Civil Engineering Reference
In-Depth Information
Length of side of square foundation of same area
=
√7850
=
88.6 m. This imaginary
square can be divided into four squares as in Example
3.5(
i). Length of sides of
squares
=
44.3 m.
B
z
z (m)
n m
= =
I
σ
4I
σ
σ
z
(kPa)
10
4.43
0.248
0.992
446
25
1.77
0.221
0.884
398
50
0.89
0.16
0.64
288
100
0.44
0.071
0.284
128
150
0.3
0.04
0.16
72
200
0.22
0.024
0.096
43
3.5.4
Irregularly shaped foundations
It may not be possible to employ Fadum's method for irregularly shaped foundations, and a numerical solu-
tion is then only possible by the use of Boussinesq's coefficients, K, and the principle of superposition.
Computer software for calculating the vertical stress increments beneath irregularly shaped foundations
is widely available and nowadays such software is routinely used to determine the stress values. Histori-
cally, however, the Newmark chart (Newmark,
1942
) was used to determine the values and any reader
interested in the use of the Newmark chart is guided to the seventh, or earlier, editions of this topic for
a full and detailed explanation.
3.5.5 Bulbs of pressure
If points of equal vertical pressure are plotted on a cross-section through the foundation, diagrams of the
form shown in Figs
3.12a and 3.12b
are obtained.
Fig. 3.12
Bulbs of pressure for vertical stress.
