AIM:
To determine the undrained shear strength of the cohesive soil using vane shear.
THEORY:
The strength test more commonly used in a research laboratory today is the triaxial
compression test, first introduced in the U.S.A. by A. Casagrande and Karl Terzaghi in
1936 – 37. The soil specimen, cylindrical in shape, is subjected to direct stresses acting
in three mututally perpendicular directions. In the common solid cylindrical specimen
test, the major principal stress σ1 is applied in the vertical direction, and the other two
principal stresses σ2 and σ3 σ2 σ3) are applied in the horizontal direction by the fluid
pressure round the specimen
APPARATUS REQUIRED:
KNOWLEDGE OF EQUIPMENT
1) A constant rate of strain compression machine of which the following is a brief
description of one is in common use.
a) A loading frame in which the load is applied by a yoke acting through an elastic
dynamometer, more commonly called a proving ring which used to measure the load.
The frame is operated at a constant rate by a geared screw jack. It is preferable for the
machine to be motor driven, by a small electric motor.
b) A hydraulic pressure apparatus including an air compressor and water reservoir in
which air under pressure acting on the water raises it to the required pressure, together
with the necessary control valves and pressure dials.
2) A triaxial cell to take 3.8 cm dia and 7.6 cm long samples, in which the sample can
be subjected to an all round hydrostatic pressure, together with a vertical compression
load acting through a piston. The vertical load from the piston acts on a pressure cap.
The cell is usually designed with a nonferrous metal top and base connected by tension
rods and with walls formed of perspex.
Apparatus for preparation of the sample:
1) 3.8 cm (1.5 inch) internal diameter 12.5 cm (5 inches) long sample tubes.
2) Rubber ring.
3) An open ended cylindrical section former, 3.8 cm inside dia, fitted with a small
rubber tube in its side.
4) Stop clock.
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