Underground Singapore 2011 stage and the end of backfilling, and the maximum normalized wall deflection (w/H) was 0.32%. The maximum normalized surface settlements (Sv/H) were greater than 0.5% at the western end of the station coinciding with the valley of Kallang Formation, but elsewhere the maximum normalized surface settlements were less than 0.34%. This is consistent with earlier observations about the maximum surface settlements being substantially higher than maximum wall deflections in the presence of compressible clays during excavations.
Kallang Formation
Jurong Formation (soils)
Jurong Formation (rocks) 0.8m-1m thick d-walls
Figure 7. Geological conditions & layout of ERSS at LBD station.
Strut removal & backfill completed
150
w / H = 0.5% 100
w / H = 0.25%
50
0
Normalised Settlement vs Deflection 1.6%
Sv / H = 1%
w / H = 1% Max settlement, Sv (mm)
Max wall deflection, w (mm)
Excavate to FEL
Max settlement vs excavation depth 200
150
Sv / H = 0.5% 100
Sv / H = 0.25%
50
0 0
5 10 15 20 Depth of excavation, H (m)
25
0
5 10 15 20 Depth of excavation, H (m)
25
Normal. max settlement Sv / H
Max wall deflection vs excavation depth 200
Sv / w = 2
1.2%
0.8%
Sv / w = 1
0.4%
Sv / w = 0.5
0.0% 0.0% 0.2% 0.4% 0.6% 0.8% Normalised max wall deflection w / H
Figure 8. Maximum wall deflection and ground settlements at LBD station.
2.5 Telok Blangah (TLB) Station Figure 9 shows the geological conditions and the layout of the ERSS for the cut-and-cover tunnel section at TLB station. The soil stratigraphy comprises of a thin layer of Kallang Formation (not more than 5m) overlying the Jurong Formation. Due to the excavation being shallower and further away from existing buildings, the ERSS at TLB station was less rigid and comprised mainly of soldier pile wall at 1.6m spacing with sheetpile lagging above and shotcrete lagging below 12m, and 1m contiguous bored pile walls at both ends of the station. The excavation depth was around 16m to 18m and this was supported using four levels of struts. The details of the design and construction at TLB station are described in Ng et al (2010). Figure 10 plots the maximum wall deflection and the maximum ground settlement during the construction of TLB station. The normalized maximum wall deflections (w/H) at the final excavation level were less than 0.19%, and the maximum w/H increased slightly to 0.40% after the strut removal and backfill stages. Considering that the soldier pile wall would be fairly flexible, the wall deflections are
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