LABORATORY VANE SHEAR TEST APPARATUS
VANE SHEAR TEST
Laboratory Vane Shear Test
Field Vane Shear Test
VANE SHEAR TEST
As per IS :2720-XXX-1980
INTRODUCTION
Vane shear test is a simple and quick test, which can
be performed either in laboratory or in the field.
It is a cheaper and quicker method.
The laboratory vane shear test for the measurement
of shear strength of cohesive soils, is useful for soils of
low shear strength (less than 0.3 kg/cm2) for which
triaxial or unconfined tests can not be performed.
The test gives the undrained strength of the soil. The
undisturbed and remoulded strength obtained are
useful for evaluating the sensitivity of soil.
A vane shear testing equipment, consist of four thin
stainless steel rectangular plates, called vanes,
welded orthogonally to a high tensile steel rod.
A torque measuring arrangement, such as a
calibrated torsion springs is attached to the rod,
which is rotated by some arrangement from the top.
APPARATUS
Vane shear apparatus.
Specimen.
Specimen container.
Weighing balance.
PROCEDURE OF LABORATORY VANE SHEAR
TEST
Prepare two or three specimens of the soil sample of
dimensions of at least 37.5 mm diameter and 75 mm length in
specimen.(L/D ratio 2 or 3).
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.
Gently lower the shear vanes 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.
Note the readings of the angle of twist.
Rotate the vanes at an uniform rate say 0.1o/s by
suitable operating the torque application handle until
the specimen fails.
Note the final reading of the angle of twist.
Find the value of blade height in cm.
Find the value of blade width in cm.
OBSERVATIONS
CALCULATION
Shear strength S= T /[πD2 (H1/2+ D/6)]
Where T =Torque applied
D = Diameter of vane
H1= Height of vane
PROCEDURE OF FIELD VANE SHEAR TEST
Fig: steps for performing the test
Test procedure
Bore Hole
Spring
Balance
Vane
Drill Rod
15 cm
PROCEDURE
Before the execution of a vane test it shall be controlled that the
vane blades are undamaged. The vane size should be chosen with
respect to the actual soil in order that the maximum value at
failure will occur in the upper 2/3 of the total range of the device.
Before all tests in boreholes loose soil at the base of the hole must
be removed and it shall be assured that an excess pore pressure
exists in the borehole.
The vane shall be pressed or hammered gently into the soil
without rotation, until the base of the blades is two blade heights
below the base of the borehole or the soil surface. However, a
depth of 0.2 m below the base of the borehole is normally used for
vane numbers V4, V5, HVA and HVB, while depths of 0.3 m and
0.6 m are used for vane number V7.5 and V9.2, respectively.
Normally the test is carried out immediately after the vane has
been installed.
The turn of the handle shall be performed in a steady manner
as slowly as possible. The maximum speed of rotation should be
1 rpm (revolution per minute). The size of the vane and the
measured maximum torque must be written in a test report
together with the depth below soil surface to the base of the
blades.
After each test in undisturbed soil the vane shall be given 10
revolutions and the test is repeated.
If less than 10 revolutions are applied this must be stated in
the test report. The measured maximum torque must also be
written in the test report.
When vane numbers V4 and V5 are used the procedure mentioned
above (test in undisturbed and remoulded soil) may be repeated 0.2
m below the first test. This is called a double test. Tests and double
tests in boreholes are normally carried out per 1.0 m depth. Tests
with vane numbers HVA and HVB are normally carried out per 0.2
m depth.
During the execution of the test the following incidents shall be
observed:
a. A large variation of the resistance e.g. because of stones. The
observation shall be reported, but no measurement is written in the
test report.
b. Uneven resistance e.g. because of sand grains. The observation
shall be reported and the measurement is written in the test report.
Deep Vane Equipment
Field Vane Showing Failure Surface
MERITS
The test is simple and quick
It is ideally suited for determination of the in-situ
undrained shear strength of non fissured, fully
saturated clay
The test can be conveniently used to determine the
sensitivity of the soil
DEMERITS
The test cannot be conducted on the fissured clay
or the clay containing silt or sand laminations
The test does not give accurate results when the
failure envelope is not horizontal
Thank You