Download CE 632 Bearing Capacity PPT.pdf PDF

TitleCE 632 Bearing Capacity PPT.pdf
TagsSolid Mechanics Physics & Mathematics Physics Applied And Interdisciplinary Physics Mechanical Engineering
File Size4.7 MB
Total Pages48
Document Text Contents
Page 1

CE-632CE 632
Foundation Analysis and
DesignDesign

Ultimate Bearing Capacity
The load per unit area of the foundation at which shear failure in soil

i ll d th lti t b i it

Ultimate Bearing Capacity

1

occurs is called the ultimate bearing capacity.

Page 2

Foundation Analysis and Design: Dr. Amit Prashant

Principal Modes of Failure:Principal Modes of Failure:

General Shear Failure: Load / AreaLoad / Area
q

m
en

t qu

S
et

tle

Sudden or catastrophic failure
Well defined failure surfaceWell defined failure surface
Bulging on the ground surface adjacent to foundation
Common failure mode in dense sand

2

Page 24

Foundation Analysis and Design: Dr. Amit Prashant

Bearing CapacityBearing Capacity
Correlations with
SPT-valueS a ue

Peck, Hansen, and
Thornburn (1974)Thornburn (1974)

&

IS:6403-1981
Recommendation

24

Page 25

Foundation Analysis and Design: Dr. Amit Prashant

Bearing Capacity Correlations with SPT-valueBearing Capacity Correlations with SPT value

Teng (1962):
1 ( )2 21 3 . . 5 100 . .
6nu w f w

q N B R N D R⎡ ⎤′′ ′ ′′= + +⎣ ⎦
For Strip Footing:

1F S d ( )2 21 . . 3 100 . .
3nu w f w

q N B R N D R⎡ ⎤′′ ′ ′′= + +⎣ ⎦
For Square and
Circular Footing:

For Df > B take Df = BFor Df > B, take Df B

Water Table Corrections: Dw

[0.5 1 1ww w
D

R R
D

⎛ ⎞
= + ≤⎜ ⎟⎜ ⎟

Water Table Corrections: w
Df

[w w
fD⎜ ⎟⎝ ⎠

[0.5 1 1w f
D D

R R
⎛ ⎞−

′ ′= + ≤⎜ ⎟⎜ ⎟ B

B

25

[0.5 1 1w w
f

R R
D

+ ≤⎜ ⎟⎜ ⎟
⎝ ⎠

B

Limit of influence

Page 47

Foundation Analysis and Design: Dr. Amit Prashant

Bearing Capacity of Footings on Slopes
B l (1997) A i lifi d hBowles (1997): A simplified approach

B α = 45+φ’/2
B

'

Df
a

f
qu

g
α = 45+φ /2

a' c'

g'
qu

f'

α α45−φ’/2
a c

e
α α

45−φ’/2
b'

c

e' ror
bd

B

b

d'

Compute the reduced factor Nc as:

. a b d ec c
L

N N
L

′ ′ ′ ′′ =

B
g'

qu
f'

Compute the reduced factor Nq as:

c c
abdeL

α α
45−φ’/2

a' c'
e'

47

. a e f gq q
aefg

A
N N

A
′ ′ ′ ′′ =b'

d'

Page 48

Foundation Analysis and Design: Dr. Amit Prashant

Soil Compressibility Effects on Bearing Capacity
Vesic’s (1973) Approach
Use of soil compressibility factors in general bearing capacity equation.
These correction factors are function of the rigidity of soilThese correction factors are function of the rigidity of soil

tan
s

r
vo

G
I

c σ φ
=

′ ′ ′+
Rigidity Index of Soil, Ir:

B
Critical Rigidity Index of Soil, Icr:

3.30 0.45

tan 45
2

B
L

φ

⎧ ⎫⎛ ⎞
−⎜ ⎟⎪ ⎪⎪ ⎪⎝ ⎠

⎨ ⎬′⎡ ⎤⎪ ⎪−⎢ ⎥⎪ ⎪⎣ ⎦⎩ ⎭
B/2

( ). / 2vo fD Bσ γ′ = +

20.5.rcI e
⎢ ⎥⎪ ⎪⎣ ⎦⎩ ⎭=

Compressibility Correction Factors, cc, cg, and cq ( )vo fγ
r rcI I≥For 1c qc c cγ= = =

( )103.07.sin .log 2.0.6 4.4 .tan rIB φφ
′⎡ ⎤⎛ ⎞ ′− +⎢ ⎥⎜ ⎟ ′⎝ ⎠

r rcI I<
1 sin 1Lqc c e

φ
φ

γ

⎢ ⎥⎜ ⎟ ′+⎝ ⎠⎣ ⎦= = ≤For

For 0 0.32 0.12 0.60.logc r
B

c I
L

φ′ = → = + +

48

L
1

For 0
tan

q
c q

q

c
c c

N
φ

φ


′ > → = −


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