Field Vane Test

 Field vane test (FVT) is governed by EN ISO 22476 Part 9 for United Kingdom and European region, and ASTM D2573 for the United States. This test aims to determine the undrained shear strength of fine-grained soils, notably the clay.

The test instrument consists of four stainless steel vane blades, and all of them are connected to a vane shaft. The thickness of blades are kept smaller than 3mm to minimize the disturbance of soil during the insertion prior to test. The vane blades can be either rectangular in shape, or tapered at the ends.

After the device is penetrated into the soil underneath a borehole, rotation rate of 6 to 12 degree per minute is applied to the vane. Maximum torque required to rotate the vane is recorded throughout the process. The test may be terminated upon the occurrence of shear failure. The failure may take place around 2 to 5 minutes after the test begins.

Data from FVT is first converted into FVT strength, which will be then corrected based on the soil plasticity index to produce the undrained shear strength value of the soil. Overconsolidation ratio may be determined as well.