Abstract
Engineering methods such as soil nails, geosynthetic reinforcement, retaining structures, gabions, and shotcrete are implemented to stabilize road cut slopes along mountainous areas. However, these structures are not environmentally friendly and, particularly in Ethiopia, it is impossible to address all road problems due to financial limitations. Nowadays, soil reinforcement with plant roots is recognized as an environmentally sustainable alternative to improve shallow slope failure along mountainous transportation corridors. The aims of this study was, therefore, to conduct slope stability analysis along a road corridor by incorporating the effect of plant roots. Five plant species were selected for the analysis based on their mechanical characteristics. Namely, Eucalyptus globules (tree), Psidium guajava (shrub), Salix subserrata (shrub), Chrysopogon zizanioides, and Pennisetum macrourum (grasses). The roots’ tensile strength and soil parameters were determined through tensile strength testing and triaxial compression tests, respectively. The factor of safety of the slope was calculated by the PLAXIS-2D software. The study showed that when the slope was reinforced with plant roots, the factor of safety (FOS) improved from 22–34%. The decreasing effect of vegetation on slope stability was observed when soil moisture increased. The sensitivity analysis also indicated that: (1) as the spacing between plants decreased, the effect of vegetation on the slope increased. (2) Slope angle modification with a combination of plant roots had a significant impact on slope stabilization. Of the five-selected plant species, Salix subserrata was the promising plant species for slope stabilization as it exhibited better root mechanical properties among selected plant species.
Highlights
Plant roots can efficiently improve the soil shear strength of the slope and forms the root–soil composition of the nearby surrounding soil
When Salix subserrata is grown on the entire slope, the factor of safety (FOS) increased from 0.956 to 1.284, which is the highest increase in FOS among all plant species
Salix subserrata, Eucalyptus globules and Psidium guajava increased the stability of the slope better than the grasses species (Chrysopogon zizanioides and Pennisetum macrourum) which are characterized by shallow root systems
Summary
Plant roots can efficiently improve the soil shear strength of the slope and forms the root–soil composition of the nearby surrounding soil. The mechanism through which root-reinforced soil is related to concrete reinforcement mainly plays the role of shear stress and tensile strength effect. The effect of root reinforcement increases the cohesive strength of soil, decreases soil deformation, prevents the incidence of surface tension cracks, and can avoid slope failure initiated by triggering factors [6,7,8,9,10,11,12,13,14,15,16]. The effect of plant roots on slope stability can be divided into hydrological and mechanical factors, which can be valuable to ensure slope stability [1,2,5,21,25,26,27,28,29,30,31,32,33,34,35,36,37]. With regards to the hydrological effects, Geosciences 2020, 10, 19; doi:10.3390/geosciences10010019 www.mdpi.com/journal/geosciences
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