Civil Engineering Reference
In-Depth Information
Figure 7.2
Permeameter tests.
in laboratory tests in a constant head permeameter, for soil with relatively large per-
meability, or in a falling head permeameter, for soils with relatively low permeability;
these are illustrated in Fig. 7.2. In both cases water flows through a soil sample and
the rates of flow and the hydraulic gradients are measured.
(a) Constant head permeability tests
In the constant head test illustrated in Fig. 7.2(a) water from a constant head tank flows
through the sample in a cylinder and is collected in a measuring jar. Two standpipes
measure the pore pressure and potential (see Sec. 14.3) at two points as shown. The
flow is steady state and, from the observations,
=
Q
V
(7.5)
A
t
=
P
i
(7.6)
s
and hence a value for
k
can be determined. In practice it is best to vary the rate
of flow in stages and plot
V
against
i
; in this way you can verify Darcy's law and
evaluate
k
.
