In the past 25 years great strides have been made in the area of static stability and deformation analysis. The widespread availability of microcomputers has brought about considerable change in the computational aspects of slope stability analysis. Analyses can be done much more thoroughly, and, from the point of view of mechanics, more accurately than was possible without computers. Still, engineers performing slope stability analyses must have more than a computer program. They must have a thorough mastery of soil mechanics and soil strength, a solid understanding of the computer programs they use, and the ability and patience to test and judge the results of their analyses to avoid mistakes and misuse. Realistic analyses of deformations of slopes and embankments were not possible until about 25 years ago. They are possible now mainly because the finite-element method has been developed and adapted to these applications. The principal requirement for achieving reasonably accurate and useful results fro...

State of the Art: Limit Equilibrium and Finite-Element Analysis of Slopes

A review on natural and human-induced geohazards and impacts in karst

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.

Desirable plant root traits for protecting natural and engineered slopes against landslides

The contribution of plant root systems to slope stability and soil erosion control has received a lot of attention in recent years. The plant root system is an intricate and adaptive object, and understanding the details of soil–root interaction is a difficult task. Although the morphology of a root system greatly influences its soil-fixing efficiency, limited architectural work has been done in the context of slope stabilization and erosion control, and hence it remains unknown exactly which characteristics are important. Many of the published research methods are tedious and time-consuming. This review deals with the underlying mechanisms of shallow slope stabilization and erosion control by roots, especially as determined by their architectural characteristics. The effect of soil properties as well as the relative importance of different root sizes and of woody versus non-woody species are briefly discussed. Empirically and intuitively, architectural features seem to determine the effect of root systems on erosion phenomena and an effort is therefore made here to link both aspects. Still, the research to underpin this relationship is poorly developed. A variety of methods are available for detailed root system architectural measurement and analysis. Although, generally time-consuming, a full 3D architectural description followed by analysis in software such as AMAPmod offers the possibility to extract relevant information on almost any root system architectural characteristic. Combining several methods of measurement and analysis in a complementary way may be a useful option, especially in a context of modelling.

The role of fine and coarse roots in shallow slope stability and soil erosion control with a focus on root system architecture: a review

Recent large-scale slides occurring during the hydraulic placement of an artificial island berm in the Beaufort Sea resulted from the liquefaction of the berm sand. Subsequent laboratory tests and ...

The liquefaction of sands, a collapse surface approach

Research is being carried out at Technion in Israel to study the influence of plant roots on the stability of slopes. The present paper describes the part of the investigation concerned with the de...

The influence of vegetation on soil strength

Plane-strain, finite-element, and finite-difference computations of the bearing-capacity factor, Nγ, have been made for smooth and rough footings, for friction angles, ϕ, in the 30°–45° range, and dilation angles, ψ, in the 0 ≤ψ≤ϕ range. The finite-element analyses were based on a tangent stiffness approach. The commercially available code, fast Lagrangian analysis of continua (FLAC), was used for the finite-difference analyses. It was found that these methods may be used to obtain reliable Nγ values provided they are used cautiously. To obtain high-quality solutions, however, it is necessary to review the results critically, and, if necessary, alter the control parameters (e.g., mesh dimensions, number of calculation increments) being used. Computational difficulties were found to increase with increasing ϕ, and with increasing difference between ϕ and ψ, and the significant of these difficulties with regard to the use of the two computational techniques is discussed here. Curves relating Nγ to ϕ are pre...

Numerical studies of bearing-capacity factor Nγ

Unsaturated soil mechanics: Critical review of physical foundations

A study has been carried out of the bearing capacity of sand layers overlying clay soils for the case where the thickness of the sand layer is comparable to the width of a rigid foundation placed on the soil surface. A review of previous work is given and a discussion is presented of the dimensionless groups that govern the behaviour of this type of foundation. A parametric study is carried out using both finite element and finite difference methods. This study is based on the use of soil parameters obtained from an assessment of the range of values that might be expected to be appropriate for full-scale structures. The results of the parametric study are used to illustrate the mechanics of the system and also to develop charts that may be used directly in design. In particular, the results illustrate that the shear strength of the clay has an important influence on the mechanisms of load spread within the fill. Resume : Lion a rOalisO une Otude sur la capacitO portante de couches de sable reposant sur des sols argileux pour le cas oo liOpaisseur de la couche de sable est comparable ‡ la largeur diune fondation rigide posOe sur la surface du sol. Lion prOsente une revue des travaux antOrieurs et une discussion sur les groupes sans dimension qui rOgissent le comportement de ce type de fondation. Une Otude paramOtrique est rOalisOe en utilisant les mOthodes tant des OlOments finis que des diffOrences finies. Cette Otude est fondOe sur liutilisation des paramtres de sols obtenus en partant de liOvaluation de la plage des valeurs que lion pourrait siattendre ‡ trouver dans des structures ‡ pleine Ochelle. Les rOsultats de liOtude paramOtrique ont OtO utilisOs pour illustrer le mOcanisme du systme et aussi pour dOvelopper des abaques qui peuvent Œtre utilisOes directement dans la conception. En particulier, les rOsultats illustrent que la rOsistance au cisaillement de liargile a une influence importante sur les mOcanismes de rOpartition de la charge ‡ liintOrieur du remblai. Mots clOs : capacitO portante, sols multicouches, analyse numOrique. (Traduit par la rOdaction)

Sam Frydman

Papers

The influence of vegetation on soil strength

Numerical studies of bearing-capacity factor Nγ

Unsaturated soil mechanics: Critical review of physical foundations

Bearing capacity of plane-strain footings on layered soils

Stability charts for pseudo-static slope stability analysis