In what scenario is the passive earth pressure used in a retaining wall?

The correct scenario for the use of passive earth pressure in the context of a retaining wall is when considering the soil over the toe of the wall. Passive earth pressure refers to the lateral pressure exerted by soil when it is in a state of passive resistance, which occurs when the retaining wall moves slightly away from the backfill. This movement allows the soil to push back against the wall, providing support and stability.

When a retaining wall is designed, the consideration of passive earth pressure is essential because it can help counteract the lateral forces exerted by the soil behind the wall. In particular, when soil exists over the toe of the wall, it can provide additional resistance through passive pressure, enhancing the overall stability of the structure. This is crucial in preventing structural failure and ensuring that the wall can maintain its position over time, particularly under varying loads and conditions.

The other scenarios presented, such as soil behind the wall, soil under the wall, and soil impacting the height of the wall, do not directly relate to the concept of passive earth pressure. Instead, they may involve factors related to active earth pressure, stability concerns, or loading calculations, but they do not contribute to the passive resistance offered by soil above the toe of the retaining wall.