Expansive soils are widely distributed in tropical and subtropical regions and are highly sensitive to moisture variations, posing significant challenges to slope stability. Rainfall infiltration alters the hydro-mechanical behavior of expansive soils, increasing the risk of landslides and slope failures. Understanding the infiltration dynamics under different slope conditions is therefore essential for improving slope stability management and disaster mitigation. To investigate the mechanisms governing the long-term stability of steep expansive soil slopes, this study designed and constructed a multi-slope combination model test box. Model experiments were conducted on rainfall-induced expansive soil slopes with varying gradients to analyze the interaction between surface runoff and seepage under different rainfall conditions. The results demonstrate that slope gradient plays a crucial role in the rainfall infiltration process. As the slope gradient decreases, the time required for runoff initiation increases, and rainfall infiltration becomes the dominant process, while runoff plays a secondary role. This effect is more pronounced at lower slope gradients. Furthermore, as the slope gradient increases, the variation in soil moisture content decreases, and the influence of rainfall on deeper soil layers is reduced. Beyond a certain threshold, further increases in slope angle result in a diminished effect on enhancing surface runoff and limiting infiltration. Additionally, steeper slopes exhibit a slower rise in soil moisture content during rainfall events. The results also indicate that as the slope gradient increases, the depth of soil affected by rainfall becomes shallower, and the migration speed of the wetting front decreases. The findings of this study provide valuable insights into slope hydrodynamics and serve as a scientific basis for sustainable slope management and soil conservation in expansive soil regions.

Expansive soil poses significant challenges for engineering due to its susceptibility to swelling and shrinkage. This study aims to explore effective methods for improving its mechanical properties using single alkaline activators, single slag, and their combination. Laboratory experiments were conducted to evaluate the unconfined compressive strength (UCS) and analyze curing mechanisms through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrate that all three treatments enhance soil strength, with the combination of alkali-activated slag being the most effective, followed by the single alkaline activator and single slag. Optimal dosages were determined as 15% for the activator and slag individually and 15% activator combined with 20% slag, yielding the densest structure and highest UCS. The activator’s modulus of 1.5 was found to be optimal, and strength improved further with extended curing time. A microscopic analysis revealed that alkaline activation formed gel-like substances and dense needle-like structures, while slag generated CaCO₃ and Ca(OH)₂. The combination produces a synergistic effect, creating substantial amounts of C-S-H, C-A-S-H gel, and dense needle-like structures, which enhance soil compactness and strength by binding particles and filling voids. These findings provide insights into the curing mechanisms and offer practical solutions for improving expansive soil in engineering applications.

By integrating laboratory tests and three-dimensional discrete element methods, this research extensively explores the macroscopic and microscopic mechanisms of static pile penetration in standard sand. Initially, the mesoscopic parameters of standard sand were established via flexible triaxial compression tests, and a three-dimensional discrete element model was created using the particle size magnification technique. The study results confirm the rationality of parameter selection and numerical modeling by comparing penetration resistance and displacement obtained from laboratory model tests and discrete element simulations. Initially, penetration resistance swiftly increases, then stabilizes progressively with increasing depth. The lateral friction resistance grows with penetration depth, especially peaking near the cone tip. Moreover, horizontal stress quickly rises during pile penetration, mainly caused by the pile foundation compressing the adjacent soil particles. Displacement of the foundation particles is primarily focused around the pile side and cone tip, affecting an area roughly twice the pile diameter. Soil particle displacement exhibits a pronounced vertical downward movement, primarily driven by lateral friction. The distribution of force chains among foundation particles indicates that the primary stressed areas are at the pile ends, highlighting stress concentration features. This research offers significant insights into the mechanical behaviors and soil responses during pile foundation penetration.

Ultra-high-performance fiber-reinforced concrete (UHPFRC) has the characteristics of high strength, toughness, and excellent crack resistance. In order to fully utilize the high-strength properties of UHPFRC and reduce the structural weight and construction cost, solid slabs can be fabricated into hollow-core slabs or composite sandwich slabs. In order to further analyze the mechanical properties and mechanism of action of UHPFRC hollow-core slabs, one solid slab and two hollow-core slabs with the same geometric dimensions, reinforcement, and steel fiber volume content are designed in this paper, and their stress performance under a static load was investigated using a four-point bending test. The research results show that the UHPFRC hollow-core slab is anisotropic, and the bending stiffness of the section with parallel, distributed tubes is slightly smaller than that of the solid slab. The addition of steel fibers can greatly limit the development of cracks on a slab surface, so the elastic limit of a UHPFRC hollow slab is higher than that of a conventional concrete hollow slab. The whole bending process is roughly divided into the elastic stage, the elastic–plastic stage, and the plastic stage; the crack development process on the bottom of the slab can be classified into the cracking stage, the stable crack development stage, and the rapid propagation stage. In the elastic stage, the cross-sectional deformation of the UHPFRC hollow-core slab in the bending process still satisfies the assumption of a flat section. A row of parallel, round tubes on the neutral axis has a little effect on the cracking load, bearing capacity, and deformation capacity of the UHPFRC slab. By conducting the comparative analysis of the hollow rate and bearing capacity, when the hollow rate reaches 13.57%, the comprehensive weight of the solid slab is reduced by 13.16%, the cracking moment is slightly reduced, and the ultimate load is only reduced by 8.78%. Under the premise of meeting the bearing capacity, the hollow rate of the UHPFRC hollow-core slab can be appropriately increased to save money and energy.

The moisture and thermal characteristics of expansive soil slopes have a significant impact on the strength and overall stability of the soil. In this study, the medium-strength expansive soil vegetated slope in Baise, Guangxi, was taken as the research object. Through the combination of numerical simulation and measured meteorological data, the impact of moisture and heat characteristics on slope stability was then analyzed, and optimal geometric parameters conducive to the stability of vegetated slopes were proposed based on these findings. The research results indicate that under long-term climatic conditions, solar net radiation has the most sensitive effect on the evaporation of slope soil. During the evaporation process, vegetation transpiration dominates in the vegetation-covered layer, while below the depth of the vegetation cover layer, soil evaporation itself plays a dominant role. Under the conditions of evaporation-rainfall-evaporation, slopes with a smaller permeability coefficient in the vegetation cover layer have significantly higher safety factors than slopes with a larger permeability coefficient and bare slopes. A steep vegetated slope with a slope gradient of 50° can maintain slope stability with proper handling of its height. The research findings have reference value for the design and construction of vegetated slopes with expansive soil.

Conducting research on the dynamic behavior of root–soil systems is crucial for accurately assessing the seismic response of ecological slopes, thereby providing a scientific foundation for the development of appropriate seismic design measures. Documentation of the improvement of soil dynamics through vegetation root systems is insufficient in the current research. This study utilizes resonance column tests to explore how root systems influence the dynamic properties of clayey soil and to uncover the mechanisms behind this enhancement. The results indicate that both root distribution and mass density have a significant impact on the soil’s dynamic shear modulus and damping ratio. When roots are distributed in the upper part of the soil, the dynamic shear modulus and damping ratio of the soil are higher than in cases of even distribution or concentration in the lower part. The dynamic shear modulus initially increases and then decreases with the increase in root mass density, reaching its peak at a root mass density of 1.5% g·cm⁻³. The damping ratio is influenced by both root mass density and confining pressure, with different critical root mass densities observed under varying confining pressures. The maximum enhancement in dynamic shear modulus is 27.6%, achieved at a 3% root mass density, with a peak damping ratio of 5.39%. Variations in both dynamic shear modulus and damping ratio with shear strain follow the Hardin–Drnevich hyperbolic curve.