Short Note on Active Earth Pressure & Passive Earth Pressure

ACTIVE EARTH PRESSURE AND PASSIVE EARTH PRESSURE :-

The magnitude of the lateral earth pressure depends upon the movement of the retaining wall relative to the backfill and upon the nature of soil. Considering a rigid retaining wall with a plane vertical face, backfilled with cohesion less soil. If the wall does not move even after filling the material, the pressure exerted on the wall is termed as Earth Pressure at Rest. The point A represent it is fig. below:-

ACTIVE EARTH PRESSURE :- If suppose the wall gradually moves away from backfill, mobilization of the internal resistance i.e. shearing resistance of soil builds up in direction away from the wall, hence, the earth pressure on the wall decreases and after a particular displacement of the wall, the pressure reaches a constant value and does not decrease beyond this point B with further movement of the wall. This minimum pressure as a result of the movement of the wall away from backfill is called the Active Earth Pressure.

PASSIVE EARTH PRESSURE :- If on the other hand, the wall moves towards the fill, the earth pressure increases, because the shearing resistance builds up in direction towards the wall. The pressure reaches a maximum value (Point C) when the shearing resistance of the soil has been fully mobilized and any further movement of the wall does not increase the pressure. This maximum pressure as a result of movement of wall towards the backfill is called the  Passive Earth Pressure