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The interface crack of a slab track is a fracture of mixed-mode that experiences a complex loading–unloading–reloading process. A reasonable simulation of the interaction between the layers of slab tracks is the key to studying the interface crack. However, the existing models of interface disease of slab track have problems, such as the stress oscillation of the crack tip and self-repairing, which do not simulate the mixed mode of interface cracks accurately. Aiming at these shortcomings, we propose an improved cohesive zone model combined with an unloading/reloading relationship based on the original Park–Paulino–Roesler (PPR) model in this paper. It is shown that the improved model guaranteed the consistency of the cohesive constitutive model and described the mixed-mode fracture better. This conclusion is based on the assessment of work-of-separation and the simulation of the mixed-mode bending test. Through the test of loading, unloading, and reloading, we observed that the improved unloading/reloading relationship effectively eliminated the issue of self-repairing and preserved all essential features. The proposed model provides a tool for the study of interface cracking mechanism of ballastless tracks and theoretical guidance for the monitoring, maintenance, and repair of layer defects, such as interfacial cracks and slab arches. [ABSTRACT FROM AUTHOR]

Featured Application: The work can be applied to data-based damage identification of structures. During the long-term service of slab track, various external factors (such as complicated temperature) can result in a series of slab damages. Among them, slab arching changes the structural mechanical properties, deteriorates the track geometry conditions, and even threatens the operation of trains. Therefore, it is necessary to detect slab arching accurately to achieve effective maintenance. However, the current damage detection methods cannot satisfy high accuracy and low cost simultaneously, making it difficult to achieve large-scale and efficient arching detection. To this end, this paper proposed a vision-based arching detection method using track geometry data. The main works include: (1) data nonlinear deviation correction and arching characteristics analysis; (2) data conversion and augmentation; (3) design and experiments of convolutional neural network- based detection model. The results show that the proposed method can detect arching damages effectively, and the F1-score reaches 98.4%. By balancing the sample size of each pattern, the performance can be further improved. Moreover, the method outperforms the plain deep learning network. In practice, the proposed method can be employed to detect slab arching and help to make maintenance plans. The method can also be applied to the data-based detection of other structural damages and has broad prospects. [ABSTRACT FROM AUTHOR]

Interface damage, which even happens in construction phase, has become a major problem for China Railway Track System (CRTS-II) slab track. The slab track in construction stage is a block structure and sensitive to daily changing temperature. In order to reveal the temperature behavior of the slab track and provide meaningful information to the control of early interface damage, a three-dimensional finite element model of slab track was developed to study the deformation and interface stress of the slab track under daily changing temperature in this paper. The daily changing temperature was measured on a testing platform constructed in open field, and imported to the model using user-defined subroutines UTEMP. Based on the developed model, the effect of initial temperature and construction seasons were then investigated. The analysis indicates that the slab deformation and stress change with time obviously and the positions of maximum interface stresses are near the slab corner, which is consistent with the location of interface disease. Initial temperature has significant influence on the slab temperature behavior. The initial temperature at 14:00 induces the largest interface tensile stress exceeding the interface bonding strength, while the interface stresses are relatively small from 19:00 to 24:00. Therefore, it is suggested that CA mortar injection should be finished before midnight. Additionally, as the overall temperature variation and temperature gradient are very obvious in summer, spring and autumn, the grouting operation of CA mortar in these three seasons is required to pay equal attention. [ABSTRACT FROM AUTHOR]

• A novel test device assessing the impact force on tamper was proposed. • Macro-mechanical properties of ballast bed and tamper were studied experimentally. • Micro-mechanical properties of ballast and tamper were analyzed numerically. • Real-time evaluation of ballast bed was innovatively achieved. Real-time evaluation of the mechanical qualities of ballast beds is essential for improving tamping effort in railway maintenance. This study aims at evaluating the mechanical qualities of ballast beds based on the impact force on tamper. A novel test device was newly developed to assess the impact force on tamper. This device has high accuracy and long service life. The mechanical qualities of ballast bed and the impact force on tamper were studied experimentally. Results indicated that tamping decreased the lateral resistance and support stiffness of ballast bed by 38.57%–54.08% and 46.92%–62.42%, respectively. Furthermore, a tamping-ballasted track coupling model was constructed and validated by comparing the mechanical qualities of ballast bed between the test and simulation. The dynamic characteristics of ballast and tamper were analyzed numerically. A mathematical expression was developed to invert the mechanical qualities of ballast bed based on the impact force on tamper according to the numerical results. Thus, an innovative real-time evaluation of the ballast bed was achieved by combining the proposed test method and mathematical expression. This study helps to conveniently collect health information of ballasted track at a low cost. [Display omitted] [ABSTRACT FROM AUTHOR]