's personal interest, though the general principles are widely applicable.

Wind speed characteristics and blown sand flux over a gravel surface in a compact wind tunnel

Abstract We investigated the influence of gravel coverage on roughness length and blown sand flux in a compact wind tunnel equipped with a turbulence generator and a piezoelectric blown sand meter. At gravel coverages from 5% to 15%, roughness length increased with increasing coverage. However, at coverages of 20% or greater, roughness length reverted to its value at 0% coverage. At the lowest wind speed of 6 m s−1, blown sand was fully trapped at gravel coverages of 15% or greater; however, coverage affected sand flux little at wind speeds of 8 and 9 m s−1 and had no effect at a wind speed of 10 m s−1. The increase in roughness length with gravel coverages from 5% to 15% corresponded to a decreased blown sand flux at heights less than 8 cm. However, at 8-cm height, a greatly decreased roughness length at higher gravel coverages (20%–30%) corresponded to a notable increase in blown sand flux, a change we attribute to aerodynamic smoothing.

The Seepage Control of the Tunnel Excavated in High-Pressure Water Condition Using Multiple Times Grouting Method

Groundwater can cause many hazardous problems when a tunnel is excavating. Seepage force acting on the support structure and the tunnel surface cannot be negligible. Under high groundwater table condition, the seepage situation becomes more complex and it is more difficult to control the leakage of groundwater to flow into a tunnel. In the paper, a multiple times grouting method is proposed, and the mechanical deformation behavior of surrounding rock is analyzed using the FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) software according to the high groundwater table condition of the Hokusatsu tunnel. The results present that multiple times grouting can control leakage and the rock deformation well, compared with one-time grouting condition in rock breaking and high water pressure area. The seepage force decrease around the tunnel and the displacement is controlled effectively. The pore pressure reduces inside the grouting zone using a new kind of grouting material, which is high permeability ultramicro particle cement (average particle size 1.5 μm). In the test fieldwork, the grouting scheme reduces the maximum discharge from 300 t/h to 40 t/h, and there is not obvious deformation and abnormal stress in the tunnel. The multiple times grouting method proposed in this research is verified effectively and can supply a positive experience to on-site construction.

Railway Freight Transport and Logistics: Methods for Relief, Algorithms for Verification and Proposals for the Adjustment of Tunnel Inner Surfaces

In Europe, the attention to efficiency and safety of international railway freight transport has grown in recent years and this has drawn attention to the importance of verifying the clearance between vehicle and lining, mostly when different and variable rolling stock types are expected. This work consists of defining an innovative methodology, with the objective of surveying the tunnel structures, verifying the clearance conditions, and designing a retrofitting work if necessary. The method provides for the use of laser scanner, thermocameras, and ground penetrating radar to survey the geometrical and structural conditions of the tunnel; an algorithm written by the authors permits to verify the clearances. Two different types of works are possible if the inner tunnel surfaces interfere with the profile of the rolling stock passing through: modification of the railroad track or modification of the tunnel intrados by mean milling of its lining. The presented case study demonstrates that the proposed methodology is useful for verifying compatibility between the design vehicle gauge and the existing tunnel intrados, and to investigate the chance to admit rolling stocks from different states. Consequently, the results give the railway management body a chance to perform appropriate measurements in those cases where the minimum clearance requirements are not achieved.

A Hybrid Ray and Graph Model for Simulating Vehicle-to-Vehicle Channels in Tunnels

Wave propagation in tunnels for vehicle-to-vehicle (V2V) communications scenarios is characterized by multiple diffuse reflections on tunnel surfaces as well as specular reflections on other objects inside the tunnel, leading to a nonstationary fading process. Such a fading process is difficult to model by ray tracing (RT), requiring a prohibitively high computational complexity due to the large number of diffuse reflections. In this paper, we propose two new ideas for modeling diffuse reflections in nonstationary scenarios: 1) We partition the nonstationary fading process into multiple stationarity regions with a given extent in time and frequency for which approximate wide-sense stationarity can be assumed; 2) we propose a hybrid model, tightly interlinking RT with a propagation graph, such that vertices for the propagation graph are obtained from interaction points calculated by RT for each stationarity region. We compare our hybrid model with measurement data in terms of the time-variant power-delay and the Doppler-power spectral-density as well as the root-mean square delay- and Doppler-spread. This analysis shows, that our hybrid model is the first numerical simulation model that is able to model diffuse reflections inside a tunnel with correct nonstationary (i.e., time-variant) temporal correlation for a nonstationary V2V communication link.