Environmental aspects in geosynthetic-soil reinforcement structures: The role of vegetation

Wherever ecological solutions are desirable, soil bioengineering methods in slope stabilisation and soil erosion control are becoming more widely used. In this context, the design and application of geosynthetic-reinforced soil structures with vegetated face steep slopes has long emphasized aspects of environmental impact. In engineering practice, vegetation is increasingly used to protect artifi cial and natural slopes against shallow landslides and for surfi cial erosion control. The potential use of protection forests to combat shallow slope instabilities is becoming increasingly important, especially in the light of recent landslides and debris/mud fl ows in certain regions, triggered by rainfalls with increased intensity. The presence of vegetation contributes to maintaining slope stability and to reducingsurface soil erosion, both by reinforcing soil shear resistance and influencing the hydro-geologic conditions of soil. Methods to measure and predict the effects of vegetation on mass-wasting processes have become of particular interest to both the academic and engineering communities. The roots of plants are anchored into the soil to support the above-ground parts of vegetation, thereby creating a reinforced soil matrix in which stress is transferred from the soil to the roots, increasing the overall strength of the matrix. The strength of rooted soil is, therefore, due to a combination of soil strength, root strength, and the strength of the bonds between the soil and roots. Vegetation influences slope stability and the erosion process with both mechanical and hydrological effects. In particular, the mechanical effects of vegetation (increase in soil shear strength) related to soil stabilisation will be described. Based on the analysis of available literature, the aim of this work is to present the specifi c role of vegetation in soil reinforcement applications through the analysis of fi eld investigation, experimental tests carried out on roots and on roots-soil systems and analytical and theoretical modelling. Due to lack of space, erosion applications will be not considered in this paper. The use of vegetation in works of civil engineering and landscaping has grown in importance, but specifi c design standards are still under discussion for the use of vegetation in slope stabilization. Therefore, the design and management of stabilization systems using plants require an accurate knowledge about the quantitative reinforcing root effects on soil strength.