Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show. Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.

1. 1
Geotechnical Engineering–I [CE-221]
BSc Civil Engineering – 4th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/2016session-geotech-i
Lecture # 25
24-Apr-2018

2. 2
WATER FLOW THROUGH SOILS
To determine the quantity of flow, two parameters are needed
* k = hydraulic conductivity
* i = hydraulic gradient
Determination of ‘k’
1- Laboratory Testing  [constant head test & falling head test]
2- Field Testing  [constant/falling head tests, pump out tests, etc]
3- Empirical Equations
Determination of ‘i’
1- From the head loss and geometry
2- Flow Nets
(how permeable is the soil medium)
(how large is the driving head)
Today’s
discussion
A
h
kAikq 


L

3. 3
SUBSURFACE FLOW OF WATER
Aquifer: Soil or rock forming stratum with sufficient porosity and permeability
to store and transmit groundwater.
(e.g. sands, gravels, fractured rock)
Aquifer

4. 4
Aquiclude/ Aquifuge: An impermeable stratum, or a stratum having
extremely low permeability.
(e.g. clays, intact rock)
Aquifer
SUBSURFACE FLOW OF WATER

5. 5
Unconfined Aquifer (water table aquifer) are bound by the water table; i.e.,
they have no confining rock layers over the top of them.
Confined Aquifer: A water bearing layer confined between less pervious (or
impervious) layers.
SUBSURFACE FLOW OF WATER

6. 6
ARTESIAN FLOW
 Artesian springs/wells are wells that flow under their own pressure.
 These require a sloping permeable layer of rock (Aquifer) with a recharge
zone higher than the well.

7. 7
Determination of Hydraulic Conductivity
in the Field
1. Pumping wells with observation holes
2. Borehole test
3. Packer test
 Constant/ falling head type
 Mostly for rocks

8. 8
In-situ Permeability Test using Pumping
Wells
Initial WT
Observation Wells
Sand
(Pervious Layer)
Clay
(Impervious Layer)
Test Well
WT after
pumping
Pumping out water
(Rate of pumping, q
(m3/hr))
 Steady state: equilibrium
state when the inflow to
the well becomes equal
to the rate of pumping.
 Water level in the test
well + observation wells
becomes constant at
steady state condition.

9. 9
 Used to determine hydraulic conductivity (k) of soil in-situ.
 Water is pumped out at a constant rate from a test well that
has a perforated casing.
 Several observation wells at various radial distances are
made around the test well.
 Continuous observations of water level in the test well +
observation wells are made after the start of pumping, until
a steady state is reached.
 The steady state is established when the water level in the
test and observation wells becomes constant.
In-situ Permeability Test using Pumping
Wells

10. 10
In-situ Permeability Test
Pumping Well in an Unconfined Aquifer
)(
ln.
2
2
2
1
2
1
hh
r
r
q
k









q
If q, h1, h2, r1, r2 are
known , k can be
calculated

11. 11
In-situ Permeability Test
Pumping Well in a Confined Aquifer
)(
ln
2 21
2
1
hh
r
r
H
q
k









q
If q, h1, h2, r1, r2 are
known , k can be
calculated
Water entering into well

12. 12
Practice Problem #7
A layer of sand 6m thick underlies a 5m thick layer of clay
stratum and overlies a bed of shale. A pumping well, sunk to
the base of sand yielded 10x10-3 m3/sec. Observation wells
placed at 15m and 30m from the well indicated groundwater
levels 2.5m and 3m above the depressed water level in the test
well, respectively. Determine the permeability of soil.
Permeability in Unconfined Aquifer
)(
ln.
2
2
2
1
2
1
hh
r
r
q
k








 )(
ln
2 21
2
1
hh
r
r
H
q
k









Permeability in Confined Aquifer

13. 13
Practice Problem #8
A field pumping test is carried out to determine
average permeability of uniform soil deposit 30m
deep. Water table in the deposit is located at a depth
of 2m below ground surface. Steady state is reached
under a uniform pumping rate of 0.02 m3/sec. The
two observation wells located at distances of 20m
and 60m show elevations of water level at 2m and
0.5m below original water table respectively.
Determine the value of soil permeability.
Permeability in Unconfined Aquifer
)(
ln.
2
2
2
1
2
1
hh
r
r
q
k








 )(
ln
2 21
2
1
hh
r
r
H
q
k









Permeability in Confined Aquifer

14. 14
CONCLUDED
REFERENCE MATERIAL
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #7 & 8