The field vane test enables the direct measurement of the undrained shear resistance of saturated cohesive soils.
It can be carried out either in the field, on the wall or at the bottom of an excavation, or even in a laboratory on a suitably contained specimen.
The test consists of forcing a vane with four orthogonal blades into the soil, and then rotating it until soil failure, measuring the maximum torque value required to generate this. Afterwards the residual shear strength of the soil after significant deformation can be measured by continuing to rotate the vane several turns until the soil is completely mixed.
The vanes have a rectangular shape and a height double their diameter, as specified in the recommendations included in EUROCODE 7 (1977) and ASTM Standard Code (D 2573); the latter also allows vanes with a tapered end.
These standards specify that the rotation must be carried out at a rate of 0.1-0.2 degrees/sec. (6-12 degrees/min).
A thin enlarging ring can be installed above the blades of the vane so that most of the resistance due to the soil friction along the path of the rod inserted into the soil is eliminated from the measurements.
Field Vane Test
The vanes which can be used with the various types of lining tubes are as follows:
Penetrometers Inner / Outer diameter of lining tubes Compatible vanes DPM30-20
20 / 33 mm 38×19 TG63-100
32 / 48 mm 60×30