Constant Head Apparatus
BS 1377; EN 1997-2; ASTM D2434; AASHTO T215
This equipment is used for testing the permeability of
granular soils (sands and gravels).The specimen is
formed in a permeability cell and water is passed through
it from a constant level tank. Take-off points located
along the sides of the permeability cell are connected to
three manometer tubes mounted on a panel complete
with a metre scale. Water passing through the specimen
is collected and measured, either for a specific quantity
or over a period of time. The reduction of head is noted
from the variation of water level in the manometer tubes.
PERMEABILITY TEST
Falling Head Apparatus
Clays and silts are tested using the falling head
technique. Flow of water through the specimen is
observed by monitoring the rate of fall of water in the
tube. It is essential that soils of very low permeability are
sealed inside the cylinder to prevent seepage along the
sides of the specimen. Before testing, the specimen must be completely saturated with water as the presence of air will restrict the flow of water.