The subgrade constructed by soil–rock mixture (SRM) usually suffers from slope instability, subgrade collapse, and uneven settlement, which are closely related to the permeability of the SRM. In order to reveal the internal influence mechanism of the seepage characteristics of the SRM, the SRM models of dense structure (DS), medium-dense structure (MDS), and loose structure (LS) were generated based on the improved Monte Carlo method (IMCM) and the self-made MATLAB program, and the lattice Boltzmann method (LBM) was introduced to study the mesoscopic seepage characteristics of SRM under different influence factors. Finally, the internal mechanism of the influence of rock content rate (RCR) on the SRM permeability under different conditions was discussed in detail with a simplified model. The results show that the permeability of the SRM in DS, MDS, and LS cases tends to increase continuously with the increase of RCR when the loose-density degree (LD) and rock size (D_R) are the same. The looser the structure of the SRM samples, the larger the permeability. When the RCR is lower than the threshold value, the larger the D_R the slower the increase of the permeability; but when the RCR is higher than the threshold value, the larger the D_R the significantly larger the increase of the permeability. In this study, the threshold value is determined to be about 35%. The RCR sensitivity index (S) shows an overall trend of increasing, then decreasing, and then slowly increasing with increasing RCR, in which large rocks and MDS have a facilitating effect on the sudden change of SRM permeability. When the soil/rock particle size is constant, the permeability of the simplified model tends to “decrease → increase → decrease” with the increase of RCR. This study provides an IMCM-LBM joint simulation method as a promising option to simulate realistic SRM particles permeability in geotechnical experiments.

This study addresses the durability concerns of concrete subjected to wet–dry cycles, particularly focusing on the impact of different recycled aggregate (RA) replacement percentages. Concrete is increasingly used with RAs for sustainability. However, its long‐term performance under environmental stress is not fully understood. The primary motivation of this study is to provide a comprehensive understanding of how varying replacement percentages of RAs influence concrete degradation, a key factor for improving material performance in real‐world applications. Through a series of wet–dry cycle tests, we analyze key degradation indicators, including surface texture changes, mass loss, and compressive strength. The study findings reveal that wet–dry cycles significantly alter the concrete surface, with higher RA content leading to more extensive pore formation, cracks, and surface roughness. Initially, concrete mass increases slightly due to water absorption, but after several cycles, mass loss becomes significant, particularly for higher replacement percentages, which is attributed to internal pore damage and degradation of the interface between the RAs and cement paste. Furthermore, the compressive strength declines steadily with increasing cycles, with more severe deterioration at higher replacement percentages. This decline is primarily due to microcrack propagation and degradation of the interfacial transition zone. A degradation model is developed to quantify the relationship between RA content and durability loss, offering practical recommendations for optimizing replacement percentages to balance sustainability and durability. This study provides valuable insights into enhancing the long‐term performance of concrete in environments exposed to wet–dry cycles.

The two-phase seepage fluid (i.e., air and water) behaviors in undisturbed granite residual soil (U-GRS) have not been comprehensively studied due to a lack of accurate and representative models of its internal pore structure. By leveraging X-ray computed tomography (CT) along with the lattice Boltzmann method (LBM) enhanced by the Shan–Chen model, this study simulates the impact of internal pore characteristics of U-GRS on the water–gas two-phase seepage flow behaviors. Our findings reveal that the fluid demonstrates a preference for larger and straighter channels for seepage, and as seepage progresses, the volume fraction of the water/gas phases exhibits an initial increase/decrease trend, eventually stabilizing. The results show the dependence of two-phase seepage velocity on porosity, while the local seepage velocity is influenced by the distribution and complexity of the pore structure. This emphasizes the need to consider pore distribution and connectivity when studying two-phase flow in undisturbed soil. It is observed that the residual gas phase persists within the pore space, primarily localized at the pore margins and dead spaces. Furthermore, the study identifies that hydrophobic walls repel adjacent fluids, thereby accelerating fluid movement, whereas hydrophilic walls attract fluids, inducing a viscous effect that decelerates fluid flow. Consequently, the two-phase flow rate is found to increase with then-enhanced hydrophobicity. The apex of the water-phase volume fraction is observed under hydrophobic wall conditions, reaching up to 96.40%, with the residual gas-phase constituting 3.60%. The hydrophilic wall retains more residual gas-phase volume fraction than the neutral wall, followed by the hydrophobic wall. Conclusively, the investigations using X-ray CT and LBM demonstrate that the pore structure characteristics and the wettability of the pore walls significantly influence the two-phase seepage process.

The hydration heat generated during the concreting of cast-in-place piles causes thermal disturbance to the surrounding permafrost, leading to its thawing. This further affects the stability of the pile foundation and degrades the construction progress. To explore the influence mechanisms of the concrete hydration heat on the permafrost temperature field around the pile, as well as that of different construction seasons on the pile-side boundary conditions and permafrost temperature field, monitoring results of on-site tests and numerical simulation were used to analyze the distribution law of the pile soil temperature field in space and time, and the pile-side boundary conditions and permafrost temperature field during construction seasons. The results show that the temperature trend of the pile foundation can be divided into three stages: a rapid rise phase (0∼2 d), a rapid decline phase (2∼10 d), and a slow decline and stabilization phase (10∼90 d). As the radial distance from the pile center decreases, there occur a corresponding acceleration in temperature increase and an elevated maximum temperature rise (MTR). The influence range of the molding temperature and the hydration heat is about 1∼2 times the pile diameter and less than 1.5 m in the depth direction. Compared to the atmospheric temperature, there is a lag in the change in the permafrost temperature caused by accumulation of ground temperature, and the significant difference between the two leads to an increased rate of heat exchange at the boundary condition. Conducting drilling operation and cast-in-place pile construction in the cold seasons is conducive to reducing the thermal disturbance to the permafrost around the pile in permafrost areas.

One of the hot topics in the study of rock and soil hydraulics is the size effect of a soil–rock mixture’s (SRM) seepage characteristics. The seepage process of the SRM was simulated from the pore scale through the lattice Boltzmann method (LBM) in this paper to explore the internal influence mechanism of sample size effect on the SRM seepage characteristics. SRM samples were generated using the improved Monte Carlo method (IMCM), and through 342 simulation test conditions the influence of size feature parameters such as resolution (R), segmentation type, model feature size (S), feature length ratio (F), and soil/rock particle size feature ratio (P) was examined. The study demonstrated that as R increases, the permeability of the SRM gradually rises and tends to stabilize when R reaches 60 ppi. At the same S, the dispersion degree of model permeability obtained by the four segmentation types is in the order of center < random < equal < top. With an increase in S, the permeability (k) of the SRM gradually decreases, conforming to the dimensionless mathematical model, $k=a_0·S^{-b_0}$, and tends to stabilize at S = 80 mm. With an increase in F and an increase in S, the permeability of the SRM exhibits a linear “zonal” distribution that declines in order. When F is greater than 12, the dispersion of the permeability value distribution is especially small. With an increase in P, the permeability of the SRM decreases gradually before rising abruptly. P is crucial for the grading and structural makeup of the SRM. Overall, this paper concludes that the conditions of R = 60 ppi, center segmentation type, S = 80 mm, F ≥ 12, and P set by demand can be used to select and generate the size of the SRM optimal representative elementary volume (REV) numerical calculation model. The SRM can serve as a general reference for test and engineering construction as a common geotechnical engineering material.