As works on the primary lining approach their finish with 96% of the works concluded, construction of the secondary lining comes to the fore. To date 10% has been completed.
During the last three months, work in the Northern tunnels was focused on linking the station’s concourse area to the Jubilee line. This was achieved by constructing the Jubilee line overbridge (JLO), which combines sprayed concrete lining (SCL) construction methods with traditional square works. An SCL canopy rests on mass concrete side walls. From the completed JLO, an inclined staircase tunnel was constructed to establish access to the binocular tunnels forming the new cross passage. After completion, the Binocular Tunnels will be the final connection to the Jubilee line platform tunnels.
In the Southern tunnels, excavation and support of Lift 3 Shaft (L3S) was challenging. L3S will provide a step-free route to the Jubilee line, access to the Central line and a link to the future Bond Street Crossrail Station. Prior to the start of shaft excavation, probing indicated unfavourable ground conditions. Water saturated sand lenses were found within the Upper Mottled Bed (UMB) Lambeth Group. Advancing excavation and support of the shaft whilst dealing with water ingress 2m above the shaft bottom level posed a demanding time for the team. To combat the water ingress, which was significant at times, a pre-support of sheet piles was driven into the ground followed by excavation of small pockets of soil and immediate SCL support. This method which was a combination of pre-designed contingency measures proved to be successful. Since the sand lens was only localized to one side of the shaft, the construction of a Passage Tunnel from the bottom of L3S went smoothly in the competent UMB.
All these works have been carried out without affecting the operations of Bond Street Station.
In the upcoming months, the primary lining will be completed. Construction will continue with secondary lining works including regulating layer and waterproofing application.