Geosynthetic Engineering and Vegetation Growth in Soil Reinforcement Applications

Abstract

In Italy, since early times, the environmental aspects have always been a key issue on the design and the application. Consequently, the geosynthetic reinforced soil structures consist of vegetated face steep slopes. Furthermore, the use of vegetation has also been recognized and incorporated in engineering practice for erosion control and for stabilization of shallow slopes. Vegetation influences slope stability and erosion process by both mechanical effects and hydrological effects. In particular, in the paper, the mechanical effects of vegetation related to soil stabilization will be described. The purpose of this paper is to present the specific role of vegetation in soil reinforcement applications, by means of the analysis of the available literature on the (i) factors affecting root reinforcement of soil, (ii) experimental tests carried out on roots and on roots-soil system, and (iii) analytical and theoretical models. The erosion applications will not treated in this paper. The use of vegetation in civil engineering and landscape works has grown in importance, even if the specific design standard concerning the use of vegetation for slope stabilization is still under discussion. Therefore, design and management of stabilization systems by plants require an accurate knowledge about the quantitative reinforcing root effects on soil strength.

Review on Types of Root Failures in Shallow Landslides

“…The debonded friction is determined by the following phenomena: the pull out force applied to the root strongly modifies the stresses in the shallow subsoil, causing the detachment of the root from the soil and a decrease of the root diameter (Poisson's effect), as well as a decrease of the confining stress around the root (Naaman et al 1991) that reduces the bonded effect, supporting the assumption of Schwarz et al (2010a). Cazzuffi et al (2014) always consider the debonded friction even if the root-soil bond is still intact. The static friction was ignored by Schwarz et al (2010a) after showing that it represents a small percentage of the total friction.…”

“…Referring to an ideal straight smooth fibre, as a basic ingredient for the analysis, the soil-root friction , or so-called bond or interface friction stress, was suggested to be given by (1) in the works of Gray and Ohashi (1983) and Cazzuffi et al (2014), as it had been assessed in the previous work of Potyondy (1961). In Eq.…”

“…inclusions characterized by failure strains larger than the maximum strains in the soil without inclusions, allowing a greater ductility of the composite material (Dupuy et al 2005). (Gray and Ohashi 1983) The force, , necessary to break the root-soil bond (also known as pull out resistance) is given by (5), where is the root length and is the root-soil frictional resistance (Cazzuffi et al 2014).…”

“…It may be of interest to mention that the strength of roots decrease when the vegetation is removed. The computation of the root strength decay can be found in more detail in Cazzuffi et al (2014).…”

Application of fibres for the stabilisation of steep slopes

“…It can be achieved by means of, e. g. hydroseeding or the use of biodegradable geotextiles or Kemafil meanders. In addition, covering the structure with a layer of soil reinforced with synthetic or natural fibers additionally protects the slope against the impact of extreme atmospheric phenomena [6][7][8][9].…”