Frozen soils exhibit unique mechanical behavior due to the coexistence of ice and unfrozen water, making experimental studies essential for engineering applications in cold regions. This review comprehensively examines laboratory investigations on frozen soils under static and dynamic loadings, including uniaxial and triaxial compression, creep, direct shear, and freeze-thaw (F-T) cycle tests. Key findings on stress-strain characteristics, failure mechanisms, and the effects of temperature and time are synthesized. Advancements in microstructural analysis techniques, such as computed tomography (CT), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), and mercury intrusion porosimetry (MIP), are also summarized to elucidate the internal structural evolution of frozen soils. While significant progress has been made, further efforts are needed to better replicate complex environmental and loading conditions and to fully understand the interactions between multiple influencing factors. Future research should focus on developing novel experimental techniques, establishing standardized testing protocols, and creating a comprehensive database to enhance data accessibility and advance frozen soil research. This review provides critical insights into frozen soil mechanics and supports validating constitutive models and numerical simulations, aiding infrastructure design and construction in cold regions.

The rheological properties and creep dynamical behavior of the granular materials are significantly influenced by the packing fraction. The granular materials with a low packing fraction tend to transit from a solid-like to liquid-like state. The strain evolution and deformation characteristics of granular materials under different packing fractions are investigated by triaxial creep tests. The result indicates that a critical packing fraction exists for the granular system under specific external loading conditions, below which the system will be broken in a short period of time. Conversely, for packing fraction that exceeds the critical value, the granular material system exhibits logarithmic creep dynamics and eventually reaches a steady state. To characterize the creep behaviors of granular materials under dynamic loading, a state evolution model is introduced. The model is verified by combining the theoretical predictions with the experimental observations. Furthermore, parametric analysis is also implemented based on the introduced model. The results demonstrate that the model can capture the fundamental spatiotemporal evolution characteristics of granular materials which are subjected to dynamic loading conditions.

Shallow soils are highly vulnerable to the combined impacts of various factors, including vehicle loading, precipitation, and groundwater. The slope soil at the roadside is inevitably subjected to long-term cyclic loading from traffic. Previous studies have demonstrated that ecological engineering measures can effectively mitigate soil deformation and reduce pore water pressure development, thereby preventing soil erosion and landslides. This study aims to investigate the influence of root distribution patterns on the elastic deformation and pore water pressure development trends in root reinforced soil by simulating cyclic traffic loading through dynamic triaxial tests. The study findings demonstrate that the presence of roots significantly enhances the soil's resistance to deformation. When the vertical root accounts for 25% (while the horizontal root accounts for 75%), experimental results indicate that the soil reinforced by roots exhibits minimal deformation and slower pore water development. Moreover, a parameter D is introduced to enhance the existing pore water pressure models with the increased coefficients of determination, thereby improving the applicability in root-reinforced soils. These findings provide valuable insights for enhancing strength and liquefaction resistance in root reinforced soils while providing guiding research for the mechanical effects of root reinforcement of soil for ecological restoration of highway slopes.

To investigate the impact of traffic loading on the deformation characteristics of soft dredger fill, a series of dynamic triaxial tests of soft dredger fill were carried out. The deformation characteristics of the soft dredger fill under varying confining pressures and dynamic stress ratios were analyzed comparatively. The test results indicate that the cumulative plastic strain curve of the soft dredger fill exhibits three distinct patterns: destructive, critical, and stable; Based on the cumulative plastic strain development law of the dredger fill, an empirical formula of critical dynamic stress and the prediction model of cumulative plastic strain development were established, considering the influence of confining pressure. Under continuous loading, the hysteresis curve of soft dredger fill showed pronounced non-linearity, and hysteresis. Initially, the curve exhibited an ellipse shape, transitioning to a crescent shape in the middle and late stages. The higher the dynamic stress ratio, the greater the height and width of the hysteresis loop. These findings provide valuable insights into the dynamic behavior of dredger fill under traffic loading.

An in-deep comprehension of the static and dynamic operational characteristics of prestressed subgrade is essential for its analysis, design, and service performance evaluation. Based on the Buckingham pi theory, a novel scaled static and dynamic model test system of the prestressed subgrade has been developed. The structural components, functional characteristics, and working mechanism of the test system were comprehensively elucidated, and a suite of static and dynamic model tests was conducted to study the deformation characteristics of the prestressed subgrade. It is demonstrated that the prestressed steel bars underwent prestress loss due to the additional stress induced creep of the soil elements below and adjacent to the load transfer plates (LTPs). Therefore, it is advisable to over-tension the prestressed steel bars in practical engineering. Upon the application of prestress, the subgrade surface experienced slight uplift deformation, which did not change the geometric shape and smoothness of the subgrade surface and demonstrated that the prestress reinforcement effect could diffuse to the subgrade surface. In the static double-load-plates tests, the prestressed subgrade presented obvious advantages in controlling the subgrade surface settlement and slope lateral deformation compared to the unreinforced subgrade, which could therefore improve the deformation resistance of the subgrade. In the shortterm dynamic loading tests, both the acceleration and dynamic displacement of the subgrade approximately linearly decreased with an increase in the prestress, implying that the horizontal prestress had a notable beneficial impact on mitigating the subgrade vibration. Additionally, with the long-term dynamic loading, the prestress reinforcements could significantly restrain the cumulative plastic deformation of the subgrade, with the cumulative deformation decreasing as the applied prestress increased. The developed test system offers viable and implementable technical means for investigating the enhancement mechanism of a prestress reinforced subgrade, and the insights gained from the tests contribute to elucidating the effect of prestress reinforcements on the subgrade's static and dynamic performance.

Dynamic loading-seepage causes the migration of railway subgrade filling particles, leading to frequent engineering problems such as ballast fouling, mud pumping, settlement, and erosion. However, few studies have focused on the permeation features and internal erosion characteristics of subgrade materials, making it difficult to uncover the evolution mechanism of service performance of subgrade under complex geo-environmental conditions. Therefore, the seepage characteristics and permeability stability of subgrade materials were investigated using self-developed equipment to reveal the seepage failure mechanism under dynamic loading. The main conclusions are as follows: (1) The internal stability of the soil is affected by fluctuations in pore water pressure and hydraulic gradients in graded aggregate and gravel-sand-silt mixtures caused by dynamic loading. (2) Critical hydraulic gradients leading to the migration of fine particles (J(cr)) and seepage failure (J(F)) in graded aggregate and gravel-sand-silt mixtures are determined as follows: J(cr) =1.30 and J(F) =6.88 for graded aggregate, and J(cr) =1.23 and J(F) =2.71 for gravel-sand-silt mixtures. (3) The seepage failure process of subgrade materials can be divided into three stages under coupled action of train loading and seepage: stable seepage, dominant flow development, and seepage failure. The relationship between flow velocity and hydraulic gradient follows the Darcy's law under the low hydraulic gradient. (4) The evolution process of subgrade performance was analyzed, and the mechanisms and types of railway flood hazard were summarized. The research provides theoretical support for the design and maintenance of railway disaster prevention, and has significant engineering implications.

Foam concrete is characterized by lightweight, self-compacting and high flowability, thereby widely used as a subgrade bed filler. High-speed railway subgrades usually experience inhomogeneous deformation due to the occurrence of freezing-thawing cycles in seasonally frozen soil areas. It is essential to study the deformation behavior of foam concrete under the coupling effect of freezing-thawing cycles and dynamic loading. In this paper, dynamic triaxial tests were performed to study the accumulative deformation of the foam concrete under different numbers of freezing-thawing cycles, freezing temperatures, amplitudes and frequencies of dynamic loading. Based on the scanning electron microscopy (SEM) tests, the characteristics of the pore structure were analyzed quantitatively by introducing the directional distribution frequency and fractal dimension. The research results illustrate that the damage caused by freezing-thawing progress to the pore structure results in more significant deformation of the foam concrete subjected to dynamic loading. There exists an accumulative damage effect induced by the coupling action of long-term dynamic loading and freezing-thawing progress on the microstructure and mechanical properties of foam concrete. The development of the fractal dimension agrees with that of the accumulative strain, indicating a close connection between the microstructure and the dynamic behavior of foam concrete. The findings concluded in this study contribute to a sufficient understanding of the performance of foam concrete used as high-speed railway subgrade fillers subjected to seasonal freezing.

The softening effect has been widely accepted as the fundamental mechanical property of the granular materials, which underlies some specific phenomena such as fluidization during vibration. In this paper, a series of resonance column experiments are performed to observe the modulus softening of granular materials. A statistical softening model is subsequently proposed and its applicability is verified through a quantitative analysis of the variation of the normalized modulus by changing the external confining pressure. The average potential energy in grain contact has been found to be a power-law scaling with grain size. An evolution model is further implemented to account for the experimental findings on the evolution of modulus of the granular system subjected to different confining pressures. The modulus evolution, including softening and recovery, can be captured by the unified evolution model.Graphical AbstractShear modulus evolution

This study compares the in-situ dynamic response of a low plasticity silt deposit subjected to multidirectional loading from vibroseis shaking and controlled blasting to a suite of element-scale, cyclic laboratory test specimens. The agreement between excess pore pressures and simple shear strain relationships over a wide range in strains is remarkable. Slightly larger excess pore pressures observed in-situ are attributed to three-dimensional loading and pore pressure migration/redistribution in the shallower portions of the deposit. Noted differences in shear modulus, G, are attributed to strain rate effects, spatial variability in the in-situ stiffness, and hydraulic boundary conditions. The variation in in-situ G/Gmax follows the trend from torsional shear specimens up to 0.4% shear strain; larger strains in the silt deposit imposed by controlled blasting yielded a stiffer response than that from cyclic torsional shear and direct simple shear specimens due in part to field drainage for deeper portions of the deposit. The in-situ cyclic resistance ratio for the deeper portion of the deposit in which plane body waves could be assumed and for the selected excess pore pressure ratio criterion was larger than that of stress-controlled cyclic direct simple shear (CDSS) test specimens, despite the detrimental effect of multidirectional shaking in the field. The effect of strain history, spatial variability, and drainage boundary conditions to drive differences between the in-situ and laboratory test specimens is identified.

The presence of ice-layers in the subgrade soils makes the hydrothermal state of road subgrade built in island permafrost regions more susceptible to external environmental influences. In order to deepen the study of the ice-layers subgrade, a hydrothermal study of subgrade under constant temperature and dynamic loading was carried out. It was found that dynamic loading can change the temperature, moisture and pore water pressure distribution. Under dynamic loading, the hydrothermal and pore water pressure state of the soil in the upper part of the ice layer changed significantly at the beginning of the test. The application of dynamic loads alters the spatial distribution of pore water pressure in the soil, resulting in pressure differences between different areas, which affects the migration of moisture and ultimately leads to the formation of areas with higher moisture content in the area below the load. However, the reduction in soil temperature will weaken the effect of the load, therefore, the temperature of the soil should be controlled for frozen subgrade with ice-layers to prevent the accumulation of moisture in the soil.