Question

An unconfined compression strength test was conducted on a cohesive soil. The test specimen failed at an axial stress of 76 kPa. The undrained cohesion (in kPa, in integer) of the soil is \underline{\hspace{2cm}.}

Hint:

In unconfined compression tests on cohesive soils:
- $q_u =$ axial stress at failure,
- $c_u = q_u/2$.
This is a standard and direct relation often tested in exams.

Answer 1

Step 1: Recall the relation in an Unconfined Compression Test (UCT).
For a cohesive soil, the unconfined compressive strength ($q_u$) is related to the undrained cohesion ($c_u$) as: \[ q_u = 2c_u \]

Step 2: Substitute the given value.
The failure axial stress is the unconfined compressive strength: \[ q_u = 76 \, \text{kPa} \] Hence, \[ c_u = \frac{q_u}{2} = \frac{76}{2} = 38 \, \text{kPa}. \]

Step 3: Conclusion.
The undrained cohesion of the soil is: \[ \boxed{38 \, \text{kPa}} \]