To address the issues of significant deformation and susceptibility to liquefaction of silt under traffic loads, while also promoting the reuse of waste lignin, lignin was used to reinforce silt. A series of laboratory experiments were conducted to investigate the effects of different lignin contents and curing periods on the compressive strength of the soil. Additionally, the study analyzed the cumulative plastic deformation and excess pore-water pressure under various conditions. Using scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy, the microstructural characteristics of silt before and after lignin modification were qualitatively and quantitatively described. The experimental results indicate that lignin can significantly enhance the compressive strength of soil, and the optimal effect was observed at an 8% lignin content. At a curing age of 28 days, the strength of the treated soil was 2.65 times that of the untreated soil. The treated soil exhibited greater shear strength than the untreated soil. The addition of lignin significantly reduced the cumulative plastic deformation and excess pore-water pressure of the soil, mitigating various risks in the subgrade, such as insufficient bearing capacity and liquefaction. Lignin binds soil particles and undergoes a cementation reaction without the formation of new minerals. The cementitious material fills the voids in the soil, gradually transforming large pores into medium and small pores. Combined with the particle pores and cracks analysis system, quantitative analysis indicates that as the lignin content increased, the soil porosity gradually decreased, reaching a maximum soil compactness at an 8% admixture. The research findings can provide theoretical references for the engineering application of lignin.

The structure, strength, and deformation characteristics of artificial structural loess can be manually controlled, which has significant advantages in scientific research on loess. By preparing and testing artificial structured loess, the natural properties of structured loess can be better investigated and studied. In this paper, the influence of varying moisture contents and additive dosages on artificial structured loess strength characteristics through triaxial shear tests were analyzed. The moisture content and additive dosage reflecting the structural properties of natural loess were obtained. Based on the microscopic test results, the mineral components, micromorphology, and pore characteristics of artificial structural loess were analyzed, and the mechanism of the structural evolution of loess under mechanical action was revealed. The results show that the minimum differences in the peak strength between W-16-Y2.0C2.0 and undisturbed soil under confining pressures of 50, 100, and 200 kPa are 6.481 kPa, 7.676 kPa, and 4.912 kPa, respectively. The minimum differences in the cohesion and inner friction angle between W-16-Y2.0C2.0 and undisturbed soil are 2 kPa and 0.2 degrees, respectively, indicating that W-16-Y2.0C2.0 is the optimal structural soil with a structural strength closest to that of undisturbed soil. Compared with the undisturbed loess, the content of calcite in the artificial structure loess increases from 9.8% to 11.2%, the proportion of plagioclase decreases from 20.5% to 17.4%, amphibole is consumed completely, and 2.1% of halite is generated. Furthermore, the pores of structured soil exhibit a three-peak distribution and are divided into four types, including micropores (= 13.5 mu m). When the pressure increases from 50 kPa to 200 kPa, micropores increase by 4.67%, small pores increase by 4.97%, medium pores decrease by 2.4%, and large pores decrease by 7.24%. The trend of pore structure changes in W-16-Y2.0C2.0 is similar to that of undisturbed loess. The research results provide a reference for preparing and applying artificial structural loess.

Granite residual soil exhibits a tendency to collapse and disintegrate upon exposure to water, displaying highly unstable mechanical properties. This makes it susceptible to landslides, mudslides, and other geological hazards. In this study, three common biopolymers, i.e., xanthan gum (XG), locust bean gum (LBG), and guar gum (GG), are employed to improve the strength and stability of granite residual soil. A series of experiments were conducted on biopolymer-modified granite residual soil, varying the types of biopolymers, their concentrations, and curing times, to examine their effects on the soil's strength properties and failure characteristics. The microscopic structure and interaction mechanisms between the soil and biopolymers were analyzed using scanning electron microscopy and X-ray diffraction. The results indicate that guar gum-treated granite residual soil exhibited the highest unconfined compressive strength and shear strength. After adding 2.0% guar gum, the unconfined compressive strength and shear strength of the modified soil are 1.6 times and 1.58 times that of the untreated granite residual soil, respectively. Optimal strength improvements were observed when the biopolymer concentration ranged from 1.5% to 2%, with a curing time of 14 days. After treatment with xanthan gum, locust bean gum, and guar gum, the cohesion of the soil is 1.36 times, 1.34 times, and 1.55 times that of the untreated soil, respectively. The biopolymers enhanced soil bonding through cross-linking, thereby improving the soil's mechanical properties. The gel-like substances formed by the reaction of biopolymers with water adhered to encapsulated soil particles, significantly altering the soil's deformation behavior, toughness, and failure modes. Furthermore, interactions between soil minerals and functional groups of the biopolymers contributed to further enhancement of the soil's mechanical properties. This study demonstrates the feasibility of using biopolymers to improve granite residual soil, offering theoretical insights into the underlying microscopic mechanisms that govern this improvement.

An updated DEM simulation scheme for clay is implemented by incorporating convex polygon shaped platelets and robust algorithm for physico-chemical-mechanical interaction between clay platelets. Clays with two typical microscopic structures, i.e., card-house structure and book-house structure, are simulated in oedometer test and triaxial compression test. Virtual Mercury Intrusion Porosimetry (MIP) and pore segmentation algorithms are utilized to extract pore statistics from the numerical samples. The simulation results and experimental results from the literature are thoroughly compared at both macroscopic and microscopic scales. It is found that the implemented DEM simulation scheme can satisfactorily reproduce the experimentally observed macroscopic behavior of clay. Especially, in triaxial compression tests, the critical state behavior, stress-dilatancy relationship and over-consolidation effects are generally consistent with existing experimental results. General consistency in pore size, orientation and shape distributions in DEM simulations and experiments can be observed. Clay platelets tend to rotate to align their normal directions along the major principal stress direction, while pores tend to align their long-axis directions in the confinement direction, leading to dynamically evolving fabric anisotropy. In the book-house structure clay, clay domains experience multiple deformation modes, including uniaxial compaction, shear distortion, spatial spin, and their combinations.

To further enhance our understanding of the microstructure of SRM and its intrinsic relationship with macroscopic properties, this paper conducted indoor freeze-thaw cycles, EIS and uniaxial compression tests. The results indicated that the number of freeze-thaw cycles has a significant exponential relationship with RCPP, RCPP1 and CDSRP. As the number of cycles increased, RCPP and RCPP1 exhibited a decreasing trend, whereas CDSRP showed an increasing pattern. The freeze-thaw cycles led to the expansion and connection of different pores, resulting in the widening or multiplication of channels in CPP, leading to a decrease in both RCPP and RCPP1. However, in DSRPP, the liquid-filled pores underwent radial expansion during freeze-thaw cycles, connecting with gas-filled pores around them. This transition led the conductive path to transform into CPP, reducing the accumulated thickness of non-continuous points. Consequently, CDSRP exhibited an increasing trend. Furthermore, the increase in porosity weakened the deformation resistance, increasing the compaction stage of pores and the peak strain, while reducing its peak strength and secant modulus. The peak strength, strain and secant modulus also exhibited significant exponential relationships with different cycles. There was a good exponential correlation between Delta RCPP of CPP and the uniaxial strength, and the freeze-thaw deterioration model constructed with it as an influence factor could better assess its peak mechanical strength after freezing and thawing.

Loess has the characteristics of loose, large pore ratio, and strong water sensitivity. Once it encounters water, its structure is damaged easily and its strength is degraded, causing a degree of subgrade settlement. The water sensitivity of loess can be evaluated by permeability and disintegration tests. This study analyzes the effects of guar gum content, basalt fiber content, and basalt fiber length on the permeability and disintegration characteristics of solidified loess. The microstructure of loess was studied through scanning electron microscopy (SEM) testing, revealing the synergistic solidification mechanism of guar gum and basalt fibers. A permeability model was established through regression analysis with guar gum content, confining pressure, basalt fiber content, and length. The research results indicate that the addition of guar gum reduces the permeability of solidified loess, the addition of fiber improves the overall strength, and the addition of guar gum and basalt fiber improves the disintegration resistance. When the guar gum content is 1.00%, the permeability coefficient and disintegration rate of solidified soil are reduced by 50.50% and 94.10%, respectively. When the guar gum content is 1.00%, the basalt fiber length is 12 mm, and the fiber content is 1.00%, the permeability of the solidified soil decreases by 31.9%, and the disintegration rate is 4.80%. The permeability model has a good fitting effect and is suitable for predicting the permeability of loess reinforced with guar gum and basalt fiber composite. This research is of vital theoretical worth and great scientific significance for guidelines on practicing loess solidification engineering.

The fabric structure and dynamic behaviour of granular materials have been extensively studied in geotechnical engineering due to their considerable impact on permeability and mechanical properties. However, particle segregation, causing significant structural changes, remains inadequately understood, especially concerning its dynamic evolution in both global and local segregation processes. This study aims to investigate the motion of particles and evolution of internal microstructure in binary mixtures under vibrational conditions. The emphasis lies in comprehending both global and local time segregation processes, along with elucidating the potential underlying mechanisms. Through DEM simulations, it is observed that large particles tend to rise to the surface of the container while small particles aggregate at the bottom, resulting in the well-known Brazil Nut Effect. As the vibration intensity increases, the degree of segregation becomes more pronounced. Vertical segregation precedes radial segregation and eventually leads to stable separation of the binary mixture. To comprehensively analyse the segregation behaviour, we introduce a segregation index and reveal a correlation between vertical and radial segregation. Additionally, the ascending process exhibits characteristics similar to compressed solid blocks, while the descending process resembles fluid-like behaviour, suggesting a phase transition phenomenon during particle segregation. The study further highlights the role of pore filling and convective rolling as driving mechanisms for particle segregation. These findings emphasize the potential impact of external disturbances on the microstructure of granular mixtures, with implications for scenarios such as earthquakes, debris flows, and traffic loads.