Foundation Design Building structural system By Dr. Sompote Youwai.
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Transcript of Foundation Design Building structural system By Dr. Sompote Youwai.
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Foundation Design
Building structural systemBy Dr. Sompote Youwai
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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
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Additional text book
• Das M. B., Foundation Engineering.• Tomlinson, M. J. Foundation Design &
Construction • Hunt, Geotechnical Engineering Investigation
Handbook.• Handout
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Method for Pile Design
• Hand Calculation• Finite Element Analysis
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2. Foundations for Signature Towers Dubai
75-F Office65-F Hotel
55-F Residential
• Nicknamed “Dancing Towers”
• Office 351 m, Hotel 305 m, 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
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Foundation Layout
Office(168 nos)
Hotel(126 nos)
Residential(184 nos)
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3DF Mesh
505m
590m
150mNo of elements = 32,000
• Pile rafts 5.5 m thick, located at 10 metre below ground level
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3DF Mesh
168 nos. 126
nos.
184 nos.
Embedded piles: 1.5 m dia. 45 m long
Pile raft
Load
Office Tower
Hotel Tower
Residential Tower
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3DF Outputs
Office Tower Hotel Tower
Residential TowerContours of Settlements
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3DF Outputs
Office ResidentialHotel
Office Hotel Residential
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3DF Outputs
Deformations of Office piles Axial forces of Office piles
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Fundamental of Soil Mechanics
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Bangkok Subsoil condition
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Bangkok Subsoil condition
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Keyword from boring log
• ST, SS• Atterberg’s limits• Water content• Unit weight• Sieve analysis• Unconfined shear• Standard penetration test
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• Soil is generally a three phase material• Contains solid particles and voids• Voids can contain liquid and gas phases
Solid
Water
Air Vs
Vw
Va
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• Soil is generally a three phase material• Contains solid particles and voids• Voids can contain liquid and gas phases
Solid
Water
Air Vs
Vw
Va
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• Soil is generally a three phase material• Contains solid particles and voids• Voids can contain liquid and gas phases
Solid
Water
Air
Phase Volume Mass Weight
Air Va 0 0
Water Vw Mw Ww
Solid Vs Ms Ws
Vs
Vw
Va
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Units
• Length metres• Mass tonnes (1 tonne = 103 kg)• Density t/m3
• Weight kilonewtons (kN)• Stress kilopascals (kPa) 1 kPa= 1 kN/m2
• Unit weight kN/m3
• Accuracy Density of water, rw = 1 t/m3
Stress/Strength to 0.1 kPa
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Weight and Unit weight
• Force due to mass (weight) more important than mass• W = M g
• Unit weight
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Weight and Unit weight
• Force due to mass (weight) more important than mass• W = M g
• Unit weight
g = r g
W
V
M g
V
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Weight and Unit weight
• Force due to mass (weight) more important than mass• W = M g
• Unit weight
g = r g
W
V
M g
V
svz sv = r g z
sv = g z
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Specific Gravity
• Gs @ 2.65 for most soils
• Gs is useful because it enables the volume of solid particles to be calculated from mass or weight
GD e n s i t y o f M a t e r i a l
D e n s i t y o f W a t e r w
GU n i t W e i g h t o f M a t e r i a l
U n i t W e i g h t o f W a t e r w
This is defined by
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Moisture Content
• The moisture content, m, is defined asm
Weight of Water
Weight of Solids
W
Ww
s
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Moisture Content
• The moisture content, m, is defined as
In terms of e, S, Gs and gw
Ww = gw Vw = gw e S Vs
Ws = gs Vs = gw Gs Vs
mWeight of Water
Weight of Solids
W
Ww
s
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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
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Sieve analysis
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Atterberg Limits• Particle size is not that useful for fine
grained soils
Moisture content versus volume relation during drying
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•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
Atterberg’s Limit
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LL - Liquid limit
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PL – Plastic limit
SL – Shrinkage limit
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Atterberg Limits
SL - Shrinkage LimitPL - Plastic LimitLL - Liquid limit
Plasticity Index = LL - PL = PI or Ip
Liquidity Index = (m - PL)/Ip = LI
Moisture contentmassof water
massof solids
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Definition of Grain Size
Boulders CobblesGravel Sand Silt and
ClayCoarse Fine Coarse FineMedium
300 mm 75 mm
19 mm
No.4
4.75 mmNo.10
2.0 mm
No.40
0.425 mm
No.200
0.075 mm
No specific grain size-use Atterberg limits
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Symbols• Soil symbols:• G: Gravel• S: Sand• M: Silt• C: Clay• O: Organic• Pt: Peat
• Liquid limit symbols:• H: High LL (LL>50)• L: Low LL (LL<50)• Gradation symbols:• W: Well-graded• P: Poorly-graded
Example: SW, Well-graded sand
SC, Clayey sand
SM, Silty sand,
MH, Elastic silt)sandsfor(
6Cand3C1
)gravelsfor(
4Cand3C1
soilgradedWell
uc
uc
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Plasticity Chart
(Holtz and Kovacs, 1981)
LL
PI
HL•The A-line generally
separates the more claylike materials from silty materials, and the organics from the inorganics.
•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.
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Soil Classification Procedure
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Effective stress theory
u
- Fully Saturated: Sr=100%
- = Total stress to boundary
- u = pore water pressure
-u = Effective stress which is transmitted to the soil structure
Bishop (1954):
’ = -u : No change in soil strength if no change in ’.
f=c’ + ’ tan(’)
c’ and ’ are effective cohesion and friction angle of soil.
- Fully Saturated: Sr=100%
- = Total stress to boundary
- u = pore water pressure
-u = Effective stress which is transmitted to the soil structure
Bishop (1954):
’ = -u : No change in soil strength if no change in ’.
f=c’ + ’ tan(’)
c’ and ’ are effective cohesion and friction angle of soil.
- Equilibrium condition
- impermeable membrane
- Equilibrium condition
- impermeable membrane
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0 50 100 150
0m
2m
4m
6m
8m
kPa
pore waterpressure Effective
stress
TotalStress (5m)
Depth
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Stresses acting on a soil element
x
y
z
xz
yz
zz
yy
xy
zy
xx
yx
zx
z
x