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Bank Station Capacity Upgrade has now reached the point everyone has been working for – construction of the shaft and tunnel works using sprayed concrete lining (SCL). Works began at Arthur Street on the sheet pile shaft at the start of 2017. The sprayed concrete facilities have been set up and works began in the middle of February. The project has had good results from the concrete site set-up trials (Fig. 1 below) and the team look forward to spraying the first advances. The shaft will be constructed through the existing disused King William Street Station, which has been backfilled with foam concrete, and is within a few metres of the piles to a new building, which is nearing completion, at 33 King William Street. The SCL works will be serviced from a tight worksite and deliveries and spoil disposal has been carefully considered and planned to support the tunnelling production (Fig. 2).
Alongside the construction, the design work continues, with work on the final design changes underway. Dr. Sauer & Partners is currently completing the design for the load transfer structure for the pile interceptions at 6-8 Princes Street. An existing 1970s office building founded on 20m deep 1.8m diameter end bearing piles is located on the alignment of the proposed new Northern line running tunnel (Fig. 3). Dr. Sauer & Partners is designing load transfer structures as part of the tunnel lining system to support these piles (and the underreams) cut by the tunnel profile (Fig. 4). These structures are also designed to support future potential storeys to the building i.e. higher pile loads than current.
In addition to this, temporary works design is being carried out for the Lower PRM Shaft. This design will use similar hybrid techniques for those employed for the DLR Temporary Works; employing an SCL canopy to create access for the construction or permanent squareworks. This initiative provides significant cost, time and health and safety benefits.
As the Deep Tube Tunnel Assessment continues, Dr. Sauer & Partners is finalising the design of the mitigation measures to be employed within the existing station linings. These will strengthen the existing London Underground (LU) assets, allowing for tunnelling works to continue with minimal impact on the station.
Finally, in line with the construction programme, Dr. Sauer & Partners is undertaking the next phase of defect surveys of LU assets within the Bank-Monument Station complex. This will include areas of the existing Northern line Running Tunnels and District and Circle line assets. The survey establishes a prior to construction documentation that will be the basis for any future impact to the undeground LU assets by the new tunnel construction.
Fig 1 - SCL concrete trials for the site set-up
Fig 2 - Arthur Street site set-up
Fig 2 - Plan view of the piles that will be intercepted for 6-8 Prince Street
Fig 4 - 3D CAD modelling for the transfer structures at 6-8 Princes Street
The below images show an updated view of the shaft at Arthur Street: