Civil Engineering Reference
In-Depth Information
Figure 5.28
Plan and elevations of Stonebridge Park Flats (Cooke
et al
., 1981):
(a) foundation plan (351 piles 450 mm diameter and 13 m long); (b) longitudinal
section
x
−
x
; (c) cross-section
y
−
y
.
The overall dimensions of the pile cap were 20.1 m by 43.3 m. Thus the average
stiffness of the cap, acting alone, may be estimated (Poulos and Davis, 1974) as
)
√
20
2
G
I
(1
k
r
=
.
1
×
43
.
3
(5.33)
−
ν
where the influence factor
I
is 0.85 for a raft of this aspect ratio. The value of
G
may
be taken as the value at a depth of
B
(1
−
0
.
5
B
/
L
), where
B
and
L
are the breadth and
length of the pile cap. This gives
G
=
42 MPa, and a cap stiffness (taking
v
=
0
.
1) of
k
r
=
3250 kN/mm.
The stiffness of the pile group by itself may be estimated, using programs such
as PIGLET, as
k
p
=
5300 kN/mm (Randolph, 1983). The piles were laid out on a
rectangular grid, with spacing of 1.60 m by 1.63 m. Thus each pile had an area of
