Correct Answer - Option 1 : Away from the backfill
Explanation:
The soil that is retained at a slope steeper than it can sustain by virtue of its shearing strength, exerts a force on the retaining wall. This force is called earth pressure.
When the wall is rigid and unyielding, the soil mass is in the state of rest and there are no deformations and displacements in the wall. The earth pressure corresponding to this state is called earth pressure at rest.
The ratio of the horizontal stress to the vertical stress is called the coefficient of Earth pressure and the same ratio is called the coefficient of active earth pressure and coefficient of passive Earth pressure when soil is in Rankin’s active and passive state respectively.
Definition of Active and Passive Earth Pressure
When the wall is moving away from the soil, the soil mass expands, resulting in a decrease in earth pressure due to mobilization of shearing resistance. A portion of the backfill tends to break away from the rest of the soil mass and tends to move downward and outward relative to the wall. A stage is reached when the entire shearing resistance is mobilized and at this stage, the force acting on the wall is called active earth pressure.
On the other hand, if the wall is pushed towards the backfill, the soil is compressed and the soil offers its resistance by virtue of its shearing resistance. Since shearing resistance builds up in the direction of the wall the earth pressure gradually increases and reaches a value where backfill cannot withstand and slip surface is formed and force acting on the wall at this stage called passive earth pressure.
