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Technical Committee 211 /
Comité technique 211
surface. In the tributary area of the instrumented piles, six earth
pressure cells and one piezometer were installed beneath the raft
at the depth of 7.2 m. Earth pressure cells E1-E3 were installed
on the intact soil and earth pressure cells D1-D3 were installed
on the deep mixing walls. The vertical ground displacements
below the raft were measured by differential settlement gauges.
LVDT-type transducers were installed beneath the raft at depths
of 8.5 m, 14.0 m, 20.0 m, 35.0 m and 50.0 m to measure the
relative displacements to a reference point at a depth of 60.0 m.
The settlements of the foundation were measured at the
monitoring points on the raft by an optical level. The
measurement of the vertical ground displacements was begun
during the excavation for the foundation construction. The
measurement of the axial loads of the piles, the contact
pressures and the pore-water pressure beneath the raft was
begun just before the casting of the 0.6-m thick foundation slab.
5 RESULTS OF MEASUREMENTS
5.1
Foundation settlement
Figure 5 shows the measured vertical ground displacements
below the raft. The measured ground displacement at the depth
of 8.5 m after the casting of the foundation slab, was
approximately equal to the foundation settlement. The
foundation settlement increased considerably just before the end
of construction (November 15, 2011) due to the water pouring
into the underground pits. Thereafter, the foundation settlement
became stable and reached 21 mm 11 months after the end of
construction (November 3, 2012). Figure 6 shows the settlement
profile of the raft measured by the optical level just before the
end of construction. The measured settlements were 12 to 24
mm and the maximum angular rotation of the raft was 1/1400
radian which satisfied the design requirements.
5.2
Pile load and contact pressures
Figure 7 shows the development of the measured axial loads of
piles P1-P4. The axial loads also increased considerably just
before the end of construction due to the water pouring.
Thereafter, the pile-head loads reached 4.7-11.2 MN in
November, 2012. Figure 8 shows the distribution of the
measured axial loads on pile P1. Since the piles were
surrounded by the deep mixing walls to a depth of 20.0 m, the
skin friction of the pile shaft between the depths of 8.5 m and
20.0 m was quite small. The average skin friction between the
depths of 20.0 m and 47.0 m was 76 kPa. The ratio of the pile-
toe load to the pile-head load was 0.21 in November, 2012.
Figure 9 shows the development of the measured contact
pressures between the raft and the soil and the pore-water
pressure beneath the raft. The measured contact pressures
between the raft and the intact soil seemed to reach a state of
equilibrium in early stage of the construction, while those
between the raft and the deep mixing walls increased with
construction loading in the same way as the axial loads of the
piles. The measured contact pressures between the raft and the
deep mixing walls were 137-180 kPa and those between the raft
and the intact soil were 66-72 kPa just before the end of
construction. The measured pore-water pressure was
approximately 40 kPa..
5.3
Load sharing between raft and piles
Figure 10 shows the time-dependent load sharing among the
piles, the soil, the deep mixing walls and the buoyancy in the
tributary area of the instrumented piles shown in Fig. 4. The
sum of the measured pile-head loads and the raft load in the
tributary area varied from 61.3 to 62.0 MN after the end of
construction, which was generally consistent with the design
load of 64.0 MN. Figure 11 shows the ratios of the load carried
Tributary area
K
Figure 4. Locations of monitoring devices
Monitoring devices
:Settlement gauges
:Instrumented pile
:Earth pressure cell
:Piezometer
5
7
9
11
9.6m 9.6m 9.6m
I
9.6m
E1
P4
D1
P1
G
9.6m
S1
W D3
1
E
9.6m
P2
P3
E2
D2
E3
Mar.11,2011
End of construction
Nov.3,2012
-30
-20
-10
0
Set t l ement (mm)
Figure 6. Measured settlement profile of raft
A
C
G
I
K
M
O
R
U
Street ⑨
Nov.3,2012
▽
Nov.3,2012
▽
-5
0
5
10
15
0
200
400
600
800
1000
Axi al l oad (MN)
Ti me (days)
8. 5m
20m
47m
Figure 7. Measured axial loads of piles
(b) Axial loads of pile P1
Depth
Mar.11,2011
▽
End of construction
▽
-5
0
0
200
400
600
800
1000
Ti me (days)
5
10
15
Axi al l oad (MN)
P1
P2
P3
P4
(a) Pile-head loads of piles P1 to P4
Mar.11,2011
▽
End of construction
▽
Foundation slab
▽
Foundation slab
▽
Figure 5. Measured vertical ground displacements below raft
-
-
-
0
200
400
600
800
1000
V al di spl acement (mm)
Ti me (days)
30
20
10
0
10
ert i c
8. 5m
14m
20m
35m
50m
-
Foundation slab
▽
▽
▽
▽
Depth
