Theory
The property which enables soil to maintain equilibrium on a sloping surface is known as shear strength of soil vane shear strength of soil vane shear test is a quick test used either on the laboratory as in the field to determine the understand shear strength of cohesive.
Item required
1. Torsion wheel
2. Shear vane
3. Torque rod etc.
Procedure
The shear vane consist of four blades called vane each fixed at 900 to the adjacent blades. The vane is designed in such a way that it causes little revolving and disturbance as possible to the soil. The vane blades were welded together to a central steel rod. The vane was rotated after fixing. It is undisturbed soil at uniform speed of 0.1 degree / speed by suitability operating the torque handle limit the specimen fails the vane rotates the soil shears along the cylindrical surface. The twisting moment is indicated by the angle of twist.
Diagram
Observation
The shear strength of soil is calculated by using the following formula.
S = T / T ( d2 h / 2 + d3 / 6 )
Where ,
S = shearing strength in kg/cm2 | h = height of vane in cm equation as per I.S. recommendation reduced to S = 0.2767 |
T = applied torque in cm.kg | |
d = over all dia. of vane in cm |
Observation table
SAMPLE NO. | STIFFNESS (kg/cm2) | ANGLE OF ROTATION (degree) | TORQUE cm.kg | SHEAR STRENGHT kg/cm2 |
01 | 6 | 380 | 0.407 | 0.0747 |
02 | 7.5 | 360 | 0.476 | 0.0876 |
Calculation
1. K = stiffness / π1
K = 6 / 3.19
= 1.90
T = K / 180 X α0
= 1.90 / 1.80 X 380
= 0.407
S = T / π ( d2 h / 2 + d3 / 8 )
= 0.0797 kg/cm2
2. K = stiffness / π
= 7.5 / 3.14
= 2.38
T = 2.38 / 180 X 360
T = 0.476
S = T / π ( d2 h / 2 + d3 / 6 )
S = 0.0876 kg/cm2
Conclusion
The soft clay have unconfined compressive strength less than 1 kg/cm2
Result
The shear strength of soil sample
No. 1 = 0.0747 kg/cm2
No. 2 = 0.0876 kg/cm2
