Question

A retaining wall has a backfill of pure clay whose unconfined compressive strength is 40 kPa and unit weight 20 kN/m\(^3\). The depth of tension crack developed in the backfill is ............

• A. 1 m
• B. 2 m
• C. 3 m
• D. 4 m

Hint:

For pure clay, always convert unconfined compressive strength to cohesion using \( c = \frac{q_u}{2} \) before applying the tension crack formula.

Answer 1

The Correct Option is B

The depth of tension crack in a cohesive soil can be calculated using the formula: \[ z = \frac{2c}{\gamma} \] where:
- \( c \) = cohesion of the soil = \(\frac{q_u}{2} = \frac{40}{2} = 20 \text{ kPa}\)
- \( \gamma \) = unit weight of soil = 20 kN/m\(^3\)
Substituting the values into the formula: \[ z = \frac{2 \times 20}{20} = \frac{40}{20} = 2 \text{ m} \] Hence, the depth of the tension crack is \( \boxed{2\ \text{m}} \).