Tunnel Surface Research Articles

Image-based intelligent detection of typical defects of complex subway tunnel surface

We propose a new hybrid model algorithm that addresses the challenges of recognizing multiple objects. Specifically, objects are recognized from massive, large-scale, and complex tunnel images without repeated parameter adjustments and high-cost annotation datasets. Our algorithm utilizes a multi-scale, fusion-based encoder–decoder segmentation model to classify objects from high-resolution images of the tunnel surfaces. To enhance the accuracy of crack identification from complex backgrounds, we incorporate the Expanded Threshold Search (ETS) algorithm and the Local Window Extraction (LWE) algorithm. The acquisition device and the algorithm, implementing the multi-object dataset, have successfully tested, whereby it recognizes five objects and attains the highest Intersection over Union (39.3% for the crack object, 65.6% for the leakage object, and 75.7% for the rest).

A novel combined intelligent algorithm prediction model for the tunnel surface settlement

To ensure the safety and stability of the shield tunnel construction process, the ground settlement induced by the shield construction needs to be effectively predicted. In this paper, a prediction method combining empirical mode decomposition (EMD), chaotic adaptive sparrow search algorithm (CASSA), and extreme learning machine (ELM) is proposed. First, the EMD is used to decompose the settlement sequence into trend vectors and fluctuation vectors to fully extract the effective information of the sequence; Second, the sparrow search algorithm is improved by introducing Cubic chaotic mapping to initialize the population and adaptive factor to optimize the searcher’s position formula, and the chaotic adaptive sparrow search algorithm is proposed; Finally, the CASSA-ELM prediction model is constructed by using CASSA to find the optimal values of weights and thresholds in the extreme learning machine. The fluctuation components and trend components decomposed by EMD are predicted one by one, and the prediction results are superimposed and reconstructed to obtain the predicted final settlement. Taking a shield interval in Jiangsu, China as an example, the meta-heuristic algorithm-optimized ELM model improves the prediction accuracy by 10.70% compared with the traditional ELM model. The combined EMD-CASSA-ELM prediction model can greatly improve the accuracy and speed of surface settlement prediction, and provide a new means for safety monitoring in shield tunnel construction. Intelligent prediction methods can predict surface subsidence more automatically and quickly, becoming a new development trend.

Path Loss and Auxiliary Communication Analysis of VANET in Tunnel Environments

Vehicular ad hoc network (VANET) communications face severe fading problems due to the signal reflections and diffractions within tunnels. Unlike the open road, the space of a tunnel is very limited, so VANET communication performance in a tunnel is seriously affected. In the process of signal transmission, the reflected signal is symmetrical with the incident signal after it is reflected by the road and the wall. In this paper, we establish a mathematical model of path loss for V2V (Vehicle-to-Vehicle) communication based on the principle of signal reflection symmetry in tunnels and considering several factors, such as the tunnel surface and the color of the tunnel wall. In addition, we use cooperative communication to form a virtual multiple-input multiple-output (V-MIMO) system, to improve the communication quality in tunnels. In the proposed system, the OBU (On-Board-unit) and RSU (Road-Side-Unit) share each other’s antennas, so that wireless cooperative communication can be employed, without increasing the number of antennas in a one-way tunnel. Therefore, this multipath fading internal electromagnetic wave propagation model can be used to improve performance. A deep reinforcement learning algorithm was used to solve the pairing problem to obtain a more accurate OBU and RSU pair, to form a V-MIMO system. Here, the RSU is regarded as an agent and interacts with the OBU in the tunnel. The optimal strategy was learned in a real-time changing simulation environment, and the experiment verified the convergence of the algorithm. The simulation results showed that, compared with the Q-learning based scheme, the optimal matching algorithm based on V-MIMO and a DQN (Deep Q-network) could effectively reduce the probability of transmission outages and improve the communication efficiency in tunnels.

Ground motion amplification pattern with TBM tunnels crossing soil-rock interface: Shaking table test

The current aseismic design has seldom considered the effect caused by underlain tunnels. Previous studies focused on the scenarios of tunnels embedded in homogeneous soil under transverse seismic excitation. This paper aims to investigate the tunnel effect on the surface acceleration response in soil-rock strata by shaking table tests. Three sets of excitations are employed and input along the shaking table in both transverse and longitudinal directions. The soil-rock site is classified as four micro-zones with varying conditions, to mount observation stations of acceleration sensors. Dynamic characteristics of the four zones are identified by the transfer function (TF) method, and the tunnel effect on the ground acceleration response is obtained by comparing the spectral acceleration results between the free-field and ground-tunnel models. The test results indicate that the tunnel effect varies with the site conditions. Distinctively, a significant amplification effect is observed at the A4 zone, located on the soil deposit near the soil-rock interface. Then, it is proved that the scattering waves generated at the interface and the standing waves trapped between the tunnel and upper ground surface account for the amplification, revealed by the discrepancies of the TF results and acceleration details between the free-field and ground-tunnel models.

A suction method to mitigate pressure waves induced by high-speed maglev trains passing through tunnels

When a high-speed maglev train travels through a tunnel, sudden pressure changes are generated in the tunnel, which have a negative impact on the comfort of passengers and the service life of equipment. Moreover, a strong micro-pressure wave is radiated, causing environmental noise at the tunnel exit. Using the unsteady compressible Reynolds-averaged Navier–Stokes equations based on the shear stress transport k-ω turbulence model, this study investigates the effectiveness of suction (deployed on the tunnel wall) to mitigate the pressure waves and compares the results obtained under different suction velocities. The results show that when the suction is actuated, a low-pressure region is generated near the suction slots, which can trim down the initial compression wave and the high-pressure region in front of the train. Moreover, the instantaneous train surface pressure, tunnel surface pressure and micro-pressure wave have a significant relationship with the suction velocity. For instance, compared to the no suction case, the suction-actuated case with the suction velocity of 50 m/s contributes to an amplitude reduction of 10.44% and 30.61% for the first and second sudden pressure changes, respectively, at train surface measuring point H1 (at the nose of the train); an amplitude reduction of more than 14% for the sudden pressure change at tunnel surface measuring point T17 (at the middle of the tunnel); and an amplitude reduction of 12.44% for the micro-pressure wave at measuring point M2 (outside the tunnel and 20 m from the tunnel exit). These indicate that the suction technique can be employed to alleviate the tunnel aerodynamic effect. Also, the results obtained under different suction velocities can serve as a guide for the design of suction actuators.

Prediction and Application of Surface Settlement of Shallow Buried Tunnels Taking into Account Strata Slip Cracks

The empirical formula is one of the traditional methods used for predicting ground deformation settlement caused by tunnel excavation. Due to its rationality and simplicity, the Peck formula is widely used for predicting surface subsidence. However, due to its limitations, it is necessary to modify it when predicting surface settlement caused by tunnel excavation in different strata. In this paper, a correction formula for the width coefficient of a tunnel surface settlement slot is derived from the Peck formula by taking into account the theory of strata slip cracks. Values are calculated using the correction formula and compared with measured data to verify the effectiveness of the correction formula. The main conclusions are: (1) The position corresponding to the width of the settlement in the Peck curve is the point where the formation is most prone to slip cracking. (2) In the general shallow buried case, the settlement groove width coefficient K and the internal friction angle φ of the ground satisfy the formula K = 1/tan(45° + φ/2 + a) + b, and the values of parameters a and b reflect the average values of the geometric properties of the tunnel based on the measured data. (3) The prediction of the correction formula is consistent with the measured data, and thus the correction formula can be applied to problems related to the stability of shallow buried tunnels.

Progressive Failure Characteristics and Failure Symptoms of Straight-Walled Arched Sandstone Tunnels

In order to investigate the development process of crack formation in shallow-buried sandstone tunnel, biaxial compression tests were conducted on a similar model of the real straight-walled arched sandstone tunnel. The results indicate that the initial crack appeared at the arch line on both sides of the tunnel and propagated downwards, eventually leading to spalling of the rock mass on the surface of the tunnel, forming a V-shaped groove. Additionally, slab cracks were observed in the straight wall on the right side of the tunnel, which were approximately parallel to the vertical load. The failure characteristics of the tunnel were closely related to the fractal dimension of the crack geometry distribution. During the tunnel compaction and elastic deformation stage, the fractal dimension of the cracks in the tunnel surface increased linearly, while during the crack propagation stage, the fractal dimension increased gradually, with a sudden increase occurring just before the rock mass reached its peak load. The acoustic emission results revealed that AE ringing counts and amplitude were inactive during the first 4239 seconds of the test. And they only increased during the crack propagation stage. The continuous decrease of the b-value and the sudden increase of the fractal dimension of cracks can serve as a reliable precursor of tunnel failure.

Strategies to promote tendon-bone healing after anterior cruciate ligament reconstruction: Present and future.

At present, anterior cruciate ligament (ACL) reconstruction still has a high failure rate. Tendon graft and bone tunnel surface angiogenesis and bony ingrowth are the main physiological processes of tendon-bone healing, and also the main reasons for the postoperative efficacy of ACL reconstruction. Poor tendon-bone healing has been also identified as one of the main causes of unsatisfactory treatment outcomes. The physiological process of tendon-bone healing is complicated because the tendon-bone junction requires the organic fusion of the tendon graft with the bone tissue. The failure of the operation is often caused by tendon dislocation or scar healing. Therefore, it is important to study the possible risk factors for tendon-bone healing and strategies to promote it. This review comprehensively analyzed the risk factors contributing to tendon-bone healing failure after ACL reconstruction. Additionally, we discuss the current strategies used to promote tendon-bone healing following ACL reconstruction.

Effects of the surface irregularity of termite tunnels on food transport efficiency: a simulation study.

Termites are believed to have evolved in a way that optimizes their foraging efficiency, which involves both searching for food and transporting it efficiently. Although the search efficiency has been well-studied through tunnel pattern analysis, transport efficiency has received limited attention due to the challenges of directly observing behavior that is highly influenced by environmental conditions. In this study, we introduce an individual-based model to simulate transport behavior and examine transport efficiency (E) by considering the tunnel surface irregularities and curvature, which are critical environmental factors. The model is characterized by four control variables: tunnel curvature (k1), termite stopping time at irregularity sites (k2), irregularity distribution (k3), and irregularity density (k4). The simulation results indicate that as k1 increases, E decreases, while k3 has little impact on E. The impact of k4 on E is decisive; when k4 ≤ 6, an increase in k4 results in increased traffic jam frequency and a faster reduction in E. However, when k4 > 6, the jamming frequency is not significantly affected, reducing the decrease in E. k2 strongly contributes to reducing E without significantly affecting the frequency. In the discussion section, we explore potential mechanisms that termites use to maintain transport efficiency in heterogeneous soils, and discuss how to improve the model to better reflect real-termite systems.

Evolution of tunnel uplift and deformation induced by an upper and collinear excavation: A case study from Shenzhen metro

This paper presented a case study in Shenzhen metro where the evolution of the tunnel uplift and deformation was investigated based on the field observation. The deformation of tunnel, diagram wall and ground surface were carefully measured over 400 days. The tunnels had been significantly uplifted by 34 mm, while less convergence deformation was observed in each section. For the long excavation collinear to the underlying tunnel in Shenzhen granite residual soil, the superposition unloading of the other adjacent upper and collinear excavation activities has a more significant impact on the tunnel uplift compared to the excavation of upper section, which lead to more than half of the tunnel uplift amount. In addition, a slight twist deformation was observed in the tunnel section, which need to be focused in the evaluation of tunnel safety because it is a main contribution to the tunnel diseases. The well-document site data and results can provide systematic field data and useful engineering reference for similar projects.

Deep learning based distortion restoration and defect segmentation from linear scanning camera images

With long-term operation of tunnels, the surface of tunnel lining is prone to crack, spalling, water leakage and other defects. Therefore, the detection of tunnel surface defects has become an important process to ensure the safety of tunnel operation. Linear scan cameras have become the main way of tunnel surface defect detection because of their ultrahigh resolution and ultrahigh scanning frequency. However, in the process of collecting tunnel surface images at high speed, the linear scan cameras are easy to cause images distortion, which leads to reduction of tunnel defect identification accuracy. Thus, this paper proposes a tunnel surface distortion image restoration method based on a supervised generative adversarial network, which introduces an attention mechanism to guide the method to calibrate the weights of feature channels. It solves the problem of distortion in the process of images acquisition of the linear scan cameras. Then, to deal with the difficulty in identifying small-size tunnel defects in complex tunnel environments, this paper combines a backbone network with a multi-scale feature fusion module based on the You Only Look At CoefficienTs (YOLACT) network, which enhances the feature extraction ability of the network and improves the accuracy of tunnel surface defect identification.

Predicting mechanical development of mine functional mortar: experiment and thermodynamic analysis

Shotcrete mortar is an imperative material for tunnel surface supporting. The mine environment with different temperature affects the mechanical development of mortar, resulting in a difficult to predict its compressive strength development at high temperature. In this investigation, the compressive strength, hydration heat, mineral evolution, pore content of mortar samples at 20 and 60 °C, containing partial steel slag powder, were comprehensively compared by experiment and simulation in order to provide a reliable approach for underground materials compressive strength prediction. Results show that the compressive strength development of the samples cured at 20 and 60 °C, is consisted with the corresponding cumulative hydration heat, and the correlation coefficient is higher than 0.96. The hydrates and heat of the samples are significantly affected by the cement type, mineral admixture, and temperature. Indeed, increasing temperature significantly accelerates the minerals’ hydration and heat release. Combining the composition, pore and single mineral hydration heat simulation, the mortar compressive strength development of the mortar in deep mine can be predicted by a thermodynamic model.

Characteristics of air flow driven by the water free surface in a free-flow spillway tunnel

Air is transported downstream by the water flow in a free-flow spillway tunnel, resulting in high negative pressure, which causes gate vibration and cavitation. In this research work, a physical model of a free-flow spillway tunnel was used to investigate the effects of water surface velocity and the area residual of tunnel cross sections on air movements. The results demonstrate that the air velocity distribution forms an S-shaped curve. As the water surface velocity increases or the area residual decreases, the air velocity increases, and the relative action height of the drag force of water flow on the air increases as well. The air velocity distribution is divided into two exponential distributions at the position where the air velocity drops by 0.2 times that of the water surface velocity. Two formulas for calculating the air velocity of the corresponding exponential distributions are developed. Subsequently, an algorithm for the air demand is presented, and the relative error compared to the reference data was less than ±20%. These results provide a reference for free-flow spillway tunnel ventilation shaft design.

Method to obtain 3D point clouds of tunnels using smartphone LiDAR and comparison to photogrammetry

Remote sensing methods, for example, photogrammetry and laser scanning can be employed to scan rock masses by digitizing underground spaces or slopes. To reconstruct a 3D model by photogrammetry, plenty of photos should be captured. This process is time-consuming and can be dangerous when the rock mass is unstable. Therefore, rapid capturing methods are needed to reduce the acquisition time. This can be achieved with LiDAR scanners that capture a 3D point cloud with a high-speed pulsed laser beam. However, the cost of laser scanners is high, which limits their usability. Apple’s iPhone 12 Pro Max smartphone is equipped with a LiDAR sensor and is much cheaper than conventional laser scanners. Several mobile applications for 3D models using the smartphone Lidar have been developed, making the scanning process easy. Therefore, smartphones can be used for rapid scanning of unstable surfaces of tunnels and slopes. In this study, 3D point clouds (3DPC) of a tunnel wall of the Underground Research Laboratory of Aalto University (URLA) are obtained by a high-resolution digital camera and smartphone LiDAR. The models are analyzed and compared. The results show the quality of the smartphone LiDAR sensor is adequate for generating 3D models of underground spaces.

Pre-Reinforcement Mechanism and Effect Analysis of Surface Infiltration Grouting in Shallow Buried Section of Long-Span Tunnel

In order to solve the problem that the hole-forming rate of boreholes is low and it is difficult to reach the designed length when supporting a long pipe shed in loose stratum in a shallow buried section of a long-span tunnel, it is necessary to pre-reinforce the loose stratum in order to improve the strength and integrity of the surrounding rock. Relying on the grouting project of the shallow buried section at the exit of Botanggou tunnel, it is assumed that the grouting material is Newtonian fluid and the steel floral tube shows cylindrical infiltration and diffusion. Through the analysis of the structural characteristics of the injected stratum, the conceptual model of infiltration grouting is established. Twelve groups of test slurry were prepared with ordinary Portland cement and ultra-fine cement, and through the analysis of the slurry parameters of each group, ordinary Portland cement slurry was selected with a water–cement ratio of 1:1 plus 3% water glass to strengthen the gravel layer, and ultra-fine cement slurry with a water–cement ratio of 1:1 plus 3% water glass and 0.3% polycarboxylate superplasticizer to strengthen the fully and strongly weathered porphyritic granite layer. Through the on-site single-hole grouting test and combining with the empirical formula, the maximum diffusion radius of single-hole infiltration grouting is calculated, and the sliding width of the sidewall is deduced using Terzaghi theory. To ensure the grouting effect, the 5 m expansion of the excavation profile is taken as the grouting range. Grouting construction adopts the overall order of periphery and then interior, and three-sequence opening and grouting are adopted in the same row of grouting holes, which can effectively prevent grouting running and grouting. For the strata treated by surface grouting, the construction of the long pipe shed is smooth and reaches the designed length, and there is no large deformation of the surrounding rock when excavated using the CD method. The treatment effect is analyzed by the P-Q-t control method, excavation observation method, and deformation monitoring method. The results show that the injected stratum is fully infiltrated and gelled, forms an obvious grouting stone body, the integrity and strength of surrounding rock are obviously improved, and the convergence values of the tunnel surface, vault subsidence, and clearance do not exceed the alarm value of 60 mm. The research results provide some awareness and understanding of the grouting pre-reinforcement of loose stratum in a shallow buried section of a long-span tunnel in the future.

New way of constructing the tunnel

The design and construction of the tunnel surface requires considerable time and cost. Therefore, improved methods of constructing the surfaces of underground structures is an urgent task in the mine industry. Everyone knows that the surface of the tunnel is a complex curvilinear surface, which must meet the pre-determined requirements. The article presents a new way of constructing the tunnel surface according to predefined conditions using the biquadratic transformation of the plane, which allows one to describe the design of each tunnel section by a single equation.

Fire effects on biochemical properties of a semiarid pine forest topsoil at cm-scale

Forest fires can greatly affect soil properties and processes. In the study of the fire effects on soil, the soil thickness affected by heat depends on the characteristics of the fire and soil itself, but also on the attribute to be measured. The objective of this work is to know to what thickness (up to 1, 2 or 3 cm) various sensitive soil properties are immediately affected by a controlled burning. To achieve this aim, unaltered fresh topsoil (mollic horizon) of a fire-prone Aleppo pine forest in the semiarid Ebro Valley (NE-Spain) were sampled and, without destroying their original structure, burned from the surface in an outdoor combustion tunnel in triplicate. Biological properties are measured, including basal and normalized soil respiration (bSR and nSR), β-D-glucosidase (GLUase) and phosphomonoestarase (PHOase) activities, and related parameters, such as total organic matter (TOM), oxidizable organic C (OxC), nonhydrolyzable carbon (NHC), P-Olsen, pH, soil moisture and soil water repellency (WR). In the unburned soil, most of these properties showed a decreasing gradient with depth which is modified after burning, in some cases inverted (as enzymatic activities and WR), in others intensified (P-Olsen) and in most, truncated, with a maximum value in the second cm. The depth of the soil in which changes were recorded varied according to the attibute considered; thus, burning significantly decreased only up to the first cm: bSR (73 %) and TOM (81 %), up to 2 cm: PHOase (89 %), OxC (17 %) and WR (96 %) and up to 3 cm depth GLUase (58 %), NHC (24 %) and moisture (73 %). However, P-Olsen and pH both increased after burning up to 1 and 3 cm soil depths, with increases of up to 240 % and 11 %, respectively. In conclusion, fire effects on soil are depth dependent, and this dependency is not uniform across soil properties.

Nanomaterials-Based Ion-Imprinted Electrochemical Sensors for Heavy Metal Ions Detection: A Review

Heavy metal ions (HMIs) pose a serious threat to the environment and human body because they are toxic and non-biodegradable and widely exist in environmental ecosystems. It is necessary to develop a rapid, sensitive and convenient method for HMIs detection to provide a strong guarantee for ecology and human health. Ion-imprinted electrochemical sensors (IIECSs) based on nanomaterials have been regarded as an excellent technology because of the good selectivity, the advantages of fast detection speed, low cost, and portability. Electrode surfaces modified with nanomaterials can obtain excellent nano-effects, such as size effect, macroscopic quantum tunneling effect and surface effect, which greatly improve its surface area and conductivity, so as to improve the detection sensitivity and reduce the detection limit of the sensor. Hence, the present review focused on the fundamentals and the synthetic strategies of ion-imprinted polymers (IIPs) and IIECSs for HMIs detection, as well as the applications of various nanomaterials as modifiers and sensitizers in the construction of HMIIECSs and the influence on the sensing performance of the fabricated sensors. Finally, the potential challenges and outlook on the future development of the HMIIECSs technology were also highlighted. By means of the points presented in this review, we hope to provide some help in further developing the preparation methods of high-performance HMIIECSs and expanding their potential applications.

Analytical and Numerical Study on the Performance of the Curved Surface of a Circular Tunnel Reinforced with CFRP

Pasting carbon fiber reinforced polymer (CFRP) has become an effective method to reinforce the circular tunnel. For this reinforcement method, the mechanical performance of the curved substrate is important to keep the coordinated deformation of CFRP and the lining concrete. To investigate the effect of interface curvature on the stresses of the reinforced interface, an analytical model is proposed for the curved reinforced interface with the consideration of the interface bond–slip relationship. Additionally, a 3D numerical model is established to further investigate the effects of some important parameters (CFRP’s layer, length, elastic modulus, thickness and the adhesive’s elastic modulus, thickness) on the reinforced interface stresses. The results reveal that the stress state of the curved reinforced interface is more complex than that of the plane reinforced interface. With decreasing the radius of the curved reinforced interface, the interface radial stresses are increased significantly, while the circumferential stresses hardly change. For the adhesive, decreasing the elastic modulus and thickness of the adhesive layer can significantly improve the stress state of the reinforced interface. For the CFRP, decreasing the thickness, elastic modulus and layer number of CFRP is conducive to full utilization of materials and long-term combined work of the concrete and CFRP.

Research Progress of Polymers/Inorganic Nanocomposite Electrical Insulating Materials.

With the rapid development of power, energy, electronic information, rail transit, and aerospace industries, nanocomposite electrical insulating materials have been begun to be widely used as new materials. Polymer/inorganic nanocomposite dielectric materials possess excellent physical and mechanical properties. In addition, numerous unique properties, such as electricity, thermal, sound, light, and magnetic properties are exhibited by these materials. First, the macroscopic quantum tunneling effect, small-size effect, surface effect, and quantum-size effect of nanoparticles are introduced. There are a few anomalous changes in the physical and chemical properties of the matrix, which are caused by these effects. Second, the interaction mechanism between the nanoparticles and polymer matrix is introduced. These include infiltration adsorption theory, chemical bonding, diffusion theory, electrostatic theory, mechanical connection theory, deformation layer theory, and physical adsorption theory. The mechanism of action of the interface on the dielectric properties of the composites is summarized. These are the interface trap effect, interface barrier effect, and homogenization field strength effect. In addition, different interfacial structure models were used to analyze the specific properties of nanocomposite dielectric materials. Finally, the research status of the dielectric properties of nanocomposite dielectric materials in the electrical insulation field is introduced.