A rise of the water table to the ground surface results in___________________?
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Answer: B. effective stress is reduced due to increase in pore water pressure only but total stress does not change
Explanation
When the water table rises to the surface, total overburden stress remains virtually constant in saturated soil. Pore water pressure increases significantly due to the added hydrostatic head of the elevated water level. Subtracting increased pore pressure from constant total stress results in a net decrease in effective stress. Effective stress governs soil skeleton strength and is calculated as total stress minus pore water pressure. Hydrostatic pore pressure increases linearly with the vertical height of the surrounding water table. Total stress reflects the combined weight of soil solids and water acting above the plane.
Rising groundwater tables during heavy monsoon seasons frequently trigger slope stability failures in hillsides. Foundation excavations must account for effective stress reductions caused by fluctuating seasonal water tables. Geotechnical site investigations record groundwater elevations to evaluate long-term effective stress profiles. Option A is incorrect because pore water pressure clearly changes when the water table rises. Option C incorrectly claims total stress is reduced, whereas total stress actually remains stable or changes slightly. Option D incorrectly states effective stress remains unchanged despite increasing pore water pressures.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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