What characterizes passive earth pressure in the context of retaining walls?

Passive earth pressure refers to the pressure exerted by soil when it is pushed or compressed against a retaining wall that is moving away from the soil. This condition arises when the wall is subjected to lateral movement, typically due to soil expansion or movement, which allows the soil particles to engage with the wall more forcefully.

The characteristic of compressing the soil in front of the wall is crucial in understanding how passive earth pressure develops. When the wall moves away from the backfill, the soil behind it gets compressed, leading to an increase in lateral pressure exerted on the wall. This creates a stabilizing effect, which is essential for the design and safety of retaining structures.

In contrast, while passive earth pressure is indeed behind the wall, the defining moment of its characteristic arises from the wall's movement and the resulting soil compression. Therefore, the focus on the interaction leading to increased pressure underscores that the soil's response is fundamentally linked to the wall's behavior in relation to it.