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–II [CE-321]
BSc Civil Engineering – 5th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session
Lecture # 23
29-Nov-2017
2. 2
RANKINE THEORY OF ACTIVE EARTH
PRESSURE
ASSUMPTIONS
1. The soil is homogeneous and isotropic.
2. The most critical shear surface is a plane. In reality, it is
slightly concave upward, but this is a reasonable assumption
(especially for the active case) and it simplifies the analysis.
3. The backfill surface is planar (although it does not necessarily
need to be horizontal).
4. There is no friction between wall and soil.
5. The wall is infinitely long so that a representative two-
dimensional section of the wall may be analyzed,
assuming there is no strain in the direction perpendicular
to the section. We refer to this as a plane strain condition.
3. 3
RANKINE THEORY OF ACTIVE EARTH
PRESSURE
If wall AB is not allowed to move
Shearstress,t
Effective Normal
stress, s’so’Koso’sa’
a
sh’
b
c
s’h = Ko s’o
Stress condition in soil Mohr’s circle a
If wall is allowed to move away from soil mass
horizontal principal stress will decrease
Circle b Circle c
4. 4
RANKINE THEORY OF ACTIVE EARTH
PRESSUREShearstress,t
Effective Normal
stress, s’so’
Koso’
sa’A O
D
C
f c
11. 11
RANKINE THEORY OF ACTIVE EARTH PRESSURE
-- DEPTH OF UNSUPPORTED CUT --
aaa KczK 2s
aa K2c-Kz
z
zC
aK2c-
General Case
(c-f soil) 0Cz
aac KcKz 20
At zC
a
a
c
K
Kc
z
2
a
c
K
c
z
2
Cohesionless Soils
(c’=0)
Cohesive Soils
(f=0)
Ka =
Height of unsupported cut (hC)
Zero Net force acting on wall
c
zc
2
WALL
hC = Ht. of
Unsupported
Cut
CC zh 2
s’a = 0
1
12. 12
RANKINE THEORY OF PASSIVE
EARTH PRESSURE
Wall movement
towards soil
Shearstress,t
Effective Normal
stress, s’so’Koso’ sp’A O
D
C
f c
13. 13
RANKINE THEORY OF PASSIVE
EARTH PRESSURE
Derivation: similar to that for active state
For cohesionless soils, c’ = 0
14. 14
RANKINE THEORY OF PASSIVE
EARTH PRESSURE
f
ff
s
s
sin1
sin1
2
45tan2
o
p
pK
2
45tan'2
2
45tan2 ff
s czp
ppp KczK 2s
16. 17
RANKINE THEORY
ACTIVE PRESSURE -- SUMMARY --
f
ff
s
s
sin1
sin1
2
45tan2
o
a
aK
aaa KczK 2s
a
c
K
c
z
2
20. 21
CONCLUDED
REFERENCE MATERIAL
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #13
Essentials of Soil Mechanics and Foundations (7th Edition)
David F. McCarthy
Chapter #17
Geotechnical Engineering – Principles and Practices – (2nd Edition)
Coduto, Yueng, and Kitch
Chapter #17