Vane shear test

Presentation on vane shear test

1. VANE SHEAR TEST

2. Purpose To find the undrained shear strength of soils ( e.g soft clays)

3. Drained and Undrained Conditions Drained Condition occurs when there is no change in pore water pressure due to external loading. the pore water can drain out of the soil easily, causing volumetric strains in the soil. Undrained condition occurs when the pore water is unable to drain out of the soil. the rate of loading is much quicker than the rate at which the pore water is able to drain out of the soil. The tendency of soil to change volume is suppressed

4. Apparatus Vertical steel rod having four thin stainless blades( vanes) fixed at its bottom (IS : 2720—1980 recommends H should be 2 D where H = height of the vane D = overall diameter) Recommended D = 2.5 mm length of rod = 60mm

5. Equipment 1Vane shear apparatus. 2.Specimen Size :D =37.5mm H = 75 mm (L/D ratio 2 or 3) 3.Specimen container. 4.Callipers

6. Experimental Procedure Prepare 2-3 specimens of soil sample Mount the specimen container with the specimen on the base of the vane shear apparatus Gently lower the shear vanes into the specimen to their full length without disturbing the soil specimen .The top of the vanes should be atleast 10 mm below the top of the specimen. Note the readings of the angle of twist. Rotate the vanes at an uniform rate say 0.1 o /s by suitable operating the torque application handle until the specimen fails. Note the final reading of the angle of twist.

7. Calculations Shear strength in N/ cm2 Where T = Torque in N- cm D= overall diameter of vane in cm H = height of vane in cm T is given by

8. Sensitivity of soils Sensitivity of soils can also be determine by vane shear test Procedure: After initial test, the vane is rotated rapidly through several revolutions such that soil becomes remoulded . The test is repeated on remoulded soil and the shear strength in moulded state is determine

9. General Remarks This test is useful when the soil is soft and its water content is nearer to liquid limit. Ideally suited for determination of in-situ undrained shear strength of non- fissured fully saturated clay

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