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 # 26
24-Apr-2018

2. 2
Equivalent Hydraulic Conductivity of Stratified Soils
Total flow
Permeability Parallel to Stratification
 Velocity of flow ‘v’
 Hydraulic gradient ‘i’
nHn
HHHH
Hik
HikHikHikHik



332211
nHn
HHH
Hik
HikHikHikq



332211
H
HkHkHkHk
k nHnHHH
H


332211
→ sum of flows though each layer
→ same for each layer
→ different for all layers
Hikq H 
Taking third dimension (i.e. into the plane of paper) as unity
Avq  )1( Hvq 

3. 3
Permeability Perpendicular to Stratification
 Velocity of flow ‘v’ and discharge ‘q’
 Hydraulic gradient ‘i’ and head loss ‘h’
nhhhhh  321
ikv v 
H
h
i 
Vn
n
VVVV k
Hv
k
Hv
k
Hv
k
Hv
k
Hv 









3
3
2
2
1
1
)1(332211  nn HiHiHiHih 
Also,
1
1
vk
v
i 
2
2
vk
v
i 
3
3
vk
v
i 
Replacing in eq. (1)
Vn
n
VVV
V
k
H
k
H
k
H
k
H
H
k



3
3
2
2
1
1
kv = average permeability perpendicular to
stratification
→ same through each layer
→ different through each layer
Equivalent Hydraulic Conductivity of Stratified Soils

4. 4
Practice Problem #4
On close investigation of a sample it was found to
be in three layers 20mm, 60mm, and 40mm. The
permeability of these layers are 3x10-3mm/sec,
5x10-4mm/sec, and 17x10-4mm/sec respectively.
Find kH and kV, and the ratio kH/kV.
H
HkHkHkHk
k nHnHHH
H


332211
Vn
n
VVV
V
k
H
k
H
k
H
k
H
H
k



3
3
2
2
1
1

5. 5
Practice Problem #5
H
HkHkHkHk
k nHnHHH
H


332211
Vn
n
VVV
V
k
H
k
H
k
H
k
H
H
k



3
3
2
2
1
1

6. 6
Practice Problem #5

7. 7
Practice Problem #6

8. 8
Practice Problem #6

9. 9
SIGNIFICANCE OF SEEPAGE STUDIES
Failure of Teton Dam
Newly completed Teton Dam as it appeared in mid May 1976, as the
reservoir was filling at the rate of 3 feet per day.
The rate of filling is usually limited to no more than 1 foot per day.
Mid May 1976
Newly completed Teton Dam

10. 10
TETON DAM FAILURE
Leakage was initially noted around 7:00 AM on Saturday June 5, 1976. This
view shows a dozer being sent down to fill in the hole at elevation 5200
around 10:45 AM.
June 5, 1976
10:45 am
Idaho, USA

11. 11
TETON DAM FAILURE
The dozer is lost in the expanding hole, around 11:20 AM on June 5th.
Note turbid nature of outflow along the abutment.
June 5, 1976
11:20 am
Idaho, USA

12. 12
TETON DAM FAILURE
Rapidly deteriorating situation as it appeared around 11:30 AM. A massive
hole has developed in the downstream face of the embankment and is
migrating upward.
June 5, 1976
11:30 am
Idaho, USA

13. 13
TETON DAM FAILURE
The hole continues to enlarge and rise toward the crest of the right abutment.
This is about 11:50 AM.
June 5, 1976
11:50 am
Idaho, USA

14. 14
TETON DAM FAILURE
Dam crest beginning to breach at 11:55 AM on Saturday June 5, 1976. Note
increasing discharge.
June 5, 1976
11:55 am
Idaho, USA

15. 15
TETON DAM FAILURE
Maximum flood discharge emanating from gap in dam’s right abutment, just after noon
on June 5th , 1976.
June 5, 1976
After noon
Idaho, USA

16. 16
TETON DAM FAILURE
Present day situation
Idaho, USA

17. 17
OROVILLE DAM
 The lake level is controlled using the main
spillway gate, which releases water down the
concrete spillway to get to the river below.
 The emergency spillway, which has a 30 ft
(9 m) high concrete wall at the top of a hill, is
unused.
Oriville Dam – Normal Operations
California, USA

18. 18
OROVILLE DAM
 The lake level is controlled using the main
spillway gate, which releases water down the
concrete spillway to get to the river below.
 The emergency spillway, which has a 30 ft
(9 m) high concrete wall at the top of a hill, is
unused.
Despite concerns that the emergency spillway
is vulnerable to erosion, a $100 million
request by community groups to upgrade it to
a concrete-lined auxiliary spillway is rejected
by the federal regulators
Oriville Dam – Normal Operations 2005: Upgrade proposal rejected
California, USA

19. 19
OROVILLE DAM FAILURE
Craters appear in the main spillway. To avoid
increasing the damage to the spillway, water
releases are slowed allowing the lake to rise.
Water flows over the emergency spillway
causing erosion and damage. This is by
design and prevents water going over the top
of the main dam. However the ground erodes
faster than expected.
7-Feb-2017: Main spillway fails 11-Feb-2017: Emergency spillway used
California, USA

20. 20
OROVILLE DAM FAILURE
Rocks and concrete (1) are placed under the
emergency spillway weir to repair erosion damage
(2). The release of water into the main spillway is
increased, to lower the lake in preparation for more
rain. This erodes the adjacent hillside considerably,
generating a debris dam (3) that blocks the river and
forces the closure of the hydroelectric plant.
While the main 770 ft (230 m) dam is not
threatened, if the erosion on either spillway
reaches the top, it would cause the weir or
gate (respectively) to collapse, causing a large
uncontrolled water release and life-
threatening floods
13-Feb-2017: Repairs made Potential risks
California, USA

21. 21
OROVILLE DAM FAILURE
While the main 770 ft (230 m) dam is not
threatened, if the erosion on either spillway
reaches the top, it would cause the weir or
gate (respectively) to collapse, causing a large
uncontrolled water release and life-
threatening floods
Potential risks
California, USA

22. 22
OROVILLE DAM FAILURE
March 2011 7-Feb-2017 27-Feb-2017
Damage to the main spillway began as a crater in the middle (center) and eventually resulted in a
separate channel eroded to the side (right). At left, the main spillway is shown in March 2011 while at
its maximum discharge rate.
California, USA

23. 23
CONCLUDED
REFERENCE MATERIAL
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #7 & 8