For the construction of the 16.2km long Liefkenshoek rail link, two single-track tunnels were bored undercrossing the river Scheldt and the B1-B2 Canal Dock. Once they have passed the Scheldt, the tunnels go upward towards the arrival shaft passing closely underneath the bottom of the Canal Dock. The soil burden above the tunnel, consisting mainly of silt deposits, would only be 4,4 m thick, which could not provide sufficient resistance.
The original design had foreseen to dredge 8 m of the silt and replace it with 138,000m³ of compacted sand and a 26,000m³ concrete deck on top of it. The compaction of the underwater sand layer to 17 MPa would have needed a 4 m thick temporary sand ballast, which would have reduced the dock's draft by 2m for a period of at least 6 months.
The main contractor Locobouw consortium designed an alternative solution using a 270m long and 32m wide sheet pile wall excavation pit. Between the sheet pile walls 42,500m³ of silt was dredged and replaced with 26,000m³ of low-strength mortar (≤ 5 MPa) and a 16,500m³ slab of steel fibre reinforced concrete.
The excavation pit was created by driving 2,212 tons of sheet piles with lengths between 23 and 31m. These lengths made it possible to pitch the sheet piles above the water level using a normal vibrator (ICE 36RFts) and impact hammer (D30 Delmag). The sheet piles were cut off by divers at the bottom of the Canal Dock. The top portions were recovered and bought back by ArcelorMittal (1,192 tons). The 540m of wall were driven in 8 weeks time only.
Driving of the steel sheet piles in the B1-B2 Canal Dock.
The alternative sheet pile solution resulted in a shorter execution time, the avoidance of 6 months limited draft for the shipping traffic and a safer solution for all stakeholders.
Kompellaan 13 bus 2
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