As Per IS 2720 (Part XBII)- 1966 BS 1377; EN DD ENV 1997-2; ASTM D2434; AASHTO T215
Clays and silts are tested using the 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. Three glass stand pipes a stand with nine glass tubes of 6mm,
10mm, 20mm, 25mm, 40mm, 50mm, 60mm, 70mm, 75mm, bore
tube is provided with over flow arrangement for constant head tests.
The remaining tubes are used for falling head test.