The document summarizes a laboratory vane shear test conducted to determine the undrained shear strength of a cohesive soil sample composed of 70% bentonite and 30% kaolinite. Two soil specimens were tested to obtain the undrained shear strength in both the undisturbed and remolded conditions. The vane shear apparatus and testing procedures are described. Test results including moisture content, bulk density, dry density, degree of saturation, and undrained shear strength are presented in a data table. The assumptions and applications of the vane shear test are discussed.

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Department of Civil Engineering, IIT Delhi
Submitted By:
Abhinav Kumar
Soil Engineering Lab
REPORT TITLE (08)
Laboratory Vane Shear
Test
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Objective: Determination of undrained shear strength of cohesive soil using lab vane shear test.
Apparatus:
1. Laboratory vane shear apparatus- The vane shall
consist of four blades each fixed at 90° to
the adjacent blades. The width of vane, from edge
of one vane to edge of another vane, is 12±0.15
mm. The height of vane is 24±0.25 mm. The
thickness of vane is 0.5±0.05 mm. The vane should
not deform under the maximum torque for which it
is designed. The penetrating edge of the vane
blades shall be sharpened having an included angle
of 90°. The vane blades shall be welded together
suitably to a central rod, the maximum diameter of
which should preferably not exceed 2.5 mm in the
portion of the rod which goes into the specimen
during the test. The height of rod, above the vanes,
is 60mm. The vane should be properly treated to
prevent rusting and corrosion.
2. Balance- sensitive to 0.01 g.
3. Oven- thermostatically controlled with interior of
non-corroding material to maintain the
temperature between 105 and 110°C.
4. Wash Bottle or Beaker- containing distilled water.
5. Containers - air-tight and non-corrodible for
determination of moisture content.
6. Soil Sample - A sample weighing about 300 g was
taken from the thoroughly mixed portion of material (70% Bentonite : 30% Kaolinite) passing 425-
micron IS Sieve [see IS : 460 (Part 1)-1978] obtained in accordance with IS : 2720 (Part 1)-1983.
Bentonite Kaolinite 70% Bentonite: 30% Kaolinite

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Testing methods and Procedures:
1. 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). This test gives the undrained strength
of the soil, in undisturbed as well as remoulded conditions both.
Vane shear test is a cheaper and quicker method of measuring the
shear strength of clay, as compared to very elaborate tri-axial shear
test or direct shear test.
2. Two specimens of the soil sample of dimensions of at least 30.0
mm diameter and 75 mm long specimen were prepared.
3. The specimen container with the specimen on the base of the
vane shear apparatus was mounted and it was securely fixed to the
base. If the specimen container is closed at one end, it should be
provided with a hole of about 1 mm diameter at the bottom.
4. Gently the shear vanes were lowered into the specimen to their
full length without disturbing the soil specimen. The top of the
vanes should be at least 10 mm below the top of the specimen. The
readings of the angle of twist were noted.
5. The vanes were rotated at a uniform rate say 0.1°/s by suitably
operating the torque applicator handle until the specimen fails.
6. The final reading of the torque indicator was noted.
7. 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.
Calculations:
For vane testing instruments that do not read the torque directly, a calibration curve to convert the
readings to cm kgf of torque was used. These calibration curves shall be checked periodically.
OR
Calculate the shear strength of the soil using the following formula:
S = (3/19) T
where,
S = shear strength in kgf/cm2
, and
T = Torque in cm-kgf.
• Spring No- 04
• Type of Soil- Remoulded
• Specific Gravity (G)= 2.64 (Assuming)
• Calibration- Using Calibration Curve.
• Rate of Testing- 0.1°/s

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Data Table
SAMPLE 1 SAMPLE 2
Mould Specifications I II III Avg I II III Avg
Initial Diameter (Do) mm 31.95 31.80 32.02 31.92 32.08 32.13 32.27 32.16
Initial Length (Lo) mm 77.13 77.16 76.96 77.08 75.08 76.06 75.97 75.94
Initial Volume (cm3
) 61.681 61.686
Weight of Tube (g) 30.93 28.48
Wt. of Tube + Soil specimen (g) 137.36 127.72
Wt. of Specimen (g) 106.43 99.24
MOISTURE CONTENT
Container No. (15) (B1/3)
Wt. of Container (g) 12.09 17.28
Wt. of Cont. + Wet Soil (g) 23.11 29.40
Wt. of Cont. + Dry Soil (g) 19.62 24.46
Wt. of Water (g) 3.49 4.94
Wt. of Dry Soil (g) 7.53 7.18
Water Content (%) 46.35 68.80
Bulk Density (g/cm3
) 1.725 1.608
Dry Density (g/cm3
) 1.179 0.953
Degree of Saturation (%) 98.76 99.98
TORQUE READINGS
Initial Reading 43 47
Final Reading 180 105
Difference (Δθ) 137 58
Undrained Shear Strength as per
Calibration Curve
[ S = 13.15 + 6.47*Δθ ] (lbs/ft2
)
899.54 388.41
Undrained Shear Strength in
N/mm2
0.04307 0.01859
Discussion:
1. The formula for shear strength is based on following assumptions:
● Shearing Strength in the Horizontal and Vertical directions are the same.
● At the peak value, Shear Strength is equally mobilized at the end surface as well as at the center,
● The shear surface is cylindrical and has a diameter equal to the diameter of the vane.
2. The test gives the undrained strength of the soil. The undisturbed and remolded strength
obtained are also useful for evaluating the sensitivity of soil. The data acquired from vane shear
test can be used to determine: Undrained shear strength, Evaluate rapid loading strength for total

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stress analysis, Sensitivity of soil to disturbance, Analysis of stability problems with embankment
on soft ground.
3. With increase in water content undrained shear strength decreases for given soil sample.
4. It is a quick test so it can be assumed as an undrained test.
References:
1. IS: 2720 (Part XXX)-1980; Methods of test for soils: Laboratory vane shear test (first revision).
Reaffirmed-Dec 2016.
2. IS: 2-1960
3. IS: 460 (Part 1)-1978
4. IS: 2720 (Part 1)-1983