Falling head permeability test

The constant head test is suited only to soils of permeability normally within the range 10 m/s to 10 m/s. For soils of lower permeability, the falling head test is applicable... 

An initial assessment of the magnitude and variability of the in situ permeability can be obtained from tests carried out in boreholes as the hole is advanced. By artificially raising the level of water in the borehole (falling head test) above that in the surrounding ground, the flow rate from the borehole can be measured. However, in very permeable soils, it may not be possible to raise the level of water in the borehole. Conversely, the water level in the borehole... 

In rising or falling head tests in which the piezometric head varies with time, the permeability is determined from the expression ... 

The apparatus, consisting of two interconnected vertical cylinders of the same diameter (minimally 50 mm), is capable of achieving water heads of at least 250 mm. Some schemes of falling head permeability test according to ISO standard 11058... 

Figure 8.9 Schemes of falling head permeability test.

---