Enhancing Slope Stability with Vegetation

Advancing Culture of Living with Landslides, 2017

Recently geotechnical engineers aim to adopt more environmental-friendly solutions (not harmful to the environment), therefore the interest on the use of vegetation as a measure to improve slope stability is increasing. The mechanical reinforcement due to roots against shallow landslides occurs when the fibres intersect the shear surface, usually at depths lower than 2 m. In the literature, the presence of roots is often taken into account by modelling the soil as an equivalent composite material: 'the root-permeated soil', by including an additional cohesion term in the Mohr-Coulomb equation. The models used to estimate the root additional cohesion are presented in the first part of the paper. In some cases, root cohesion is calculated based on the resistant properties of the fibres and assuming an order for the progressive roots failure, either breaking, slipping out or buckling. On the other hand, some authors used structural models of the roots investigating not only the stresses in the roots, but also in the surrounding soil to obtain a better estimation of the root cohesion. In the second part of the paper, the calculation of the root reinforcement is used to assess the safety factor (SF) of the slope. Both Limit Equilibrium analyses (LE) and Finite Element Methods (FEM) are discussed, stressing the limitations of both the approaches.

2009

Slope stability models traditionally use simple indicators of root system structure and strength when vegetation is included as a factor. However, additional root system traits should be considered when managing vegetated slopes to avoid shallow substrate mass movement. Traits including root distribution, length, orientation and diameter are recognized as influencing soil fixation, but do not consider the spatial and temporal dimensions of roots within a system. Thick roots act like soil nails on slopes and the spatial position of these thick roots determines the arrangement of the associated thin roots. Thin roots act in tension during failure on slopes and if they traverse the potential shear zone, provide a major contribution in protecting against landslides. We discuss how root traits change depending on ontogeny and climate, how traits are affected by the local soil environment and the types of plastic responses expressed by the plant. How a landslide engineer can use this information when considering slope stability and management strategies is discussed, along with perspectives for future research. This review encompasses many ideas, data and concepts presented at the Second International Conference 'Ground Bio-and Eco-engineering: The Use of Vegetation to Improve Slope Stability-ICGBE2' held at Beijing, China, 14-18 July 2008. Several papers from this conference are published in this edition of Plant and Soil.

Ecological Engineering, 2016

This paper is dedicated to numerical analysis of the influence of vegetation on slope's stability using the calculation of the safety factor of different slopes by a classical shear reduction method with the software PLAXIS in 2D. The soil is modelled as an elastic perfectly plastic material. The shear strength of the soil is also modelled using the Mohr-Coulomb criterion. Slope stability is influenced by vegetation mechanical parameters: plant's root matrix system and surcharge due to presence of trees. Based on 2D finite element method, this paper investigates the combined effects of different rectilinear slope geometries, soil types and vegetation mechanical parameters on the slope's factor of safety. The effects of the roots are modelled by increasing the soil cohesion following a classical Wu model. The additional cohesion depends on the vegetation type and on the depth from soil surface. The analysis examined reinforcement effects of the roots' systems of four idealised types of vegetation growing on three different types of soil composing the slope. The case study was performed on different slope configurations where slope's height and angle were allowed to vary significantly. Two key parameters of the root matrix system had been considered for the finite element analysis: additional cohesion due to the presence of roots and depth of the root matrix. Moreover, influence of geometrical parameters, height and angle of the slope, on the stability of different slope configurations had been analysed by computing slope's factor of safety. Parametric studies were performed to assess the variation of the factor of safety of a slope in case of different geometrical configurations combined with several types of vegetation coverage. Results showed that the slope angle had the greatest impact on variation of factor of safety. Additional cohesion is regarded as the second most important parameter influencing the factor of safety. These two parameters combined play an important role in shallow failures of slopes and significantly affect stability of a slope regardless of a soil type composing the slope. Results of the current study can help practitioners determine if a slope is at risk by the lack of additional roots cohesion combined with different types of soil and young vegetation. Hence, the proposed method helps evaluate slope's vulnerability and could be efficiently used as management or informative tool for ecological engineers and forest conservative practitioners.

Procedia Engineering, 2016

Peer-review under the responsibility of the organizing and scientific committees of CNRIG2016

2010

The foothills of Himalayan mountain ranges are areas where landslides and erosion are frequent. The aim of this study is to propose a new approach for slope stabilisation, by focussing on the careful management of degradation hotspots. We are studying how plant roots reinforce soil, with an emphasis on rooting strategies of plants growing under strong ecological and mechanical constraints e.g. landslides and erosion. We examined root and shoot structure as well as mechanics of local herbaceous species, shrubs and creeping plants to determine which might have a mechanically reinforcing effect on a slope, as well as ethno botanical advantages. Thus we will identify those which can be considered as “tools for eco-engineering” in this area. The use of a numerical model will enable us to simulate and calculate the Factor of Safety (FOS) of slopes for different management actions. The outcome of this study will be to determine practical recommendations for local stakeholders, who can then...

Geotechnical and Geological Engineering, 2012

Land sliding is a geotechnical event that includes a wide range of ground movements such as rockfalls, deep failure of slopes and shallow debris flows, and it can cause various problems in varied civil fields such as roads and dams. Since most conventional methods are neither inexpensive nor applicable everywhere, attention has nowadays been drawn to soil bioengineering using vegetation as the environment-friendly method for slope stabilization. Soil bioengineering or using vegetation in civil engineering design is mostly applicable to shallow slope stabilization projects characterized by unstable slopes with surface movement. Vegetation has both a silent effect on soil improvement to predict the landslide and a mechanical role to increase shear and pulling-out stress on the soil. During the last decade, many researches have been carried out to clarify the effect of vegetation on slope stability, but many questions still remain to be answered.

IOP Conference Series: Earth and Environmental Science, 2018

Vegetation is one of the alternative technologies in the prevention of shallow landslide prevention that occurs mostly during the rainy season. The application of plant for slope stabilization is known as bioengineering. Knowledge of the vegetative contribution that can be considered in bioengineering was the hydrological and mechanical aspects (hydromechanical). Hydrological effect of the plant on slope stability is to reduce soil water content through transpiration, interception, and evapotranspiration. The mechanical impact of vegetation on slope stability is to stabilize the slope with mechanical reinforcement of soils through roots. Vegetation water consumption varies depending on the age and density, rainfall factors and soil types. Vegetation with high ability to absorb water from the soil and release into the atmosphere through a transpiration process will reduce the pore water stress and increase slope stability, and vegetation with deep root anchoring and strong root binding was potentially more significant to maintain the stability of the slope.

Land

A landslide is a significant environmental hazard that results in an enormous loss of lives and properties. Studies have revealed that rainfall, soil characteristics, and human errors, such as deforestation, are the leading causes of landslides, reducing soil water infiltration and increasing the water runoff of a slope. This paper introduces vegetation establishment as a low-cost, practical measure for slope reinforcement through the ground cover and the root of the vegetation. This study reveals the level of complexity of the terrain with regards to the evaluation of high and low stability areas and has produced a landslide susceptibility map. For this purpose, 12 conditioning factors, namely slope, aspect, elevation, curvature, hill shade, stream power index (SPI), topographic wetness index (TWI), terrain roughness index (TRI), distances to roads, distance to lakes, distance to trees, and build-up, were used through the analytic hierarchy process (AHP) model to produce landslide ...

Vegetation has been recognized as an effective and sustainable eco-engineering mitigation measure against shallow landslides. However, its contribution has been largely attributed to the roots mechanical reinforcement while the hydrological effects have been poorly quantified. Moreover, the effect of vegetation on slope stability will depend on many other factors and the assessment of its success may be expensive and time consuming. The implementation of physically-based models may represent a time and cost-effective technique for the assessment of the vegetation success for slope stabilisation, and assist in the optimisation of strategies before any intervention is done. The aim of this paper is to assess the hydrological effect of vegetation against shallow landslides through a physically-based, open source code model based on low cost and time effective requirements.

Soil bioengineering is an environmentally friendly method which employs vegetation to contribute sloping terrain by reinforcing the soil. The vegetation can contribute to slope stability with two effects: mechanical and hydrological. Vetiver grass (Vetiveria nemoralis A. Camus), a perennial grass that had been promoted to help conserve the soil and runoff by the World Bank in the 1980s, has been developed to become an important soil bioengineering tool. This paper demonstrates the effect of vetiver root matrix on the soil slope focusing on the mechanical reinforcement. The vetiver grass specimens grown under one year were used in this study. The investigation program includes root observations and direct shear tests. The growing rate of the vetiver roots and the root area ratios were observed during the tests. The cohesion and angle of internal friction of root-reinforced soils were determined from a standard direct shear and a large direct shear apparatus. The results indicated that the roots of vetiver grass were fast growing. Shear strength of the root-reinforced soil was significantly increased because of roots bundling as well as the increased number of root hair. Electron microscopic results revealed that the bundling and adhesion contributed from large surface area of root hair can help to improve the slope stability by increasing shear strength of the soil. Keywords: Laboratory tests, root area ratio, shear strength, cohesion, electron microscope