Which of the following are the correct design requirements regarding underground water tanks? 1. Walls are to be designed for saturated soil up to the extent of water above the base slab 2. Base slab is to be designed for the net uplift pressure of water (less weight of slab for tank empty) 3. Check has to be applied for stability of the tank as a whole against uplift Select the correct answer.
- A1 and 2 only
- B1 and 3 only
- C2 and 3 only
- D1, 2 and 3Correct
Solution
Concept
Design conditions for underground tanks
Step-by-step solution
1. The walls must be checked for earth plus groundwater pressure when the tank is empty (saturated soil up to the water level) (statement 1). 2. When the tank is empty, groundwater pushes the base slab upward; the slab is designed for net uplift, less its self-weight (statement 2). 3. The whole tank must be checked for flotation (statement 3).
Explanation
An empty underground tank is subject to external earth and water pressure and to uplift. IS 3370 requires all three checks.
Why the other options are wrong
Each option that omits a requirement is incomplete.
Shortcut
Underground tank: wall pressure + base uplift + flotation check.
Common mistake
Ignoring the flotation check.
Correct answer: D) 1, 2 and 3