Ili loess is susceptible to substantial collapsible deformation due to water infiltration, leading to various engineering failures. To investigate the characteristics of water infiltration and the mechanisms of collapsible deformation, a field immersion test was conducted in the collapsible loess region of Ili. The changes in water content, water diffusion form, infiltration water volume, and surface collapsible deformation during immersion were analyzed. Numerical simulations explored surface collapsible deformation characteristics under varying saturation infiltration ranges. The results showed that the average vertical diffusion rate in the experimental area was 0.38 m/d, while the average radial diffusion rate was 0.17 m/d. Over time, the water diffusion pattern transitioned from elliptical to conical, with a wet front angle of 41 and a saturated front angle of 20. The quantitative analysis of the vertical and radial water diffusion rates and infiltration water volume of Ili loess over time was conducted. A mathematical relationship between infiltration range and cumulative infiltration volume per unit area was derived. The correction coefficient for collapsible in the experimental area was determined to be 0.74, exceeding the recommended value of 0.5 in the specifications. The surface collapsible deformation correlates with water infiltration and can be divided into four stages: stable immersion, severe collapse, slow collapse, and consolidation settlement. As the saturation front angle increases, the surface collapsible deformation value maintains good consistency with the calculation results of the subsidence trough formula. The variation in the width of the subsidence trough aligns with the influence range of surface collapsibility, both following an exponential increase.

Elucidating the effects of long-term cultivation on pore structure and infiltration characteristics is essential for understanding soil degradation mechanism and improving cropland sustainability. In this study, we evaluated a number of indicators regarding soil properties, pore structure, and water infiltration during long-term cultivation and the relationship of basic properties and pore structure with soil infiltration in northeast Mollisol region of China. The studied cropland involved four cultivation durations (20, 40, 60, and 100 years) and one forest (FR) as the control. X-ray computed tomography (CT) and mini disk infiltrometer were applied to assess the effects of long-term cultivation on soil pore structure and infiltration characteristics at soil depths of 0-100 cm. The pore properties including soil porosity (TP), pore number (PN), pore size distribution, mean shape factor (MSF), fractal dimension (FA), anisotropy (DA), and Euler number (EN), and infiltration properties including mean (IR), initial (IIR), stable infiltration rate (SIR), and saturated hydraulic conductivity (Ks) were planned to be measured in this study. The results showed that soil organic carbon (SOC) in cropland was significantly lower than that in FR, while bulk density (BD) and mean weight diameter (MWD) exhibited an opposite trend. Long-term cultivation altered the soil pore size and shape distribution, and decreased the macroporosity (>500 mu m) and elongated porosity, which suggested that long-term cultivation results in a simpler pore network. FR took a longer time to reach a stable state in infiltration curve over time, while cropland had lower IR, IIR, SIR and Ks, indicating negative effects of cultivation on water infiltration. > 500 mu m porosity and elongated porosity were positively correlated with infiltration characteristics (P<0.01). The infiltration parameters were mainly affected by soil pore properties (MSF, PN, and DA) and basic properties (SOC, MWD, and BD), highlighting the importance of pore morphology in the infiltration process. Our results provide new insights into the evolution of soil structure and properties and explanations for water infiltration dynamics under long-term cultivation from the microscale.

In this investigation, coral sand is presented as a sustainable substitute for conventional river and machine-manufactured sand. This study comprehensively investigated the macro-scale strength, deformation, and permeability characteristics of coral sand, alongside analyzing the mechanical behavior, deformation, and permeability under various conditions and in relation to distinct particle characteristics. It revealed that coral sand primarily consists of biotite and high-Mg calcite, featuring abundant internal pore space. Its compressive properties resemble clayey soils, displaying minimal unloading rebound and predominant plastic deformation during compression. In direct shear tests, the stress-strain relationship follows an approximate hyperbola, with no pronounced strain softening. Describing particle fragmentation in the process proves challenging, making indicators like internal friction angle less applicable in engineering. Triaxial tests indicate a rapid initial bias stress increase, followed by a gradual decrease post-stress peak, suggesting a strain softening phenomenon. As surrounding pressure rises, the axial strain needed to reach peak strength also increases. The permeability coefficient of coral sand correlates linearly with pore ratio increase, represented by 10e. The complex interaction of multiple factors influences the strength, deformation, and permeability of coral sand blown fill mixes, with specimen porosity having the greatest impact. The design and construction of high-weight foundation elements in coral sand blown fill projects should consider porosity effects.