Geotechnical Engineering and Slope Stability Flashcards
6 cards from real Civil Engineering PE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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The factor of safety for slope stability is defined as the ratio of:
Answer: Resisting forces to driving forces
Factor of safety equals resisting moment (or force) divided by driving moment (or force), with FS > 1 indicating a stable slope.
For a soil with friction angle φ = 30°, Rankine's active earth pressure coefficient Ka equals:
Answer: 0.33
Ka = tan²(45° − φ/2) = tan²(30°) ≈ 0.33 for φ = 30°.
Bishop's simplified method of slices assumes that:
Answer: Interslice shear forces are zero
Bishop's simplified method neglects interslice shear forces while retaining normal interslice forces, improving accuracy over the ordinary method.
Jaky's formula for the coefficient of earth pressure at rest (K₀) for a normally consolidated soil is:
Answer: K₀ = 1 − sin φ
Jaky's empirical formula K₀ = 1 − sin φ gives a reliable approximation for normally consolidated cohesionless soils.
For a cohesionless infinite slope under drained conditions, the factor of safety simplifies to:
Answer: FS = tan φ′/tan β
When c′ = 0, Terzaghi's infinite slope equation reduces to FS = tan φ′/tan β, independent of slice weight.
Tension cracks at the crest of a cohesive slope reduce stability primarily because they:
Answer: Can fill with water, adding a hydrostatic driving force
Water-filled tension cracks add a lateral hydrostatic force that increases the driving moment and reduces the factor of safety.