Lest check Bearing Capacity for a rectangular foundation first
Assume 2m x 3m rectangular footing B=2m L=3m
We are assuming the depth of footing D
f
=2m inorder to pass soft Organic top soil
qu
=
cNc
(
1
+
0.3
∗
B
L
)
+
γDfNq
+
1
2
γBNγ
(
1
−
0.2
∗
B
L
)
Eq.134
C: Cohesion from laboratory testing (0,93kg/cm3) :
91,22 kN/m2
?
:
unit weight of soil at foundation level from laboratory test : 20.11 kN/m
N
c
, N
q
and N
ɣ
are the bearing capacity factors.
They are functions of the angle of friction
𝝓.
Figure 215
Hawever Before that we need to get Anfle of Shear Resistance
186
Figure 216
We can get the blow N number from SPT log which is 14
Figure 217
Figure 218
N
c
(38)
, N
q
(25)
and N
ɣ
(25)
qu
=
cNc
(
1
+
0.3
∗
B
L
)
+
γDfNq
+
1
2
γBNγ
(
1
−
0.2
∗
B
L
)
qu
=
91.22
∗
38
∗
(
1
+
0.3
∗
2
3
)
+
20.11
∗
2
∗
25
+
1
2
20.11
∗
25
∗
(
1
−
0.2
∗
3
2
)
qu
=
5382.13
kN
m
2
qnu
=
5382.13
−
γDf
(
20.11
∗
2
)
=
5341.91
kN
m
2
qna
=
5341.91
3
=
1780
kN
m
2
q
=
Fd
+
Wf
A
−
γDf
Eq. 135
q
= Structural Loading
G
= 4190.15 Tn = 41750.72 kN (From Static Calculations)
Q
= 948.86 Tn = 9454.45 kN
Fd
= 1.4G + 1.6Q = 58451 + 15127 = 73578 kN
A
= Area under the foundation(2*3) 6 m
2
187
?
D
f
= 21.11*2 = 42.22 kN/m
2
W
f
= (B*L*D*
?
con
) = 2*3*2*23.6 = 319.2 kN (unit weight of concrete = 23.6 kN/m
3
)
q
= (73578 + 319.2)/6  42.22 = 12273 kN/m
2
qna (
1780
kN/m
2
) < q (12273 kN/m
2
)
NOT ACCEPTABLE
!!!
11.11
TRY RAFT FOUNDATION
We used modifide equation of Meyerhof (1963)
qn
(
u
)
=
cu
∗
c
∗
Fcs
∗
Fcd
¿
{
cu
∗
Nc

1
+
B
L
(
Nq
Nc
)

∗

1
+
0.4
(
Df
B
)

}
Eq. 136
qn
(
a
)
=
{
cu
∗
Nc

1
B
L
(
Nq
Nc
)

∗

1
+
0.4
(
Df
B
)

}
Fs
Eq. 137
Where
q
n(U)
= net ultimate bearing capacity
q
n(a)
= net allowable bearing capacity
c
u
= undrained cohesion
N
c
,N
q
= bearing capacity factors with respect to cohesion and surcharge respectively
188
F
cs
= shape factor with to cohesion
F
cd
= shape factor with respect to depth
B,L
= breadth and length of foundation respectively
D
f
= depth of foundation
FS = factor of safety
From Structural Engineers Suggestions we use;
Df : 1,5m
B : 14m
L : 28m
Cu : 91,22 kN/m2
Nc (38) , Nq(25)
and Nɣ (25)
qnu
=
91.22
∗
38
∗
[
1
+
14
28
(
25
38
)
]
∗
[
1
+
0.4
(
1.5
14
)
]
=
4804
kN
m
2
qna
=
4804
3
=
1600
kN
m
2
q
=
Fd
+
Wf
A
−
γDf
q
= Structural Loading
G
= 4190.15 Tn = 41750.72 kN (From Static Calculations)
Q
= 948.86 Tn = 9454.45 kN
Fd
= 1.4G + 1.6Q = 58451 + 15127 = 73578 kN
A
= Area under the foundation(14.71*28) 411 m
2
?
D
f
= 21.11*2 = 42.22 kN/m
2
189
W
f
= (B*L*D*
?
con
) = 14*28*1.5*23.6 = 14580 kN (unit weight of concrete = 23.6 kN/m
3
)
q
= (73578 + 14580)/411  42.22 = 172 kN/m
2
qna (
1600
kN/m
2
) > q (172 kN/m
2
)
NOT ACCEPTABLE
!!!
11.12
SETTLEMENT
11.12.1
Elastic Settlement (Si)
Jambu. Bjerrum and Kjaernslı formulation for unitial settlement
Se
=
qo
(
α B
'
)
(
1
−
μs
2
)
Es
IsIf
Eq. 138
q
o
= qn from raft foundation bearing capacity calculation = 172 kN/m
2
α = 4 for the centre of the foundation
B’ = B/2 for the centre of foundation = 14/2 = 7m
µ
s
= 0,3 poisons ratio
E
s
: Elastic modulus
Butler and Bjerrum relationship for consolidated clays
: Es/Cu = 400
E
s
= 400 x 91,22 = 36488 kN/m
2
For example ;
190
If = 0.97
Df/B = 1.5/14 = 0.11
L/B = 28/14 = 2
Figure 219
m
'
=
L
B
=
28
4
=
2
n
'
=
H
B
2
=
2
14
2
=
0.28
F
1
= 0.022
F2 = 0.060
Is
=
F
1
+
1
−
2
μs
1
−
μs
F
2
Eq. 139
Is
=
0.022
+
1
−
2
∗
0.3
1
−
0.3
∗
0.060
=
0.056
Se
=
172
∗
4
∗
14
2
∗
1
−
0.3
2
36488
∗
0.056
∗
0.97
=
0.006
m
=
6
mm
11.12.2
Consolidation Settlement (Sc)
Sc
=
mv Δσ ' H
Eq. 140
191
Mv
=
1
1
+
e
0
∗
(
e
0
−
e
1
)
σ
1
−
σ
0
Eq. 141
Mv
=
1
1
+
e
0
∗
(
e
0
−
e
1
)
σ
1
−
σ
0
=
1
1
+
0.79
∗
0.79
−
0.59
294
−
29
=
4.2
∗
10
−
4
m
2
kN
=
0.42
m
2
MN
Şekil 220
H= 2m settlement will occur in that layer from log
Figure 221
192
Figure 222
m = 2 m
mz = 14/2 = 7 m = 3.5
nz = 7/2 = 3.5 n = 1.75
I
r
= 0.23
??
'
0
= 4*0.23*172 = 158.24 kN/m
2
S
c
= 0.42*158.24*2 = 132 mm
(Eq.140)
Total Settlement ST = S
e
+ S
c
= 132+6 = 138 mm
193
CHAPTER 12
PILE FOUNDATIONS
12.1
OUTLINE of LECTURES
Pile Types Selection
Capacity of Single Piles
Capacity of Pile Groups
Settlement Considerations
12.2
LOAD/SETTLEMENT RESPONSE
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