Field shearvane test (Torvane)

The Field shear vane test (Torvane) provides a good indication of the undrained shear strength (Cu) of any cohesive material as a function of the torque needed for shearing. The consistency of cohesive soils may vary from very soft (<20kPa) to hard (>300kPa), although the latter points to soils which behave like soft rock and should, therefore, be described as rock instead of soil.

The vane test is conducted on the surface of an undisturbed soil sample; the device is pressed carefully with one of three vane sizes – small, medium or large -  into the soil, after which the top of the device is turned clockwise until the soil shears. The value at the time of shearing can then be read from the device and corrected for the type of vane. The undrained shear strength can finally be calculated and expressed in kN/m² or kPa.