This document discusses deep foundations and pile design. It begins by explaining why deep foundations are needed when near surface soils are inadequate or there are concerns about settlement. It then describes the main types of deep foundations - driven piles, bored concrete piles, and other alternatives like driven cast in situ piles. Specific pile materials and installation methods are outlined for different pile types. The document also covers site investigation considerations, design aspects like geotechnical strength calculations, and factors of safety.

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DEEP FOUNDATIONS
Dr. Youssef Gomaa Youssef

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Textbook:
• Tomlinson, J.J., 1977. Pile Design and Construction
Practice, Garden City Press Ltd., Letchworth.
• Canadian Foundation Engineering Manual, 1978,
Canadian Geotechnical Society, Montreal.
• Engineer Manual “DESIGN OF PILE FOUNDATIONS”,
EM 1110-2-2906.

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Why go deep?
[A] Near surface soils inadequate
• weak relative to applied loads
• erodible
− watercourses, scour of soil
[B] Load orientation
• lateral loading – raked piles
• uplift loading - anchors
[C] Settlement concerns

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Types of Deep Foundations
1. Driven Piles
MATERIALS
- wood, precast concrete, steel
SECTIONS
- octagons, solid circles, rings, H-sections
LIMITATIONS
Vibrations due to driving? Head room?
Deep foundations usually L/B > 5
L = pile length, B = dia. or breadth of pile

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Pile material
 Steel; H- piles, Steel pipe
 Concrete; Site cast or Precast
 Wood; Timber
 Composite

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DRIVEN
PILING

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Types of Deep Foundations
2. Bored Concrete Piles
• Large diameter?
• Increased base diameter?
– underreamed
• Excavation support?
– Bentonite slurry
• Limited practical depth
• Soil restrictions

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Caisson Installation Sequence
 Hole drilled with a large drill rig
 Casing installed (typically)
 Bell or Tip enlargement (optional)
 Bottom inspected and tested
 Reinforced
 Concrete placement (& casing removal)

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Site Cast Concrete Piles
Cased Piles Uncased Piles

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Bentonite slurry
Weak soil,
high WT
Concrete
displaces
fluid

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Types of Deep Foundations
3. Other
• Driven cast in-situ piles
– driven tube pile, filled with concrete
• Continuous flight augur piles
– hollow augur string
– concrete slurry inserted through tip as
string withdrawn
• Etc, etc,etc

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Reference http://www.keller-ge.co.uk/index.html
Cast in-situ piling

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For construction, piles may be subdivided into:
1. Displacement (or large-displacement) piles
2. Small-displacement piles
3. Non-displacement piles
Types of Deep Foundations

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NON-DISPLACEMENT PILE
Soil is removed
• The excavation may or may not be
supported
DISPLACEMENT PILE
Soil is ‘displaced’ within the adjoining
soil mass
• Displaced volume  pile volume

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SINGLE PILE LOAD CAPACITY
Capacity dependent on construction
• relaxation of field soil stresses?
− less contact with side soil, less support
• Bentonite slurry used?
− slippery side contact (smeared)
Stress relaxation expected for
DISPLACEMENT PILES

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SITE INVESTIGATION FOR PILING
1. Soil strength and stiffness
2. Soil chemical analysis  corrosion
3. Possible obstructions to installation
4. Potential for damage to adjoining
structure due to “ground heave”
5. Vibrations

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SITE INVESTIGATION FOR PILING
After-construction effects of:
1. Expansive soil
2. Negative friction / downdrag
3. Slope instability

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PILES - design
1. Geotechnical
- strength and stiffness
 “serviceability”
2. Pile structural strength
3. Pile material “durability”

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GEOTECHNICAL STRENGTH
Vertical compression loading:
ULTIMATE GEOTECHNICAL STRENGTH
- or capacity, Pu
bbssu AfAfP 

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fs = average, fully mobilized, “skin friction”
(= INTERFACE friction and adhesion)
fb = ultimate base bearing pressure
Dependent upon –
SOIL TYPE
SOIL PROFILE
PILE MATERIAL
INSTALLATION

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Low load Ultimate load
fs =  max
fs =  max
for the
full
lengthfs <<  max
Base resistance,
fb, mobilized

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Calculations
Circular pile, length, L:
Pu = fs(Dl) + fb(Db
2/4)
where Db = diameter of base
Note 1: fs may vary down the shaft
(add contributions)
Note 2: fb only at base

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The equivalent factor of safety is usually
between 2 and 2.5 for static analysis
based on
good soil data
and site investigation