ce 632 pile foundations part-1 ppt

5/28/2018 CE 632 Pile Foundations Part-1 PPT

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-Foundation Analysis and

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Foundation Analysis and Design: Dr. Amit Prashant

IS 2911 : Part 1 : Sec 1 : 1979 Driven cast in-situ concrete piles

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IS 2911 : Part 1 : Sec 3 : 1979 Driven precast concrete piles

IS 2911 : Part 1 : Sec 4 : 1984 Bored precast concrete piles IS 2911 : Part 2 : 1980 Timber piles

IS 2911 : Part 3 : 1980 Under reamed piles

IS 5121 : 1969 Safety code for piling and other deep foundations

IS 6426 : 1972 Specification for pile driving hammer

IS 6427 : 1972 Glossary of Terms Relating to Pile Driving Equipment

IS 6428 : 1972 Specification for pile frame IS 9716 : 1981 Guide for lateral d namic load test on iles

IS 14362 : 1996 Pile boring equipment - General requirements

IS 14593 : 1998 Bored cast-in-situ piles founded on rocks - Guidelines

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: on- es ruc ve n egr y es ng o es -Guidelines


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Top layers of soil are highly compressible for it to support.

Rock level is shallow enough for end bearing pile.

Lateral forces are relatively prominent.

n presence o expans ve an co aps e so s a e s e. 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.

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Steel Piles

Pipe piles

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Concrete Piles

Pre-cast Piles

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Bored-in-situ piles

Timber Piles

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ompos e es


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Usual length: 15 m 60 m

Usual Load: 300 kN 1200 kN

Advanta e: Relatively less hassle during installation and easy to achieve

cutoff level.

g r v ng orce may e use or as ns a a on Good to penetrate hard strata

Disadvantage:

Noise pollution during installation

Corrosion

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Bend in piles while driving


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Pre-cast Piles:



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Advantage: Relatively cheap

It can be easily combined with concrete superstructure

Corrosion resistant

Disadvantage:

Difficult to trans ort

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Difficult to achieve desired cutoff


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Types of Piles Based on Their Function and EffectTypes of Piles Based on Their Function and Effect

of Installationof Installation

es ase on e r unc on

End Bearing Piles r c on es

Compaction Piles

Uplift Piles

Effect of Installationsp acemen es

Non-displacement Piles

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In loose cohesionless soils

Densifies the soil u to a distance of 3.5 times the ile diameter(3.5D) which increases the soils resistance to shearing

The friction angle varies from the pile surface to the limit of

compacted soil In dense cohesionless soils

The dilatancy effect decreases the friction angle within the zone ofinfluence of dis lacement ile 3.5D a rox. .

Displacement piles are not effective in dense sands due to abovereason.

Soil is remolded near the displacement piles (2.0 D approx.) leading

to a decreased value of shearing resistance.-

effective stress and consequently lower shearing resistance.

Excess pore-pressure dissipates over the time and soil regains itsstrength.

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Example: Driven concrete piles, Timber or Steel piles


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Due to no displacement during installation, there is no heave inthe round.

Cast in-situ piles may be cased or uncased (by removing

casing as concreting progresses). They may be provided withre n orcemen econom ca w e r re uce ame er.

Enlarged bottom ends (three times pile diameter) may be

capacity.

Soil on the sides ma soften due to contact with wet concreteor during boring itself. This may lead to loss of its shear

strength. oncre ng un er wa er may e c a eng ng an may resu ng

in waisting or necking of concrete in squeezing ground.

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Load Transfer Mechanism of PilesLoad Transfer Mechanism of Piles

With the increasing load on a pile initially the resistance is offered by side frictionand when the side resistance is fully mobilized to the shear strength of soil, therest of load is supported by pile end. At certain load the soil at the pile end fails,usually in punching shear, which is defined as the ultimate load capacity of pile.

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The frictional resistancezQ=

depth .S zperimeter of pileS=

z

resistance of pile suQ

Qz

Ultimate point load .pu pu pQ q A=bearing capacity of soilpuq =

Ultimate load capacity u u suQ Q Q= +

p

=

in compression

u su

Q Q= uQ usQ

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in tensionuQ


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Point Load ca acit of Pile: General BearinPoint Load ca acit of Pile: General Bearin

Capacity approachCapacity approach

capacity equation. Shape, inclination, and depth factors areincluded in bearing capacity factors

* * *0.5pu c qq cN q N DN = + +

Since pile diameter is relatively small, third term may be droppedout

* *

Hence Pile load capacity

pu c q

( )* *. .pu pu p c q pQ q A cN qN A= = +

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Point Load capacity of Pile: Meyerhofs (1976)Point Load capacity of Pile: Meyerhofs (1976)

MethodMethod Granular soils:

Point bearing capacity of pile increases with depth in sands andreaches its maximum at an embedment ratio L/D = (L/D)cr.

Therefore, the point load capacity of pile is*. . .pu p q p ulQ A q N A q=

ce 632 pile foundations part-1 ppt

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