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GATE 2024 CE (CE2) – Question 40

Geotechnical Engineering · Earth pressure theories: Rankine and Coulomb, sheet piles · 2 marks · Multiple choice

Consider the statements P and Q related to the analysis/design of retaining walls.
P: When a rough retaining wall moves toward the backfill, the wall friction force/resistance mobilizes in upward direction along the wall.
Q: Most of the earth pressure theories calculate the earth pressure due to surcharge by neglecting the actual distribution of stresses due to surcharge.

Which one of the following options is CORRECT?

  1. Both P and Q are TRUE
  2. P is TRUE and Q is FALSE
  3. Both P and Q are FALSE
  4. P is FALSE and Q is TRUE

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Correct answer: (D) P is FALSE and Q is TRUE

Explanation

When the wall moves toward the backfill (the passive state), the soil wedge is pushed upward relative to the wall, so the friction on the soil acts downward (and the wall friction on the wall is the reaction): the statement that the friction is upward is the active-state behaviour, so P is false. Most earth pressure theories (Rankine and Coulomb) treat the surcharge simply as an equivalent extra height of soil or a uniform extra pressure and neglect the actual distribution of the stresses of the surcharge in the soil, so Q is true.