De=effective grain size, diameter of sphere for which ratio of its volume to its surface area is same as similar ratio for a given assemblage of soil particles.

In 1892, Allen Hazen concluded that linear dependency between velocity of flow and hydraulic gradient exists if effective size of soil did not exceed 3mm.

The constant head test apparatus consists of three tubes: inlet tube, overflow tube and outlet tube.

From Darcy?s law, V=ki
And V_s=k_pi
? V_s/V=k_p/k=1/n
? k_p=k/n.

The remoulded specimen can be prepared eir by static compaction, or b dynamic compaction, at desired density.

Based on his experiments, Loudon found out value of a and b s 1.365 and 1.515 for permeability of 10�c.

There are two possible cases of flow, one is parallel to bedding plane and anor is perpendicular to plane.

Consider a capillary tube of length L and radius R.
dq=(2?rdr)v
substituting for velocity,
\(dq=(2?rdr)*\frac{h?_w}{4?L}(R^2-r^2)\)
\( ? dq=\frac{h?_w}{4?L}(R^2-r^2)2?rdr.\)

In Jodhpur permeameter, both falling head and constant head test can be performed on remolded as well as undisturbed specimens.

Given,
h=0.1m
?=8.9*10^-3 dynes-s/cm²
?_w=1 g/cm³
L= 10m
d= 20cm.
Since \(v = \frac{h?_w}{4?L}(R^2-r^2)\)
\(v = \frac{10*1}{4*8.9*10^{-3}*1000}(10^2-0^2)\)
v=28 cm/s.