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