This preview shows page 1. Sign up to view the full content.
30
Q3.2 Solution
Diagram of falling head permeameter: see main text Figure 3.10
The derivation of the equation follows the main text Section 3.4.2.
At the start of the test (time t=0), the water level in the upper (smallbore) tube is at a height
h
0
above the permeameter outlet. After a general time t, the water level in the upper tube has
fallen to a general height h above the permeameter outlet. Applying Darcy's Law at a general
time t to the soil sample in the large tube,
q = Aki = A
1
kh/L
(main text Equation 3.8)
In the smallbore tube, the flowrate is given by the crosssectional area multiplied by the
velocity
q
=
A
2
v
but the velocity v = dh/dt so
q
=

A
2
.dh/dt
(main text Equation 3.9)
(the negative sign is needed because v has been taken as positive downward, while h is
measured as positive upward)
This is the end of the preview. Sign up
to
access the rest of the document.
 Fall '11
 StuartChalk
 Analytical Chemistry

Click to edit the document details