What represents the most critical stability condition for the upstream slope of an earthen dam_______________?
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Answer: A. sudden drawdown
Explanation
Sudden reservoir drawdown rapidly removes the stabilizing hydrostatic pressure against the upstream dam slope. Saturated embankment soils retain high pore water pressures while external water support is lost. The resulting unbalanced seepage forces create the most critical slope instability condition for earthen dams. Earthen dam stability analyses evaluate various critical loading conditions including steady seepage and construction. Pore water pressure acts outward within embankment pores, reducing effective shear strength in soils. Upstream slopes face severe stability hazards when reservoir water levels drop rapidly during operations.
Geotechnical engineers design upstream slope flattening and drainage blankets to withstand sudden drawdown. Dam safety monitoring programs track pore pressure responses during rapid reservoir water level fluctuations. Preventing upstream slope failure protects the core impermeable membrane of embankment dams. Option B steady seepage represents a long term condition but generates lower destabilizing shear forces. Option C during construction represents a critical phase for clay cores but involves lower water pressures. Option D sloughing refers to shallow surface erosion rather than deep seated slope failure mechanics.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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