According to Coulomb's wedge theory, the active earth pressure slides the wedge:

Explanation:

Coulomb's wedge theory:

• Coulomb (1776) developed a method for the determination of the earth's pressure.
• In which he considered the equilibrium of the sliding wedge which is formed when the movement of the retaining wall takes place.
• The sliding wedge is torn off from the rest of the backfill due to the movement of the wall. In the Active Earth Pressure case, the sliding wedge moves downwards & outwards on a slip surface relative to the intact backfill & in the case of Passive Earth pressure, the sliding wedge moves upward and inwards.

Important Points The following are the assumptions of Coulomb’s Theory:

1. The backfill is dry, homogeneous, and isotropic

2. The backfill is ideally elastically undeformable but breakable.

3. The backfill is cohesionless

4. The heel surface is a plane surface that passes through the heel of the wall

5. The wall surface is rough

6. The sliding wedge itself acts as a rigid body