The Electric Vane Sheer Test (VST) is used to estimate the undrained shear strength of fully saturated clays, without disturbance.
The VST equipment consists of a four-blade, stainless steel vane attached to a steel rod that will be pushed into the ground.
Probedrill uses the GeoMil GVT 100 Vane Shear which comes with three rectangular vane types:
- 70mm x 35mm;
- 100mm x 50mm; and
- 150mm x 75mm vanes.
- Typically, a rotation speed of 0.1 degrees/second is used, however speeds of up to 20 degrees/second are available.
The rotation rods are protected against friction and buckling by CPT casing rods and a protection shoe is used to encase the vane. This allows it to be pushed through harder layers. In addition, the weight (and any remaining friction) of the inner rods is measured using a slip coupling between the rods and vane. This measured value is later removed during post processing, giving a true and accurate shear reading.