Correct option is B
The
vane shear test is commonly used to determine the undrained shear strength of soft clays, both in the field and in the laboratory. In this test, a vane (with thin, rectangular blades) is inserted into the soil sample, and a torque is applied until the soil fails in shear. The torque required to cause failure is used to calculate the shear strength of the soil. This method is particularly suitable for soft and sensitive clays because it minimizes soil disturbance and gives an accurate representation of the undrained strength.
Direct shear test is generally used for cohesionless soils and gives approximate values for cohesive soils.
Triaxial compression test is more versatile but may not be as convenient for soft clays.
