Soil Mechanics – Earth pressure state when a retaining wall moves away from the backfill Identify the correct term for the pressure condition on the wall.

Introduction / Context:
Earth pressure on retaining structures depends on wall movement. Small outward movements reduce lateral stress to a minimum state known as “active” pressure; inward movements raise it toward “passive.” Correctly identifying the state is essential for safe design.

Given Data / Assumptions:

• Retaining wall supporting granular backfill.
• Wall moves away from the soil mass (outward).
• Drainage adequate so that pressures are effective (total versus pore pressure distinguished).

Concept / Approach:

With outward wall movement, the soil mass tends to dilate and expand laterally, allowing shear along a failure surface to mobilize. The lateral stress decreases until the active state is reached, characterized by Rankine or Coulomb active pressure coefficients (Ka).

Step-by-Step Solution:

Verification / Alternative check:

Conversely, when the wall is pushed into the backfill, lateral stress increases to the “passive” state (Kp), confirming that outward movement corresponds to “active.”

Why Other Options Are Wrong:

Passive requires inward movement; swelling pressure concerns expansive clays; pore pressure is a hydraulic component, not the overall earth pressure state.

Common Pitfalls:

Ignoring drainage and water table effects, or confusing active/passive with at-rest (K0) conditions when the wall does not move.

Final Answer:

Active earth pressure