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In the era of high-speed trains, it is very important to ensure the safety and stability of rail tracks under adverse conditions including seasonal freezing and thawing. Freeze–thaw cycles (FTCs) affecting the engineering performance of coarse-grained soil (CGS) is one of the major reasons for track deterioration. The reported results of a number of static freeze–thaw triaxial tests on the shear behaviour of CGS are analysed herein. It was observed that confining pressure (σ3) and FTCs have a significant influence on the shear behaviour of CGS. In this paper, an empirical mathematical model has been proposed to capture the dilatancy of CGS subjected to FTCs during shearing. The empirical constants a, b, and c proposed in the model are a function of σ3 and FTCs. The results of the model have been compared with the laboratory experiments and are found to be in good agreement. [ABSTRACT FROM AUTHOR]

To evaluate the service performance of the track substructure of heavy axle load (HAL) railway transportation, an inverse analysis was performed to estimate the resilient modulus values of the track substructure, based on the deflection data obtained from light falling weight deflectometer testing. Subsequently, a three-dimensional finite element model was developed to simulate the effect of the train speeds (v) and axle loads (F) on the typical dynamic responses in the railway track system. The results convincingly indicated that increasing v or F can amplify the track vibration. Finally, a critical stress ratio method was adopted to evaluate the service performance based on the numerical results. A recommended range of v and F was determined to maintain the long-term stability of the HAL railway line. The findings can provide guidance for designing the track and maintenance plans to avoid track support failures and ensure track infrastructure resiliency. [ABSTRACT FROM AUTHOR]

High-speed trains (HSTs) induce vibrations that deteriorate the embankments of ballastless tracks, particularly in frozen regions, necessitating vibration assessments for existing high-speed railways (HSRs). This study developed an indirect thermal-dynamic coupled two-dimensional (2D) finite element (FE) model to investigate the dynamic responses of the embankment of ballastless tracks to various subgrades and subsoils, train speeds, and frost depths in frozen regions. The results indicate that subgrade is the key parameter to analysing the dynamic response of the train–track–ground system considering train speeds. A fast and high-accuracy prediction method for the vibration responses was developed using an artificial neural network (ANN) and used to predict the vibration level under different conditions. Prediction results determined train speeds under 400 km/h safe for HSRs. This study can improve knowledge of ballastless track substructure design and extend the applicability of the current railway code to higher train speed conditions in frozen regions. • Proposed an accurate and reliable artificial neural network-based prediction model. • Train speeds under 400 km/h are safe for high-speed railways in frozen regions. • Subgrade is key to analysing the dynamic response of train–track–ground systems. • Substructure layer reinforcement is recommended for higher speeds. [ABSTRACT FROM AUTHOR]

Abstract With the rapid development of high-speed railways (HSRs) in seasonally frozen regions in China in recent years, there is an increasing need for better understanding of how the construction materials behave. In particular, the dynamic behavior of granular base course materials used for China's HSRs subjected to combined actions of cyclic loading and freeze-thaw (F-T) cycles has attracted much attention. In this study, a series of cyclic triaxial tests were performed to investigate the characteristics of granular base course materials. A number of factors including effect of F-T cycles were considered in these tests. As such, representative test results of dynamic shear stress amplitude (τ ¯ d), dynamic shear modulus (G d), and damping ratio (λ) are presented and discussed. Based on the Hardin-Drnevich model, a fitting equation for determining maximum dynamic shear modulus (G d,max) is proposed. Then, a unified normalized dynamic shear modulus (G d / G d,max) curve is drawn and well validated by the test results. Furthermore, equations for λ are expressed in terms of an exponential function of G d / G d,max. The test results show that the G d / G d,max curves are not completely consistent with previous studies. Overall, this study provides further insights into the dynamic behavior of granular base course materials subjected to F-T cycles. Highlights • The effect of freeze-thaw cycles on the dynamic behavior of base course granular materials was analyzed and discussed. • A unified normalized dynamic shear modulus curve considering multiple factors were proposed. • The relationship between normalized dynamic shear modulus and damping ratio was developed. [ABSTRACT FROM AUTHOR]

Rapid growth and implementation of high-speed trains (HSTs) have made commuting easier. However, the vibrations induced by HSTs deteriorate the embankment of ballastless tracks, particularly of those constructed in frozen regions. In this study, a series of field tests are conducted on the Harbin–Dalian high-speed railway in frozen regions to investigate the vertical acceleration (A z) at the embankment in terms of the train speed (v) and distance from the track centreline (d). The characteristics of A z in the time and frequency domains are analysed based on the field test results. The results show that A z under the unfrozen condition is greater than that in the frozen condition. The periodic excitation of the HSTs can be identified from the time histories of A z within the range of 13.2 m from the track centreline. Moreover, the frequencies of A z can be characterized by v and geometrical characteristics of the train, regardless of seasonal variations. The peak vertical acceleration (A p,z) and frequency-weighted vertical acceleration level (L az) are investigated with respect to v and d. In the unfrozen and frozen conditions, A p,z and L az decrease in the form of a power function with increasing d. The higher the v value, the higher the A p,z value. The dynamic impact coefficient of embankment is introduced to identify the A z performance. Some useful recommendations are provided, and the results can be used for validating numerical predictions related to HST-induced vibration. • Field test on embankment vibrations in unfrozen and frozen conditions due to China's high-speed trains are conducted. • Effects of seasonal variations and train speeds on time- and frequency-domain characteristics are analyzed. • The range on the dynamic impact coefficient in unfrozen and frozen conditions are compared. [ABSTRACT FROM AUTHOR]

Finite element (FE) simulations are increasingly providing a versatile environment for conducting dynamic response studies on the embankment induced by high-speed train (HST). In this environment, vibration mitigation strategies for the subgrade may be assessed to achieve economic and practical solutions. To investigate the vibration behaviors of embankment induced by HST in seasonally frozen regions, an FE modeling was developed and validated by the field test. The investigation noted significant differences in response features in different seasons. For the sake of providing useful engineering information relating to vibration mitigation, a parametric study was conducted to preliminarily investigate the effect of constructing a wave impeding barrier (WIB) at the site. The influences of the material modulus, the size and the embedded depth of WIB on the vibration mitigation were also systematically analyzed in the time domain and frequency domain and then discussed. It showed that the stiffening effect of the WIB led to a shift of response from a large one to a small one. The results convincingly indicated that the vibration mitigation effect of WIB would be improved when its modulus and size increased or the embedded depth decreased. And it also revealed that the WIB might amplify rather than reduce the ground vibration when its embedded depth was larger than a threshold value. Overall, the conducted study highlights the potency of vibration mitigation in seasonally frozen regions by installing a WIB in the subgrade. • The vibration behaviors of HST subgrade in seasonally frozen regions are simulated. • The vibration isolation effect of WIB used in seasonally frozen regions are investigated. • The effectiveness of WIB increases as its stiffness and size increase and decreases as its embedded depth increases. • The analyses indicate that improper design of WIB may amplify the vibration. [ABSTRACT FROM AUTHOR]