High-strength mortar (HSM) gradually has wide applications due to its exceptional strength, micro-expansion properties, and excellent fluidity. Behavior deterioration of structures in saline soil areas is primarily attributed to freeze-thaw cycles and sulfate attack. In this study, the coupling effect of freeze-thaw cycles and sulfate attack on the appearance, mass loss, and relative dynamic elastic modulus of HSM was investigated during erosion. Then, compressive experiments were conducted to assess the mechanical properties of HSM subjected to both freeze-thaw cycles and sulfate attack. The influences of coupling freeze-thaw cycles and sulfate attack on the compressive properties of HSM were quantified through regression analysis of experimental results. Empirical models for compressive stress-strain curves and damage constitutive behavior of HSM were developed, taking the coupled adverse effect into account. The results indicate that the coupled effect of freeze-thaw cycles and sulfate attack causes performance deterioration of HSM. The empirical models reproduce the compressive behaviors of HSM subjected to freeze-thaw cycles and sulfate attack.

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.

Aiming at mitigating the high risks associated with conventional explosive blasting, this study developed a safe directional fracturing technique, i.e. instantaneous expansion with a single fracture (IESF), using a coal-based solid waste expanding agent. First, the mechanism of directional fracturing blasting by the IESF was analyzed, and the criterion of directional crack initiation was established. On this basis, laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF. The results indicate that the IESF presents an excellent directional fracturing effect, with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces. Moreover, during concrete fracturing tests, the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the non-fracturing direction, respectively. Finally, the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine. The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation, achieving an average cutting rate and maximum roadway deformation of 94% and 197 mm, respectively. These on-site test results verified its excellent directional rock fracturing performance. The IESF technique, which is safe, efficient, and green, has considerable application prospects in the field of rock mechanics and engineering. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

This study aims to systematically investigate the influence mechanism of particle size and surface roughness on the shear mechanical behavior of spherical particle materials. Rough glass beads with different particle sizes (2 mm, 3 mm, 4 mm) were prepared using sandblasting technique. Together with smooth glass beads, they were used as test raw materials for indoor triaxial consolidated-drained (CD) tests. Based on the quantitative characterization of particle surface roughness, the differences in the shear mechanical properties of spherical particle materials, including stress-strain curves, strength parameters, critical state characteristics, and stick-slip behavior, etc., were discussed from the aspects of the particle size effect (R), the surface roughness index (Ra), and the normalized roughness effect (Ra/R). The main research results show that: increasing the surface roughness of particles can improve various shear mechanical parameters to a certain extent. This includes effectively increasing the peak deviatoric stress, expanding the range of the strength envelope, and raising the deviatoric stress corresponding to the specimen in the critical failure state. It can significantly increase the peak friction angle phi by approximately 10 %-40 % and the critical state line slope (CSL slope) by about 5 %-23 %. Moreover, the increase becomes more pronounced as the particle size decreases. Meanwhile, as the normalized roughness effect (Ra/R) increases, the friction coefficient becomes larger, which greatly weakens the stick-slip behavior between particles.

Lateritic clay is widely distributed in southern China, and its strength is greatly affected by water content. The elevated moisture content in lateritic clay during monsoon periods frequently results in insufficient shear strength for standard engineering applications. Large quantities of solid waste, including steel slag, fly ash, and granulated blast furnace slag, are produced as industrial by-products. This paper is based on the backfilling resource utilization of steel slag, fly ash, and ground-granulated blast-furnace slag as lateritic clay improvement admixtures, along with the stress-strain behavior, strength characteristics, and microstructure of steel-slag-modified lateritic clay, fly-ash-modified lateritic clay, and ground-granulated blast-furnace slag-modified lateritic clay, by combining uniaxial compression tests, straight shear tests, and scanning electron microscopy observation. The experimental results were analyzed to determine the appropriate dosages of three kinds of solid waste and their mechanisms in lateritic clay modification. The results indicate that the unconfined compressive strength of SS-modified lateritic clay exhibited an increase with an increase in SS dosage in the range of 1-7%, the unconfined compressive strength of FA-modified lateritic clay showed an increase with an increase in FA dosage in the range of 1-5%, and the unconfined compressive strength of GGBFS-modified lateritic clay increased with an increase in the use of GGBFS in the range of 1-5%. Under the condition of a 7-day curing age, the unconfined compressive strength of lateritic clay modified with 7% SS increased by approximately 397%, while that modified with 5% FA and 5% GGBFS exhibited increases of about 187% and 185%, respectively. The stress-strain relationship of fly-ash and blast-furnace slag-modified lateritic clays showed elastic-plastic deformation. But the stress-strain behavior of steel-slag-modified lateritic clay at a steel slag dose greater than 5% and a maintenance age greater than 7 days showed elastic deformation. Analyzing the SEM images shows that the more hydration products are generated, the relatively higher the unconfined compressive strength of modified lateritic clay is, and the form of deformation of modified lateritic clay is closer to elastic deformation. Through comparative analysis of modified lateritic clay samples, this study elucidates the property-altering mechanisms of waste powder additives, guiding their engineering utilization.

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.

Foamed lightweight soil is widely used in subgrade engineering as a lightweight, high fluidity material. However, due to the use of cement as the main raw material, its cost is relatively high. Therefore, the preparation of foamed lightweight soil by mixing muck excavated at the project site with iron ore tailings (IOT) is not only helpful to reduce costs, but also can promote the efficient and comprehensive utilization of inactive solid waste. In this paper, the fluidity, wet density, compressive strength and specific strength of muck-IOT foamed lightweight soil with different content were tested, and the optimal mixing ratio was selected according to the engineering specifications. Then, through uniaxial and triaxial compression tests, the strength and deformation characteristics of muck-IOT foamed lightweight soil under different dosage, wet density and confining pressure conditions were studied. Finally, the influence mechanism of muck and IOT on the strength and structure of foamed lightweight soil was revealed through Scanning Electron Microscope (SEM) analysis. The research results show that the wet density of foamed lightweight soil prepared by the optimal mixing amount (20% muck and 10% IOT) is 894 kg/m3, and the uniaxial compressive strength is 4.6 MPa. While meeting the requirements of fluidity, the mixing amount of solid waste is higher, with the specific strength increased by 28.12%. In the triaxial compression test, for every 100 kg/m3 increase in wet density, the peak strength and residual strength increase by 1.30 MPa and 1.00 MPa, respectively; For every 200 kPa increase in confining pressure, the peak strength and residual strength increase by 0.27 MPa and 0.32 MPa, respectively. In addition, the shear strength levels of muck-IOT foamed lightweight soil under different normal stress conditions under different wet densities were determined by establishing the linear equations of c and phi related to the wet density. From the microstructure, it can be seen that the pores in the muck-IOT foamed lightweight soil are evenly distributed, resulting in a denser structure and reduced stress concentration, which significantly enhances the material's compressive strength.

In order to explore the mechanical properties and microstructure changes of frozen saline silty clay in the Hexi region of Gansu Province, triaxial compression tests and scanning electron microscopy (SEM) analysis experiment were conducted to explore the effects of moisture content, confining pressure, and temperature on the stress-strain characteristics and failure modes of frozen soil, as well as the changes in the internal microstructure of the sample. The experimental results show that the strength of frozen sulfate saline soil first increases and then decreases with the increase of moisture content, and the maximum strength corresponds to a moisture content of 15%. The changes in confining pressure and strength have the same trend. The lower the temperature, the greater the strength of the sample. During the entire loading process, the specimens undergo a gradual transition from volume shrinkage to volume expansion. Due to the strain harden behavior of the stress-strain curve throughout the entire loading process, the failure mode of the specimens is plastic failure. The internal microstructure of the sample gradually transitions from point-point contact and edge-point contact before shearing to edge-surface contact and edge-edge contact after shearing, and the pore size inside the sample increases after shearing, with a loose arrangement of the particle skeleton. The above research conclusions can lay a certain theoretical foundation for the engineering design and construction of sulfate saline soil in cold and arid areas.

This study reveals the mechanical behavior of silt in the Yellow River floodplain under 3D stress. A true triaxial apparatus was used to conduct consolidated drained shear tests under different intermediate principal stress coefficients (b) and consolidation confining pressures to investigate the influence of the intermediate principal stress on the deformation and shear strength of silt. The stress-strain curves exhibited strong strain-hardening characteristics during shearing. Due to enhanced particle interlocking and microstructural reorganization, the silt demonstrated complex b-dependent deformation and strength characteristics. The cohesion rose with increasing b, whereas the internal friction angle followed a non-monotonic pattern, increasing and decreasing slightly as b approached 1. The strength envelope of the silt fell between that predicted by the Lade-Duncan and the extended von Mises strength criteria., which is best predicted by the generalized nonlinear strength criterion when the soil parameter alpha was 0.533. The findings reveal the stress-path-dependent mechanisms of Yellow River floodplain silt and provide essential parameters for optimizing the design of underground engineering projects in this region.