Deep Foundation Part 2 Pile Capacity,Static Analysis.pdf

7/24/2019 Deep Foundation Part 2 Pile Capacity,Static Analysis.pdf

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Note No. 2

Piles Capacity fromStatic Analysis

2014-2015


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Deep Foundation (Part 2) Pile Capacity (Static Analysis) Dr. Nagwa

1

Individual Pile Capacity

1-Load capacity of piles from Static Analysis:

.

For compression Loading:

Static Formula Method ( ) ultimate capacity for axial load

= bearing resistance at the tip of the pile

tipend bearing

= friction resistance along the pile shaft..

Q f A f = Unit Frictional Resistance or adhesion

.

A= Shaft Area (Pile surface area)


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2

(=.)

*

Q A qq= Unit Bearing CapacityA= Area of Pile Base

.

Base Resistance

()

[

] ()

Tipcohesiveorfriction.

Where;

A area of pile base .

C= average cohesion of soil at the pile tip.

N 9 Constant.N Given in Tables depend on . minof{ effective vertical stress at depth Z or pile tip. effective vertical stress at critical depth.


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3

Shaft Resistance

.

. Due to cohesion or friction or both.

() == ()

Where;

A Pile Surface Area (m Z).

* )C= average adhesion of the soil around the shaft. (from table)KH( = ratio between horizontal and vertical earth pressure forcompression. (from table)

= angle of soil and pile friction.

m = perimeter of the cross section of the pile. ( B)D = Z H(C)(C)

().


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4

H()

()().

H

.

Values of KHCand KHTfrom the Egyptian Code

Pile type H- Pile 0.5-1.0 0.3-0.5Driven Pile Constant section 1.0-1.5 0.6-1.0

Driven Pile, Variable Section 1.5-2.0 1.0-1.3

Driven Pile, with water Jetting 0.4-0.9 0.3-0.6

Bored Pile (D

L


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1.Very soft clay

2.Fill

3.

Tension cracks

4.Organic soil

5.Agricultural soil

Earth pressure along pile and critical depth.

D

B

ZL=20BZcr

Weak SoilZs

-Zs

-Lcr

-D

D

B

Z

L=20B

Z

cr

Weak SoilZs

-Zs

-D


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8

60.

.

Effective lateral earth pressure.Total Pile Resistance in compression

For Piles in cohesive soils (Clay) only

Q ACN ACFor Piles in ()only

Q

A

[

N

]

tan =

=

Tension PilesT Q W

T KH

tan m Z

=D

= W In Sand

T AC W In clayW = Pile Weight

T . W


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9

KH Ratio between horizontal and vertical earth pressure forTension. (from table)

.

.

.

Compression pile Tension pile

thepilemovedownward

Qult

Qb

Qf

thepilemoveupward

W

QTult

Qf


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10

EXAMPLE

Determine the allowable capacity for the concrete boredpile.

Pile Diameter B = 0.50 mPile Length D = 14.0 m

Medium stiff clay:

C = 30 kN/m2

Ca = 25 kN/m2

= 18 kN/m3

Dense Sand: 40= 19kN/m3KH 1.0

Solution:

Q Q QQ A N (A C tan )== From sand only From clay and sand

Medium stiff

= 18 KN/msat

Dense sand= 19 KN/msat

12m

2m

K=1HC

C= 30 KN/m

C= 25 KN/ma

Clay


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A B 0.5 0.196 m

L

20B 20 0.5 10 m

L < Z L 1 0 8 8 0 K N / m

For Bored Pile 3 4 0 3 3 7

35 40

N 75 150

5 2

N 75 X 2 7 55 30 N 30+75=105

for Concrete 4 0 3 0

Medium stiff

= 18 KN/msat

Dense sand= 19 KN/msat

12m

2m

Clay

L=10mcr

m


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0.5 1.57

Q A N (A C tan )=

=

Q 0.196 80 105 (1.571225) 1 8 0 t a n 3 0 1 . 5 7 2Q 1646471145Q 1646 616 2262 KNAllowable Pile Capacity

Q .. Q 22623 754 KN

Check of Concrete Capacity (as a short column under

compression):

P 0.35 f A 0.67 f AP 0.35 2 0 1 0 0.196 0.67 240 10 10 0.00196 4523.68 KN

Taking serviceability factor, 1.5deflection , buckling and cracking

ultimate to working.

Pwg 4523.681.5 3015.78> Q(O. K. )


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13

Example 2

A 10 m cased pile, with radius 25cm, was drive in a non-homogeneous

soil, where the first 2m was fill followed by 5m medium cohesive soil,

then loose sand with 2 8. The casing is 8mm thick. Find theallowable pile loading in compression and in tension. Check the

strength of pile material. f 20Mpa, and mild steel for the shellwith f 240Mpa

Solution:

.

.

.

Clay

= 18 KN/msat

loose sand= 19 KN/msat

2mFill

5m

3m

G.W.T= 16.5 KN/m


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.

1)

The allowable pile loading in compression

Q Q Q

Q A N (A C tan )==

From sand only From clay and sand

A B 0.5 0.196 m

L 20B 20 0.5 10 m

L > Z zFill

Clay= 18 KN/msat

loose sand= 19 KN/msat

2m

5m

3m

= 16.5 KN/m

m

m

m

C= 30 KN/ma

0.5

0.08


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For Driven Pile

402 28 402 34

30 35

N 30 75

5 4

N 45 X 4 4 55 36 N 3 0 3 6 6 6

20 for Steel

0.5 1.57 K(H) 1.25 for drivenK(H) 0.8 for drivenC 30

+ 86.5 KN/mQ A N (A C tan )== Q 0.196 100 66 (1 . 5 7 5 3 0)

1.2586.5tan201.573


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Q 1293.6235.5185.35Q 1293.6 420 1714.46 KNAllowable Pile Capacity

Q QF.S.Q 1714.53 571.5 KN

2)

The allowable pile loading in tension

T Q WW A L

W R AR L A LAssume

R 25 KN/m 78 KN/m^3

W 25 4 0.484

7 8 4 (0.5

0.484

) 10

W 55.64 KNT A C tan ==


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T (1. 57 5 30) 0.886.5tan201.573 55.64T 235.5118.6355.64=409.8 KNAllowable Pile Capacity

T 354.133 55.64 173.68 KN .

3)

Check the strength of pile material.

Check of Concrete Capacity (as a short column under

compression):P 0.35 f A 0.67 f AP 0.35 2 0 1 0 4 0.484

0.67 240 10 4 0.5 0.484

3275KN Taking serviceability factor, 1.5

deflection , buckling and cracking

ultimate to working

Pwg 32751.5 2183.33> Q(O. K. )


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Example 3

A precast driven pile having square cross section 400 x 400 mm, is to be 22 m in

length. Design the pile reinforcement that may be determined by the lifting

operation.Consider the two-point left to decrease the bending moment. = 30MPa for concrete and fy 240 MPafor steel.Solution

Weight of the pile, . 0.4 x 0.4 x 25 4 kN/mImpact factor for the sudden snatch of the crane books at each lift. I 1 . 4The suddenly applied load is twice that for the same gradually applied or static

loading.

Design weight, WD W I 2 4 x 1.4 x 2 11.2 kN/m 32 11.22232 169.4 The x-sec. of the pile is subjected to bending moment and axial compression. It is

designed with USD for members subjected to eccentric forces using interaction

diagrams. Since the moment can take any direction, () 1and the foursides of the x-sec. is reinforced similarly.

Precast pile is having good quality concrete. Then, the concrete cover is takin 4

cm then, ) 0.8.

169.4(30 10 0.4 0.4) 0.0875, 22 113 0 1 0 0.40.4 0.0504

from interaction design curves with 1, 0.8, 240 , 3.5:. Reinforcement ratio 10 3.5 35 10 1.125% ,

One side =


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. 40 40 18 Choose 4 13mm per face ( 21.23 ) and min stirrups of 5 8 mm/m'.Or (11.25)% 1.25100 4 0 4 0 2 0 1016and use stirrups 58

Deep Foundation Part 2 Pile Capacity,Static Analysis.pdf

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