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.

Internal erosion, which involves the detachment and migration of soil particles from the soil matrix driven by seepage flow, occurs frequently in natural slopes, dikes and many other geotechnical and hydraulic structures. Previous studies primarily focused on soil internal erosion under the isotropic stress state and monotonic hydraulic loadings. However, the soil in engineering practices is under more complicated hydro-mechanical conditions, i.e. anisotropic stress states, and subjected to large and cyclically unsteady hydraulic loadings due to water level fluctuations. Under such conditions, the soil internal erosion process differs significantly from that under the monotonic seepage and isotropic stress states. Therefore, in this study, extensive laboratory tests were carried out to investigate the soil hydro-mechanical behavior subject to high cyclic hydraulic gradients and various stress states. Results show that the soil experienced a gradual internal erosion process under an isotropic or low shear stress state, whereas it experienced rapid erosion followed by a complete failure when the stress ratio (eta) was high. The cyclic hydrodynamic loading accelerated the occurrence of internal erosion due to strong disturbances to the soil structure. The soil pores became continuously connected under high cyclic hydraulic gradients, leading to significant soil deformations due to the collapse of soil force chains by massive particle loss. Additionally, the peak and critical friction angles for all the post-erosion soils decreased considerably and the soil tended to exhibit strain softening behavior after erosion at large cyclic hydraulic gradients.

Initial damage is a significant factor leading to alterations in the mechanical properties of discarded tire materials. With reinforced soil being at its serviceability limit state, the one-dimensional tensile stress state predominates within the reinforcement material. The tensile properties of tire-derived geotechnical reinforcement material(TGRM) with initial damage directly determine whether the reinforcement effect can stably exist within the reinforced soil. To investigate the tensile properties, damage mechanisms, and the relationship between the failure mode of TGRM and its absorptive capacity for strain energy under initial damage conditions, static tensile tests were conducted to obtain the stress-strain relationships, post-fracture elongation rates and fracture morphologies of both strip-shaped and ring-shaped TGRM. During the tensile process, research indicates that the non-zero-degree steel fibers within TGRM undergo a symmetrical interlaminar relative displacement. This ensures that the cross- remains macroscopically planar throughout, ultimately leading to a interlayer cracking in the belt layers. Prior to the cracking, a reliable anchoring relationship constantly exists between the steel fibers and the rubber matrix. Initial damage determines the integrity of zero-degree belt layer and the depth of non-zero-degree steel fibers embedded into the rubber matrix, which in turn affects the strain energy storage capacity and the failure mode of TGRM. The results may provide references for the establishment of the constitutive relationship and strength theory of TGRM under initial damage conditions.

To address environmental concerns related to cement-stabilized expansive soil and the safety risks of caustic-activated blast furnace slag, this study explores the use of lime-activated blast furnace slag as an alternative stabilizer in northern Hebei, China. The effects of slag dosage, curing time, and osmotic pressure on the expansion, osmotic properties, and strength of the improved soil were evaluated through free expansion rate, permeability coefficient, and unconfined compressive strength tests. Results show that adding slag-lime significantly reduces soil expansion. As slag content increases, the free expansion rate decreases exponentially. During the curing period of 3-7 days, expansion declines and stabilizes between 7-14 days. Similarly, the permeability coefficient permeability coefficient decreases with higher slag content, following a quadratic trend. Under osmotic pressures of 0.1-0.2 MPa, the permeability coefficient permeability coefficient increases but stabilizes between 0.2-0.4 MPa.Furthermore, slag-lime significantly enhances unconfined compressive strength, which increases linearly with slag content. The stress-strain curve follows a logistic function in the rising stage and a rational fractional equation in the descending stage.This study demonstrates that lime-activated blast furnace slag is a sustainable and effective alternative for stabilizing expansive soils while reducing dependence on cement.

The formation of multi-layer horizontal ice lenses in frozen soil significantly alters its internal structure, leading to changes in its mechanical properties. To quantitatively analyze the effects of multi-layer ice lenses on mechanical properties, a series of freezing tests were conducted with frost-susceptible clay materials at varied freezing ratios. Then, the uniaxial compression tests were conducted to investigate the deformation and strength properties of frozen soil at different freezing ratios and temperatures. The experimental results indicate that the unique ice skeleton structure formed by horizontal ice lenses and inclined ice wedges can significantly improve the strength of the samples, leading to the peak stress and secant modulus E-50 increase with the freezing ratio, and the presence of an ice skeleton makes the strength more sensitive to temperature changes. The frozen soil samples exhibit two failure modes (bulging failure and shearing failure), which significantly affect the mechanical parameters of the soil. Based on the test results, a frost heave-induced damage coefficient is introduced into the strain softening model to account for the initial stiffness reduction caused by microcracks generated during the ice skeleton growth. This modified model effectively predicts the stress-strain relationship of soils with varying ice skeleton structures. These findings have practical implications for predicting the properties of frozen soil constructed using artificial freezing methods.

This paper presents a mathematical description of the failure law of anisotropic properties from the following three aspects. Firstly, a generalized nonlinear failure criterion, revision Matsuoka-Nakai-Lade-Duncan (RMNLD) criterion, is proposed, which can describe a series of failure curves via von Mises and spatial mobilized plane (SMP) criterion on the partial plane. Secondly, a new stress tensor with a fabric tensor is proposed to describe the particle arrangement characteristics of rock or soil materials in 3D space, and it can be adapted to express the anisotropic RMNLD. Finally, the mapping relationship from anisotropic RMNLD to isotropic von Mises criterion was established on the deviatoric plane. The validity and feasibility of the proposed anisotropic RMNLD criterion and stress transformation method are experimentally verified.

In order to study the mechanical propertied and change rules of undrained shear behavior of saline soil under the freeze-thaw cycles, an improved constitutive model reflecting the effects of freeze-thaw cycles was proposed based on the traditional Duncan-Chang model. The saline soil in Qian'an County, western Jilin Province, was selected as the experimental object. Then, a set of freeze-thaw cycles (0, 1, 10, 30, 60, 90, 120) tests were conducted on the saline soil specimens, and conventional consolidated undrained triaxial shear tests were conducted on the saline soil specimens that underwent freeze-thaw cycles. The stress-strain relationship was obtained by the triaxial shear test. The model parameters have a corresponding regression relationship with the number of freeze-thaw cycles. Finally, based on the function expression of the model parameters, the modified Duncan-Chang model with the number of freeze-thaw cycles as the influence factor was established, whilst the calculation program of the modified model is compiled. Based on the test results, the stress-strain relationship of the saline soil specimen shows strain hardening. The shear strength gradually decreases with the increase of freeze-thaw cycle. The 10 freeze-thaw cycles are the turning point in the trend of changes of the mechanical properties of saline soils. The calculated and experimental stress-strain relationship are compared, and the comparison between the calculated value of the model and the experimental value showed that the two had a good consistency, which verified the validity of the modified Duncan-Chang model in reflecting the effects of the freeze-thaw cycle.

Mixed fiber reinforced technique has been widely used in reinforcing the concrete due to its excellent performance in enhancing the strength, durability and stiffness. The improvement of fiber-reinforced soil (FRS) on the mechanical behaviour (e.g., stiffness and ductility) is limited due to the properties of single fibers. However, much studies focus on the single fiber based reinforced soil, two fibers or more mixing with soil do not be covered. Mixed fiber-reinforced soil (MFRS) is defined as the improvement of FRS, in which two different types of fibers are mixed into the soil to improve the shear strength and stiffness simultaneously. The tests were conducted using clay soil and Yongjiang sand, which were collected from the practical construction site of metro and Yongjiang River, respectively. The test results show that under the same test conditions (e.g., void ratio, confining pressure and fiber content), the MFRS always show higher deviator stress than the FRS. As carbon fibers and polypropylene fibers give higher stiffness and tensile strength respectively. Besides, the friction angle and cohesion of MFRS are also affected by fiber content. It is concluded that half of the carbon fiber content of MFRS has the same performance in the stress-strain relationship as the FRS with 100% carbon fiber content. However, the effectiveness of the reinforcement to clay soil is insignificant. As the reinforcements is relatively dependent on the characteristics of clay soil (e.g., mean diameter, coefficient uniformity). For the use of MFRS, it could decrease the cost of purchasing special fiber such as pure carbon fiber and aramid fiber, which are expensive, and it could be used in the long-terms constructions, which are required to last at least 100 years.

Sandy soil in the north of Hebei region of China is widely distributed, the temperature difference between day and night is large, the phenomenon of freezing and thawing is obvious, and the soil body before and after the freezing and thawing cycle of sandy soil slopes is affected by the changes. This paper takes the stability of a sandy soil anchorage interface under a freeze-thaw cycle as the research background and, based on the self-developed anchor-soil interface shear device, analyses the influence of changing sand rate, confining pressure, and the number of freeze-thaw cycles on the shear characteristics of an anchor-soil interface in anchorage specimens. The research findings indicate that, at 50-60% sand contents, the shear strength increases with a higher sand content and is positively correlated with confining pressure within a higher range. A higher sand content stabilises the anchoring body, but an excessively high sand content can lead to failure. Increasing the sand content, confining pressure, and freeze-thaw cycle number all result in a reduction in the shear displacement at the peak strength. After 11 freeze-thaw cycles, the shear strength of the anchoring body stabilises, with a reduction in strength of approximately 32%, and a higher sand content effectively reduces the reduction in strength.

Strength characteristics of graded gravels are essential in the construction of roadway and railway substructures. Traditional constitutive models, primarily nonlinear elastic and plastic types, fall short in accurately capturing the strain-softening properties of such materials. To address this limitation, the current study introduces a statistical damage model designed to outline the stress-strain behavior of densely compacted graded gravels in transport infrastructures. Utilizing medium-sized triaxial tests, the model examines variations in strength and deformation parameters in relation to compaction levels and incorporates a unique damage-softening index (DSI) along with a threshold axial strain to improve accuracy. The study establishes that the DSI and threshold axial strain effectively regulate stress-strain relations in the postpeak segment, the model's statistical parameters and threshold axial strain can be precisely determined through the introduction of DSI, and the model closely aligns with experimental data across multiple compaction levels. These findings are especially relevant for engineering design in the context of roadway and railway construction and indicate potential for further refinement, such as the incorporation of loading rate considerations.