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Geotechnical and Foundation Engineering
SCE5331
Geotechnical and Foundation Engineering
Dr. Hong Chengyu, Joey
Office: 301, Tel: 2176-1545
Email: cyhong@vtc.edu.hk
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TOPICS & SYLLABUS:
Topic 1: Review of Soil Mechanics
Topic 2: Shallow Foundations
Topic 3: Lateral Earth Pressure and Retaining Walls
Topic 4: Pile Foundations
Topic 5: Subsoil Exploration
Topic 6: Slope Stability
Textbook: Braja M. Das. (2007). Principles of Foundation
Engineering, 6th Edition, ISBN 0-495-08246-5.
Reference book:
Foundation Design and Construction (2006), GEO
Publication No. 1/2006, 376 p.
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COURSE DESCRIPTION:
The course introduces civil engineering students the fundamental
concepts of foundation analysis and design. Upon completion of this
course, students should be able to interpret field and laboratory data
to get design properties and able to design and analyze shallow
foundations, retaining walls and pile foundations.
PREREQUISITE:
SCE4231 - Engineering Geology and Soil Mechanics
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ASSESSMENT METHOD:
Final Marks = 50% (Assignments + Quiz + Reports) +
50% (Final exam)
QUIZ and EXAMS:
Quiz and exams will consist of a mixture between discussion and
technical questions to evaluate your comprehension of the material.
The final exam will be closed book. However, formulas, design
charts, and similar materials will be given when needed. In addition,
you should bring a straight edge and calculator to the exams.
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ASSIGNMENTS:
Prepare your homework in a professional manner and show discussions and all steps of calculations in your assignments. Any submission which is illegible or difficult to understand will receive a reduced grade.
Students may consult with each other about homework assignments. However, each student is responsible for preparing their own homework and displaying their understanding of the principles behind the homework solution.
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REPORTS:
Prepare your Reports in a professional manner and show discussions and all steps of your experimental processes (using photos or ?). Prepare the lab report in a logical and clear manner. All figures, tables and data should be clearly presented and analyzed in your report.
Participation in the work of a course is a precondition for a students achievement of credits in that course.
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ATTENDANCE:
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The foundation of a structure is in direct contact with the ground and transmits the load of the structure to the ground. When designing foundations, two principal criteria must be satisfied:
Bearing Capacity There must be an adequate factor of safety against collapse (plastic yielding in the soil and catastrophic settlement or rotation of the structure).
Settlement Settlements at working loads must not cause damage, nor adversely affect the serviceability of the structure
Other considerations that may be relevant to specific soils, foundation types and surface conditions.
FOUNDATION DESIGN
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Soil mechanics
Engineering geology
Proper judgment from past experience
Foundation Engineering is an art!
The most basic aspect of foundation engineering deals with the selection of the type of foundation. Foundations are commonly divided into two categories:
shallow and deep foundations.
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Foundation Types
Mat/Raft foundation
Spread footings Concrete footing
Wall footings Battered Piles Caissons
Shallow Foundations: D 3~4 B 9
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The problems for
Regina homeowners
(Regina is the capital of Saskatchewan, Canada.)
UNEVEN SETTLEMENT!!!
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Regina
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Source of the problem:
glacial-lake clays
Many communities in
southern Saskatchewan
experience foundation
problems. All these
communities share one
thing in common - they are
built on clay sediments
deposited in ancient glacial
lakes.
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Looking for solutions?
Swelling and shrinking are limited to the uppermost part of the
ground, which gains and loses moisture through the year due to
changes in precipitation and vegetation growth.
Below this 'active zone', the ground is stable.
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One engineering solution
is to build foundations on piles
that extend through the active zone
to stable ground below.
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Any other suggestions?
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Some Historical Cases for Foundation Engineering
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Leaning Tower of Pisa (unsuccessful)
Shallow foundation on deep soft deposits.
The axis of the tower is not straight.
Maximum inclination reached 5.5 in 1990s.
Using soil extraction to stabilize the tower in 1999.
Further info: http://en.wikipedia.org/wiki/Leaning_Tower_of_Pisa
Eiffel Tower (successful)
Adjacent to the Seine River underlain by deep and soft alluvium.
Two legs closest to the river were founded on 12m below the ground surface.
Two legs furthest from the river were on shallow but firm soils.
The tower has not experience excessive differential settlement for over 100 years.
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Soft Soil Engineering Problems
Transcona ,191331m,23m,8.8m,1.5m,27 degree38850T,4m
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Tallest buildings in the world
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Ultima Tower, is it possible?
3200 m high, more than 1 million residents, 500 floors
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To reach a far-distance goal by starting here
All total buildings are founded on the ground
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Geotechnical Properties of Soil Fo
un
dat
ion
De
sign
The Load that will be transmitted by the superstructure to the foundation system
The requirements of the local building code
The behavior and stress-related deformability of soils
The geological conditions of the soil
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Grain Size Distribution
Weight-Volume Relationships
Relative Density
Atterberg Limits Standard
Compaction Test
Hydraulic Conductivity of
Soil
Steady State Seepage
Effective Stress Consolidation
Consolidation Settlement
Shear Strength Unconfined
Compression Test
Review of Soil Mechanics
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Weight-Volume Relationships
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Atterberg Limits
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The optimum water content Wopt,
which results in the maximum dry
density rdmax for a given soil under the same compaction energy
Too wet Too dry
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ds
s
wssw V
M
M
MM
VM
MM
VM
wr
r
/
/1
/
1
wV
M sd
1
rr
Standard Compaction Test
Proof:
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The optimum water content Wopt, which is just right (water being
lubricate and soil having enough air voids) to achieve the maximum
dry density rdmax 27
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Effective Stress
Without seepage With seepage Quick condition (failure by heave)
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u
A
uA
A
N
A
P
uANP
'
'
'
Note: Particle contact areas are zero.
Thus, force due to u is uA
Consider the fully saturated soil (water and solids only, no air)
Consider vertical force equilibrium:
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Hydraulic Conductivity of Soil
o Laboratory tests
o Typical values
o Empirical equations
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Steady State Seepage
2-dimension
3-dimension
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FLOW NET METHOD
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Hydraulic Conductivity of Soil
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The quick condition
icr is the critical hydraulic gradient
Effective stress at A:
)( satwwvA zh
)]([
)(
)(
wAw
AAwA
w
hzh
zhu
zhu
Effective stress =0 as critical
case or quicksand condition
wh
Ah
zA
Az
crAA
w
wsat
Awwsat
wAwsatwwv
vv
iz
h
z
h
hz
hzhzh
u
0)(
)()('
'
e
Gi s
ww
wsatcr
1
1'
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Bedrock or soil
Marine Deposits
Water Table
Pre-loading fill
Sand fill
Confined or 1-D Straining Consolidation
(or Oedometer) Condition:
Soil layers are horizontal and uniform
Loading is uniform
Deformation & water flow are in vertical only
Consolidation
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Consolidation
34 Void ratio-effective stress relationship
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From the e-log s curve, what parameters can be determined?
Preconsolidation pressure
35 e-log relationship
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Compression: for each layer Hj (thickness), if mv and are constant with depth z, then (loading):
jvjvcj HmHs'
Compression: for normally consolidated clay, use Cc for loading:
''
1
'
2
'
1
'
2
0
log1
j
cjvcj H
e
CHs
Recompression/Heave/Swelling: for normally consolidated clay, use
Cr or Ce for un-loading:
je
jvcj He
CHs
'
1
'
2
0
log1
Consolidation Settlement
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)1(,1
,1
111
0
00
0
00
0000
0
0
10
0
10
0
10
0
eH
He
H
e
H
e
H
H
e
e
H
H
AH
HA
V
V
V
V
VV
VV
e
ee
e
ezv
V
sv
vv
V
V
V
V
V
Vs
s
v
s
v
s
v
)/log( '' 1
1
ii
iic
eeC
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z
uc
t
u ev
e
wv
vm
kc
The initial value of excess pore water pressure (initial condition):
The boundary conditions of excess pore water pressure:
Free-draining, double drainage
1-D Terzaghi Consolidation Thoery
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848.0%90
196.0%50
v
v
TU
TU
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Determination of coefficient of consolidation
wv
vm
kc
t
dTc
d
tcT vv
vv
2
2;
(1)The log time method
(due to Casagrande)
(2) The root time method (due to Taylor)
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2196.0
t
dcv
90
2848.0
t
dcv
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Correction for construction period
Previous solution/chart is for suddenly applied load
Common real load is ramp loading (construction loading)
linear increase and then constant
How to find a solution to this or make a correction?
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Shear Strength
Direct shear test
Triaxial tests
CD Tests CU Tests UU Tests
Attention to:
Effective stress parameters
Total stress parameters
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Unconfined Compression Test
Sometimes conducted on
unsaturated soils
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