Question

Given below are two statements:
Statement I: The lateral pressure exerted by the soil when the retaining wall moves away from the back fill, is generally known as active earth pressure of the soil.
Statement II: Rankine's theory of earth pressure assumes that the back of the wall is vertical and smooth.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Hint:

Remember the direction of wall movement:
- Wall moves away from backfill \(\rightarrow\) Active pressure (minimum pressure).
- Wall moves toward backfill \(\rightarrow\) Passive pressure (maximum pressure).
- No wall movement \(\rightarrow\) At-rest pressure.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Earth pressure theories describe the lateral forces exerted by a soil mass against a retaining structure.
These pressures depend on the magnitude and direction of the movement of the retaining wall relative to the backfill.

Step 2: Detailed Explanation:
Let us evaluate both statements:
- Statement I: Active earth pressure occurs when the retaining wall moves outward, away from the backfill.
As the wall moves away, the soil mass behind it expands laterally, mobilising its internal shear strength.
This reduces the lateral pressure acting on the wall until it reaches a minimum constant value, which is defined as the active earth pressure.
Therefore, Statement I is correct.
- Statement II: Rankine's classical theory of earth pressure is widely used to calculate active and passive lateral pressures.
This theory is based on several simplifying assumptions:
1. The soil is homogeneous, isotropic, and semi-infinite.
2. The back of the retaining wall is perfectly vertical and smooth, which means there is no shear force or friction developed between the soil and the wall face (\( \delta = 0 \)).
3. The failure plane is planar, and the soil is in a state of plastic equilibrium.
Therefore, Statement II is correct.
Since both Statement I and Statement II are correct, option (A) is the correct choice.

Step 3: Final Answer:
Both Statement I and Statement II are correct.