Tensile-pullout properties of roots of Magnolia multiflora in different growth stages and stability of slope with its root

To study the root tensile-pullout characteristics of shrubs in different growth periods and analyze their effects on slope protection. A indoor tensile test and a field pull-out test using the roots of Magnolia multiflora which is a typical slope-protection shrubs with a growth period of three months, six months, nine months, twelve months, fifteen months and eighteen months were carried out, respectively. The indoor tensile test and field pull-out test of Magnolia multiflora's roots were conducted at a constant displacement rate of 0.02 mm/s and 10 mm/min, respectively. Under the different growth periods, root mechanical effect indexes and physiological indexes were determined, respectively. Root mechanical effect indexes include the single root tensile resistance, single root tensile strength and root pull-resistance. The physiological indexes include the ground diameter, subterranean biomass and lateral root quality. The two-dimensional finite element method was used to simulate the enhancement of the slope stability in terms of the Magnolia multiflora's roots at different growth stages. The results are as follows: Under different growth periods, the tensile resistance of the Magnolia multiflora's single root increases with the increasing of root diameter according to a good power function, and the tensile strength decreases with the increasing of root diameter according to a good power function, when the single root diameter is constant, both the tensile resistance and the tensile strength increase with the growth period. Under the influence of different growth periods, the pull-resistance increases with the increasing of ground diameter, subterranean biomass and lateral root quantity according to a significant exponential function, the increase rate of the average biological index and the average pull-resistance of the Magnolia magnolia's roots are the largest in the growth period of three to six months. After six months, the average biological index and the average pull-resistance of the Magnolia magnolia's roots decrease with the growth period increasing, the increase rates of the ground diameter decrease from 102.78% to 9.8%, the increase rates of subterranean biomass decrease from 117.55% to 19.70% and the increase rates of lateral root quantity decrease from 104.35% to 6.67%, the increase rates of pull-resistance decrease from 102.78% to 31.55%.The safety factor of Magnolia magnolia's roots slope is greater than that of the bare slope, the increase rates of the safety factor are from 1.09% to 23.36% and the safety factor of the slope increases with the Magnolia magnolia's growth period increasing, which indicates that Magnolia magnolia's roots can improve the stability of slope. The equivalent plastic strain and the maximum displacement decreases with the Magnolia magnolia's growth period increasing, among them, the maximum equivalent plastic strain is reduced by 24% to 72% compared with that of the bare slope. The Magnolia magnolia's roots can effectively reduce the slope's maximum horizontal displacement and vertical displacement at different growth stages, the decreasing proportions of maximum horizontal displacement and maximum vertical displacement is increase with the growth period increasing and the reduction of the maximum horizontal displacement are about half of the maximum vertical displacement, it indicates that the growth and development of roots can effectively reduce the displacement of slopes. This research has important research value and practical significance for the coordinated development of infrastructure construction and ecological environment protection using shrub slopes such as Magnolia magnolia.