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The impact of cyclic loading frequency (f cyc) on the permanent deformation (ε p) of freeze–thaw coarse–fine mixture of geomaterials (FTCF) has been extensively investigated. In this work, long-term cyclic triaxial tests were conducted on FTCF specimens with varying f cyc and deviatoric stress (q cyc) with different numbers of freeze–thaw cycles (N FT), in order to investigate ε p under freeze–thaw cycling. This study systematically analysed and discussed the effects of f cyc and q cyc on ε p of FTCF samples with different fine particle contents (FC). A rate-dependent multistage load-prediction model for ε p was proposed and evaluated. The results showed that the freeze–thaw cyclic had a less significant impact on ε p when compared to the dynamic triaxial loading. The speed and piston effects of the FTCF under dynamic loads were mutually restricting, with their combined impact closely related to the loading frequency. A higher deformation resistance for a coarse-grained skeleton is attained with the effective filling of fine particle clusters in the pores of skeleton. A function was proposed to describe the relationship between the hyperbolic model parameters and f cyc , q cyc , as well as FC. This function could be used to estimate the hyperbolic model parameters under different dynamic stresses and material states. An equivalent stress-state parameter was introduced to consider the effect of the loading frequency, enabling the exploration of dynamic loading's influence on the equivalent vibration number (N eq). A comparison between the predicted results and the test data showed that the proposed model could accurately reproduce the cumulative behaviour of the ε p of FTCF under different f cyc and q cyc. • Proposed a rate-dependent multistage loading predicted model of ε p. • A threshold of f v must exist to maximize the material's resistance to ε p. • Load similarity analysis is essential for studying the coupling of freeze-thaw and vibration. [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]

The effect of freeze-thaw (F-T) cycles on dynamic behavior of coarse-grained materials (CGMs) (i.e., coarse-grained materials used in railway subgrade named as base course materials) is critical to ensure the service status of railway subgrade in seasonally frozen regions. In this study, a series of stress-controlled dynamic triaxial tests were conducted on CGMs with various fines contents (FC s) exposed to F-T cycles. Typical test results were then analysed and discussed, highlighting the environmental effect on the dynamic properties. The results demonstrated that the dynamic shear modulus decreased with the increase of FC or the number of freeze-thaw cycles (N FT), but the damping ratio (D) results indicated just the reverse characteristic. In this regard, a modified empirical model was determined to describe the relationship between dynamic shear modulus (G d) and dynamic shear strain amplitude (γ ¯ d). Meanwhile, a unified mathematical formula was proposed to characterize D. Furthermore, the two proposed empirical equations were found to be severely inconsistent with the previous ranges suit for seismic loading. The study provides a useful reference for preliminary evaluation of the response to train loading for CGMs subjected to F-T cycles. • The effect of freeze-thaw cycles on the dynamic behavior of railway's base course materials was analysed. • The modified empirical equations for dynamic shear modulus and damping ratio were proposed. • The difference of dynamic behavior of coarse-grained materials between train and earthquake loading were discussed. [ABSTRACT FROM AUTHOR]

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 behaviours of coarse-grained materials (CGMs) 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 CGMs considering the effects of number of F-T cycles (N FT), confining pressures (σ 3), dynamic stress amplitude (σ ¯ d), and fines content (FC). Representative test results of accumulative axial strain (ε acc), resilient modulus (M r), dynamic shear modulus (G d) and damping ratio (D) are then presented and discussed. Empirical models are proposed and validated for predicting the evolution of ε acc and M r for CGMs under the cyclic loading. In addition, the evolution models of G d and D were established, which can be used for computing the response of CGMs under various influencing factors. Overall, this study provides further insights into the cyclic behaviours of CGMs in seasonally frozen regions. • Cyclic triaxial tests were carried out on prepared thawed coarse-grained materials. • Effects of freeze-thaw cycles, confining pressure, dynamic stress amplitude, and fines content were discussed. • Models for accumulative strain, resilient modulus, dynamic shear modulus and damping ratio were proposed and validated. [ABSTRACT FROM AUTHOR]