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/forum/#!forum/geotech-i
Lecture # 3
31-Jan-2017

2. 2
S: Solid Soil particle
W: Liquid Water
A: Air Air
SOIL AS A THREE PHASE SYSTEM

3. 3
SOIL AS A THREE PHASE SYSTEM
V = Total volume of soil mass
Vs = Volume of soil solids
Vw = Volume of water
Va = Volume of air
Vv = Va+Vw = Volume of voids
W = Total weight of soil
Ws = Weight of soil solids
Wa = Weight of air ≈ 0
Ww = Weight of water

4. 4
1) Void ratio, e
(0 < e < ∞)
For sands, 0.5 ≤ e ≤ 0.9
For clays, 0.7 ≤ e ≤ 1.5 (or even higher)
)V(solidsofVolume
)V(voidsofVolume
e
s
v

VOLUMETRIC RATIOS

5. 5
2) Porosity, n
(0 < n < 1)
Typical range, 9-70%
For sands, 25% ≤ n ≤ 50%
3) Air Porosity, na’
(0 < na’ < 1)
4) Percentage Air Voids, na
(0 < na < 1)
)V(samplesoilofvolumeTotal
)V(voidsofVolume
n
t
v

VOLUMETRIC RATIOS
)(
)(
'
t
a
a
VsamplesoilofvolumeTotal
VairofVolume
n 
)(
)(
v
a
a
VvoidsofVolume
VairofVolume
n 

6. 6
5) Degree of Saturation/ Saturation Ratio, S (or Sr)
(0 < Sr < 100%)
6) Volumetric Water Content, θv
(0 < θv < 1)
VOLUMETRIC RATIOS
%100
)(
)(

v
w
VvoidsofvolumeTotal
VwatercontainingvoidsofVolume
S
)(
)(
t
w
v
VsamplesoilofvolumeTotal
VwatercontainingvoidsofVolume


7. 7
1) Moisture/Water Content/Gravimetric Water Content, w
(0 < w < ∞)
Typical value for Sands >> 10-30%
For clays >> 10% or higher typically
For some organic soils w>100%, even up to 500%.
For quick clays w is typically > 100%.
WEIGHT RELATIONSHIPS
%100
)(
)(

s
w
WsolidssoilofWeight
WwaterofWeight
w

8. 8
2) Unit Weight, γ
3) Dry Unit Weight, γd
4) Bulk Unit Weight, γb
5) Unit Weight of Soil Solids, γs
WEIGHT RELATIONSHIPS
);;( 333
cmgftlbmkN
V
Mg
Volume
Weight

t
s
d
V
W
VolumeTotal
solidssoilofWeight

t
b
V
W
VolumeTotal
WeightTotal

s
s
s
V
W
soildssoilofVolume
soildssoilofWeight


9. 9
6) Saturated Unit Weight, γsat
7) Submerged Unit Weight, γsub (or γbouyant)
γw = 9.81 kN/m3 → 1 g/cm3
= 1000 kg/m3
= 62.4 lb/ft3
WEIGHT RELATIONSHIPS
wsatsub  
VolumeTotal
soilsaturatedofWeight
sat 
Archimede’s principle:
The buoyant force on a body immersed
in a fluid is equal to the weight of the
fluid displaced by that object.

10. 10
SPECIFIC GRAVITY (Gs)
w
s
s
CatwaterofvolumeequalofweightUnit
soildssoilofweightUnit
G





4
Generally for soils 2.6 ≤ Gs ≤ 2.7

11. 11
WEIGHT-VOLUME RELATIONSHIPS
w
b
d


1


n
n
e


1
e
e
n


1
VG
W
n
ws
s 1
.
1 

1
..

s
ws
W
GV
e










e
w
G wsb
1
1
.
e
G ws
d


1
.

S
Gw
e s.

 
e
eG ws
sat



1


 
 e
Gsw
sub



1
1

rv Sn.

12. 12
CONCLUDED
REFERENCE MATERIAL
An Introduction to Geotechnical Engineering (2nd Edition)
By R. D. Holtz, W. D. Kovacs and T. C. Sheahan
Chapter #2
Geotechnical Engineering – Principles and Practices - (2nd Edition)
By Donald P. Coduto, M. R. Yeung and W. A. Kitch
Chapter #4
Fundamentals of Soil Mechanics
By M. S. Qureshi & Aziz Akbar
Chapter #3