In this study, impact compression tests on low-temperature concrete were conducted using a split Hopkinson pressure bar. The impacts of low temperatures on the strength, fractal, and energy characteristics of concrete were analyzed. The damage evolution mechanism of the microcrack density was discussed based on microscopic damage theory and microscopic tests. The results demonstrated that the impact fractal dimension and energy dissipation density of low-temperature concrete were positively correlated with the strain rate. The strain rate sensitivity of the impact fractal dimension was significantly affected by low temperature at low strain rates; however, low temperature had little effect at high strain rates. The pore water transformed into ice at negative temperatures, the fracture energy of the concrete increased, and the energy dissipation density increased. More than 50 % of the capillary and free water inside the concrete was frozen at -10 degrees C; approximately 30 % of the capillary and free water and 65 % of bound water did not freeze when the temperature was -30 degrees C. The macropores did not collapse under the action of ice filling at high strain rates; however, microcracks were generated around them. With a decreasing temperature, the threshold stress for microcrack propagation increased, crack propagation required more energy, and the microcrack density decreased.

In the concurrent extraction of coal and gas, the quantitative assessment of evolving characteristics in mining-induced fracture networks and mining-enhanced permeability within coal seams serves as the cornerstone for effective gas extraction. However, representing mining-induced fracture networks from a three-dimensional (3D) sight and developing a comprehensive model to evaluate the anisotropic mining-enhanced permeability characteristics still pose significant challenges. In this investigation, a field experiment was undertaken to systematically monitor the evolution of borehole fractures in the coal mass ahead of the mining face at the Pingdingshan Coal Mining Group in China. Using the testing data of borehole fracture, the mining-induced fracture network at varying distances from the mining face was reconstructed through a statistical reconstruction method. Additionally, utilizing fractal theory, a model for the permeability enhancement rate (PER) induced by mining was established. This model was employed to quantitatively depict the anisotropic evolution patterns of PER as the mining face advanced. The research conclusions are as follows: (1) The progression of the mining-induced fracture network can be classified into the stage of rapid growth, the stage of stable growth, and the stage of weak impact; (2) The PER of mining-induced fracture network exhibited a typical progression that can be characterized with slow growth, rapid growth and significant decline; (3) The anisotropic mining-enhanced permeability of the reconstructed mining-induced fracture networks were significant. The peak PER in the vertical direction of the coal seam is 6.86 times and 4446.38 times greater than the direction perpendicular to the vertical thickness and the direction parallel to the advancement of the mining face, respectively. This investigatione provides a viable approach and methodology for quantitatively assessing the anisotropic PER of fracture networks induced during mining, in the concurrent exploitation of coal and gas. (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/).

To investigate the effects of the maximum principal stress direction (theta) and cross- shape on the failure characteristics of sandstone, true-triaxial compression experiments were conducted using cubic samples with rectangular, circular, and D-shaped holes. As theta increases from 0 degrees to 60 degrees in the rectangular hole, the left failure location shifts from the left corner to the left sidewall, the left corner, and then the floor, while the right failure location shifts from the right corner to the right sidewall, right roof corner, and then the roof. Furthermore, the initial failure vertical stress first decreases and then increases. In comparison, the failure severity in the rectangular hole decreases for various theta values as 30 degrees > 45 degrees > 60 degrees > 0 degrees. With increasing theta, the fractal dimension (D) of rock slices first increases and then decreases. For the rectangular and D-shaped holes, when theta = 0 degrees, 30 degrees, and 90 degrees, D for the rectangular hole is less than that of the D-shaped hole. When theta = 45 degrees and 60 degrees, D for the rectangular hole is greater than that of the D-shaped hole. Theoretical analysis indicates that the stress concentration at the rectangular and D-shaped corners is greater than the other areas. The failure location rotates with the rotation of theta, and the failure occurs on the side with a high concentration of compressive stress, while the side with the tensile and compressive stresses remains relatively stable. Therefore, the fundamental reason for the rotation of failure location is the rotation of stress concentration, and the external influencing factor is the rotation of theta. (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/).

The relationships between soil aggregates, aggregate-associated carbon (C), and soil compaction indices in pomegranate orchards of varying ages (0-30 years) in Assiut, Egypt, were investigated. Soil bulk density (Bd) and organic carbon (OC) content increased with orchard age in both the surface (0.00-0.20 m) and subsurface (0.20-0.40 m) layers 0.20-0.40 m). The percentage of macroaggregates (R-0.25) and their OC content in the aggregate fraction > 0.250 mm increased as the pomegranate orchard ages increased in the surface layer (0.00-0.20 m). Older pomegranate orchards show improved soil structure, indicated by higher mean weight diameter (MWD) and geometric mean diameter (GMD), alongside reduced fractal dimension (D) and erodibility (K). As orchard ages increased, maximum bulk density (BMax) decreased due to an increase in OC, while the degree of compactness (DC) increased, reaching a maximum at both soil layers for the 30 Y orchards. Soil organic carbon and aggregate-associated C significantly influenced BMax, which led to reducing the soil compaction risk. Multivariate analyses identified the >2 mm aggregate fraction as the most critical factor influencing the DC, soil compaction, and K indices in pomegranate orchards. The OC content in the >2 mm aggregates negatively correlated with BMax, DC, and K but was positively associated with MWD and GMD. Moreover, DC and Bd decreased with higher proportions of >2 mm aggregates, whereas DC increased with a higher fraction of 2-0.250 mm aggregation. These findings highlight the role of aggregate size fractions and their associated C in enhancing soil structure stability, mitigating compaction, and reducing erosion risks in pomegranate orchards.

Frozen soil resistivity exhibits high sensitivity to temperature variations and ice-water distribution. The conversion of soil water content (SWC) and resistivity based on petrophysical relationships enables the characterization of spatial distribution and changes in freezing and thawing states. Monitoring ground resistivity is essential for understanding frozen soil structure and evaluating climate change and ecosystems. The previous studies demonstrate that estimating soil resistivity below zero degrees based on the empirical model has significant errors. This work proposes a capillary bundle fractal model for frozen soil resistivity estimation based on SWC hydrologic parameters. The fractal theory describes the geoelectrical features of frozen porous media through the variable pore geometry and representative elementary volume. The sensitivity analysis discusses the potential relationships between pore parameters, conductance components, and fractal geometric parameters within frozen soil resistivity and reconstructs the hysteresis separation of freeze-thaw processes. The field test application in the seasonal freeze-thaw monitoring site demonstrates that the estimated resistivity and experimental samples are consistent with the field monitoring resistivity data. By combining unified conceptual assumptions, we established the connection between electrical permeability and thermal conductivity, offering a basis for exploring coupled hydro-thermal mechanisms in frozen soil. The proposed model accurately estimates the variations in seasonal frozen resistivity, providing a reliable reference for quantitatively analyzing the mechanisms of freeze-thaw processes.

The time-dependent deformation behavior of silty mudstone brings pronounced difficulties for the construction and maintenance of slope engineering, which has attracted much attention. This study examines the creep characteristics of silty mudstone through multistaged loading tests and studies the creep-induced microstructural evolution using Scanning Electron Microscopy (SEM). To mitigate the variability caused by natural defects in the rock, similar material specimens were prepared to substitute silty mudstone for experiments. The results demonstrate that creep strain escalates stepwise with stress level, with the magnitude of each increment being contingent upon the applied confining pressure (sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document}). The strain rate undergoes three phases including attenuation, stabilization, and acceleration. Cumulative strain correlates positively with sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document}, while the initial creep rate declines before slightly increasing. Creep failure predominantly manifests in a shear pattern, with sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} controlling the development of fractures in terms of their length, number, and angle. SEM analysis reveals that increased sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} facilitates the expansion of transgranular cracks, displaying a coupled ductile-brittle fracture mode. Furthermore, sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} variably affects the micropore morphology (pore size, area, roughness, and regularity), with the differences in pore structures under various sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} being distinguished by the fractal dimension. Also, the fractal dimension is positively correlated with porosity, which can be quantitatively characterized using a nonlinear logarithmic function. The interaction between particles and cement, coupled with the development of cracks and pores, is identified as the primary mechanism of structural failure during the creep process.

Reutilising waste argillaceous gangue (AG) in road engineering is crucial to reducing its environmental pollution. To effectively control settlement and long-term performance of subgrade filled with AG, the effects of humidification and loading on the particle crushing evolution of AG were investigated. The effects of dry-wet cycles, compaction work, and initial coarse grain content (CGC) on the breakage characteristics were evaluated. The relationship among fractal dimension D and compaction work, initial CGC, and breakage index Bg was established. The results show that the initial CGC and compactness are essential factors affecting the breakage characteristics of AG. It is recommended that the CGC be controlled at 50% when AG is used as subgrade filler. The fractal dimension increases logarithmically with the increase of compaction work and decreases linearly with the rise of CGC. Fractal dimensions D and Bg can effectively evaluate the breaking process of AG and the gradation after compaction.

Insight into the growth of internal microstructure and surface morphology is critical for understanding the robustness of red sandstone artifacts in frigid environments. Since freeze-thaw (F-T) cycles can exacerbate the surface deterioration of water-bearing sandstone, a series of investigation on fresh and weathered water-bearing sandstone samples with different F-T cycle numbers (i.e. 0-100) is performed in this study, including three-dimensional (3D) laser scanning, scanning electron microscope (SEM) and computed tomography (CT) scanning tests, thermal property tests, Brazilian tests, and multi-field numerical simulations. Our results demonstrate that with increasing F-T cycles, the surface fractal dimension and specific surface area of red sandstone samples increase, and the pore size distribution inside rocks shifts from ultrananopores (10-100 nm) to micro-pores (0.1-100 mm) and ultramicropores (100 mm & thorn;). Spatially, the pores generated by the F-T cycles are more prominent near the surfaces of rock samples. Numerical simulation indicates that the uneven pore distribution leads to surface degradation. After 100 F-T cycles, the intergranular (IG) cement of the samples cracks, and the IG fractures are widened; eventually, due to the structural integrity weakening, the tensile strength is drastically reduced by over half. The thermal properties of the water-saturated sandstone can be improved during the F-T cycles, and a strong coefficient of determination of 0.98 exists between the fractal dimensions of sandstone surface and the tensile strength. When assessing the mechanical properties of stone artifacts under F-T cycles, the morphological damage of red sandstone should first be investigated when in situ sampling is inappropriate. (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/).

Sandy cobble soil is a composite made of soil matrix and cobbles, and the estimation of its shear strength always requires expensive large-scale experiments. The strength of the sandy cobble soil exhibits macroscopic anisotropy with respect to the direction of the major stress due to the observed dominant distribution of the cobble dip angle. In the present paper, a numerical homogenization procedure for anisotropic strength identification of the sandy cobble soils is established, which can take into account the influencing factors of the size, shape, and inclination of the cobbles and the mesoscopic strength of the soil-rock interface. To consider the condition of plain strain, the particle size distribution of the cross of the stratum is derived based on the fractal theory and the transformation method of Walraven. The mesostructure of the sandy cobble soils is randomly produced using ellipses to model the cross of the cobbles. An iterative procedure is utilized to represent the major stress orientation-dependent macroscopic strengths. The results are validated against the data from indoor experiments and global mesoscopic computations. It is shown that the macroscopic strength of the sandy cobble mixtures can be accurately determined and the iterative multiscale limit analysis method is reliable and efficient. Parameter analysis is finally conducted to discuss the effect of the mesoscopic properties on the macroscopic strength.

In order to reveal the intrinsic mechanism of the mechanical properties of lime-treated sandy soil from a microscopic perspective, triaxial tests were conducted to analyze the macroscopic mechanical characteristics of sandy soil with different lime contents (0%, 5%, 8%, and 12%). The changes in the microstructure of the lime-treated sandy soil were studied through scanning electron microscopy, energy-dispersive spectroscopy, and mercury intrusion tests, combined with fractal theory for quantitative characterization. The results indicate that the stress-strain curve of lime-treated sandy soil can be divided into four stages: linear elastic, non-linear, failure, and residual strength. With the increase in lime content, the peak stress and cohesion first increase and then decrease, while the internal friction angle first decreases and then increases, suggesting the presence of an optimal threshold for lime content between 5% and 12%. The failure mode transitions from diagonal shear failure to bulging failure, significantly enhancing stability; both the fitted Mohr-Coulomb and Drucker-Prager failure criteria effectively reflect the failure patterns of the specimens in principal stress space. The results based on the three fractal dimensions demonstrate that lime-treated sandy soil exhibits clear fractal characteristics, with the highest fractal dimension value at a lime content of 8%, corresponding to the highest overall strength. In addition, the fractal dimension shows a binomial relationship with pore characteristic parameters and shear strength parameters; it can effectively characterize the complexity of the microstructure and accurately predict changes in shear strength parameters.