The detailed design for the permanent works required to complete the construction of the tunnel on the Tesco Gerrards Cross project has now received Form B approval from Network Rail. Preparation of the site in order to resume permanent works on the tunnel was completed in February 2009.

The first stage of this permanent construction process was to keep the existing tunnel framework and use a crane to add in 63 new replacement tunnel. This work was completed in April 2009.

These units will be used as a cast for the new permanent reinforced concrete arch structure, with concrete being poured over them. The advantage of this is that while the original arch is made from precast units which connect in the middle, the reinforced concrete arch will be seamless, as well as adding a significant layer of extra support that will bear the weight of the store and store foundations.

This process of pouring concrete will be completed in stages from east to west, progressively moving away from the Marsham Lane Bridge and towards Packhorse Road Bridge, with the reinforced concrete arch structure then waterproofed. This structure will in turn support lightweight foamed concrete and fill material to produce a suitable building platform.

Once the tunnel has been completed, construction of the store will commence which we estimate will take 21 weeks. The store’s foundations will be modified but the store will remain the same as it was originally designed and approved. Meanwhile extensive carriageway and footway improvements will be carried out on Packhorse Road and completed in November 2010.

With construction work completed and the station car park area reinstated the store will open towards the end of 2010.