The Loess Plateau region of China has an anomalous climate and frequent geological disasters. Hipparion laterite in seasonally frozen regions exhibits heightened susceptibility to freeze-thaw (F-T) cycling, which induces progressive structural weakening and significantly elevates the risk of slope instability through mechanisms including pore water phase transitions, aggregate disintegration, and shear strength degradation. This study focuses on the slip zone Hipparion laterite from the Nao panliang landslide in Fugu County, Shaanxi Province. We innovatively integrated F-T cycling tests with ring-shear experiments to establish a hydro-thermal-mechanical coupled multi-scale evaluation framework for assessing F-T damage in the slip zone material. The microstructural evolution of soil architecture and pore characteristics was systematically analyzed through scanning electron microscopy (SEM) tests. Quantitative characterization of mechanical degradation mechanisms was achieved using advanced microstructural parameters including orientation frequency, probabilistic entropy, and fractal dimensions, revealing the intrinsic relationship between pore network anisotropy and macroscopic strength deterioration. The experimental results demonstrate that Hipparion laterite specimens undergo progressive deterioration with increasing F-T cycles and initial moisture content, predominantly exhibiting brittle deformation patterns. The soil exhibited substantial strength degradation, with total reduction rates of 51.54% and 43.67% for peak and residual strengths, respectively. The shear stress-displacement curves transitioned from strain-softening to strain-hardening behavior, indicating plastic deformation-dominated shear damage. Moisture content critically regulates pore microstructure evolution, reducing micropore proportion to 23.57-28.62% while promoting transformation to mesopores and macropores. At 24% moisture content, the areal porosity, probabilistic entropy, and fractal dimension increased by 0.2263, 0.0401, and 0.0589, respectively. Temperature-induced pore water phase transitions significantly amplified mechanical strength variability through cyclic damage accumulation. These findings advance the theoretical understanding of Hipparion laterite's engineering geological behavior while providing critical insights for slope stability assessment and landslide risk mitigation strategies in loess plateau regions.

Microstructure and pore characteristics of soil determine its physical and mechanical properties such as deformation, strength, and permeability. The accurate characterization of soil microstructure is a crucial prerequisite for understanding soil texture and for the effective characterization of soil properties. This study aimed to evaluate the applicability and limitations of various soil micro-test methods, compare the resolution of different micro-test techniques, and present their results. Several different techniques and methods have been used to analyze soil micropore structures. In terms of micro-visualization, scanning electron microscopy (SEM) and computed tomography (CT) are common imaging methods that can present the microstructure of the soil surface and its interior through optical means. In addition, some methods, such as soil-water retention curve (SWRC), mercury intrusion porosimetry (MIP), gas adsorption (GA), and nuclear magnetic resonance (NMR,) indirectly assess the size-related information of soil pores through the pore characteristics of porous media. The targeted joint application may be selected according to varying objectives-MIP is used to obtain the main structure when studying the overall internal pores, supplemented by CT for three-dimensional remodeling; NMR is used when studying local pore damage to reflect the evolution of pore characteristics related to water storage, supplemented by SEM to support observations of surface or morphological structure damage. Finally, the direction for future development is to process the test results and transform the existing technical equipment.

In order to gain a deeper understanding of the changes in pore characteristics of undisturbed loess under the influence of acid pollution and the underlying microscopic mechanisms, this study investigates the alterations in pore characteristics caused by acid pollution and their relationship with macroscopic strength. Strength tests, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) tests were conducted on undisturbed loess under various acid pollution conditions to comprehend the evolution of these characteristics. The research findings indicate the presence of a critical acid pollution level in soil. Below this level, increasing acid pollution results in a more uniform distribution of pores, a decrease in the difference between the long and short axes, and a complex edge shape. The arrangement of pores also tends to be disordered. However, when the acid pollution exceeds the critical level, it leads to uneven distribution of pores and an increase in the difference between the long and short axes. The shape of the edges becomes more regular and the pore arrangement becomes more orderly. As the acid pollution intensifies, the total volume of pores between aggregates decreases, while the total volume of pores within aggregates increases. This study examines the impact of acid pollution on the characteristics of loess pores, providing valuable insights into the soil-water-acid properties and deformation management of loess in practical engineering applications. These findings are of practical significance for the construction and protection of loess engineering in loess areas.

Microbial-induced carbonate precipitation (MICP) is a novel geotechnical reinforcement method that can be used for slope protection, erosion mitigation and seepage control without compromising the soil structure. Based on computed tomography (CT) 3D reconstruction, pore parameters such as the connected porosity, pore equivalent diameter and coordination number are extracted to quantitatively evaluate the effect of the calcium carbonate content on the microstructure of biocemented sand. Then, simulations are conducted to analyze the seepage characteristics of single-phase water flow in the pore space, and 3D visualization of porous seepage in biocemented sand is achieved. The results indicate that as the calcium carbonate content increases, there is a noticeable decrease in total porosity, which is accompanied by an increase in the number of isolated pores and a decrease in the number of connected pores. Concurrently, the average pore equivalent diameter increases, while the pore coordination number decreases. Seepage simulation shows that the permeability of biocemented sand has strong anisotropy, and the pore structure has a strong control effect on the seepage. With increasing calcium carbonate content, the biocemented sand streamlines gradually develop from a network to a branching shape until several main stems remain.

Microscale alterations in soil physical characteristics resulting from long-term soil health practices can contribute to changes in soil nitrous oxide (N2O) emissions. In this study, we investigated soil N2O emissions in relation to pore characteristics influencing soil gas diffusivity under long-term tillage and cover cropping practices. Intact soil cores from tillage (conventional tillage, Conv. T versus no tillage, NT) and cover crop (hairy vetch, HV versus no cover crop, NC) treatments were used for N2O measurements and computed tomography (CT) scanning. Using X-ray CT technique with a resolution of 59 mu m, pore structure parameters including macroporosity, number of macropores, anisotropy, fractal dimension, tortuosity, and connectivity were determined. The results showed that Conv. T and HV emitted significantly higher N2O than NT and NC, respectively. A similar trend was observed for macroporosity, Conv. T soils had 27.4 % higher CT-derived macroporosity than the NT soils and HV increased macroporosity by 31.1 % over the NC treatment. The number of macropores and fractal dimension were significantly higher whereas degree of anisotropy was significantly lower under HV compared to NC. In the upper 3 cm of soil, HV had a connected porosity, whereas the pores were disconnected and isolated in NC. These CTderived properties; however, were not impacted by tillage treatments. N2O emissions were positively and significantly correlated to relative soil gas diffusivity, CT -derived macroporosity, number of macropores, and fractal dimension. Our results demonstrated that soil macroporosity and relative gas diffusivity could lead to improved understanding and predictability of N 2 O emissions under high soil moisture conditions.

The effect of K-0 consolidation-induced initial stress anisotropy on the mechanical behavior of soft soil and the evolution patterns of structural damage of soil during triaxial loading were investigated. A series of K-0 consolidated and isotropically consolidated undrained triaxial compression tests were carried out. Microstructural information of specimens was obtained using field-emission scanning electron microscopy and mercury intrusion porosimetry techniques. Results show that K-0 consolidated specimens exhibit higher shear strength and stiffness and lower pore water pressure than the isotropically consolidated ones. The effect of initial shear stress was explored to explain why K-0 consolidation can restrain the build-up of the pore water pressure. Nevertheless, the underlying mechanism is that specimens form a sturdier skeleton after K-0 consolidation characterized by a larger interparticle contact area. The pore size distribution index and shape fractal dimension were used to define damage variables for characterizing microstructural deterioration. The relationship between damage variables and the axial strain can be fitted by an exponential function reasonably well, where the damage increases rapidly before 6% similar to 8% strain. In addition, slip zones with a preferred particle orientation of 30 degrees similar to 50 degrees concerning the horizontal direction appear at shear failure regardless of initial structural states, with which the effective internal frictional angle is closely correlated. The macroscopic mechanical characteristics of soil are subject to microstructural damage and the initial stress anisotropy.

As the buffer/backfill material for geological disposal of high-level radioactive waste, the sealing performance of compacted bentonite is affected by its volume deformation characteristics. During the operation of the geological disposal repository, the suction and temperature of bentonite changes due to the groundwater level and heat released by radioactive waste. On this premise, to study the thermal effect on the volume change of bentonite induced by suction variations, a series of wetting/drying tests were conducted on cubic bentonite samples under controlled temperatures of 20celcius, 40celcius and 60celcius. The corresponding microstructure changes during the test were investigated by the mercury injection porosity (MIP) technique. The results show that the increasing temperature accelerated the change in water content and weakened the water retention capacity of bentonite. Additionally, the volume deformation induced by suction change, regardless of swelling or shrinkage, was inhibited by heating. During the process of suction equilibrium, the compacted bentonite showed significant anisotropy, which was positively correlated with temperature and negatively correlated with suction. The sample deformation was due to the changes in the microstructure of the inter-aggregate pores and intra-aggregate pores. The total volume of macro pores decreased obviously with increasing suction, while, the volume of micropores remained almost unchanged. Both the peak value and total volume of the macro pores were reduced by the rising temperature. Furthermore, a threshold suction of approximately 90 MPa was observed, where the temperature effect changed from inhibition of dilation to inhibition of contraction, indicating the suction-dependent temperature effect.