Analytical study on the role of tree roots system in slope stability

The objective of this paper is to investigate the role of a tree roots system in slope stability through an analytical method. Variations of the diameter and the area ratio of the roots depending on its position in the soil were determined using two actual Japanese cedar trees (Cryptomeria japonica D. Don). The shape of the whole roots of a tree was assumed to be a hemisphere centered at the middle of the tree stump, thus the diameter and the area ratio of the roots is distributed on the surface of the hemisphere with an arbitary radius. The role of the tree roots system was clarified by the Spencer method for two-dimensional analysis. The conventional studies of many researchers have adopted fixed and linear slip surfaces in stability analysis. In this study, the safety factor against slope failure was optimized to determine the critical slip surface of the non-circular shape. The analytical examination using model slopes of homogeneous soil material revealed that a tree located at the toe of a slope is far more effective inslope stability than at any other position of the slope, and the role of this system has the function of increasing the critical safety factor against slope failure, on the contrary the depth of the slip surface (i. e. the scale of slope failure) will increase.