Start of SCL construction is imminent as Dr. Sauer & Partners submit Arthur Street Construction Shaft Design to LU for Compliance. In parallel DLR Sprayed Concrete Lining (SCL) temporary works designs have evolved.
The first major section of tunnelling work for the Bank Station Capacity Upgrade will be the SCL construction shaft in Arthur Street and construction will commence in the coming months. The constrained worksite in the City of London has involved significant utility diversions and the shaft excavation will encompass an existing disused LU station and will be constructed immediately adjacent to a number of buildings. This complex design package (figure 1) has now been submitted to LU for Compliance Review.
Figure 1 - Indicative View of Arthur Street Construction Shaft
Another significant development has been the SCL temporary works solution for two proposed DLR cross passages, CP2 and A1. These temporary works were initially intended as squareworks construction. However, due to constructability issues associated with roof support other options were reviewed. After a feasibility study and modelling of impacts on the existing DLR tunnels it was decided that SCL provided the optimal solution.
The solution for both passages requires SCL shafts to be constructed from SCL tunnels at Northern line level (figure 2). Elements of the permanent works will be constructed as the shafts are sunk to help restrain movements of the existing assets and the permanent reinforced concrete cross passages will be completed and externally waterproofed from within the SCL temporary works
Figure 2 - View of SCL Temporary Works at DLR Cross Passages CP2 and A1
Parallel to the design of the new tunnels the assessment of the existing LU and DLR assets continues. The results of the Deep Tube Tunnel Assessment have been used as part of the risk based mitigation process resulting in a full suite of Instrumentation & Monitoring drawings for the existing infrastructure plus trigger values. The mitigation measures fall into three broad categories: physical mitigation measures, monitoring or in some cases defined inspection. Dr. Sauer & Partners are working with LU and Dragados to establish trigger values for existing track and escalator tunnels and are undertaking a risk review of the impact of ground movements on the existing finishes within the station. A set of trigger values has been developed for the proposed tunnels along with the respective action plans.