Experiments and discussions on the shear strength of root-soil complexes after phytoremediation of ionic rare earth tailings soils.

Herbaceous vegetation roots play a crucial role in improving soil shear strength during ecological restoration. This study investigates the shear strength characteristics of root-soil complexes in ionic rare earth tailings under the influence of various herbaceous plants and evaluates the applicability of the shear strength increment coefficient within the Wu-Waldron Model (WWM). By determining the physical parameters of soil samples and root system characteristics, this study compared actual shear strength increments obtained via direct shear and root tension tests against theoretical increments. The results indicate that the experimentally obtained shear strength increment of the root-soil complex is significantly higher than the value calculated using the standard WWM model. Root reinforcement is primarily concentrated in the 0-10 cm soil layer, with shear strength decreasing as depth increases. The order of shear strength increments for different vegetation types within the same soil layer is: Vetiveria zizanioides > Paspalum notatum Flüggé > Cynodon dactylon (L.) > Setaria viridis. The stress increment correction coefficient for the WWM model applied to these tailings ranged from 1.66 to 8.04. The WWM coefficients are relatively high. Its value range may be influenced by factors such as the physical properties of rare earth tailings, the calculation of the tensile strength spectrum, variations in matric suction, and assumptions regarding root failure. The coefficients derived in this study clarify the influence of different roots on shear strength and provide a valuable reference for the selection and configuration of vegetation in the reclamation of ionic rare earth tailings.