Vane Shear Test

Vane shear test is used to determine the undrained shear strength of cohesive soils especially soft clay. This test is done in laboratory or in field directly on the ground. This test is carried out with equipment consisting of a rod with vanes mounted to it that is inserted into the ground and rotated. This test was introduce by L Carlson and AW Skempton in 1948. This test give accurate results for soils of low shear strength i.e, less than 0.3 kg/cm2.

Apparatus Required

1. Vane Shear Apparatus
2. Vernier Callipers
3. Soil Specimen Container

Vane Shear Apparatus

Procedure Of Vane Shear Test

1. Clean the vane shear apparatus and apply grease to the lead screw for better movement off handles.

2. Take the soil specimen in container which is generally 75 mm in height and 37.5 mm in diameter.

3. Level the soil surface on the top and mount the container on the base of vane shear test apparatus using screws provided.

4. Lower the vane gradually into the soil specimen until the top of vane is at a depth of 10 -20 mm below the top of soil specimen.

5. Note down the reading of the pointer on circular graduated scale which is initial reading.

6. Rotate the vane inside the soil specimen using torque applying handle at a rate of 0.1°/sec.

7. When the specimen fails, the strain indicator pointer will move backwards on the circular graduated scale and at the point stop the test and note down the final reading of pointer.

8. The difference between initial and final reading is nothing but the angle of torque.

9. Repeat the procedure on two more soil specimens and calculate the average shear strength value.

10. Measure the diameter and height of vane using vernier caliper.

11. Sensitivity of given sooil sample is determined by repeating the above test procedure on remoulded soil which is nothing but soil obtained after rapid stirring of vane in the above test.

Sensitivity (St) = Undisturbed shear strength/Remolded shear strength.

Advantages Of Vane Shear Test

• This test is flexible.
• Vane shear test is quick and easy.

Disadvantages Of Vane Shear Test

• It cannot be conducted on the fissured clay.
• This test is not suitable for clays which contain sand or silt laminations in it.