Permeability Test for Granular Soils (Constant-Head Method) - Soil Properties: Testing, Measurement, and Evaluation - page 258

v = Q/At ), directly proportional to hydraulic gradient, i (where
i = h/L ). When departures from the linear relation become apparent,
indicating the initiation of turbulent flow conditions, 1-cm intervals
of head may be used to carry the test run sufficiently along in the
region of turbulent flow to define this region if it is significant for
field conditions.

Note 4 —Much lower values of hydraulic gradient, h/L , are
required than generally recognized, in order to ensure laminar
flow conditions. The following values are suggested: loose com-
pactness ratings, h/L from 0.2 to 0.3, and dense compactness
ratings, h/L from 0.3 to 0.5, the lower values of h/L applying
to coarser soils and the higher values to finer soils.

(3) At the completion of the permeability test, drain the specimen
and inspect it to establish whether it was essentially homogeneous
and isotropic in character. Any light and dark alternating horizon-
tal streaks or layers are evidence of segregation of fines.

Data collected during this test consist of the following:

DATA

Diameter of specimen (inside diameter of permeameter), D (cm)
Length between manometer outlets, L (cm)
Height, H 1 (see “Preparation of Specimens” and Figure 18-1) (cm)
Height, H 2 (see “Preparation of Specimens” and Figure 18-1) (cm)
For water content determination:
Mass of air-dried soil plus can (g)
Mass of oven-dried soil plus can (g)
Mass of can (g)
Mass of air-dried soil before compaction, M 1 (g)
Mass of unused remaining portion of air-dried soil left in pan after
compaction, M 2 (g)
Manometer readings, h 1 and h 2 (cm)
Quantity of water discharged through soil specimen, Q (cm 3 )
Total time of discharge, t (s)
Water temperature, T (°C)

CALCULATIONS [A] Unit Weight Determination

By using the preceding data, values of the unit weight of the soil speci-
men (air dried), water content of the air-dried soil, dry unit weight of the
soil specimen, and void ratio e can be computed. The void ratio is the ratio
of volume of voids to volume of solids; the other (computed) parameters
listed have been covered in detail in previous chapters.