Crack Line Research Articles

A method of lining seam elimination with angle adaptation and rectangular mark for road tunnel concrete lining images

Road Tunnels are an important part of the current road transportation infrastructure. As the main form of tunnel lining diseases, cracks are easy to interact with other areas, which seriously affects the safe operation of the tunnel. Due to the similarity of brightness and linearity between surface cracks and lining cracks, the existing crack detection algorithms can not extract cracks accurately and quickly. An algorithm of lining seam crack elimination with rectangular mark is proposed here. First, the line segments in the image are detected by the Line Segment Detector algorithm based on the coarse percolation detection of the crack. Second, the distribution directions are calculated, and cracks from the lining seams are distinguished by the adaptive threshold judgment method. Third, by using the distribution characteristics of pixels, the line segments are extended to form rectangular marks perpendicular to the direction of lining seams. Finally, the marking information is used to remove the lining joints and obtain the real surface cracks of tunnel lining. Experimental results show that the algorithm can quickly and effectively remove any shape distribution of lining seam. The algorithm fills in the blank of concrete tunnel lining surface crack detection technology.

An Analysis of Loess Tunnel Failure and Its Mechanism

A series of changes of mechanical properties such as fracture development, relaxation, collapse deformation, and strength decreasing of the surrounding rock of loess tunnels occur due to shearing and immersing, and loess tunnels will be prone to engineering failures, including large deformation, fissure, ground collapse, landslide, and lining cracking, seriously threatening the construction and operation safety of tunnels. These problems are especially prominent for long-span loess tunnels. Based on the understanding of features in the construction and operation of the loess tunnel project and proceeding from the perspective of structural evolution of loess, distribution of the shear deformation zone, instability of the excavation face, and adverse effects of geological conditions, the predisposing factors of damage of the surrounding rock and the supporting structure of large-span loess tunnels, common types of failures, and their formation mechanisms are analyzed in this paper. According to the relationship between the evolution of the loess structure and the law of strength change, an improved Mohr–Coulomb elastic-plastic, tension-compression-shear, constitutive model, considering the loess structural property, is established and applied in numerical calculation. The formation mechanism of different failures in the course of loess tunnel construction is revealed by numerical analysis, in which the structural property of loess, loess strata, geological conditions, and excavating and supporting actions are simulated by the numerical method. A reference is provided for the prevention and remediation of engineering failures of a loess tunnel.

SH Wavelet Propagation Through the Random Distribution of Aligned Line Cracks Based on the Radiative Transfer Theory

This paper studies the propagation of SH wavelet intensity through the random distribution of aligned line cracks in a two-dimensional (2-D) homogeneous medium as the simplest mathematical model of the heterogeneous Earth medium. The scattering process of a single line crack is described by Mathieu functions. The random distribution of cracks is well represented by the scattering coefficient, that is, the scattering power per unit area. Two methods are proposed for the derivation of the space–time distribution of the intensity Green function for the unit isotropic radiation from a point source: one is the single scattering approximation and the other is the Monte Carlo simulation. The former and the latter are deterministic and stochastic methods, respectively. In the case that the wavenumber is larger than the reciprocal of the crack length, synthesized time traces show that direct wavelets near the ray direction parallel to the line cracks decrease according to the geometrical decay with increasing travel distance as if there exists a transparent channel along the crack line direction; however, those near the direction normal to the line cracks decrease more rapidly because of strong scattering attenuation. At large lapse times, multiple scattering produces a swelling around the source location, which is prolonged to the crack line direction. Those characteristics well reflect the anisotropy of the line crack scattering. The Monte Carlo simulation presented here could be a fundamental base for the study of more realistic crack scattering problems.

Concrete lining work analysis of mountain railway tunnels in geodynamical active regions

Concrete lining work analysis of mountain railway tunnels in geodynamical active regions. Railway tunnel concrete lining stress-strain state located in a geodynamical active mountainous region were discussed in this article. The study aims to assess the external factors influence, such as gravitational and seismic effects, on concrete lining deformation and cracking. The concrete lining work analysis was performed on the Severomuisk railway tunnel section example. The tunnel is located in different soil conditions and has a variety of supporting structures; the work analysis was performed for a site located in weakly fractured granite rocks. To assign the seismic impact level, the adjacent to the tunnel area seismic setting was calculated based on historical data and the area seismic monitoring. It has been established that the occurrence of earthquakes with a magnitude of 7–8 on the MSK-64 scale is expected every 10 years on average, the obe level with a recurrence period of 1 time in 50 years corresponds to an 8.7 points intensity. The tunnel structures’ stress-strain state calculation was performed by the finite element method in the GTS NX program. The analysis takes into account the main tunnel design features, drainage and transport adits, and cross slit. The calculations were performed in a linear-elastic formulation for the main tunnel concrete structures, the cross slit, and the adit’s cast-iron structures. The soil mass is modeled by materials according to the Hawke-Brown strength criterion (Hoek E.; Brown E.T.). It has been established that with an isotropic structure of the enclosing rock mass, tunnel structures resist well the destructive strong earthquakes impact. Crack formation in concrete lining only occurs in the event of a strong design-basis earthquake. At the same time, the various niches presence, cross slit, and other load-carrying structure complex geometry leads to the stress concentrations appearance and, as a consequence, cracks in concrete at lower seismic effects. Crack distribution patterns are consistent with field survey data.

Analysis of Detection and Treatment Schemes of Highway Tunnel Lining Cracks

Highway tunnels play a very important role in people's daily life. Among them, lining is an essential part of tunnel engineering, and the quality of lining greatly affects the overall quality of the tunnel. On this basis, the causes of lining cracks and the detection methods of existing highway tunnel lining cracks are analyzed, and the treatment countermeasures for highway tunnel lining cracks are proposed.

Occlusal stress distribution and remaining crack propagation of a cracked tooth treated with different materials and designs: 3D finite element analysis

ObjectiveHere we used 3D finite element analysis (FEA) to analyze and directly compare stress distribution and crack propagation in identical cracked tooth models after treatment with various materials and designs. MethodsA 3D model of a cracked tooth was generated. We then applied eight restoration models, comprising combinations of three kinds of restoration designs (inlay, onlay, and crown) and four types of restoration materials (direct composite resin, indirect composite resin, ceramic, and gold). A 1000-N occlusal load was applied on the three reference points of the ball-shaped part in the direction of the longitudinal axis, causing crack line separation in the buccolingual direction. Stress distribution was analyzed on the occlusal surface, bottom level of the restoration, and mesiodistal longitudinal section. The stress on the lower margin of the crack surface was measured at 15 points on each model. ResultsCeramic inlay and onlay showed stress concentration at the restoration bottom, and low stress on the lower margin of the crack surface. Direct and indirect resin restorations exhibited low stress on the restoration bottom, and high stress on the proximal end of the lower margin of the crack surface. With a resin-unfilled gold crown, stress was concentrated on the crown bottom and the lower margin of the crack surface. Direct resin filling inside the gold crown yielded significantly decreased stress on both areas. SignificanceOur results suggest that inlay and onlay ceramic restorations, and gold crown with resin filling inside, are advantageous methods for preventing further crack propagation.

Crack Repairing of Aluminum Alloy 6061 by Reinforcement of Al<sub>2</sub>O<sub>3</sub> and B<sub>4</sub>C Particles Using Friction Stir Processing

Crack repairing of aluminum alloys is done using conventional welding techniques or mechanical methods, which results in the redundancy of mechanical properties due to defects formation. Friction Stir Welding/Processing (FSW/FSP) is a solid-state joining technique which is used to join various different similar and dissimilar metals, along with the fabrication of surface composites to cater the mentioned problem. The objective of this study is to repair the crack produced in 6061 aluminum alloy by the reinforcement of ceramic particles, Al2O3 and B4C, to further increase the efficiency of the joint along the crack line. Weld parameters, equipment used and the processing conditions are emphasized. The mechanical testing and the characterization of the weld as well as base metal was done and compared using tensile testing, micro hardness test and microstructural analysis. X-Ray Diffraction (XRD) was performed for crystallinity and intermetallic study. The dispersion of the particles was investigated using Field Emission Scanning Electron Microscope (FESEM). The crack in the Al-6061 was effectively repaired using FSP. The reinforced samples showed improved mechanical properties as compared to non-reinforced ones.

Observation of Surface and Subsurface Crack Propagation in PPS Thrust Bearings under Rolling Contact Fatigue in Water

In this study, crack propagation in PPS thrust bearings under rolling contact fatigue (RCF) in water was observed in order to investigate the relation between cracks and flakings. RCF tests in water under loads of 700 N and 900 N were performed. The semi-circular cracks propagated in a direction perpendicular to the rolling direction were observed under a load of 700 N. The line cracks propagated in a direction parallel to the rolling direction at periphery of contact area and the semi-circular cracks were observed under a load of 900 N. To study the subsurface cracks, full section of rolling contact area was observed. It is concluded that the flaking mechanism in PPS thrust bearing has three features as follows: Initiation and propagation of surface cracks depend on the load; When load is 700N, the semi-circular cracks growing from the surface and the cracks branching from the main subsurface cracks join to form the flaking; When load is 900N the line cracks and the semi-circular cracks growing from the surface join to form the flaking.

Mechanical and Numerical Simulation on Weathered Argillaceous Siltstone under Cyclic Loading

Secondary lining cracking always occurs in existing tunnels when the tunnel passes through the weathered argillaceous siltstone layer, which seriously affects the safety of the tunnel. In order to study the mechanical properties of weathered argillaceous siltstone and the cracking law of the secondary lining, this study analyzes the relationship of accumulative plastic strain between the dynamic stress amplitude and static deviator stress, as well as the cracking law of the secondary lining of the sample. The results show that under cyclic loading, there are obvious accumulative plastic strain in weathered argillaceous siltstone; the bearing capacity of the secondary lining structure at the biased part shows an evident increase than that of others with cracking generating faster. The research results provide a reference for the safety and operation of the tunnel that runs through the weathered argillaceous siltstone layer.

Cracking characteristics and mechanism of entrance section in asymmetrically-load tunnel with bedded rock mass: A case study of a highway tunnel in southwest China

Serious cracks of secondary lining appear at the entrance section of a highway tunnel in southwest China after excavation. The entrance section of the tunnel has geological characteristics of bedded rock mass with inclined structural plane, asymmetrically loaded terrain, shallow buried depth, and soft surrounding rock. This paper aims to explore the cracking mechanism of lining at the entrance section and propose reinforcement measures to prevent the structural damage accordingly. Site investigation was conducted to demonstrate the cracking characteristics (process, distribution, width, and depth) of tunnel lining. Cracks mainly appeared on the interior lining of left arch-haunch and right side-wall, as well as on the exterior lining of right arch-haunch. The deformation of secondary lining in cracking section was monitored and analyzed to explore the deformation characteristics after the appearance of cracking and installation of temporary supporting. Then, a three-dimensional finite difference numerical model based on the actual terrain was built to analyze the spatial mechanical characteristics of the entrance section. A deformation analysis model including four zones of the surrounding rock was used to analyze the cracking mechanism of asymmetrically-loaded tunnel with inclined weak structural plane. Finally, ground reinforcement measures and reversed loading to control deformation of bedded rock mass and tunnel structures are proposed. Investigating the cracking case of the tunnel has significance to the excavation of entrance section in relevant engineering.

Influence of cracks at the invert on the mechanical behavior of the tunnel structures

Studies show that lining cracks are one of the most common anomalies that occur in the operational tunnels. Therefore, investigating the performance of the cracked linings is of significant importance during the tunnel maintenance. In the present study, model tests and numerical simulations are performed to investigate the influence of the longitudinal cracks at the invert on the mechanical behavior of the tunnel linings. Obtained results show that (1) the pre-existing cracks at the invert aggravate the crushing failure at the back of the fracture zone, leading to the brittle instability of the tunnel; (2) the deformation process of the cracked tunnels initially develops linearly up to a drastic increase. Moreover, the magnitude and the growth of the deformation at the damaged area of cracked linings before the abrupt failure are larger than those of the intact linings; (3) the cracks result in a distinct decrease in the bending moment at the damaged area, whereas the thrust force is less sensitive to the number of cracks; (4) the pre-existing cracks in the invert weaken the lining's ability to resist the pressure of surrounding rock and increase the share of the arch foot in the contact pressure; (5) the pre-existing cracks at the invert reduce the bearing area of linings, thereby weakening the flexural stiffness and favoring the crushing failure at the invert, which is the main reason for the decrease in the bearing capacity of the cracked tunnels.

Analysis on Disease State of Urban Operational Subway Tunnels

Structure form, steel bar and service time were considered to be the main factors of the tunnel disease state, based on the disease inspection results of subway tunnels in Beijing. The conclusion indicated that the diseases of shield tunnel such as ovalization of tunnel cross section, lining cracks, crushing and dislocation of duct pieces and water leakage were caused by the deformation of segment joints. Lining crack was the main disease form in monolithic tunnel. The width and depth of cracks were greatly influenced by tunnel operation time and had the characteristics of discreteness and random. Steel bar used in concrete lining could significantly enhance safety of tunnel structures. Water leakage in subway tunnel was influenced by rainfall and usually could be observed at the gaps of tunnel structures, such as bolt holes and segment joint of shield tunnel or the construction joints, deformation joints and lining cracks of monolithic tunnel. The most lining cavities were found located at the vault and the cavity shape was similar to strip, square or oval with lining cracking nearby. The carbonation depth of lining concrete was proportional to tunnel operation time and its value and speed at ballast bed was most, sidewall less and vault least. It is hoped that the results can provide some reference for the disease law analysis and treatment of urban tunnel.

Study on mechanical response and crack development law of tunnel

Considering the linear elastic fracture mechanics and complex function theory, considering the non hydrostatic pressure field, the stress solutions of lining and surrounding rock of deep buried circular underground cavern with lining under the action of external internal pressure are studied. The fracture mechanics model of underground cavern supporting structure is established, and the numerical verification is carried out. The analytical solution of circular pressure cavern with lining shows that when the internal pressure is 0, it can degenerate into the existing classical solution. The results of finite element calculation and analytical calculation show that the tensile stress of lining is very large at the vault and arch bottom under the action of strong external supporting force. The calculation shows that the cracks of lining will expand and open under the action of tensile stress, and the lining is in the shape of “flat duck egg”, However, if there is no through rupture, there will be great stress concentration at the top and bottom of the arch, and the tensile stress value is much larger than that calculated by elastic mechanics. Therefore, it is a good method to configure a certain amount of reinforcement to enhance the stiffness and tensile strength of the lining.

Free vibration analysis of functionally graded plates containing embedded curved cracks

In the present paper, the free vibration behavior of functionally graded plates containing straight and curved embedded crack is investigated. A NURBS-based multi-patch isogeometric analysis formulation is utilized based on the firstorder shear deformation plate theory. The Nitsche technique is implemented to meet the inter-patch connection constraints. The crack line is assumed as a narrow cut along a straight or free-shape curve path within the plate. The crack growth phenomena are overlooked. The accuracy and quality of the obtained results are compared to those available in the literature. Subsequently, the effect of various material and geometry parameters on the free vibration characteristics of cracked FG plate including the volume-fraction index, crack shape, crack length, crack orientation and, crack location are examined. It learned that the straight crack inclination angle mainly influences the fifth and fourth natural modes. Moreover, the FGM mixture index doesn't noticeably affect the frequency trends. No considerable impact is noted between the edge constraint setups on the fundamental frequency.

Automatic Identification and Location of Tunnel Lining Cracks

The lining crack is common for the tunnel in the stage of operation, which has seriously influenced the service life and safety of tunnel engineering. It is a new trend to use computer vision to detect tunnel cracks over the past few years in China and foreign countries. By image processing technology and intelligent algorithm, the computer has a hominine visual perception system which understands, analyzes, and determines input image information, thus recognizing and detecting specific objectives. However, the effect of image recognition for tunnel crack now cannot satisfy the demands of practical engineering. SSD algorithm has been used when analyzing features of lining surface image, while comparison analysis has been made from image recognition results, error rate, and running time. The results indicate that the SSD algorithm can accurately and rapidly detect and mark the position of the tunnel crack. The tunnel information obtained from image recognition is subsequently imported into the team independently developed software GeoSMA‐3D, which is useful for determining tunnel grade.

Influence of constraint conditions on the seasonal variation of the concrete temperature cracks in a tunnel final lining

Temperature and shrinkage cracks are still not rare in tunnel and underground cast-in-place concrete linings. The features of the constraint conditions during temperature dropping stage of the lining in construction are rigorously concerned in terms of crack prevention and magnitude control. The width seasonal variations of the temperature cracks in a tunnel concrete final lining, monitored with vibrating strain gauges, imply that the constraint conditions, on which the temperature and shrinkage cracks developed in the lining concrete during the temperature dropping stage, are working and of successive features in the post-construction period. Therefore, the seasonal variation of the crack widths can partially indicate the constraint conditions of the cast-in-place lining concrete cracking in construction period. Considering the cracks beyond the planned allowable values, the results from this case imply that it is beneficial to apply a flexible layer on the outer surface of cast-in-place concrete lining in concrete crack resistance design and construction quality control, especially for a tunnel with cast-in-place concrete monolithic lining or two-pass lining.

Static method of rock destruction with using a non-explosive destructive mixture

The authors developed a mathematical model of the location of boreholes when using a non-explosive destructive mixture (NDM), which contributes to the formation of a continuous line of cracks and the smooth separation of rocks in the massif. The dependences of the change in the effective distance between contour holes on their diameter, compressive stress at the hole wall, Poisson's ratio, the tensile strength of the rock, and the additional stress directed at moving the block walls and opening them when using the NDM are established. A series of experiments on finding an optimum compounding of structure of NDM which would allow to accelerate process of hydration without additional heat release and to provide high pressure during 5-8 h after use of structure was carried out. Variants of the chemical mixture that maximizes the expansion and destruction of rocks were optimized. More than 200 experiments on rupture of samples of various materials (glass bubbles, plaster, brick, marble) were conducted. On the basis of the received results, a method was developed for formulating composition of NDM with using components from local raw materials, which is safe for storage, transportation and use, creates high internal pressure in the holes and contributes to static destruction and rupture of rocks. The method for separating monoliths from the massif with use of new composition of the NDM is also developed. Implementation of the proposed method allows to displace a block of monolith into the goaf of the pit under the influence of high pressure of self-expansion with no spontaneous outburst of mixture. Experimental-industrial tests of the proposed composition and method of the NDM production were carried out in the Nuratinsky marble deposit of the Navoi region. As compared with the drilling and blasting method, method of separation of monoliths from massif by using the new composition of NDM makes it possible to reduce labour intensity of performed works, provides protection of environment, reduces cost of production and energy intensity of mining works, as well as increases safety of their execution Keywords: mathematical model of the location of holes, non-explosive destructive mixture, formation of continuous line of cracks, high internal pressure in the holes.

Crack orientation detection in plate-like structures via Lamb wave specular reflection analysis

The determination of crack orientation plays an important role in the non-destructive evaluation (NDE) of plate-like structures. In this paper, the interaction between Lamb waves and cracks is investigated using the time domain spectral element method (SEM) as the simulation tool. On that basis, we analyse the geometric principle of specular reflections and propose an efficient crack angle detection algorithm. During the process, four sensors take turns to excite the Lamb wave which would result in twelve crack reflection signals. Using the corresponding actuator as the centre and the reflection length as the radius, we can obtain twelve reflection circles in total. When these reflections are specular, the mirror points of the actuators with respect to the crack line are exactly the intersection points of the circles. Thus, we can obtain the crack angle by this geometric relation. Validations on different cracks are made and the result of the algorithm shows a good agreement with the real value.

A Lamb wave-based crack evaluation method in plate-like structures using specular reflections and tip diffractions

The comprehensive assessment of crack angle, length and profile could provide an important reference for the non-destructive evaluation of plate-like structures. In this paper, we aim at fully exploiting information carried by reflections, so that details of the crack could be displayed as much as possible. Firstly, the Lamb wave reflections from a crack are classified into specular waves and tip diffractions. Under the linear assumption of crack profile, the specular waves could be regarded as being transmitted from the mirror point of the actuator with respect to the crack line, thus the corresponding reflection points can be located with geometric methods. On the other hand, diffractions are used to visualize crack tips where a fusion strategy is adopted to get the localization image. Both reflection points and tips are not only interpolated to show the crack position and profile, but also linearly fitted to display the crack trend for the estimation of its length and angle. Numerical investigations and experiments are carried out on different cracks, and related parameters are also discussed. Results show that the proposed method could make an accurate crack evaluation and reconstruct a detailed crack shape.

Numerical Investigation on Mixed Mode (I-II) Fracture Propagation of CCBD Specimens Under Confining Pressure

A new numerical method, verified by the analytical solution of the weight functions and experimental paths, is developed to evaluate the crack initiation and propagation generally in mixed mode (I-II). This numerical method combining the interaction integral method and the maximum tangential stress (MTS) criterion is based on the finite element method of secondary development. The influence of combined confining pressure and diametric forces on crack propagation trajectories for CCBD specimens are studied. It is indicated that the crack propagation direction independent of the confining pressure keeps the same with the line of original crack as the loading angle is equal to [Formula: see text]. But when the loading angle is greater than [Formula: see text], the curvature of the curve trajectory in the early stage of crack propagation increases with a larger confining pressure. Further, it is found that larger values of the loading angle and relative length will make the effect of confining pressure more significant at the early stage of crack growth.