Biopolymer stabilization of soils has emerged as a viable solution for enhancing the engineering properties of soils in recent years. Xanthan gum and guar gum are two commonly used biopolymers. When combined, these materials have the ability to create stronger gels or gel strengths comparable to those achieved by using xanthan or guar gum individually, but at lower total concentrations. However, the extent of this synergistic viscosity-enhancing effect on soil improvement remains unclear. This study analyzes the effects of xanthan gum and guar gum on the physical and mechanical properties of clay under both individual and combined conditions using Atterberg limits tests, compaction tests, and triaxial consolidation undrained tests. At a 2% biopolymer content, the liquid limit of clay treated with a combination of XG and GG compounds increases by up to 8.0%, while the plastic limit increases by up to 3.9% compared to clay treated with a single colloid. With an increase in the mixing ratio, the optimal water content initially rises and then declines, peaking at 27.3%. The maximum dry density follows a pattern of initially decreasing and then increasing, with the lowest value recorded at 1.616 g·cm⁻³. Moreover, the shear strength of specimens treated with the XG and GG combination generally surpasses that of specimens treated with XG or GG alone. Furthermore, the combined treatment results in increased plasticity, highlighting its potential to enhance safety and stability in engineering applications.

Vegetation slope protection plays an important role in improving the slope stability and protecting the environment. In this study, the mechanical properties of root–soil composites in different growth periods and their effects on slope stability were investigated. First, the shear strength of undisturbed root–soil composites associated with Cynodon dactylon (C.d), Magnolia multiflora (M.m) and grass and shrub mixture (G.s) were measured by large direct shear tests. Then, the effects of plant reinforcement in different growth periods on slope stability were analyzed using ABAQUS. The results show that the shear strength of the root–soil composites were significantly higher than that of the unreinforced soil. The root–soil composites met the Mohr–Coulomb criterion. The shear strength of the three root–soil composites increased first and then decreased during the vegetation growth period. The calculation results show that the factor of safety (FS) of the bare slope was 1.482. The FS values of the C.d, M.m, and G.s slopes were 1.601, 1.658 and 1.715, which increased by 8%, 11.9% and 15.7% compared to the bare soil slopes. Therefore, vegetation could significantly improve slope stability, especially the grass–shrub mixture model. This could provide a rational basis for designing and constructing plant slope protection.

Accurate determination of soil-water characteristic curve (SWCC) is of immense importance for understanding the mechanical behavior of unsaturated soils. Due to the difficulty and long duration of experimental procedures, it is of great significance to estimate the SWCC by indirect methods. To address this issue, in this article an effective fractal method is proposed for predicting the SWCC based on mercury intrusion porosimeter (MIP) data. Only two characteristic parameters, namely the fractal dimension and air-entry value, are needed in the presented approach. Detailed procedures for determining the parameters are clearly elaborated. Due to the influence of sample size difference on the equivalent connected pore size, a sample scale effect coefficient is proposed to predict air-entry values. The concept of “critical pore size” is introduced to obtain the optimal fractal dimension, which can accurately reflect the fractal behaviour of SWCC samples. By comparisons between predicted and experimental SWCCs, the validation of the proposed method is verified. The comparisons reveal the good agreement between the proposed approach and laboratory experiments.

This study investigated naturally-restored plant communities on wind farm slopes and analyzed the effects of various habitat factors on the plant diversity. The findings provide a technical support for the ecological restoration of mountainous slopes.Twenty-one slopes on five wind farms were selected and the characteristics of the habitat, including slope position, slope aspect, slope gradient, altitude, years since restoration, and plant communities, were recorded. The species richness of the plant communities and the vegetation diversity indexes of these wind farms were measured and calculated, including the Shannon-Wiener diversity index (H′), Pielou’s species evenness index (J), and Margalef’s richness index (R). The key factors influencing plant diversity were identified using a stepwise regression analysis. A total of 36 families, 54 genera, and 57 species of plants were identified in this study with the Gramineae, Compositae, Rosaceae, Liliaceae, and Juglandaceae families the mostly predominant. Cynodon dactylon, Rubus lambertianus Ser., and Lindera glauca were the dominant species of herbs, shrubs, and trees, respectively. The highest number of species were found on lower slopes, slopes with semi-sunny aspects, slopes with gradients 30–50°, elevation below 500 m, and on slopes with at least five years since restoration. The plant diversity H′ and R tended to be higher on lower slopes than on upper slopes, and higher on slopes with semi-shady aspects than on slopes with semi-sunny aspects (P < 0.05). Vegetation diversity increased with the years since restoration. Slope position and slope aspect were identified as the primary influencing factors, and the H′ and R indexes were major indicators of changes in plant diversity on mountainous slopes.

Under the combined action of soil evaporation and vegetation transpiration, the law of soil water dissipation at different depths of vegetated slopes is unknown and the related influencing factors are unclear. In this paper, six large-scale slope models were constructed for long-term dynamic monitoring of soil water. The effects of slope ratio and vegetation on the dynamic changes in soil water at different depths were analyzed. Pearson correlation analysis was used to analyze the relationship between slope conditions, meteorological factors, and soil water dissipation. The results show that under the condition of natural evaporation, slope ratio has little effect on the dynamic change in soil water in bare slopes. However, the greater the slope ratio of vegetated slopes, the faster the soil water decreases in the 40 cm depth range. Additionally, soil water dissipation follows a logarithmic functional relationship with evaporation time in both bare and vegetated slopes. The correlation between slope conditions and soil water dissipation is stronger than that of meteorological factors. The research results can provide some theoretical support for exploring the hydrological effects of vegetated slopes.

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.