What characterizes the condition of a wall under active pressure?

Active pressure is a critical concept in soil mechanics and structural engineering, particularly in the context of retaining walls. When a wall is in a state of active pressure, it means that the earth behind the wall has sufficient lateral earth pressure to cause the wall to move outward. This outward movement occurs because the soil will exert a force on the wall that increases as the wall moves away from the retained soil.

In this condition, the wall is not simply stationary or resisting lateral pressures without movement; instead, it is actively yielding or moving in response to the soil's pressure. This movement reduces the lateral stress experienced by the wall because as the wall displaces outward, the soil's resistance is diminished, leading to an equilibrium point where the forces are balanced.

The other options present scenarios that do not accurately represent the active pressure condition. For instance, a stationary wall would be in a state of passive pressure or simply resisting earth pressure without any yielding. A wall that moves inward would imply a negative stress situation that is not characteristic of active pressure. Lastly, the notion of constant pressure does not apply; active earth pressure is not constant but is instead a function of the wall's movement and the height of soil behind it.

Understanding these dynamics is crucial for the design and