Which statement best describes active and passive earth pressures on a retaining wall?

Which statement best describes active and passive earth pressures on a retaining wall?

• A. Active pressure occurs when the wall yields and soil pushes outward with lower force.
• B. Active pressure occurs when the wall yields and soil resists movement with higher force.
• C. Passive pressure is generated when the wall remains completely rigid with no movement.
• D. Both active and passive pressures are independent of wall movement.

Answer: (A)

Active earth pressure is the force from soil on a retaining wall when the wall yields and moves away from the backfill, causing the soil pressure to drop to a lower, active value. The statement that active pressure occurs as the wall yields and the soil pushes outward with a lower force captures this behavior—the wall moves away and the horizontal load on it is reduced compared to the at-rest condition. In contrast, passive pressure arises when the wall moves into the soil and the soil resists that movement, producing a much higher force on the wall. A completely rigid wall with no movement corresponds to at-rest pressure, not passive. And since the pressure levels change with how the wall moves, saying the pressures are independent of wall movement isn’t accurate.

Active earth pressure is the force from soil on a retaining wall when the wall yields and moves away from the backfill, causing the soil pressure to drop to a lower, active value. The statement that active pressure occurs as the wall yields and the soil pushes outward with a lower force captures this behavior—the wall moves away and the horizontal load on it is reduced compared to the at-rest condition.

In contrast, passive pressure arises when the wall moves into the soil and the soil resists that movement, producing a much higher force on the wall. A completely rigid wall with no movement corresponds to at-rest pressure, not passive. And since the pressure levels change with how the wall moves, saying the pressures are independent of wall movement isn’t accurate.