Earth pressure is the lateral pressure exerted by the soil on a shoring system. It is dependent on the soil structure and the interaction or movement with the retaining system.
Following are the types of earth pressure:
- At rest state:
(When the wall is stationary and back fill soil have no tendency to move.)
under the rest condition the Retaining wall is stationary therefore lateral stress will be zero.
2. Active state:
(when wall moves away from from fill)
Active state is developed when the wall moves away from the back fill.The active earth pressure is less than pressure at rest because the internal resistance is mobilize in the soil of back fill when wall moves away from the back fill.
3. passive pressure:
(when wall moves against the fill)
In passive state the wall is pushed towards the back fill. The passive earth pressure is greater than earth pressure at rest because shearing resistance is built up between two surface of soil mass.
NOTE:Active and passive earth pressures are the two stages of stress in soils which are of particular interest in the design or analysis of shoring systems. Active pressure is the condition in which the earth exerts a force on a retaining system and the members tend to move toward the excavation. Passive pressure is a condition in which the retaining system exerts a force on the soil. Since soils have a greater passive resistance, the earth pressures are not the same for active and passive conditions.