Presentation on industrial training undergone at Soft-Tech Engineers Pvt. Ltd.

Introduction toSlope Stability analysisRutvik ShethM.Tech (Structures)D.D.U, NadiadintroductionSlopes either occur naturally or are engineered by human being. Furthermore, the increasing demand for engineered cut and fill slopes on construction projects has also increased the need to understand analytical methods, investigative tools, and stabilization methods to solve slope stability problems. Slope stability analysis is feasible forNatural cut slopeHill slopesOpen excavationEmbankments for damsWaterfront structures

Slope Stability Analysis22introductionSlope stability methods vary in their theoretical background and approach and hence the analysis results vary depending on the used theory. In addition, simplified assumptions in 2D slope stability methods have led to factors of safety that differ from the more rigorous 3D slope stability analysis methods. In practice, 3D analysis of slope stability is not performed unless the geometry of the slope is very complicated or the failure mechanism is complex. It is essential that a research effort be devoted to gain better understanding of the slope failure analysis methods and to understand the weakness and strength of the methods and to point out practical aspects in the analysis procedures.Slope Stability Analysis33AIMS OF SLOPE STABILITY ANALYSISTo understand the development and form of natural slopes and the processes responsible for different natural features.To assess the stability of slopes under short-term (often during construction) and long-term conditions.To assess the possibility of landslides involving natural or existing engineered slopes.To analyze landslides and to understand failure mechanisms and the influence of environmental factors.To enable the redesign of failed slopes and the planning and design of preventive and remedial measures, where necessary.To study the effect of seismic loadings on slopes and embankments.Evaluation of instability due to liquefaction.

Slope Stability Analysis44AIMS OF SLOPE STABILITY ANALYSISDetermination of stable cut and fills slopes. To determine factor of safety against slidingGround water changeEarthquake effectChange in slope angle due to erosionDecreasing strength due to weatheringAssessment of overall stability of shallow and deep foundations for structures located on slopes or over potentially unstable soils, including the determination of lateral force applied to foundations and walls due to potentially unstable slopes.

Slope Stability Analysis55LIMIT EQUILIBRIUM ANALYSISFailure, sudden or gradual, is caused by overstress in a slope or its foundation with respect to the available strength.Limit equilibrium analysis is the basis for most methods available for slope stability evaluations. It usually considers that the Mohr-Coulomb failure criterion ( = c + *tan) is satisfied along an assumed failure surface. A free body is taken from the slope and the body and the known or assumed forces acting on the body and the shearing resistance required for stability are calculated. Most practical problems are statically indeterminate and assumptions must be made regarding the force systems and their directions of applications in order to render the problem determinate..Slope Stability Analysis66LIMIT EQUILIBRIUM ANALYSIS - WeaknessThe most important weakness in limiting equilibrium analysis is the assumption that FOS along the entire failure surface is constant. In connection with existing stable slopes there are a number of factors not considered in the present state of art of analysis, including initiation and growth of failure surfaces, stress distribution, energy release due to progressive failure, and rate of movement. The classical limit equilibrium analysis considers the ultimate limit state of the system and provides no information on the development of strain which actually occurs. For a natural slope, it is possible that part of the failure mass is heavily stressed so that the residual strength will be mobilized at some locations while the ultimate shear strength may be applied to another part of the failure mass. This type of progressive failure may occur in over consolidated or fissured clays or materials with a brittle behaviour.Slope Stability Analysis77Modes of FailuresSlope failures usually occur due either to a sudden or gradual loss of strength by the soil or to a change in geometric condition (steepening of existing slopes). These usually take form of either:TranslationalPlane or wedge surfaceCircularNon circularThe planar failure surfaces are usually expected in slopes where a soil layer, or relict jointing, with a relatively low strength. The translational type of failure occurs in shallow soils overlying relatively stronger materials and circular failure surfaces usually occur in slopes consisting of homogeneous materials. As most soils are heterogeneous, non circular surfaces, consisting of a combination of planer and curved sections, are most likely.

Slope Stability Analysis88Equilibrium conditionsTwo different approaches are used to satisfy static equilibrium in the limit equilibrium analysis procedures. Some procedures consider equilibrium for the entire mass of soil bounded beneath by an assumed slip surface and above by the surface of the slope. This procedure is termed as Mass Procedure. In these procedures, equilibrium equations are written and solved for a single free body.In other procedures the soil mass is divided into a number of vertical slices and equilibrium equations are written and solved for each slice. This procedure is termed as Method of Slices. Three static equilibrium conditions are to be satisfied:Equilibrium of forces in the vertical direction,Equilibrium of forces in the horizontal direction,Equilibrium of moments about any pointSlope Stability Analysis99Thank you Slope Stability Analysis10