The earth pressure at rest is defined as the lateral pressure exerted by soil
- Awhen it is at rest
- Bwhen the retaining wall has no movement relative to the back fillCorrect
- Cwhen the retaining wall tends to move away from the back fill
- Dwhen the retaining wall moves into the soil
Solution
Concept
Earth pressure at rest acts when the wall does not move at all relative to the backfill.
Formula
p0 = K0 γ z, K0 = 1 − sin φ' (Jaky)
Step-by-step solution
1. No wall movement gives pressure at rest (K0). 2. Wall moving away from the backfill gives active pressure (Ka). 3. Wall moving into the backfill gives passive pressure (Kp). 4. So the answer is no movement relative to the backfill.
Explanation
Pressure at rest is the lateral pressure when the wall is rigid and does not move. Examples are basement walls and bridge abutments fixed at the top. Its value lies between the active and passive pressures.
Why the other options are wrong
A: 'Soil at rest' is vague. The definition depends on wall movement. C: Movement away from the backfill gives active pressure. D: Movement into the soil gives passive pressure.
Shortcut
No movement = rest, away = active, towards soil = passive.
Common mistake
Choosing option A because it uses the word 'rest'.
Correct answer: B) when the retaining wall has no movement relative to the back fill