Permeability Test for Fine-Grained and Granular Soils (Falling-Head Method) - Soil Properties: Testing, Measurement, and Evaluation - page 272

Figure 19-1 Schematic of the Falling-Head Permeability Setup [1]

After obtaining these preliminary data, permeability tests can be
performed. The general test procedure does not differ a great deal from
the constant-head method. The soil specimen is first saturated with wa-
ter. Water is then allowed to move through the specimen under a falling-
head condition (rather than a stable-head condition), while the time
required for a certain quantity of water to pass through the specimen
is measured and recorded. Using these data together with others
described previously, one can determine the coefficient of permeability.
A total of three permeability tests should be performed, one for
each test specimen with different dry densities. Each specimen's void
ratio can be computed using the specific gravity of the soil and the cor-
responding dry density. A curve of permeability k versus void ratio
e can then be plotted on semilogarithmic paper, with void ratio on
the arithmetic scale and permeability on the logarithmic scale.
The actual step-by-step procedure is as follows [1]:

(1) Weigh the permeameter (mold) with base plate and gasket
attached. Measure the inside diameter of the permeameter (mold).
Note that the area a of the standpipe must be evaluated. Since the
burette is graduated in cubic centimeters, measuring the distance
between graduations will yield a as a simple, direct computation. Take
a small portion of the soil sample for water content determination.

(2) Place the air-dried soil sample into the permeameter (mold) and
compact it to a desirable density. Weigh the permeameter (mold)