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Deep foundation- Piles

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Deep foundation- Piles

Purpose: to transmit structural loads to greater depths

Used when:

(1) soil beneath structure has insufficient strength- therefore

used to transmit a foundation load to a solid ground(2) non-uniform soil or structural loads would give rise to

unacceptable differential settlements

(3) excavation to a firmer stratum would be too expensive

(4) resistance to lateral loads or uplift is required

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Deep foundation- Piles

Components include a pile cap and piles

Concrete, steel and (timber)

Piles are driven, drilled or bored, jacked into the ground and

connected to pile caps. Cost estimates often justifies the choice for piles against other

ground improvement methods.

Piles also resist horizontal loads

Used for structure constructed over water- jetties and bridgepiers

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Deep foundation- Piles

Classification of piles used: Construction and installation

method; load transmission and functional behaviour

Classification of piles used- From the installation method:

Driven piles

Driven and cast in place piles

Jacked piles Bored and cast in place piles

Composite piles

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Deep foundation- Piles

Classification of piles used- From the construction method:

Large displacement piles

Small displacement piles Non displacement piles

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Deep foundation- Piles

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Deep foundation- Piles

Classification of piles used- From the construction method:

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Deep foundation- Piles

Classification of piles used- From the load transmission

method:

End bearing piles

Friction piles CombinationEnd bearing and friction

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Deep foundation- Piles

https://www.google.mu/search?q=friction+and+end+bearing+piles&biw=1440&bih=737

&source=lnms&tbm=isch&sa=X&sqi=2&ved=0ahUKEwi5sdHT0rLKAhUCQBQKHa6sAK4Q_AUIBi B#im rc= h8iXT1- 4E3vM%3A

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Phases during the life of a pile

Installation

Reconsolidation of soil around pile

Loading

Driving depth: Influenced by the magnitude of load, nature

of load, stiffness and strength of soil

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Ultimate Load capacity of Single piles

The unit shaft friction qs usually varies with depth

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Ultimate Load capacity of Single piles- in cohesive soils

Undrained- Total stress analysis

Clay soils, it is usually necessary:

Calculate the capacity of the pile in both the undrainedcondition (using a total stress analysis and the undrainedshear strength failure criterion)

In long term using effective stress and frictional failurecriteria

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Ultimate Load capacity of Single piles- in cohesive soils

qf= scNccu+ q

Qbu= Ap(scNccu)

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Ultimate Load capacity of Single piles- in cohesive soils

scNc Pile limits to 9

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Ultimate Load capacity of Single piles- in cohesive soils

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Ultimate Load capacity of Single piles- in cohesive soils

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Ultimate Load capacity of Single piles- in cohesive soils

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Ultimate Load capacity of Single piles- in cohesive soils

qs

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Ultimate Load capacity of Single piles- Drained analysis

Effective Stress (Drained) Analysis

From: qf = sqNqq+1/2 BsN+scNcc

Qbu = Abqb = Ap(Nqq)

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Ultimate Load capacity of Single piles- drained analysis

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Ultimate Load capacity of Single piles- drained analysis

qs =Ks. .tan v

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Ultimate Load capacity of Single piles- drained analysis

Qs= As qs

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