Geotechnical Engineering, Civil Engg, Bhimaji Dashrath Kanawade

1. Experiment No: 07 (B) Date:
DETERMINATION OF COEFFICIENT OF PERMEABILITY OF SOIL BY FALLING HEAD
TEST
Object & scope:
To determine the coefficient of permeability of soil in the laboratory by falling head test using
permeameter.
Reference:
IS: 2720 (Part 17)-1986
Theory:
The permeability of a given soil is measured in terms of coefficient of permeability ‘k’ which is defined
as the velocity of flow or discharge through a soil of unit cross sectional area under a unit hydraulic
gradient and it is expressed in cm/second or m/day.
Equipments:
1) Permeameter mould including drainage base and drainage cap
2) Glass stand pipe for falling head (variable head) test arrangement
3) Compaction rammer
4) Stopwatch
5) Meter scale
6) Straight edge or trimming knife
7) Containers for water content determination
Procedure:
1) Prepare the remoulded soil specimen in the permeameter & saturate it.
2) Keep the permeameter mould assembly in the bottom tank with water upon its outlet.
3) Connect the water inlet nozzle of the mould to the stand pipe filled with water. Permit water to flow
for some time till steady state of flow is reached.
4) With the help of stop watch note the time interval required for water level in stand pipe to fall from
some convenient initial value.
5) Repeat step (4) at least twice and determine time for the water level in stand pipe to drop from the
same initial head to the same final value.
Observations:
1) Area of Stand pipe (a) cm2 =
2) Cross sectional area of soil sample (A) cm2 =
3) Length of the soil sample = (L) cm

2. Observation Table:
Sr.
No.
Description Sample- 1 Sample- 2 Sample- 3
1 Initial head (h1) cm
2 Final head (h2) cm
3 Time Interval (t) sec
4 Coefficient of permeability (k) m/sec
5 Average kavg.
Calculations:
Coefficient of permeability k = 2.3 × [(
a×L
A×t
) × log (
h1
h2
)]
Result:
Coefficient of permeability of soil = k =
Uses of permeability:
1) Design of earthen dams
2) Estimation of uplift pressure on hydraulic structure
3) Yield of wells
4) Seepage of water through hydraulic structure.
5) De-watering and drainage of excavations, back fills and sub-grades.
6) Computing losses from canals.

3. Fig. Variable Head Permeability test