A case study of effect of lateral roots of Pinus yunnanensis on shallow soil reinforcement

A traction effect refers to the mechanical effect of lateral to horizontal roots, normally in shallow soil, to enhance the in-plant tensile strength of soil in the rooted soil zone. It is one way. in which plant roots can contribute to lateral reinforcement of a shallow soil mass. To verify whether or not a traction effect exists in the root system of a pine forest (Pinus yunnanesis French) in the Hutiaoxia Gorge. southwest China, and evaluate the magnitude of any such effect, an experiment-based modelling and a direct in situ test were conducted at the Erdui site in the gorge. The modelling prediction indicates that the lateral roots produce tremendous tractive resistance in the upper soil (0-60 cm below the surface), with a magnitude of 4169 N, on a vertical cross-section area of 10(5) mm(2) at the top depth interval of soil (0-20 cm). The direct in situ test shows that the tractive resistance exerted by the lateral roots averages 561 N in the top depth interval and for the same vertical area, or an increase of sliding-pulling resistance by 38%. Under the influence of this tractive resistance, the tensile strength of the upper rooted soil was increased by at least 5.7 kPa. Together with the strong vertical anchorage of the taproot of the pine and sinker roots, the lateral roots are able to stabilise the shallow soil mass to a certain degree. (C) 1998 Elsevier Science B.V.