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.

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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.

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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)