3 What factors might inflate the vane shear test results Tha

3. What factors might inflate the vane shear test results. That is what might make the test results higher than the actual strength of the soil. Hint: think about how the vane is constructed and what might make the test results higher than the actual soil

Solution

The strength of the soil is usually considered as a problem for shear strength. Vane shear test is a laboratory test, usually used to calculate the shear strength of the soil.

Shear strength of the soil is determined by,

where S = shear strength of soil is in kg/cm2

T= Torque in cm kg

D= Overall diameter of vane in cm

H = spring constant/180⁰ x difference in degrees

From the above expression, we can formulate that the shear strength of the soil depends on the diameter of the vanes. If the diameter of vane is more the shear strength will be less, similarly, if the diameter of vane is less the shear strength will be more.

Also, the vane shear strength works on the principle that a shear force is applied or soil is applied to shear on a given area, but in actual case, compression force is acted upon the soil which results in shearing of soil. Hence it can be concluded that the shear strength of the soil will be more in vane shear strength compared to actual value on site.