Effect of vetiver grass root on the shear strength of completely decomposed volcanic tuff and pull-out resistance of the root

Abstract

The effects of vétiver grass roots on the strength of completely decomposed volcanic tuff and the pull-out resistance of the grass roots were studied.the investigation, vétiver grass was planted on a steep cut slope in the Kardoorie Research Institute - Shek Kong Centre and allowed to grow under 'natural' conditions for 18 months. Block samples, both rooted and un-rooted, were then retrieved and the shear strengths of the samples were determined so that comparison on the strengths can be made. The test results show that the friction angle and cohesion remain nearly unchanged. The pull-out resistance of the grass roots as determined by in-situ pull-out test vanes from 1 kN to 2.5 kN, depending on the root system and the failure pattern.