Underground Singapore 2011 about 20m. Figure 4 plots the maximum wall deflection and the maximum ground settlement during the construction of PPJ station. Due to the very rigid ERSS, the wall deflections are low and the maximum wall deflections are less than 0.2% times of the excavation depth. However, due to the thick compressible layer from the Kallang Formation, there is some consolidation during the excavation and the maximum surface settlements went up to 0.39% of the excavation depth. The effect of this consolidation is to cause settlement of the ground to go beyond two times that of the wall deflection where there is thick Kallang Formation – this is in contrast to the excavation response at WCT station in the absence of compressible clays. Another observation of Figure 4 is that whilst the maximum wall deflection remained nearly the same between the final excavation stage and the end of backfilling stage, the maximum surface settlement increased substantially. This is because the wall is rigid enough so that there is not much additional deflection during backfill stage, but the consolidation was still ongoing and this result in increased surface settlement during backfilling stage.
Kallang Formation
Jurong Formation (soils)
Jurong Formation (rocks)
Figure 3.Geological conditions & layout of ERSS at PPJ station. Max wall deflection vs excavation depth
w / H = 1%
Strut removal & backfill completed
150
w / H = 0.5% 100
w / H = 0.25% 50
0
Excavate to FEL
5 10 15 20 Depth of excavation, H (m)
25
Sv / H = 1%
Strut removal & backfill completed
150
Sv / H = 0.5% 100
50
Sv / H = 0.25%
0 0
Normalised Settlement vs Deflection 0.5%
0
5 10 15 20 Depth of excavation, H (m)
25
Normal. max settlement Sv / H
Excavate to FEL
Max settlement vs excavation depth 200 Max settlement, Sv (mm)
Max wall deflection, w (mm)
200
Sv / w = 2
Sv / w = 1
0.4% 0.3%
Sv / w = 0.5
0.2% Excavate to FEL 0.1%
Strut removal & backfill completed
0.0% 0.0% 0.1% 0.2% 0.3% 0.4% 0.5% Normalised max wall deflection w / H
Figure 4. Maximum wall deflection and ground settlements at PPJ station.
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