Tunnel Sidewall Research Articles

Driver's visual luminance model considering the reflection characteristics of a tunnel’s inner wall: Theory and practice I

A driver's visual luminance value under one-time stopping sight distance is the basic value for highway tunnel lighting design and quality evaluation. Currently, the driver's visual luminance value is obtained using the pavement reflection coefficient method with or without considering the diffuse reflection coefficient of the sidewall. This does not fully consider the influence of the reflection characteristics of the tunnel’s sidewall and pavement materials, potentially resulting in a large discrepancy between the measured and theoretically calculated values of driver’s visual luminance, which significantly affects the lighting design and quality evaluation of highway tunnels. Therefore, this study first establishes a driver's visual luminance theoretical model considering the reflection characteristics of the tunnel sidewall and pavement and uses the five-parameter model to fit the measured eigenvalues of the tunnel sidewall and pavement reflection to obtain a bidirectional reflectance distribution function. Theoretical calculation and actual measurement verification are performed using a 1:10 tunnel simulation model. Finally, the theoretically calculated value of visual luminance and the calculated values of the JTG and IESNA specifications are compared with the measured data of the tunnel simulation model. The results show that the mean error between the theoretically calculated value of visual luminance and the measured data remains at 6.0%, which is significantly lower than the corresponding errors in the JTG and IESNA specifications. After calculation, when a high diffuse reflection coating is applied to the sidewall of the tunnel, the driver's visual luminance can be increased by 16.8% on average.

Effect of Different Tunnel Distribution on Dynamic Behavior and Damage Characteristics of Non-Adjacent Tunnel Triggered by Blasting Disturbance

When a blasting is executed near two tunnels, the blasting wave will trigger a dynamic response and damage to the tunnels. Depending on the tunnel distribution, the path of the blasting wave to the remote non-adjacent tunnels will change. The aim of this study is to analyze the effect of the tunnel distribution on the dynamic response characteristics of a remote non-adjacent tunnel. Numerical models of two tunnels were established by PFC2D and three different tunnel distributions were considered. The two tunnels were divided into the adjacent tunnel and the non-adjacent tunnel according to their relative distance to the blasting source. The dynamic stress evolution, damage characteristics and the evolution of strain energy of the non-adjacent tunnel were initially analyzed. The results show that the stress wave amplitude of the non-adjacent tunnel is closely related to the tunnel distribution, but only near the sidewalls of the non-adjacent tunnel is the stress wave waveform sensitive to the tunnel distribution. The larger the tunnel dip, the more severe the damage to the non-adjacent tunnel. In addition, as the tunnel dip increases, the maximum strain energy densities (SEDs) in the roof, floor and sidewalls of the non-adjacent tunnel exhibit different trends. The influence of the wavelength of the blasting wave is further discussed. It is shown that the dynamic stress amplification factor and damage degree around the non-adjacent tunnel is usually positively correlated with the wavelength of the blasting wave. Moreover, the release of strain energy around the non-adjacent tunnel has a positive correlation with the wavelength. The SED variations in different areas around the non-adjacent tunnel also exhibit different trends with the increase of tunnel dip.

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.

Numerical study on the critical criterion for predicting the plug-holing under lateral mechanical exhaust in tunnel fires: Considering the effect of smoke flow in longitudinal direction

This paper has analyzed the phenomenon of plug-holing under lateral mechanical exhaust in tunnel fires by conducting large eddy simulations (LES) with Fire Dynamics Simulator (FDS). The lateral mechanical smoke exhaust is a method of smoke controlling in tunnel fires with exhaust vents set in the tunnel sidewall. The results show that the phenomenon of plug-holing occurs at the lateral exhaust vent as the exhaust rate increases. The occurrence of plug-holing will lead more fresh air discharged through the vent, thereby reducing the smoke exhaust efficiency. The smoke layer thickness and temperature downstream the vent in the tunnel are analyzed to evaluate the exhaust effectiveness of lateral mechanical exhaust. When the plug-holing does not occur, increasing exhaust rate can effectively reduce the smoke layer thickness. While the plug-holing occurs, the increasing exhaust rate will increase the smoke layer thickness on the contrary. In terms of reducing smoke temperature in the tunnel, increasing exhaust rate has very limited effect in this study. Therefore, it is not the case that the higher the exhaust rate, the better the smoke exhaust efficiency and effectiveness. There is a critical exhaust rate under which the plug-holing can be avoided. Furthermore, considering the horizontal and vertical inertial forces of the smoke beneath the vent, a critical criterion (Ri'critical) for predicting the occurrence of plug-holing of lateral mechanical exhausting is proposed. Based on the results of different exhaust rates, heat release rates and vent sizes, the critical criterion (Ri'critical) that corresponds to the occurrence of plug-holing can be determined as 0.6.

Field Test of Concrete Impermeability of Side Wall of Lakeside Highway Tunnel

The impermeability of concrete of the exterior wall of the underground tunnel in water-rich stratum is a key concern of engineers. Taking the Aixihu highway tunnel in Nanchang city as an example, the impermeability of the concrete in the side wall of the highway tunnel is tested, through multiple tests, such as the embedded steel pipe, water injection, and field observation. The results show that, under the action of 2mpa of water pressure, no water flow permeates from the side wall of the concrete tunnel, indicating that the impermeable performance of concrete tunnel in this section meets the engineering requirements, and hoping that this research can be used as a reference for other similar projects.

Evaluation of the effect of decorated sidewall in tunnels based on driving behavior characteristics

As a novel traffic safety facility, the decorated sidewall in tunnels plays a crucial role in improving the safety and upgrading the driving environment. The design element spacing, frequency patterns and color, are important elements in the design of the tunnel wall decoration. In order to analyze the impact of the tunnel sidewall decoration element complexity on the driving behavior under different driving conditions, this paper performs a detailed visual-action-cognitive driving task design. In the driving simulation test, three sidewall decoration schemes for different element complexities (character, character and ribbon, ribbon and snowflake) are designed at the level of pattern frequency and spacing respectively fixed at 1.26 Hz and 17.5 m, compared with the tunnel without sidewall decoration. Therefore, thirty drivers are recruited. Six indexes, including the acceleration and lateral position, are considered to construct the evaluation index system from the aspects of speed adjustment, operation stability and attention concentration levels. The significance and effect size of the indexes are explored using the ANOVA two-way repeated measures. The fuzzy comprehensive evaluation model based on the entropy weight method, is used to compare the effects of four sidewall decoration schemes.The results show that the complexity of the sidewall decoration elements highly affects the speed adjustment level, operation stability level and attention dispersion level of the drivers. The results of the fuzzy comprehensive evaluation show that, compared with the four sidewall decoration schemes in the whole and middle sections of the tunnel, the design scheme with the mural elements as characters under the condition of fixed frequency and spacing, has a higher comprehensive score. This indicates that adding appropriate mural elements on the sidewall of the tunnel improves the longitudinal driving stability and speed control ability of the driver, and makes the driving experience more comfortable. This paper demonstrates that a reasonable tunnel sidewall decoration plays a crucial role in improving the safety of the tunnel driving environment. Finally, it provides a theoretical support and technical guarantee for improving the traffic safety using tunnel sidewall decoration.

Effects of Sidewall Brightness on LED Lighting Environment and Visual Performance in Road Tunnels

The lighting design of a road tunnel focuses on the setting of pavement luminance. As for the tunnel sidewall luminance, it simply follows the principle of no less than 60% of the pavement luminance. In fact, the sidewall is one of the important components of the tunnel lighting environment; however, the impact of the improvement of sidewall brightness on the LED lighting environment in a tunnel has not attracted enough attention. In this study, the impact of the improvement of tunnel sidewall brightness on the lighting environment and visual characteristics of human eyes were analyzed based on the lighting experiments when the tunnel sidewalls were decorated with two different types of materials and illuminated by LED lamps with five different color temperatures. The test results show that the tunnel sidewall luminance will increase if the energy-storage and luminescent coating with high reflectance is decorated on tunnel sidewalls, and the pavement luminance increases with the increasing sidewall luminance. After the improvement of the sidewall and pavement luminance, the visible distance for a small object in the tunnel will increase to a certain extent. Furthermore, there is no discomfort for drivers during driving, and the changing of eye pupil diameter is relatively stable, which indicates that the increase in tunnel sidewall luminance has a positive effect on the visual performance of drivers.

Investigation of critical velocity in curved tunnel under the effects of different fire locations and turning radiuses

Toxic smoke is one of the main threats to people trapped in tunnel fires. Propagation characteristics of smoke flow differ between curved and straight tunnels, depending on the tunnel turning radius. In this study, experiments and numerical simulations were conducted to analyze the critical velocity of a curved tunnel under different fire scenarios, where different heat release rates, tunnel turning radiuses and fire locations were considered. Results showed that the critical velocity varied as the transverse fire location changed, reaching its minimum value when the fire was located at the transverse center of the tunnel, and increased gradually as the fire source approached the tunnel sidewall. For a given fire location, the critical velocity increased with the tunnel turning radius. It is speculated that a decrease in the tunnel turning radius may increase the resistance to smoke flow and has the advantage of preventing smoke propagation. A predicted correlation of the critical velocity considering the effects of different heat release rates, tunnel turning radiuses, and fire locations has been proposed. Predicted results of the improved correlation are consistent with results obtained from the numerical simulation. The outcomes of this study may provide a reference for tunnel ventilation system design.

Enhanced lighting on the road surface with TIR-PA optical element on tunnel sidewall.

Both the lighting quality and driving safety inside the tunnel have been quite a concern around the world. In this study, a plate with prism array of total internal reflection (TIR-PA) has been designed to enhance the lighting on the road surface inside the tunnel in adherence to traffic safety as well as energy savings. Such optical elements, above the tunnel sidewall, can redirect the rays emitted from both the headlight and lighting devices to the road surface, which supports higher flux on the road. Simultaneously, the simulation is conducted with consideration of practical factors based on the mathematical model and edge-ray principle to attain the effect of the TIR-PA plates. On the one hand, for the rays from the lighting devices, the enhancement rate of illuminance has reached 12.60%-16.58%, which is attributed to TIR-PA plates above the different sidewalls of the Lambertian scattering property. TIR-PA can be suitable for various sidewall materials due to the small effect of illumination reduction. On the other hand, 30.2%-32.2% rays of the headlight source received by the sidewall, due to the effect of TIR-PA plates, are redirected to the driving distance for 27.3-71.9 m, which makes 15.9-31.1m2 of road surface brighter. It makes contributions to the improvement of illuminance distribution and drivers' pre-judgment. In the future, broader applications regarding the TIR-PA plates will be explored widely in tunnel lighting systems due to the low production cost.

Effect of Stagger on Low-Speed Performance of Busemann Biplane Airfoil

In this study, the low-speed performances of the Busemann biplane were clarified, focusing on the relative contributions of the upper and lower elements to the total aerodynamic characteristics of the biplane. Also, the effects of the staggered biplane, which changes the horizontal distance between two wings in a biplane configuration, were investigated by balance measurements and numerical simulations. The flow velocity was 15 m/s, and the Reynolds number based on the airfoil chord length was 2.1 × 105. In the tests of the integrated biplane wing, the attack angles of the wing elements were varied by a balance system and turntable, which were set in the wind tunnel sidewall. The results show that the lower element generated most of the lift and drag of the Busemann biplane (or the baseline biplane model with no stagger) at high angles of attack. At angles above 20 deg, the contribution of the lower element to total aerodynamic characteristics is almost constant, with 95% of the total lift and 88% of the total drag. The total lift and drag of the baseline model were smaller than the sum of the individual elements that were treated as a single configuration. The increments of lift and drag due to the stagger effects were confirmed, especially at high angles of attack. When the stagger value increases, the high-pressure area near the leading edge of the lower surface of the upper element also increases, which increases the lift and drag of the up-per element. This is the main reason for the increments of total lift and drag of the biplane model. The stagger effects also prevented the leading-edge separation of the lower element in the biplane configuration and increased the lift slopes of the biplane model.

Effect of flexibility ratio on seismic response of rectangular tunnels in sand: Experimental and numerical investigation

The flexibility ratio(F) is defined as the stiffness of a structure relative to that of soil, a critical factor affecting the soil–structure interaction. This study aimed to investigate the effect of F on the seismic response of rectangular tunnels constructed in sand. Shaking table tests were performed based on a scale model of a tunnel with different stiffness values. A 3D finite element model was established using ABAQUS, and the numerical results were compared with the test results. Subsequently, the verified model was implemented in a parametric study. The results showed that tunnels with lower F have higher acceleration responses in the high frequency-range of input motions. In addition, the amplification of the ground acceleration decreases with an increase in F, and the maximum response occurs in a longer period relative to the free-field. The distribution of the dynamic earth pressure along the tunnel lining with different F is relatively complex; nevertheless, overall, rigid tunnels have greater values than flexible tunnels. The dynamic bending moment along the tunnel sidewall decreases with increasing F, but it has the same trend along the sidewall. The presented results may lead to a better understanding of the seismic response of rectangular tunnels constructed in sand, providing practical references for the seismic design of similar underground structures.

Mechanical response of inclined TBM tunnel due to drainage settlement of deep sandstone aquifer

Drainage of deep aquifers can cause stratum settlement, which has significant effects on the architectural structures within them. Especially for inclined TBM tunnels, the settlement may lead to the longitudinal differential deformation and damage of segments. However, most previous studies on the effects of aquifer drainage settlement on deep structures have focused on the vertical shaft in coal mines, and little attention has been paid to inclined TBM tunnels in deep sandstone aquifers. Through the physical model test and numerical simulation, in this study, the mechanical characteristics and deformation behavior of an inclined TBM tunnel in the deep water-bearing sandstone and impermeable mudstone before and after the aquifer drainage were investigated. The distribution and variation of stresses, internal forces, and deformation on tunnel segments before and after drainage were systematically analyzed along the tunnel longitudinal and circumferential directions. Results show that the whole tunnel is always under compression and mainly subjected to the coupling effect of bending moment and axial compression in the longitudinal direction. After drainage, the longitudinal and circumferential stresses as well as circumferential axial force increase remarkably at the tunnel sidewall but decrease at the tunnel crown and invert. While for the circumferential bending moment, by contrast, it increases at the three positions. In addition, the tunnel experiences a noticeable bending at the junction of the two strata after drainage due to the synchronous settlement with the sandstone, resulting in severe stress concentrations and the formation of the longitudinal shear band at the stratigraphic junction.

Environmental and Fecal Indicator Organisms on Fruit Contact Surfaces and Fruit from Blueberry Mechanical Harvesters

Although previous studies have examined microbial loads on food contact surfaces in blueberry packing plants, there is currently no information regarding microbial risks associated with mechanical berry harvesters used in commercial blueberry production. In this study, we surveyed up to nine fruit contact surfaces on seven mechanical harvesters in each of 2015 and 2016 in the field. These surfaces included the shaking rods at the front of the harvester, the sidewalls of the harvesting tunnel behind the shaking mechanism, the catcher plates collecting the detached berries, horizontal and vertical fruit conveyor belts, and berry lugs collecting the fruit at the back of the harvester. Swab samples were collected from each surface three times a day (morning, noon, and evening) and assessed for environmental and fecal indicator organisms including total aerobes, total yeasts and molds, coliforms and fecal coliforms, and enterococci. At the same time points, fruit samples were assessed for microbial loads before the fruit entered each harvester and after they exited the harvester. Results showed statistically significant differences in microbial loads among harvester surfaces, whereas the effect of sampling time was generally not significant. High levels of total aerobes and total yeasts and molds were recorded, especially on horizontal surfaces and/or those located at the bottom of the harvester such as the lower sidewall, the catcher plates, and the horizontal conveyor belt. These surfaces therefore should be targeted by cleaning and sanitization practices. There was also statistical evidence that passage through the harvester may increase the levels of the environmental microorganisms on fruit in the field. In contrast, fecal indicator organisms such as fecal coliforms and enterococci were detected only sporadically and at very low densities on harvester surfaces and blueberry fruit, and there was no evidence that passage through the harvester increased their levels on the fruit. Berry lugs consistently harbored microbial loads, and given their movement back and forth between the field and the packing plant, deserve particular attention with regard to cleaning, sanitization, and storage protocols.

Characterization of Underlying Twin Shield Tunnels Due to Foundation-Excavation Unloading in Soft Soils: An Experimental and Numerical Study

Excavation near or above existing shield tunnels often results in adverse impacts on tunnel stability. To ensure the serviceability of existing tunnels, this paper presents experimental and numerical studies with reference to a foundation pit case history excavated above twin-tube shield tunnels in soft soils. The experimental tests were firstly applied to study the deformation characteristics and structural response of the shield tunnels. Thereafter, an extensive numerical investigation was performed to determine the influence of some factors such as cover-to-excavation depth ratio, length-to-depth ratio, and unloading ratio on tunnel displacement behaviors. It was demonstrated that the tunnel heaves as the excavation proceeds, and heaves and horizontal displacements reach their maximum values when the excavation is finished. The earth pressure around the tunnels is symmetrically distributed in a gourd shape, with a larger reduction at the tunnel crown and invert and a smaller reduction at tunnel side walls. Additionally, the earth pressure at the tunnel crown and invert changes more significantly than that at other parts. The tunnel moment increment is significantly affected by the tunnel excavation depth. The axial force at or near the side walls of the tunnel is the most sensitive to the unloading effect induced by the excavation activity.

Spatial resolution enhancement of rotational-radar subsurface datasets using combined processing method

Effective visualisation of railway tunnel subsurface features (e.g. voids, utilities) provides critical insight into structural health and underpins planning of essential targeted predictive maintenance. Subsurface visualisation here utilises a rotating ground penetrating radar antenna system for 360° point cloud data capture. This technology has been constructed by our industry partner Railview Ltd, and requires the development of complimentary signal processing algorithms to improve feature localisation. The main novelty of this work is extension of Shrestha and Arai’s Combined Processing Method (CPM) to 360° Ground Penetrating Radar (360GPR) datasets, for first-time application in the context of railway tunnel structural health inspection. Initial experimental acquisition of a sample rotational transect for CPM enhancement is achieved by scanning a test section of tunnel sidewall - featuring predefined target geometry - with the rotating antenna. Next, frequency data separately undergo Inverse Fast Fourier Transform (IFFT) and Multiple Signal Classification (MUSIC) processing to recover temporal responses. Numerical implementation steps are explicitly provided for both MUSIC and two associated spatial smoothing algorithms, addressing an identified information deficit in the field. Described IFFT amplitude is combined with high spatial resolution of MUSIC via the CPM relation. Finally, temporal responses are compared qualitatively and quantitatively, evidencing the significant enhancement capabilities of CPM.

On-Site Monitoring for the Stability Evaluation of a Highway Tunnel above Goaves of Multi-Layer Coal Seams

This paper presents the on-site monitoring of a medium–long highway tunnel constructed above a goaf of a multi-layer coal seam, in order to evaluate and maintain safety during operation. The case study of the Tianzimiao medium–long highway tunnel in Shanxi province was conducted above a goaf of a multi-layer coal seam with typical geological and engineering conditions in China, where a total of four coal seams (seam no. 3, 8, 12, and 15) were mined out with a total thickness of up to 11 m. Methods including data collection, engineering geological survey, drilling, geophysical prospecting, testing, and on-site monitoring were adopted, and a geo-mechanical model was established to conduct the research. Stratified monitoring was applied to investigate the individual settlement and deformation of the four layers of the goaf below, and a prediction of the possible deformation in tunnel floor ground was made based on the stratified measurements. The settlement of the tunnel sidewall, the internal stress in the fractured zone of the surrounding rock, and the deformation above the tunnel entrance were also monitored, and the monitoring data were compared with the numerical simulation results for the safety evaluation of the tunnel. The results show that the current tunnel deformation values and trend are both within the safety scope of the evaluation and prediction. The stability evaluation method for the multi-layer goaf used in this paper and the long-term on-site monitoring and timely feedback during operation is helpful to ensure the safe use of the tunnels above the goaves of multi-layer thick coal seams.

Mechanical Characteristic and Length Optimization of System Anchor in Loess Tunnel Based on Field Measurement and Analytical Solution

In this paper, field measurement is used to obtain the force of system anchor in its actual working condition and stress situation of system anchors in different parts of loess tunnel is analyzed based on field test results, indicating the reasons why values of measured axial force of system anchor are different in different parts of loess tunnel. Based on the displacement solution of Mindlin problem, this paper deduces the analytical solution to stress distribution of system anchors in the sidewall of loess tunnel under the pull-out force, analyzes the distribution forms and influencing factors of shear stress and axial force. At the same time, analytical solutions to system anchor stress and surrounding rock plastic zone radius are tentatively applied to the analysis of stress characteristics and length optimization of system anchor in loess tunnel. The research results are of great significance to understand the mechanical characteristics of anchors in loess tunnel and to optimize the design of anchors in the primary support system of loess tunnel, which leads to accelerated construction progress and low economically cost, especially in loess tunnels with large cross section and long span.

STUDY ON STABILITY CONTROL OF COAL MINE TUNNEL EXCAVATED IN WEAK ROCK MASS IN INDONESIA

This paper focuses on the stability analysis and support design of the coal mine tunnel excavated in weak rock mass in an Indonesian underground coal mine through numerical simulations using the FLAC3D software. The PT Gerbang Daya Mandiri (GDM) coal mine situated in Indonesia was selected as a mine site in this study. According to the results of a series of numerical simulations, the stability of the mine tunnel decreases by increasing the depth and stress ratio. Ground control problems, for example falling roof, sidewall collapse, and floor heave are expected unless an appropriate support system is anticipated. Three support systems, including friction rockbolt, steel arch, and shotcrete are discussed as methods to stabilize the roof and sidewalls of the mine tunnel. From the simulated results, the steel arch is considered to be the most effective support method when compared with other support systems. The steel arch which is installed with closer space and larger crosssection delivers a better stability control to the roof and sidewalls of the mine tunnel. Although the stability of the roof and sidewalls of the mine tunnel can be maintained effectively by the steel arch support, the occurrence of floor heave is expected when the mining depth is increased. To control the floor stability of the mine tunnel, three techniques by applying cablebolt, invert-arch floor, and grooving method are therefore investigated and discussed. Based on simulated results, the heaving of the floor is well controlled after the cablebolt, invert-arch floor, and grooving methods are applied. Nevertheless, it is found that controlling the floor heave by cablebolt support could be the most suitable method comparing with other support systems in terms of the installation process, providing flat and safe working conditions of the floor, and economy. Additionally, the cablebolt with closer row space and longer length works more effectively to control the heaving problem of the floor. Keyword

Seismic data inversion with acquisition adaptive convolutional neural network for geologic forward prospecting in tunnels

Seismic forward prospecting is essential because it can identify the velocity distribution in front of the tunnel face and provide guidance for safe excavation activities. We have developed a convolutional neural network (CNN)-based method to invert forward-prospecting data recorded in tunnels for accurate and rapid estimation of seismic velocity distribution. Targeting the unusual seismic acquisition setup in tunnels, we design two separate encoders to extract features from observation data recorded on both tunnel sidewalls. Subsequently, these features are concatenated to a decoder for velocity prediction. Considering the various acquisition setups used in different tunneling projects, the deep-learning inversion network must be flexible in terms of the seismic source/receiver positions for practical application. We have generated two auxiliary feature maps that can be used to feed acquisition information to our network. Our network, acquisition adaptive CNN ([Formula: see text]-CNN), can be trained by defining the loss function based on the [Formula: see text]-norm and multiscale structural similarity. Compared with traditional CNNs, our method has superior performance on data sets with fixed and random acquisition setups and also demonstrates certain robustness when handling synthetic data with field noise. Finally, we test how the network performs when feeding the modified acquisition setup information. It turns out that the inversion result will demonstrate a shift when the provided acquisition setup information shift, which verified the validity of the network and its use of acquisition information.

Macroscopic and Mesoscopic Characteristics of a Small-Span Metro Tunnel in the Development of a Disaster Under Load

A similarity model with a volumetric similarity ratio of 1:100 and a granular flow model for the tunnel were designed. By comparing macroscopic and mesoscopic information (such as fracture process, strain evolution, stress transfer, crack propagation, and stress distribution) of the tunnel models under load, the failure mechanism of the metro tunnel under load was investigated. The result showed that: 1) under the loading path, the instability area of the tunnel is mainly distributed in the straight wall on both sides. When the load is 1.5 MPa, a large number of cracks on both sides of the straight wall run through, resulting in the initial failure of the rock mass; 2) the surface rock mass of arch bottom is under tensile stress and the deep rock mass is under pressure stress, therefore, the fracture does not develop continuously. The surface of straight wall produces continuous development crack under the action of tensile stress; 3) the arch bottom first responds during the stress redistribution of the small-span tunnel; the top and middle parts of the side walls of the running tunnel with greatest potential for damage respond most; 4) in the process of stress redistribution, the peak stress of the deep measuring points of the straight wall is greater than that of the free surface; 5) at the initial stage of loading, tensile cracks account for a high proportion of all cracks found. When the load is 1.5 MPa, the proportion of shear cracks increases to 28%, and when the load is 1.6 Mpa, the proportion of shear cracks increases to 31%. Finally, the tensile-shear effect triggers the failure of the tunnel.