Lime stabilization is a traditional method for improving foundation soils, and it also has potential applications for embankments and earth structures. In this study, several experimental techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR), were used to provide a clear picture of the microstructural evolution of a lime-stabilized loess (LSL) from China. SEM micrographs were used not only to qualitatively highlight the dual porosity nature of the material, but also to provide quantitative information using Image-Pro Plus (IPP) 6.0 software. As the lime content increases, the pore area ratio decreases, the shape of the macropores and mesopores flattens, and the pore angle distribution becomes more uniform. The FTIR results show that the functional group strength of the LSL samples first increases and then decreases with increase in lime content, while the pore volume continues to decrease. A non-monotonic evolution of the strength with the lime content is then expected, as also confirmed by unconfined compression tests performed at different lime contents and curing times: at low lime contents, the reduction of the pore volume and the increase in the functional group strength imply an increase in the strength; at high lime contents, the competing effects of the reduction of the pore volume and the increase in the functional group strength lead to an overall decrease in the strength with the lime content. Then, as an intermediate step toward further quantitative predictions of the hydromechanical behavior of LSL, a pore size distribution model inspired by the proposal of Della Vecchia et al. (Int J Numer Anal Meth Geomech 39:702-723, 2015) was developed and used to reproduce NMR experimental data. The pore size distribution model proved to be able to reproduce the cumulative porosity curves for the whole range of lime content and curing time studied, with only four parameters kept constant for all the simulations. The predictive capabilities of the model were also confirmed by simulating experimental data from recent literature.

This study introduces a novel discrete element method (DEM) model for compacted loess, incorporating a bond rate parameter within a linear contact bond model to simulate constitutive damage behavior. This enhancement significantly improves the characterization of structural damage from repeated wet-dry cycles, offering a quantitative method for predicting damage progression. Unlike existing DEM models, our model directly uses a bond rate parameter to quantitatively describe inter-particle bond deterioration, reflecting reduced bonding strength due to pore structure development and the weakening effect of water. Rigorous calibration and validation were performed using comparative experiments. A key innovation is the systematic analysis of microscopic parameters (contact stiffness, friction coefficient, contact strength, and bond rate) and their impact on macroscopic mechanical behavior. Our findings show that decreasing the bond rate significantly reduces the macroscopic mechanical properties, providing valuable insights into the micro-macro relationship. We comprehensively evaluated prediction sensitivity to these parameters. This methodology offers a new perspective on using DEM for predicting crucial civil engineering material properties, providing a valuable reference for incorporating bond rate parameters into future modeling, particularly for long-term geotechnical material behavior under environmental degradation. The model's accurate representation of wet-dry cycle effects on loess strength improves earth structure design and safety.

Owing to the alternating processes of rainfall and evaporation, the compacted loess employed in ground and roadbed construction frequently experiences drying and wetting (D-W) cycles. These cycles are prone to induce substantial deformation of the soil mass, posing a risk to the integrity of buildings and infrastructure. Consequently, this study delved into the effects of D-W cycles on the deformation behavior of compacted loess, considering varying initial dry densities and water contents. To achieve a profound understanding of the deformation characteristics of the compacted loess, we meticulously monitored the resistivity ratio, crack ratio, and microstructure throughout the tests. Furthermore, a constitutive model was developed to forecast the deformation of compacted loess under D-W cycles. The findings revealed that both the vertical strain and crack ratio exhibited an upward trend with the increase in D-W cycle numbers, while they exhibited a downward trend as dry density increased. Notably, water content was identified as a significant factor affecting both the crack ratio and resistivity ratio. Additionally, the occurrence and progression of D-W cycles and cracks led to a slight increase in particle abundance and the proportion of total pore area. Meanwhile, during the wetting process, the infiltration of water softened the cementing substances, resulting in a disruption of the connections between aggregates. This made it much easier for cracks in the soil to expand after the sample dried. The constitutive model was meticulously constructed by incorporating yield surfaces that account for decreasing and increasing water contents. The validity of the proposed model was substantiated through a comparative analysis of the measured and calculated data. This comprehensive investigation furnishes a theoretical foundation for assessing the stability of compacted loess ground and roadbeds subjected to D-W cycles.

This research examines the impact of lateral constraints on the deformation and mechanical properties of compacted loess, a prevalent material for road construction foundations. Through laboratory compression tests on samples from a specific project area, it evaluates how compactness, confining pressures, and vertical loads affect compacted loess's stress-strain behavior and lateral deformation. The study demonstrates that lateral constraints significantly influence soil deformation behavior and mechanical characteristics, particularly under complete confinement. A new formula for accurately calculating soil compression deformation in engineering practices is introduced, enhancing the prediction and management of subgrade settlement in loess regions. This work contributes to improved construction methodologies and infrastructure durability in challenging terrains by offering insights into compacted loess's compressibility under various lateral constraints.

In this paper, the EC-5 water sensor and the MPS-6 water potential sensor were used to measure water content and suction, respectively, to investigate the evolution of soil-water retention properties of compacted loess samples prepared at different dry densities and subjected to different numbers of wetting-drying cycles. The water retention data were integrated with a detailed microstructural investigation, including morphological analysis (by scanning electron microscopy) and pore size distribution determination (by nuclear magnetic resonance). The microstructural information obtained shed light on the double porosity nature of compacted loess, allowing the identification of the effects of compaction dry density and wetting-drying cycles at both intra- and inter-aggregate levels. The information obtained at the microstructural scale was used to provide a solid physical basis for the development of a simplified version of the water retention model presented in Della Vecchia et al. (Int J Numer Anal Meth Geomech 39: 702-723, 2015). The model, adapted for engineering application to compacted loess, requires only five parameters to capture the water retention properties of samples characterized by different compaction dry densities and subjected to different numbers of wetting-drying cycles. The comparison between numerical simulations and experimental results, both original and from the literature, shows that only one set of parameters is needed to reproduce the effects of dry density variation, while the variation of only one parameter allows the reproduction of the effects of wetting and drying cycles. With respect to the approaches presented in the literature, where ad hoc calibrations are often used to fit density and wetting-drying cycle effects, the model presented here shows a good compromise between simplicity and predictive capabilities, making it suitable for practical engineering applications.

Stiffness of soil at very small strains G0 is mainly affected by void ratio, effective stress and suction. Empirical equations considering those factors have been proposed to estimate G0. However, for collapsible soil like loess, variations in suction might induce changes in void ratio of soil. The combined effect of these two factors poses challenges in accurately estimating of G0. This paper first presents an experimental study on the G0 of collapsible loess under various conditions, including as-compacted states, wetting/drying and K0 loading. G0 is estimated from shear wave velocity obtained with bender element technique. The changes of G0 with respect to void ratio, suction, effective stress, and wetting under K0 stress conditions are evaluated. Test results reveal that power relationships can be defined between G0 and void ratio, suction and effective stress, respectively. The changes in G0 along wetting/drying shows an S shape due to the different dominant effects on soil structure, as well as the induced non-uniform volume changes when suction change at different zones. Under K0 loading, G0 decreases upon wetting at stresses below the compaction stress, while it increases upon wetting at stresses above the compaction stress, due to the combined effects of densification caused by volume collapse during wetting and softening induced by suction decrease. Finally, a G0 model considering net stress and suction as independent stress variable is proposed. This model could effectively capture the change of G0 during wetting, drying and loading, as well as upon wetting under K0 loading for collapsible loess.

Mountain excavation and city construction (MECC) projects being launched in the Loess Plateau in China involve the creation of large-scale artificial land. Understanding the subsurface evolution characteristics of the artificial land is essential, yet challenging. Here, we use an improved fiber-optic monitoring system for its subsurface multi-physical characterization. The system enables us to gather spatiotemporal distribution of various parameters, including strata deformation, temperature, and moisture. Yan'an New District was selected as a case study to conduct refined in-situ monitoring through a 77 m-deep borehole and a 30 m-long trench. Findings reveal that the ground settlement involves both the deformation of the filling loess and the underlying intact loess. Notably, the filling loess exhibits a stronger creep capability compared to underlying intact loess. The deformation along the profile is unevenly distributed, with a positive correlation with soil moisture. Water accumulation has been observed at the interface between the filling loess and the underlying intact loess, leading to a significant deformation. Moreover, the temperature and moisture in the filling loess have reached a new equilibrium state, with their depths influenced by atmospheric conditions measuring at 31 m and 26 m, respectively. The refined investigation allows us to identify critical layers that matter the sustainable development of newly created urban areas, and provide improved insights into the evolution mechanisms of land creation. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting 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/).

Loess, featured by its low permeability and cost-effectiveness, has become an increasingly popular material for landfill cover systems. However, the occurrence of cracks in loess caused by rainfall and evaporation poses challenges to the performance and durability of these cover systems. This study aims to comprehensively investigate variations in air permeability of compacted loess under normal and dry-wet cycle conditions. The conventional triaxial instrument was modified to meet the requirements of the air permeability test of loess. The influence of factors such as permeability pathway, water infiltration time, dry density, and water content as well as dry-wet cycles on the air permeability was thoroughly explored. And the applicability of established models in describing loess air permeability was assessed. The results confirmed that the airflow in compacted loess followed Darcy's law, and there was a clear correlation between air permeability and these influencing factors. Loess samples with a diameter of 38 mm and a height of 76 mm were found to be more suitable for air permeability testing. Cracking in loess significantly increases air permeability, with longitudinal cracking having a greater effect than transverse cracking. Lower-density samples exhibit more pronounced cracking than higher-density samples. Both initial water content and humidification water content were identified as influential factors during dry-wet cycling and have a substantial impact on the variation of air permeability. These findings contribute to a better understanding of the air permeability characteristics of compacted loess in landfill cover systems, enabling improved design and performance evaluation for sustainable waste management practices.

The understanding of the dynamic behavior characteristics and mechanisms of seismic landslides in seasonal frozen soil areas following severe freeze-thaw damage is currently limited. Taking a compacted loess slope in Lanzhou National New Area of China as the prototype, freeze-thaw cycle tests and large-scale shaking table tests were conducted, and the dynamic responses of freeze-thaw slope and non-freeze-thaw slope under different amplitudes, directions, and intensities of seismic waves were compared and analyzed. The results indicate that the acceleration responses of compacted loess slopes increase with the increase of the slope height and the value of the slope shoulder is the largest. The acceleration responses also increase with higher seismic intensity. On the other hand, earth pressure responses decrease as the slope height increases, but initially increase with higher seismic strength before eventually decreasing prior to slope failure. Comparatively, the acceleration responses of the freeze-thaw slope are stronger than those of the non-freeze-thaw slope, while the earth pressure responses are smaller, particularly in frost-heaving zones The compacted loess slope demonstrates good stability under seismic waves. However, the loosed and wetted surface after freeze-thaw cycles may experience abrupt shear slip during high-intensity seismic waves. These findings hold significance for stability analysis and reinforcement strategies for engineering slopes in the Loess Plateau with seasonal freezing and thawing.

The mechanical properties of loess are strongly dependent on the environment where it is deposited. To investigate the effects of acidic, alkaline, and saline environments on the strength and deformation properties of compacted loess, the consolidation test and direct shear test were carried out on loess samples contaminated with different concentrations of acetic acid, sodium hydroxide, and sodium sulfate. In addition, changes in zeta potential, mineralogy, chemical composition, and microstructure of the loess samples at different chemical environments were also measured. The results show that the reduction in the thickness of the diffuse double layer for the loess contaminated with acetic acid leads to the aggregation of clay particles, laying the foundation for the expansion of loess pores, while the dissolution of carbonate cement and chemical cement makes the soil structure looser. Hence, the compacted loess has significantly lower shear strength and higher compressibility in an acidic environment. The mechanical properties in the saline environment show similar variation characteristics to the acidic environment, but this is mainly due to carbonate solubilization. In the alkaline environment, the degree of interparticle cementation of the loess is enhanced by the generation of calcite due to dedolomitization and the generation of colloidal flocs of Al(OH)3, Fe(OH)3, and H2SiO3. In addition, the pore connectivity is greatly reduced by the extensive distribution of clay particles caused by the development of a diffuse double layer. As a result, its compressibility and shear strength are improved compared to uncontaminated loess. These findings can be used as a reference for geoengineering practice in loess areas.