Lab Vane Shear Test

1. objective

The laboratory vane shear test for the measurement of shear strength of cohesive soils, is useful for soils of low shear strength of less than about 0.5 kgf/cm2). The test gives the undrained strength of the soil and the undisturbed and remoulded strength obtained are used for evaluating the sensitivity of soil.

2. Apparatus required





3. reference

IS 2720(Part 30):1980 Methods of test for soils: Laboratory vane shear test (first revision). Reaffirmed- Dec 2016.

4. procedure

  1. Prepare two or three specimens of the soil sample of dimensions of at least 37.5 mm diameter and 75 mm long specimen.
  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 0.10/s by suitably operating the torque applicator handle until the specimen fails.
  5. Note the final reading of the torque indicator. Torque readings and the corresponding strain readings may also be noted at desired intervals of time as the test proceeds.
  6. Just after the determination of the maximum torque rotate the vane rapidly through a minimum of 10 revolutions. The remoulded strength should then be determined within 1 minute after completion of the revolution.

5. observation and recording

<
S.No. Initial Reading(Deg) Final Reading(Deg.) Difference(Deg.) T=Spring Constant/180x Difference (Kg-cm) G = 1/π(D2h/2 + D3/6) S=TxG (Kg/cm2) Average 'S' (Kg/cm2) Spring Constant (Kg-cm)
01
02
03
04
05

Table 1 : Recordings during Lab Vane Shear Test

6. calculation

Torque, T = Ø * K/180

Where,
T = Torque applied in cm kgf
Ø = Difference of angle (angle of torque)
K = Spring factor

G = 1/{π*[(d2h/2) + (d3/6)]}

Where,
d = diameter of vane (cm)
h = height of the vane (cm)

Shear Strength, S = T * G

or

S = (3/19)*T

Where,
S = Shear Strength in kgf/cm2
T = Torque applied in cm kgf

7. General Remarks

  • This test is useful when the soil is soft and its water content is nearer to liquid limit.
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