Foundation Design
Building structural system
By Dr. Sompote Youwai
Contents
• Fundamental of Soil Mechanics
• Interpretation from Soil Report
– Subsurface investigation
– Field and laboratory testing
• Pile Foundation Design
– Single Pile
– Pile Group
• Fundamental of retaining structure
– Sheet pile
– Diaphragm wall
Additional text book
• Das M. B., Foundation Engineering.
• Tomlinson, M. J. Foundation Design &
Construction
• Hunt, Geotechnical Engineering Investigation
Handbook.
• Handout
Method for Pile Design
• Hand Calculation
• Finite Element Analysis
2. Foundations for Signature Towers Dubai
• Nicknamed “Dancing Towers”
75-F Office
65-F Hotel
• Office 351 m, Hotel 305 m,
55-F Residential
Residential 251 m high
• Piled raft foundations
• Bored piles 483 nos., 1.5 m dia, 45 m
long
• Ground conditions:
0-10 m: Sand
10-25 m: Very/Weak Sandstone
25-30 m: Very/Weak Siltstone
30-40 m: Very/Weak Conglomerate
>40m: Very/Weak Claystone
5
Foundation Layout
Residenti
al
(184
Hotel nos)
(126
Office nos)
(168
nos)
6
3DF Mesh
590m
505m
150m
No of elements = 32,000
• Pile rafts 5.5 m thick, located at 10 metre
below ground level
7
3DF Mesh
Office
Tower
Hotel
Tower
Pile
raft
168
nos.
126
nos.
Residential
Tower
Loa
d
184
nos.
Embedded piles: 1.5
m dia. 45 m long
8
3DF Outputs
Office Tower
Contours of
Settlements
Hotel Tower
Residential Tower
9
3DF Outputs
Office Hotel Residential
10
3DF Outputs
Deformations of Office piles
Axial forces of Office piles
11
Fundamental of Soil Mechanics
Bangkok Subsoil condition
Bangkok Subsoil condition
Keyword from boring log
•
•
•
•
•
•
•
ST, SS
Atterberg’s limits
Water content
Unit weight
Sieve analysis
Unconfined shear
Standard penetration test
Solid
Water
Air
• Soil is generally a three phase material
• Contains solid particles and voids
• Voids can contain liquid and gas phases
Va
Vw
Vs
Solid
Water
Air
• Soil is generally a three phase material
• Contains solid particles and voids
• Voids can contain liquid and gas phases
Va
Vw
Vs
Va
Vw
Solid
Water
Vs
Air
• Soil is generally a three phase material
• Contains solid particles and voids
• Voids can contain liquid and gas phases
Phase
Volume
Mass
Weight
Air
Va
0
0
Water
Vw
Mw
Ww
Solid
Vs
Ms
Ws
Units
•
•
•
•
•
•
Length
Mass
Density
Weight
Stress
Unit weight
• Accuracy
metres
tonnes (1 tonne = 103 kg)
t/m3
kilonewtons (kN)
kilopascals (kPa) 1 kPa= 1 kN/m2
kN/m3
Density of water, rw = 1 t/m3
Stress/Strength to 0.1 kPa
Weight and Unit weight
• Force due to mass (weight) more important than mass
• W = Mg
• Unit weight
Weight and Unit weight
• Force due to mass (weight) more important than mass
• W = Mg
W
g 
• Unit weight
V
g 
Mg
V
g = rg
Weight and Unit weight
• Force due to mass (weight) more important than mass
• W = Mg
W
g 
• Unit weight
V
g 
Mg
V
g = rg
z
sv
sv = r g z
sv = g z
Specific Gravity
This is defined by
Density of Material
r
G 

Density of Water
rw
Unit Weight of Material
g
G 

Unit Weight of Water
gw
• Gs @ 2.65 for most soils
• Gs is useful because it enables the volume of solid
particles to be calculated from mass or weight
Moisture Content
• The moisture content, m, is defined as
Weight of Water
Ww
m 

Weight of Solids
Ws
Moisture Content
• The moisture content, m, is defined as
Weight of Water
Ww
m 

Weight of Solids
Ws
In terms of e, S, Gs and gw
Ww = gw Vw = gw e S Vs
Ws = gs Vs = gw Gs Vs
Procedure for grain size determination
• Sieving - used for particles > 75 mm
• Hydrometer test - used for smaller particles
– Analysis based on Stoke’s Law, velocity proportional to diameter
Sieve analysis
Atterberg Limits
• Particle size is not that useful for fine
grained soils
Moisture content versus volume relation
during drying
Atterberg’s Limit
•Liquid Limit – The minimum water content at which the soil can
be flow under its own weight
•Plastic Limit – The minimum water content at which soil can be
roller into a thread 3 mm diameter with out breaking up
•Shrinkage – The maximum water content at which further loss
of moisture does not cause a decrease in the volume of soil
LL - Liquid limit
PL – Plastic limit
SL – Shrinkage limit
Atterberg Limits
SL - Shrinkage Limit
PL - Plastic Limit
LL - Liquid limit
mass of water
Moisture content 
mass of solids
Plasticity Index = LL - PL = PI or Ip
Liquidity Index = (m - PL)/Ip = LI
Definition of Grain Size
No specific
grain size-use
Atterberg limits
Gravel
Silt and
Sand
Boulders Cobbles
Clay
Coarse
300 mm
Fine
75 mm
19 mm
Coarse
Medium
Fine
No.4
No.200
4.75 mm
0.075
mm
No.10
No.40
2.0 mm
0.425 mm
Symbols
•
•
•
•
•
•
•
Soil symbols:
G: Gravel
S: Sand
M: Silt
C: Clay
O: Organic
Pt: Peat
Example: SW, Well-graded sand
SC, Clayey sand
SM, Silty sand,
MH, Elastic silt
•
•
•
•
•
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Liquid limit symbols:
H: High LL (LL>50)
L: Low LL (LL<50)
Gradation symbols:
W: Well-graded
P: Poorly-graded
Well  graded soil
1  C c  3 and C u  4
(for gravels )
1  C c  3 and C u  6
(for sands )
Plasticity Chart
L
H
• The A-line generally
separates the more
claylike
materials
from silty materials,
and the organics
from the inorganics.
PI
• The U-line indicates
the upper bound for
general soils.
Note: If the measured
limits of soils are on
the left of U-line,
they
should
be
rechecked.
LL
(Holtz and Kovacs, 1981)
Soil Classification Procedure
Effective stress theory
- Fully Saturated: Sr=100%
- s = Total stress  to boundary
u
s
- Equilibrium condition
- impermeable membrane
- u = pore water pressure
s-u = Effective stress which is
transmitted to the soil structure
Bishop (1954):
s’ = s-u : No change in soil
strength if no change in s’.
f=c’ + s’ tan(’)
c’ and ’ are effective cohesion
and friction angle of soil.
0
50
100
150 kPa
0m
2m
4m
6m
Depth
8m
Total
Stress
pore water
pressure
Effective
stress
(5m)
Stresses acting on a soil element
s zz
z
z
s yz
s zy
s xz
s zx
s yy
s yx
x
s xx
y
s xy
x