METHOD OF SLICES

METHOD OF SLICES

LEARNING OUTCOMESSLOPE STABILITY BASED ON TAYLOR DIAGRAMBASIC THEORY OF SLICE OF SLOPESCALCULATION OF SAFETY FACTOR

TAYLOR DIAGRAM FOR COHESION SOIL( = 0)

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Nd = stability number

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Stability diagram for cohesive soil and >53o

Hard layerZ=depth of hard layerHigh of slopes

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SLOPES STABILITY FOR COHESION LESSSOIL; >0 (TAYLOR, 1948)

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The sliced methodYulvi zaika

Sliced methodThis method can be used for soil in different shearing resistance along the failure plane Proposed by Fellenius ,Bishop, JANBU, ETCAssumed circular failure plane

Regulation of slicesSliced performed vertical direction The width of the slice does not have the same measurementOne slice must have one type of soil in the failure surface The width of the slice must be such that the curve (failure plane) can be considered a straight line The total weight of soil in a slice is the soil wedge itself, including water and external load

Fellenius (Ordinary) Method of Slices

formulation

Step by Step Procedure1. Draw cross-section to natural scale2. Select failure surface3. Divide the failure mass into some slices4. Compute total weight ( WT ) of each slice5. Compute frictional resisting force for each slice N Tan ul6. Compute cohesive resisting force for each slice Cl7. Compute tangential driving force (T) for each slice8. Sum resisting and driving forces for ALL slices and compute FS

BISHOP METHOD- Also known as Simplified Bishop method- Includes interslice normal forces- Neglects interslice shear forces- Satisfies only moment equilibrium

3. Simplified Bishop Method

Recommended Stability MethodsOrdinary Method of Slices (OMS) ignores both shear and normal interslice forces and only moment equilibriumBishop method- Also known as Simplified Bishop method- Includes interslice normal forces- Neglects interslice shear forces- Satisfies only moment equilibrium

othersSimplified Janbu method- Includes interslice normal forces- Neglects interslice shear forces- Satisfies only horizontal force equilibriumSpencer method- Includes both normal and shear interslice forces- Considers moment equilibrium- More accurate than other methods

Recommended Stability MethodsOMS is conservative and gives unrealistically lower FS than Bishop or other refined methodsFor purely cohesive soils, OMS and Bishop method give identical resultsFor frictional soils, Bishop method should be used as a minimumRecommendation: Use Bishop, Simplified Janbu or Spencer

Remarks on Safety FactorUse FS = 1.3 to 1.5 for critical slopes such as end slopes under abutments, slopescontaining footings, major retaining structuresUse FS = 1.5 for cut slopes in fine-grained soils which can lose strength with time