Shear resistance characteristics and influencing factors of root–soil composite on an alpine metal mine dump slope with different recovery periods

Artificial vegetation restoration is the main measure for vegetation restoration and soil and water conservation in alpine mine dumps on the Qinghai–Tibet Plateau, China. However, there are few reports on the dynamic changes and the influencing factors of the soil reinforcement effect of plant species after artificial vegetation restoration under different recovery periods. We selected dump areas of the Delni Copper Mine in Qinghai Province, China to study the relationship between the shear strength and the peak displacement of the root–soil composite on the slope during the recovery period, and the influence of the root traits and soil physical properties on the shear resistance characteristics of the root–soil composite via in situ direct shear tests. The results indicate that the shear strength and peak displacement of the rooted soil initially decreased and then increased with the increase of the recovery period. The shear strength of the rooted soil and the recovery period exhibited a quadratic function relationship. There is no significant function relationship between the peak displacement and the recovery period. Significant positive correlations (P < 0.05) exists between the shear strength of the root–soil composite and the root biomass density, root volume density, and root area ratio, and they show significant linear correlations (P < 0.05). There are no significant correlations (P > 0.05) between the shear strength of the root–soil composite and the root length density, and the root volume ratio of the coarse roots to the fine roots. A significant negative linear correlation (P < 0.05) exists between the peak displacement of the rooted soil and the coarse-grain content, but no significant correlations (P > 0.05) with the root traits, other soil physical property indices (the moisture content and dry density of the soil), and slope gradient. The coarse-grain content is the main factor controlling the peak displacement of the rooted soil.