OBJECTIVE
To find shear strength of a given soil specimen.
NEED AND SCOPE
The structural strength of soil is basically a problem of shear strength.
Vane shear test is a useful
method of measuring the shear strength of clay. It is a cheaper and quicker
method. The test can also be conducted in the laboratory. The laboratory vane
shear test for the measurement of shear strength of cohesive soils, is useful
for soils of low shear strength (less than 0.3 kg/cm2) for which
triaxial or unconfined tests can not be performed. The test gives the undrained
strength of the soil. The undisturbed and remoulded strength obtained are useful
for evaluating the sensitivity of soil.
PLANNING AND ORGANIZATION
EQUIPMENT
1.Vane shear apparatus.
2.Specimen.
3.Specimen container.
4.Callipers.
EXPERIMENTAL PROCEDURE
1.Prepare two or three specimens of the soil sample of dimensions of at least 37.5 mm diameter and 75 mm length in specimen.(L/D ratio 2 or 3).
2.Mount the specimen container with the specimen on the base of the vane shear apparatus. If the specimen container is closed at one end, it should be provided with a hole of about 1 mm diameter at the bottom.
3.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.
4.Rotate the vanes at an uniform rate say 0.1o/s by suitable operating the torque application handle until the specimen fails.
5.Note the final reading of the angle of twist.
6.Find the value of blade height in cm.
7.Find the value of blade width
in cm.
Calculations:
Observations:
Name of the project:
Soil description:
| S.No |
Initial Reading (Deg)
|
Final Reading (Deg.)
|
Difference (Deg.)
|
T=Spring Constant/180x Difference Kg-cm
|
 |
S=TxG Kg/cm2
|
Average 'S' Kg/cm2
|
Spring Constant Kg-cm
|
General
remarks:
This test is useful when the soil is soft and its water content is nearer to liquid limit.