The Insitu Vane Shear Test gives the in place shearing resistance of soft, saturated clays which are sensitive and are susceptible to sampling disturbances. The test give undrained shear strength of soil, along a cylindrical surface without change in volume or soil structure.
The test consists of pushing a vane with four blades into soil and rotating it till the cylindrical surface in soil fails in shear. The torque or turning moment required to cause this failure is measured on a Torque Meter.
The maximum moment of the total shear mobilized about the axis of rotation is equal to the applied torque. The unit shear resistance of the cylindrical surface can thus be computed.
IS:4434 specifies two methods, namely testing at the bottom of a bore hole and testing by direct penetration from the ground surface. HS 34.140 is used in bore holes and HS34.145 for direct penetration from ground surface.
The unit incorporates a two speed geared drive assembly and is provided with two handles for ease of operation. The essential features are a frame to which is mounted a two column structure. The cross head carries the winch mechanism with a pinion driving a long travel geared rack.
The apparatus is suitable for testing at the bottom of a bore hole.
This consists of Torque Applicator mounted on a detachable stand. By applying torque, deformation of torque ring can be read on a dial gauge. From the calibration curve, deformation can be converted into torque in Kg. Cm.
Known, as Norwegian Vane Borer, this is simple and rugged in design and is meant for penetration boring. It can be used without casing down to 30 meters depth. The lower part of the apparatus is forced down, with the vane withdrawn into a protection shoe. At the desired depth the vane is unlocked and pushed into the undisturbed soil and rotated at a constant rate of strain of 60 /min or 0.10 per second.
The maximum torque is recorded on the torque meter.
The equipment comprises the following :-