The Vane Shear Test is used to determine the undrained shear strength of soft cohesive soils (especially clay). A four-bladed vane is inserted into soft soil and rotated. The soil resists rotation due to shear strength. The torque required to rotate the vane is used to calculate shear strength. Applications • Determining strength of soft clay deposits • Foundation design in clayey soil • Stability analysis of slopes • Embankment construction • Evaluating soil sensitivity Important Points (Exam Tips) • Used only for cohesive soils (clay) • Not suitable for sand or gravel • Quick and undisturbed testing method • Gives both undisturbed & remoulded strength • Sensitivity = Undisturbed / Remoulded strength