Standard Method of Test for
Field Vane Shear Test in Cohesive Soil
AASHTO Designation:T 223-96 (2004)
1.1.This method covers the field vane test in soft, saturated, cohesive soils. Knowledge of the nature of the soil in which each vane test is to be
made is necessary for assessment of the applicability and interpretation of the test.
1.2.The values stated in SI units are to be regarded as the standard.
2.SUMMARY OF METHOD
2.1.The vane shear test basically consists of placing a four-bladed vane in the undisturbed soil and rotating it from the surface to determine the torsional force
required to cause a cylindrical surface to be sheared by the vane; this force is then converted to a unit shearing resistance of the cylindrical surface.
It is of basic importance that the friction of the vane rod and instrument be accounted for; otherwise, the friction would be improperly recorded as soil strength.
Friction measurements under no-load conditions (such as the use of a blank stem in place of the vanes, or a vane that allows some free rotation of the rod prior to
loading) are satisfactory only provided that the torque is applied by a balanced moment that does not result in a side thrust.
As torsional forces become greater during a test, a side thrust in the instrument will result in an increase in friction that is not accounted for by initial no-load readings. Instruments involving side thrust are not recommended.
The vane rod may be of sufficient rigidity that it does not twist under full-load conditions;
otherwise a correction must be made for plotting torque-rotation curves.
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