Working Instructions
General Procedure
1. Connect required vane and extension rods to the inspection vane instrumen
WHILE SCREWING VANE OR RODS TO INSTRUMENT, HOLD ONTO LOWER PART
of the instrument.
2. Push vane into the ground to the required position.
MAKE NO TWISTING MOTION TO VANE DURING PENETRATION.
3. Make sure that the graduated scale is set to 0 position.
4. Tum handle clockwise.
TURN AS SLOWLY AS POSSIBLE WITH CONSTANT SPEED.
5. When the lower part moves at same rate as upper part (4) around or even falls
back, failure has occurred and maximum shear strength has been attained in the
clay at the vane.
6. Holding handle firmly, allow it to return to zero-position.
DO NOT ALLOW THE HANDLE TO SPRING BACK as damage to mechanism
could occur.
7. Note the reading on the graduated scale.
DO NOT TOUCH OR IN ANY WAY DISTURB THE POSITION OF THE GRADUATED
RING UNTIL THE READING IS TAKEN.
8. Record the reading together with position of hole and depth.
9. Tum the graduated scale counter-clockwise back to 0 position.
10. To determine the remolded shear strength, the following procedure is used: Tum
the vane quickly at least 25 revolutions. Zero the scale and take at least two
measurements by turning the instrument as slowly as possible. The minimum value
is considered the correct one.
11. Push the vane down to next position. If necessary add on another extension rod.
12. Repeat the above measurement procedure (3-10).
13. When the last reading is taken pull the vane up. If the clay is comparatively soft, this
can be done by hand, gripping the handle. In harder clays, some mechanical device
might be necessary. It is then advisable to remove the instrument and pull the rods
directly.
Special Procedure
When measuring the shear strength at greater depths, friction between the clay and
the extension rods can be appreciable and must be taken into consideration.
To measure this friction, extension rods and a vane-shaft without vane (dummy) are
pushed into the ground to the depths required for shear force measurements. Friction
is then measured in the same way as when using vanes (above 3-9). The friction-value
obtained is deducted from the measured shear strength to determine the actual shear
strength.
To penetrate through firm layers, a preboring using a rod with the same diameter as the
vane may be helpful.
