The mechanism of the plant roots’ soil-reinforcement based on generalized equivalent confining pressure

Abstract

Background To quantitatively evaluate the contribution of plant roots to soil shear strength, the generalized equivalent confining pressure (GECP), which is the difference in confining pressure between the reinforced and un-reinforced soil specimens at the same shear strength, was proposed and considered in terms of the function of plant roots in soil reinforcement. Methods In this paper, silt loam soil was selected as the test soil, and the roots of Indigofera amblyantha were chosen as the reinforcing material. Different drainage conditions (consolidation drained (CD), consolidation undrained (CU), and unconsolidated undrained (UU)) were used to analyse the influences of different root distribution patterns (horizontal root (HR), vertical root (VR), and complex root (CR)) and root contents (0.25%, 0.50%, and 0.75%) on the shear strength of soil-root composites. Results The cohesion (c) values of the soil-root composites varied under different drainage conditions and root contents, while the internal friction angle (φ ) values remain basically stable under different drainage conditions. Under the same root content and drainage conditions, the shear strength indexes ranked in order of lower to higher were HR, VR and CR. The GECP of the soil-root composites with a 0.75% root content was 1.5–2.0 times that with a 0.50% root content and more than 5 times that with a 0.25% root content under the CD and CU conditions. The GECP in reinforced soil followed the sequence of CD > CU > UU. The GECP of the plant roots increased as confining pressure increased under CD and CU conditions while showed a complex change to the confining pressure under the UU condition. Conclusion It was concluded that the evaluation of plant root reinforcing soil based on GECP can be used to measure effectively the influences of roots on soil under different drainage conditions and root distribution patterns.

The Shear Strength of Root–Soil Composites in Different Growth Periods and Their Effects on Slope Stability

“…The root-soil composite improved the τ of the soil through a reinforcement mechanism similar to that of conventional reinforcement materials in reinforced soil. Specifically, the roots interacted with the soil to enhance its strength, resulting in an increase in the τ of the composite compared to bare soil [15]. Under different normal stresses, the τ of the bare soil was less than that of the root-soil composites, which shows that plant roots have a reinforcing effect on soil.…”

“…Xiong et al [13] performed in situ shear tests to evaluate the effect of vegetation roots on the shear strength of soils. It is generally accepted that slope stability can be improved by the reinforcement effect of plant roots [14,15]. Mohsen et al [16] confirmed that vegetation could effectively reduce shallow landslides but had limited influence on deep landslides.…”