Consider the following statements regarding energy heads : 1. The velocity head in soils is negligible. 2. Direction of flow is determined by the difference in total head. 3. Negative pore pressure cannot exist. Which of the above statements are correct ?
- A1 and 2 onlyCorrect
- B1 and 3 only
- C2 and 3 only
- D1, 2 and 3
Solution
Concept
Total head in seepage
Formula
h = p/γw + z (velocity head neglected)
Step-by-step solution
1. Seepage velocities are very small, so velocity head is neglected (true). 2. Water flows from higher to lower total head (true). 3. Negative pore pressure (suction) exists in partly saturated soil and in the capillary zone (statement false).
Explanation
Total head = pressure head + elevation head. Negative pore pressures are possible above the water table.
Why the other options are wrong
Options with statement 3 are wrong.
Shortcut
Seepage: no velocity head; flow from high to low total head.
Common mistake
Thinking pore pressure cannot be negative.
Correct answer: A) 1 and 2 only