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.

This paper quantitatively analyses the macroscopic characteristics of soil hysteretic curves under dynamic loading and examines the elastic properties, viscosity, meso-damage degree and energy consumption of soil from a macroscopic perspective. Given the lack of research on the hysteresis characteristics of bioenzyme-modified silty soil, a series of dynamic triaxial tests were conducted under varying bioenzyme dosages, confining pressures, loading frequencies, and other conditions. The analysis focused on several parameters: the slope of the major axis of the hysteretic curve k, the ratio of the major to minor axes alpha, the distance between the central points of adjacent hysteretic curves d, and the area enclosed by the hysteretic curve S. These were used for quantitative analysis of the morphological characteristics, influencing factors, and changing patterns of the hysteresis curve in bioenzyme-modified silty soil. The results showed that the hysteresis curve of the bioenzyme-improved silty soil resembled an inclined ellipse. Under the influence of different bioenzymes dosages, confining pressures, and loading frequencies, k and alpha decreased as dynamic stress increased, while d and S increased exponentially with rising dynamic stress. When the bioenzyme dosage was 0.01%, the k value was largest, and alpha, d and S were smallest. With increasing confining pressure, k increased, while alpha, d, and S decreased. As the loading frequency increased, k, alpha, and d decreased, while S gradually increased. At a bioenzyme dosage of 0.01%, the bioenzyme had the greatest effect on improving the silty soil.

Infrastructure construction on coastal areas such as ports, bridges and airports require ground improvements when marine soils contain soft ground which includes fine grains in general. Fine-grained soils consist of clastic or non-clastic grains. Based on the mineralogy of soils, compressibility of soils shows different behavior. Fine-grained clay mineral soils show plastic and time-dependent deformation due to consolidation during constructions while silty soils without clay minerals show low compressibility. However, biogenic soils such as diatomaceous earth are more compressible than other silty fine-grained soils. Although fine-grained soils with clastic minerals and biogenic minerals are classified as silt, the behavior of clastic soils are less compressible compared to biogenic soils which have inner pores. We conducted one-dimensional consolidation experiments to investigate compressibility of diatomaceous earth and non-plastic mineral fines such as silica silt. The coefficient of consolidation, and volumetric compressibility are estimated, and show that the trends of diatomaceous earth properties are different from other silty soil properties based on the consolidation tests. We found that particle breakage plays a crucial role in compressibility of diatomaceous soils. While the compressibility of diatomaceous soils is similar to clastic soils at low stress, the differences in compressional behavior between two soils are distinct at high stress. The diatomaceous earth shows time-dependent compressibility due to creep or secondary compression by particle breakage process. Thus, settlement analysis should include the impact of morphology and mineralogy of fine-grained soils.

To investigate the unloading mechanical properties of deeply buried silty soil in dam foundation cover layers, a series of consolidated drained triaxial compression tests along multi-stage loading-unloading path were performed on both undisturbed samples (including horizontally and vertically oriented samples) and remolded samples. The test results demonstrate that: (1) the vertically oriented soil samples exhibit strain softening under low confining pressures (100, 200, and 400 kPa), transitioning to strain hardening at high confining pressures (800 and 1600 kPa). In contrast, the horizontally oriented specimens consistently exhibit strain softening across all confining pressures, whereas the remolded samples display strain hardening under all confining conditions; (2) the strength of vertically oriented soil specimens is significantly higher than that of horizontally oriented specimens, ranging from 1.18 to 1.43 times greater. Remolded samples, however, remolded samples are slightly weaker than horizontally oriented specimens under low confining pressures (100, 200, and 400 kPa), while at high confining pressures (800 and 1600 kPa), their strength approaches that of horizontally oriented specimens; (3) the deeply buried silty soil also exhibits pronounced unloading-induced volume contraction characteristics, which increase with the initial axial strain at the beginning of unloading and diminish as confining pressure increases; (4) the unloading modulus is obviously higher than the initial loading modulus, with the ratio of the unloading modulus to the initial loading modulus ranging from 1.4 to 3.6. This ratio increases with increasing confining pressure but decreases with increasing axial strain at the onset of unloading.

This study investigates the strain development of saturated silty soil of Yellow River under varying initial consolidation inclination angles zeta by principle stress rotation tests. The results revealed that distinct patterns in axial, circumferential and torsional shear strains show the influence of zeta on the mechanical response of silty soil. Notably, the axial strain exhibits compressive behaviour at zeta=90 degrees during the first cycle, while the circumferential strain displays tensile behaviour. Anisotropy initiates at zeta=90 degrees and around 60 degrees for other zeta angles. Different values of zeta exhibit stabilization trends in strain fluctuations, with zeta=90 degrees and zeta=75 degrees showing intriguing similarities. The case of zeta=45 degrees stands out, with the highest fluctuation and strain amplitude. Torsional shear strain similarities are observed among most zeta angles except for zeta=90 degrees and zeta=60 degrees. Volumetric strain emphasizes the significant impact of consolidation angle inclination on anisotropic characteristics. With the increase of the initial solidification angle, the hysteresis curve shifts to the left, indicating cyclic creep characteristics, with negligible shear strain for the case of zeta=60 degrees. As the cycle period increases, the hysteresis loop contracts, indicating the continuous strengthening and eventual stabilization of shear stiffness. This comprehensive exploration provides valuable insights into the complex behaviour of saturated silty soil under rotational stress conditions, highlighting the role of initial consolidation inclination angles in shaping its mechanical response.

The deformation characteristics of silty soils under vibrational loads can easily change due to the wetting process, leading to the failure of roadbed structures. Commonly used methods for improving silty soils in engineering often yield unsatisfactory economic and ecological outcomes. As an environment-friendly soil improvement material, Xanthan gum has broad application prospects and is therefore considered a solidifying agent for enhancing silty soil properties in the Yellow River Basin. In this study, a series of tests is conducted using a scanning electron microscope and a dynamic triaxial testing apparatus to investigate the microstructure and dynamic deformation characteristics of unsaturated silty soil with varying xanthan gum contents during the wetting process. The results show that xanthan gum effectively fills voids between soil particles and adheres to their surfaces, forming fibrous and network structures. This modification enhances the inherent properties of the silty soil and significantly improves its stability under dynamic loading. Specifically, with increasing xanthan gum content, the dynamic shear modulus increases while the damping ratio decreases. During the wetting process, as suction decreases, the dynamic shear modulus decreases while the damping ratio increases. Xanthan gum reduces the sensitivity of the dynamic deformation characteristics of the treated silty soil to changes in suction levels. Finally, based on the modified Hardin-Drnevich hyperbolic model, a predictive model for the dynamic shear modulus and damping ratio of treated silty soil is proposed, considering the xanthan gum content. These research findings provide a theoretical basis for the construction and maintenance of water conservancy, slope stabilization, and roadbed projects in the Yellow River Basin. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published 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/).

This study investigated the impact of major principal stress direction angle (alpha) and intermediate principal stress coefficient (b) on the stress-strain behavior of silt sand soil through directional shear tests under isotropically consolidated drained conditions. Analyzing octahedral stress-strain relationships, shear stress-strain behaviors, radial and circumferential strains, shear stress ratios, and non-coaxial characteristics, findings show that both b and alpha significantly influence strain components with radial strain remaining stable and circumferential strain being dependent on both factors. Anisotropy in circumferential strain is notably affected by alpha and b, while radial strain transitions from tensile to compressive states by increasing b values. Initial loading stages exhibit similar characteristics, but it increased anisotropic with shear stress particularly at b = 0.5 and b = 1. Shear strength is notably influenced by b and alpha, with peak shear stress exhibiting direct proportionality to alpha angles between 0 and 45 degrees, and an inverted relationship beyond 45 degrees. Material strength is significantly impacted by stress orientation with pronounced non-coaxial behavior observed at angles other than 0 degrees, 45 degrees, and 90 degrees. These findings emphasize the intricate relationship between stress coefficients and material behavior providing significant insights into silt sand soil responses under varying stress conditions.

In cold regions, the extensive distribution of silt exhibits limited applicability in engineering under freeze-thaw cycles. To address this issue, this study employed rice husk carbon and calcium lignosulfonate to stabilize silt from cold areas. The mechanical properties of the stabilized silt under freeze-thaw conditions were evaluated through unconfined compressive strength tests and triaxial shear tests. Additionally, scanning electron microscopy was utilized to analyze the mechanisms behind the stabilization. Ultimately, a damage model for rice husk carbon-calcium lignosulfonate stabilized silt was constructed based on the Weibull distribution function and Lemaitre's principle of equivalent strain. The findings indicate that as the content of rice husk carbon and calcium lignosulfonate increases, the rate of improvement in the compressive strength of the stabilized silt progressively accelerates. With an increase in the number of freeze-thaw cycles, the deviatoric stress of the stabilized soil gradually diminishes; the decline in peak deviatoric stress becomes more gradual, while the reduction in cohesion intensifies. The decrease in the angle of internal friction is relatively minor. Microscopic examinations reveal that as the number of freeze-thaw cycles increases, the soil pores tend to enlarge and multiply. The established damage model for stabilized silt under freeze-thaw cycles and applied loads demonstrates a similar pattern between the experimental and theoretical curves under four different confining pressures, reflecting an initial rapid increase followed by a steady trend. Thus, it is evident that the damage model for stabilized silt under freeze-thaw conditions outperforms traditional constitutive models, offering a more accurate depiction of the experimental variations observed.

Silty soil is a transitional soil between clay and sand and is widely distributed around the world. With the rapid urban development and associated infrastructure need, silty soil has become more widely used as the bearing soil for foundations and roads. The liquefaction of silty soil under the earthquake can cause serious damage to buildings and infrastructure resting on such soil. Correctly analyzing the dynamic characteristics of silty soil in earthquake areas plays a major role in the success or failure of infrastructure construction. Therefore, it is particularly important to study the various factors affecting the dynamic characteristics of silty soil and to analyze the changing trend and associated mechanism on the dynamic characteristics of silty soil. In this paper, a set of cycle triaxial tests were carried out using the orthogonal design method to study the effects of four factors, namely initial void ratio, load frequency, clay content and silt content, on the dynamic characteristics of saturated silty soil at different levels. The orthogonal design method is used to study the order of influence of four factors on the dynamic strength and excess pore water pressure of silty soil, and the significance level of each factor was also assessed.

Silty soil was widely used as filling soil materials for the replacement of expansive soil in cold regions. This paper presents a straightforward approach for the effects of wetting-drying-freezingthawing cycles on mechanical behaviors of silty soil and expansive soil by laboratory tests. The results showed that the silty soil and expansive soil after 7th wetting-drying-freezing-thawing cycles presented the decreases of elastic modulus, failure strength, cohesion and angel of internal friction by 8.9 %-12.0 %, 7.7 %-9.0 %, 7.9 %, 4.5 % and 17.6 %-37.0 %, 20.5 %-29.4 %, 43.2 %, 13.0 %, respectively, indicating that wetting-drying-freezing-thawing cycles had little impact on mechanical property of silty soil and a great influence on that of expansive soil. Among them, the mechanical property attenuation ratio in the first three wetting-drying-freezingthawing cycles accounted for over 90 % of the total. In the meantime, the micro-structure damage, surface crack characteristics and grain size distribution variations of expansive soil were all more significantly than these of silty soil exposed to wetting-drying-freezing-thawing cycles, which brought insight into the causes of the differences in mechanical properties for silty soil and expansive soil. It is found that the silty soil properties were more stable than expansive soil properties, and the silty soil is very effective for replacing the expansive soil below canal structures in cold regions.