In the context of soil mechanics involving walls, passive pressure typically requires what behavior from the wall?

Passive pressure in soil mechanics refers to the resistance that a wall experiences due to soil when the wall moves towards the soil. For passive pressure to develop, the wall must be able to move outward. This outward movement allows the soil to resist the displacement, generating passive lateral pressures that act on the wall.

When a wall moves outward, the soil behind it undergoes a rearrangement, allowing for greater forces to mobilize. This behavior is essential in the design of retaining walls and structures that retain soil, as it influences the overall stability and safety of the structure.

Movement inward or vibration of the wall would not contribute to developing passive pressure but rather would lead to active pressures where the soil exerts less force against the wall. Therefore, the correct interpretation of how passive pressure relies on the wall's outward movement is critical for understanding soil-structure interactions and for the effective design of retaining walls.