Influence of Willow Root Density on Shear Resistance Parameters in Fine Grain Soils using in situ Direct Shear Tests

摘要

This study presents an experimental study on the effect of root density on the shear strength of fine grain soils by conducting in situ direct shear tests. The plant used in the shear tests was Willow, a tree compatible with the climates of many sliding regions in Iran. Stabilization of river terraces and natural soil slopes by means of tree roots as a reinforcement agent is an environmental adopted method which needs to be developed. In this research a series of tests was carried out on soil blocks both containing and without Willow roots using a large scale in situ direct shear test apparatus. The results were analyzed based on direct shear theory to calculate the apparent cohesion and internal friction angle of rooted and non-rooted soil. The results reveal that in spite of a slight decrease of 5% in the internal friction angle, the apparent cohesion of lean clay soils increases significantly up to 80%. Since, the effect of tree roots on the improvement of shear strength in lower depths is less than surface layers, implanting Willow is recommended as an effective technique for preventing superficial sliding. The results of this research are presented in forms of linear relations between increased apparent cohesion and shear strength and Willow root density (RAK) at different depths of soil.