foundation engineering eciv...
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Foundation Engineering
ECIV 4352
Chapter (11) Deep Foundation
Instructor : Dr. Jehad Hamad
2016-2015
Chapter 11
Pile Foundation
October 16, 2016 ECIV 2204 Engineering Geology
Civil Engr. Dept.
3
Foundation- Design Considerations
Factors to be taken into consideration when determining the type of the building foundations: • Function of the structure • Loads from the structure • Bearing capacity of foundation material • Total and differential settlement of foundation • Uplift forces acting on the foundation Costs
October 16, 2016 ECIV 2204 Engineering Geology
Civil Engr. Dept.
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When is it needed Top layers of soil are highly compressible for it to support structural loads through shallow foundations. Rock level is shallow enough for end bearing pile foundations provide a more economical design. Lateral forces are relatively prominent. In presence of expansive and collapsible soils at the site. Offshore structures Strong uplift forces on shallow foundations due to shallow water table can be partly transmitted to Piles. For structures near flowing water (Bridge abutments, etc.) to avoid the problems due to erosion.
October 16, 2016 ECIV 2204 Engineering Geology
Civil Engr. Dept.
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Types of Piles
• Steel Piles • Pipe piles • Rolled steel H-section piles • Concrete Piles • Pre-cast Piles • Cast-in-situ Piles • Bored-in-situ piles • Timber Piles • Composite Piles
October 16, 2016 ECIV 2204 Engineering Geology
Civil Engr. Dept.
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Steel Piles: Facts • Usual length: 15 m – 60 m • Usual Load: 300 kN – 1200 kN
• Advantage: • Relatively less hassle during installation and easy to achieve cutoff
level. • High driving force may be used for fast installation • Good to penetrate hard strata • Load carrying capacity is high
• Disadvantage: • Relatively expensive • Noise pollution during installation • Corrosion • Bend in piles while driving
October 16, 2016 ECIV 2204 Engineering Geology
Civil Engr. Dept.
7
Concrete Piles: Facts Pre-cast Piles: Usual length: 10 m – 45 m Usual Load: 7500 kN – 8500 kN Cast-in-situ Piles: Usual length: 5 m – 15 m Usual Load: 200 kN – 500 kN Advantage: Relatively cheap It can be easily combined with concrete superstructure Corrosion resistant It can bear hard driving Disadvantage: Difficult to transport Difficult to achieve desired cutoff
October 16, 2016 ECIV 2204 Engineering Geology
Civil Engr. Dept.
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Types of Piles Based on Their Function and Effect 0f Installation
Piles based on their function End Bearing Piles Friction Piles Compaction Piles Anchor Piles Uplift Piles
Effect of Installation Displacement Piles Non-displacement Piles
Soil Bearing Capacity
The soil bearing capacity needs to be
determined. This can be done by:
Local or State Building Codes
Uniform Building Code (UBC)
Soil testing/analysis
Site inspection and simple soil testing
Soil borings taken at proposed foundation
locations
Foundations - Deep
Pile Foundations - vertical structural members that are
forced into the ground by pile drivers (similar to driving
nails into wood)
Caissons – similar to pile foundations, but are created
by auguring (drilling ) a deep hole into the ground and
then filling the hole with concrete. Caissons may be
belled at the base. Steel reinforcement may also be
used. Caissons can extend to bedrock.
Foundations
Mat or raft foundations – the entire building is
placed on one large continuous footing.
Typically used in locations where the soil is
weak/poor and bedrock is too deep.
Mat foundations with caissons or piles – a
combination of a mat foundation with piles or
caissons.
Introduction
Pile foundation used to support structure
poor quality soil
bearing capacity failure
excessive settlement
End-bearing pile
Pile driven until it comes to rest on a hard impenetrable layer of
soil or rock
Friction pile
load of the structure must come from the skin friction or
adhesion between surface of the pile and the soil
October 16, 2016 ECIV 4352 Foundation Engineering
Civil Engr. Dept.
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Piers : are foundations for carrying a heavy
structural load which is constructed in-situ in a deep excavation.
Caissons: are a form of deep foundation which are constructed above ground level, then sunk to the required level by excavating or dredging material from within the caisson.
Drilled Caissons
Deep foundation that is constructed in-place
Drilling and casting concrete in-place
straight-shaft
belled ( reduced contact pressure)
Advantages
lighter and less expensive drilling equipment
quieter than pile drivers
reduce ground vibrations
visual inspection of subsoil
Advantages and Disadvantages of Drilled
Pier Foundation
Advantages”
1- Pier of any length and size can be
constructed at the site,
2- Construction Equipment is normally
mobile and construction can be proceed
rapidly
Bearing Capacity of Caissons
Q(ult) = Q(friction) + Q(tip)
Cohesive soils
Q(total) = cNc *A(bottom) + f*A(shaft)
Cohesionless soils
Q(ult) = p(v)*Nq*A(bottom) + (Ko*p(v)*tan )A(shaft)