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 horizo ntal 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 plan t 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. so uthwest China, and evaluate the magnitude of any such effect, an exper iment-based modelling and a direct in situ test were conducted at the Erdui site in the gorge. The modelling prediction indicates that the l ateral 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 e xerted by the lateral roots averages 561 N in the top depth interval a nd for the same vertical area, or an increase of sliding-pulling resis tance by 38%. Under the influence of this tractive resistance, the ten sile strength of the upper rooted soil was increased by at least 5.7 k Pa. Together with the strong vertical anchorage of the taproot of the pine and sinker roots, the lateral roots are able to stabilise the sha llow soil mass to a certain degree. (C) 1998 Elsevier Science B.V.