Background The role of vegetation (grasses, shrubs, and trees) in slope stability and erosion has been well recognized and incorporated. The plant material especially the root system plays an important role in stabilizing slope and enhancing soil strength. The root system is very significant especially in karst areas with little soil and lots of stones. Root tensile properties are the basis for enhancing slope stability, and the process of root tensile deformation reflects the process of root system resisting external force. Therefore, it is useful to study the tensile properties of plants in karst area.

Methods In order to explore the tensile deformation characteristics of a single root of Cassia bicapsularis, 5-year-old shrubs were selected as the research objects. Under the condition of different root diameter levels, different root length levels (50 and 100 mm) and different tensile rate levels (10 and 500 mm/min), the tensile force of a single root and tensile strength of a single root were assessed via tensile test for a single root. Furthermore, the stress-strain curves during the tensile process were recorded by experimental machine.

Results 1) The tensile force of a single root of C. bicapsularis increased with the increase of root diameter according to a power function, while the tensile strength of a single root decreased with the increase of root diameter according to a logarithmic function. 2) The tensile deformation modes of C. bicapsularis were various and the process was complex. According to the shape of stress-strain curve, the curves were divided into three types: serrated type, single peak type and multi-peak type, and different types of curves corresponded to different deformation processes of a single root. The roots deformed in different ways to resist external forces, including elastic deformation, elastic-plastic deformation and root skin tearing. Different single roots exerted maximum tensile force through different deformation modes. 3) Chi-square test was carried out for stress-strain curves with different root lengths and different tensile rates. The results showed that there was no significant correlation between root length and tensile deformation characteristics of a single root, but the tensile rate had significant effect on the tensile deformation characteristics. When the tensile rate was 500 mm/min, all of the stress-strain curves were single peak type, because the fiber bundles were broken before they exerted tensile properties to external forces at a faster rate.

Conculsions In this study, the root system of C. bicapsularis plays a better role in stabilizing the slope through complex deformation during tension. In the process of stretching, the complex deformation mode is used to resist deformation by the single root of C. bicapsularis. When landslide occurs, the complex deformation mode is more conducive to maintaining the stability of slope. But the root system is more likely to be destroyed at a faster stretching rate. The mechanical characteristics of single root deformation of plant roots were discussed in order to provide a theoretical basis for the mechanism of soil consolidation and slope protection of roots in karst areas.