The stabilization of slopes using vegetation as reinforcement

The role of plant roots in slope stabilization is important however the effect is varied in different species. For this study, both pull-out and tensile strength tests were conducted on some local shrub species namely Lantana camara (Wild Sage), Triumfetta tomentosa (Burrbark) and Tagetes lemmonii (Marigold) found in the central region of Kenya.
From the pull out test, a single peak value was observed for all the species. Overall results showed that T. tomentosa offered the highest pull out resistance. The pull out was sudden however the irregular sound of root snapping was heard just before failure. This could be a warning sign. The pull out resistance however reduces with increase in soil moisture content.
For the tensile strength test, the shrub with the highest tensile force is the wild sage (136N) followed by burrbark (119N) and finally marigold (37N). The tensile strength however reduces with increase in root diameter, following a power law in the form of
. Root Area Ratio (RAR) was also calculated for all species, and the highest values were observed within a depth of 0.15m. The root reinforcement, in terms of cohesion, decreases with increase in depth. The maximum reinforcement is from the wild sage and burrbark species at 125Kpa while the marigold species has a maximum of 70Kpa, all at depths of 0.2m.