Quantifying the effect of brush layering on slope stability

Soil bioengineering techniques that use vegetation as a structural element gained popularity in the field of natural and man-made slope stabilisation due to their ability to combine safety and environmental conservation elements. In spite of such popularity, little research has been done to quantify their effect on slope stability. This work presents a simple scheme for the evaluation of the Factor of Safety for slopes reinforced by brush layering, which is one of the most common techniques adopted in slope stabilisation works. The proposed model is based on the limit equilibrium principle and accounts for geotechnical soil properties (cohesion, friction angle, unit weight of soil), soil saturation, slope steepness, and brush layer design parameters (number of stems per meter, length and diameter of stems, distance between brush layers). The model provides the value of the Factor of Safety for a given slope and soil depth. Laboratory pullout tests were carried out in order to estimate relevant parameters of cuttings of purple willow (Salix purpurea L.) and to perform a slope stability analysis via the model.