Surface soil cracking in alpine meadows signifies the transition of degradation from quantitative accumulation to qualitative deterioration. Quantitative research remains insufficient regarding changes in the mechanical properties of degraded meadow soils and the mechanical thresholds for cracking initiation. This study explored the relationships between surface cracking and the physical properties, tensile strength, and matrix suction of root-soil composites in alpine meadow sites with different stages of degradation (undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)) under different water gradients (high water content (HWC), medium water content (MWC), and low water content (LWC)) corresponding to different drying durations at a constant temperature of 40.0 degrees C. The Huangcheng Mongolian Township in Menyuan Hui Autonomous County, Qinghai Province, China was chosen as the study area. The results indicated that as the degradation degree of alpine meadow intensified, both water content of root-soil composite and the fine grain content of soil decreased. In contrast, the root-soil mass ratio and root area ratio initially increased and then decreased with progressive degradation. Under a consistent water content, the tensile strength of root-soil composite followed a pattern of MD>HD>LD>UD. The peak displacement of tensile strength also decreased as the degradation degree of alpine meadow increased. Both the tensile strength and matrix suction of root-soil composite increased as root-soil water content decreased. A root-soil water content of 30.00%-40.00% was found to be the critical threshold for soil cracking in alpine meadows. Within this range, the matrix suction of root-soil composite ranged from 50.00 to 100.00 kPa, resulting in the formation of linear cracks in the surface soil. As the root-soil water content continued to decrease, liner cracks evolved into branch-like and polygonal patterns. The findings of this study provide essential data for improving the mechanical understanding of grassland cracking and its development process.

The Qinghai-Xizang Plateau of China faces challenges like thaw slumping, threatening slope stability and infrastructure. Understanding the mechanical properties of the roots of the dominant herbaceous plant species in the alpine meadow layer of the permafrost regions on the Qinghai-Xizang Plateau is essential for evaluating their role in enhancing soil shear strength and mitigating slope deformation in these fragile environments. In this study, the roots of four dominant herbaceous plant species-Kobresia pygmaea, Kobresia humilis, Carex moorcroftii, and Leontopodium pusillum-that are widely distributed in the permafrost regions of the Qinghai-Xizang Plateau were explored to determine their mechanical properties and effects in enhancing soil shear strength. Through indoor single root tensile and root group tensile tests, we determined the root diameter, tensile force, tensile strength, tensile ratio, and strength frequency distributions. We also evaluated their contributions to inhibiting slope deformation and failure during the formation and development of thermal thaw slumps in the alpine meadow. The results showed that the distribution of the root diameter of the dominant plant species is mostly normal, while the tensile strength tends to be logarithmically normally distributed. The relationship between the root diameter and root tensile strength conforms to a power function. The theoretical tensile strength of the root group was calculated using the Wu-Waldron Model (WWM) and the Fiber Bundle Model (FBM) under the assumption that the cumulative single tensile strength of the root bundle is identical to the tensile strength of the root group in the WWM. The FBM considers three fracture modes: FBM-D (the tensile force on each single root is proportional to its diameter relative to the total sum of all the root diameters), FBM-S (the cross-sectional stress in the root bundle is uniform), and FBM-N (each tensile strength test of individual roots experiences an equal load). It was found that the model-calculated tensile strength of the root group was 162.60% higher than the test value. The model-derived tensile force of the root group from the FBM-D, FBM-S, and FBM-N was 73.10%, 28.91%, and 13.47% higher than the test values, respectively. The additional cohesion of the soil provided by the roots was calculated to be 25.90-45.06 kPa using the modified WWM, 67.05-38.15 kPa using the FBM-S, and 57.24-32.74 kPa using the FBM-N. These results not only provide a theoretical basis for further quantitative evaluation of the mechanical effects of the root systems of herbaceous plant species in reinforcing the surface soil but also have practical significance for the effective prevention and control of thermal thaw slumping disasters in the permafrost regions containing native alpine meadows on the Qinghai-Xizang Plateau using flexible plant protection measures.

To reveal the evolution law of the mechanical failure of the root-soil composite and identify the main control factors and their coupling and mutual feeding relationship, this paper takes the most common naturally growing plants in Yan 'an area as the research object and studies the evolution process of the mechanical deformation and failure of the root-soil composite by applying the methods of in-situ pull-out test, indoor direct shear test of the root-soil composite, numerical simulation, and theoretical analysis. The mechanical characteristics of root-soil interaction were analyzed, and the mechanism of root-soil fixation was explained. The results show that: (1) the root-soil composite's mechanical deformation and failure characteristics have obvious regularity and stages and are affected by plant growth state, root morphology, soil physical and mechanical properties, and other factors. (2) There are obvious evolutionary stages in the deformation and failure process of the root-soil composite, that is, the coordinated deformation stage of the root-soil, the stress redistribution stage, the secondary root break stage, the main root break stage and the complete failure stage, which correspond to the linear deformation section, the acceleration section, the shock rise section, the steep fall and the residual deformation of the F-S curve (Force-displacement curve)obtained by the in-situ pull out test. (3) In the in-situ pull-out test, the final failure body of the root-soil composite was inverted cone shape. The root fracture interface was basically near the boundary of the final inverted cone failure body, in which the stress state of the root system was directly affected by the stress-strain state of the microelement and the characteristics of the root material. (4) The plant roots showed obvious oblique deformation and axial tensile stress with the soil shear dislocation on the fracture surface, which verified the rationality of the oblique root hypothesis based on the transformation of shear stress to tensile stress.

In order to understand the mechanical characteristics of tree roots and their mechanical effects on slopes, the landslide in Wuping high vegetation coverage area of Fujian province was selected as the research site, and the root tensile mechanical properties of typical tree roots in the study area were tested after classification by diameter class. Furthermore, in-situ direct shear tests of root-soil composites under different root cross-sectional area ratios (RAR) and moisture content were conducted at the landslide site, and investigations were made into the distribution characteristics of roots in the profile to explore the mechanical effects of roots on shallow landslides. The results showed as follows: (1) The tensile force of Pinus massoniana and Cunninghamia lanceolata ranged from 12.45-673.09 N in 1-7 diameter class, and the tensile force was positively correlated with the root diameter by power function; The tensile strength ranges from 7.16 MPa to 60.95 MPa, and the tensile strength is negatively correlated with the root diameter as a power function. The average tensile force and tensile strength of Cunninghamia lanceolata root were higher than those of Pinus massoniana. (2) Tree roots significantly improved the shear strength of soil, and the additional cohesion provided by roots to soil was significantly positively correlated with the shear plane RAR. The root structure of Cunninghamia lanceolata is closer to R type, and that of Pinus massoniana is VH type. Under similar RAR, Cunninghamia lanceolata roots has a better reinforcing effect on the soil than Pinus massoniana. (3) With the increase in moisture content, the shear strength of the root-soil composites of Pinus massoniana and Cunninghamia lanceolata significantly decreases, as water infiltration diminishes the additional cohesion provided by the root systems to the soil. (4) Based on the Wu model, considering the influence of moisture content on soil cohesion and additional root cohesion, an estimation model for the shear strength value of root-soil composites considering moisture content was established. Upon verification, the accuracy of this model proved to be higher than that of the Wu model, and the results were reasonable. (5) Although the root system has a reinforcement effect on shallow landslides, its contribution to the stability of shallow landslides under heavy rainfall is limited due to the influence of root distribution depth, density and water infiltration.

To address the significant cutting resistance and fracture susceptibility of rotary blades, an innovative blade design was conceived to minimize resistance and enhance fracture resistance. By analyzing the interaction between the blade, soil, and root systems, an optimized design for the blade structure's breakage resistance was developed. The theory of eccentric circular side cutting edges was applied to redesign the curve of the side cutting edge, and kinematic analysis was conducted to determine the optimal edge angle (26.57 degrees). A flexible body model of corn residues was established, and cutting resistance measurements indicated a 15.1% reduction in cutting resistance. The breakage resistance of the rotary blade was validated using a discrete element method-finite element method (DEM-FEM) coupling approach. The results demonstrated the following: neck stress (-16.85%), specific strength efficiency (+9.72%), specific stiffness efficiency (+9.78%), fatigue life (+39.08%), and ultimate fracture stress (+20.16%), thereby meeting the design objectives. The comparison between field trial results and simulation data showed an error rate (<5%), confirming the simulation test's feasibility. These findings provide theoretical references for reducing cutting resistance and enhancing breakage resistance in rotary blades.

Vegetation reinforcement is considered to be an environmentally friendly measure for slope improvement, which helps to prevent shallow landslides through roots' mechanical and hydrologic reinforcements. This study focuses on the mechanical reinforcement of the seedling roots of Ficus virens, a rich root system that is widely grown in the southern parts of China. Triaxial tests on the root-soil composite were carried out in silty clay and mixed soils to investigate the effects of root morphologies, including its layout and distribution angle of the main and lateral roots, on the stress-strain relationship, build-up of excess pore water pressure, and stress path. The test results indicate that two types of the soil reinforced by a curved main root and horizontal lateral root (CH) are proved to be the optimal scheme for yielding the best root reinforcement effect. Based on this scheme, the shear strength parameters are determined by fitting a straight-line tangent to Mohr circles under different cell pressures. It is found that soil shear strength is significantly improved by root reinforcement, with the root effect principally on soil cohesion, increasing up to 10 kPa, and negligible on internal friction angle. A modified equation is proposed for characterizing the critical state line of the rooted soil, and an additional cohesion term is proven to be valid for representing the root reinforcement. Different types of failure mechanism are observed in silty clay and mixed soils with/without roots. The findings provide novel insights into the shearing behavior of rooted soil and theoretical evidence for the improvement of slopes reinforced by Ficus virens.

Serious riverbank erosion, caused by scouring and soil siltation on the bank slope in the lower reaches of the Tarim River, Northwest China urgently requires a solution. Plant roots play an important role in enhancing soil shear strength on the slopes to maintain slope soils, but the extent of enhancement of soil shear strength by different root distribution patterns is unclear. The study used a combination of indoor experiments and numerical simulation to investigate the effects of varying plant root morphologies on the shear strength of the sandy soil in the Tarim River. The results showed that: (1) by counting the root morphology of dominant vegetation on the bank slope, we summarized the root morphology of dominant vegetation along the coast as vertical, horizontal, and claw type; (2) the shear strength of root-soil composites (RSCs) was significantly higher than that of remolded soil, and the presence of root system made the strain-softening of soil body significantly weakened so that RSCs had better mechanical properties; and (3) compared with the lateral roots, the average particle contact degree of vertical root system was higher, and the transition zone of shear strength was more prominent. Hence, vegetation with vertical root system had the best effect on soil protection and slope fixation. The results of this study have important guiding significance for prevention and control of soil erosion in the Tarim River basin, the restoration of riparian ecosystems, and the planning of water conservancy projects.

The slope erosion in the distribution area of completely weathered granite is often relatively severe, causing serious ecological damage and property loss. Ecological restoration is the most effective means of soil erosion control. Taking completely weathered granite backfill soil as the research object, two types of slope protection plants, Vetiver grass and Pennisetum hydridum, were selected. We analyzed these two herbaceous plants' soil reinforcement and slope protection effects through artificial planting experiments, indoor simulated rainfall experiments, and direct shear tests. The test results showed that the runoff and sediment production rates of the two herbaceous plant slopes were significantly lower than those of the bare slope, with the order of bare slope > Vetiver grass slope > Pennisetum hydridum slope. Compared with the bare slope, the cumulative sediment production of the Vetiver grass slope at 60 min decreased by 56.73-60.09%, and the Pennisetum hydridum slope decreased by 75.97-78.45%. The indoor direct shear test results showed that soil cohesion decreases with increasing water content. As the root content of Vetiver grass roots increases, soil cohesion first increases and then decreases, reaching a maximum value when the root content is 1.44%. As the root content of Pennisetum hydridum increases, soil cohesion increases. The internal friction angle increases slightly with increasing water content, while the root content does not significantly affect the internal friction angle. Therefore, the shear strength of soil decreases when the water content increases. The shear strength of the Vetiver grass root-soil composite reaches a peak at a root content of 1.44%, while the shear strength of the giant king grass root-soil composite increases as the root content increases. At the same root content, the shear strength of the Vetiver grass root-soil composite is slightly higher than that of giant king grass. The reinforcement effect of roots on shallow soil is better than on deep soil. Both herbaceous plants have an excellent soil-fixing and slope-protecting impact on the fully weathered granite backfill slope. Pennisetum hydridum's soil and water conservation effect is significantly better than that of the Vetiver grass. In contrast, Vetiver grass roots slightly outperform Pennisetum hydridum in enhancing the shear strength of the soil. The research results can provide a theoretical basis for the vegetation slope protection treatment of fully weathered granite backfill slopes.

A large alpine meadow in a seasonal permafrost zone exists in the west of Sichuan, which belongs to a part of the Qinghai-Tibet Plateau, China. Due to the extreme climates and repeated freeze-thaw cycling, resulting in a diminishment in soil shear strength, disasters occur frequently. Plant roots increase the complexity of the soil freeze-thaw strength problem. This study applied the freeze-thaw cycle and direct shear tests to investigate the change in the shear strength of root-soil composite under freeze-thaw cycles. This study examined how freeze-thaw cycles and initial moisture content affect the shear strength of two sorts of soil: uncovered soil and root-soil composite. By analyzing the test information, the analysts created numerical conditions to foresee the shear quality of both sorts of soil under shifting freeze-thaw times and starting moisture levels. The results showed that: (1) Compared to the bare soil, the root-soil composite was less affected by freeze-thaw cycles in the early stage, and the shear strength of both sorts of soil was stabilized after 3-5 freeze-thaw cycles. (2) The cohesion of bare soil decreased more than that of root-soil composite with increasing moisture content. However, freeze-thaw cycles primarily influence soil cohesion more than the internal friction angle. The cohesion modification leads to changes in shear quality for both uncovered soil and root-soil composite. (3) The fitting equations obtained via experiments were used to simulate direct shear tests. The numerical results are compared with the experimental data. The difference in the soil cohesion and root-soil composite cohesion between the experiment data and the simulated result is 8.2% and 17.2%, respectively, which indicates the feasibility of the fitting equations applied to the numerical simulation of the soil and root-soil composite under the freeze-thaw process. The findings give potential applications on engineering and disaster prevention in alpine regions.