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Pile FOUNDATION

By

Dr. Yavuz YARDIM

Dept. of Civil Engineering

14 December 2015

Foundation

Foundation

Pad Footing

Combined Footing

Raft Footing

Wall / strip Footing

Pile Foundation

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Pile foundation Concrete

Steel

Timber

Hard strata

3m

Pile foundation consists of two parts

•Pile

•Pile cap

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Raft footing• Raft footing is an inverted flat slab

(column at top & slab at bottom) When choose raft footing? For large combined footingWhen column is very closeWhen soil bearing capacity for

each column is different For large load on weak type of soil Large differential settlement

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Design Foundation

Related to soil(soil bearing

capacity)

Related to structure

How to choose type of footing

Depends on soil property

Depends on profile of soil

Depends on load

Depends on water table inside the ground

Depends on cost

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Raft footing• Raft footing is an inverted flat slab

(column at top & slab at bottom) When choose raft footing? For large combined footingWhen column is very closeWhen soil bearing capacity for

each column is different For large load on weak type of soil Large differential settlement

General considerations

• Foundations transfer loads from the structureor building or individual columns to the earth

• Type of foundation to be used depends on anumber of factors

– Soil properties & condition

– Type of structure & loadings

– Permissible amount of different settlement

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Pile foundation

Why Pile foundations-

• When a solid bearing stratum is deeper thanabout 3m below the base level of thestructure a foundation supported on bearingpiles will provide an economical solution

BS 8004: Code of practice for foundation

Pile foundation Concrete

Steel

Timber

Hard strata

3m

Pile foundation consists of two parts

•Pile

•Pile cap

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100mm

column

Pile cap

Pile

S = not less than2Φ

Φ

Due to Pile arrangement shape of pile cap also different

More economical

More conservative

100mm

Abutment

Pile cap

Pile

Beam / bridge girder

Pile

d= ½SPile cap

Type of

pile cap

Rigid (act as rigid body i.e. move as one unit

Flexible

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N = total no. of pile

N1 = total no of pile per row

N2 = total no. of inclined pile per row

S = pile spacing

W = weight of pile cap

P = weight of column / pier

Fv = axial force in the pile due to vertical load

FH = axial force in the pile due to horizontal / lateral load

Fm = axial force in the pile due to moment

F = total force/load of pile = Fv+ FH+ Fm

Calculation of Forces in Pile

Step-1: calculate the forces in each pile due to axial load, lateral load and moment in the column / pier

Step-2: Assume soil confine the pile

Step-3: design the pile as a short column / get the pile size from the table

100mm

Pile cap

Pile

P

W

4321

S S S

R

1R

1

H

h

Vertical load calculation (act at center point of pile cap)

N

WPFV

For vertical pile

N

WPFV

N

WPFV

21cos

R

R

VF

N

WP

Again

cos,

For inclined pile

N

WP

R

1

)R(1 2

FV

FV

R

R

N

WPFV

21

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Horizontal / Lateral load calculation

Note:

Horizontal load will be distributed on the inclined piles only, vertical pile

will carry zero horizontal load

For inclined pile

2N

H

R

1

)R(1 2

FH

FH 21

1sin

R

HF

N

H

Again 2sin,

1

1 2

2

R

N

HFH

Moment Force calculation

σ = (Fm/A) = (M/z) = (My / IN.A)

IN.A = I0 + Ad2

Where, A = area of single pile

Take 1st row

I = N1x A.(1.5S)2

Take 2nd row

I = N1 xA.(0.5S)2

Total IN.A = N1 xA[(1.5S)2 + (0.5S)2] x 2 (for

symmetrical axis)

(Fm/A) = (My / IN.A) = [M*y] / [N1 xA[(1.5S)2 +

(0.5S)2] x 2

Fm = [M*y] / [2 N1 [(1.5S)2 + (0.5S)2]

0

Y

100mm

Pile cap

Pile

P

W

4321

S S S

R

1R

1

H

h

M1

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R

R

I

yMF

AN

m

2

.

1

)R(1 2

For inclined pile

ANI

yM

.

R

1

Fm

Fm

Total moment M = M1 + Hxh

Where, y - is the distance from the pile cap center (NA) to the individual pile