The Vane Shear Test is a geotechnical testing method used to determine the in-situ shear strength of cohesive soils, such as clay. It is a quick and economical test, often performed directly in the field to assess the undrained shear strength of soft or saturated soils.
A shear vane is a device used to perform the test, typically consisting of four steel blades arranged in a cross pattern and welded to a central steel rod. The steel vane is pushed into the undisturbed soft clay soil and rotated by hand at a constant rate. The amount of torque necessary for rotation is measured and calculated the shear strength.
Apparatus:
The apparatus required to conduct the vane shear test are:
- Vane shear apparatus.
- Soil Specimen.
- Specimen container.
- Callipers.
Procedure:
Insertion of Vane: A four-bladed vane (usually cruciform in shape) is pushed into the soil at the desired depth.
Rotation of the Vane: The vane is rotated at a controlled rate. As it rotates, the soil around the vane resists the motion due to its shear strength.
Measurement of Torque: The torque required to rotate the vane is measured. This torque is directly related to the shear strength of the soil.
Observations:
Name of the project:
Soil description:
| S.No. | Initial Reading | Final Reading | Difference | Torque (T) | Shear strength (\( \tau \)) |
|---|---|---|---|---|---|
| 1. | |||||
| 2. | |||||
| 3. |
Calculation of Shear Strength:
The undrained shear strength (τ) of the soil can be calculated using the torque (T) and the dimensions of the vane (height and diameter). The relationship is given by the following formula:
\( \tau = \frac{T}{\pi D^2 H/2 + \pi D^3 /6} \)
Where:
- ( T ) = measured torque
- ( D ) = diameter of the vane
- ( H ) = height of the vane
Result of Vane Shear Test:
Shear strength of soil specimen = ________ kg/cm2.
Applications:
- Soft clay soils: Primarily used for soft to very soft clays where other methods may not be feasible.
- Undrained shear strength: Suitable for conditions where the soil is undrained (i.e., no drainage occurs during the test).
- Stability analysis: Useful in evaluating the stability of foundations, embankments, and slopes.
Advantages:
- Quick and easy to perform.
- Provides a direct measure of undrained shear strength in soft soils.
- Can be performed in the field with minimal disturbance.
Limitations:
- Less accurate for stiff clays or soils with a significant sand content.
- May not provide reliable results for layered or heterogeneous soils.
References:
- Bureau of Indian Standards. (1978). IS 4434. Code of Practice For In-Situ Vane Shear Test For Soiles. (1st rev.) Bureau of Indian Standards (BIS)
- Venkatramaiah. C. (2006). Geotechnical Engineering. New Age International Publication
- Chudley, R., & Greeno, R. (2016). Building Construction Handbook (11th ed.). Routledge.
- Shear strength of soil by vane shear Test. (2018, September 26). theconstructor.org. https://theconstructor.org/geotechnical/shear-strength-soil-vane-shear-test/3435/
