ce 632 pile foundations part-1 ppt
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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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
Pre-cast Piles:
Usual length: 10 m 45 m
Usual Load: 7500 kN 8500 kN
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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
Disadvantage:
Difficult to trans ort
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Difficult to achieve desired cutoff
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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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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Foundation Analysis and Design: Dr. Amit Prashant
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=
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