HARDING PRIZE COMPETITION 2023 | BTS
The excavation of a pre-tunnel or cavern was rejected
due to the size of the adit and the shallow and difficult ground conditions. Also, the system adopted would allow the reuse
of the same launching structures and, in Silvertown, achieve the learning curve for the re-launch of the machine at the Greenwich rotation chamber. One of the main challenges in the project was the
assembly and launch of the TBM in such a confined shaft. Not only was the TBM to be fitted in but also all the logistics and muck conveying. This limitation with the space drove the study and design of a launching structure that was literally constructed around the shield thus using all the available space within the chamber. Although this type of launch was developed and used
in previous projects, our challenge was complicated by the size of the tunnel, its gradient at 4.12% downhill and the constraints of the assembly area. I was tasked with the detailed planning and execution
of the launch in the Silvertown shaft. This paper presents the solution implemented by the Riverlinx CJV to launch the UK’s largest TBM. The decision taken for the method to launch the
machine is driven by different factors that converged into one special approach for the TBM to start the excavation.
COORDINATION AND INTERFACE WITH CONSTRUCTION OF THE LAUNCH CHAMBER The interface between the tunnel and the civil departments was crucial. A detailed sequence to assemble the machine had to be studied in depth to minimise any unforeseen collision or interference that might occur during the assembly of the shield, the backup gantries as well as the launching structures and the other auxiliary equipment.
TBM vs thrust eye Best fit contour Thrust eye
With such a small shaft it was essential that the shaft
base and walls were designed and constructed to allow the sequence of the TBM launch. The base slab also had to be designed and
constructed to support the weight and size of the TBM and gantries. This was complicated by the gradient and need for all temporary upright structures and concrete headwall to be inclined so as to be square to the gradient.
LAUNCHING STRUCTURES Shutter Can This circular structure was embedded into the concrete headwall and acted as a support for the subsequent structures to be bolted to Due to the size of the portal, the headwall had to be constructed in several lifts, leaving a void inside of the structure to place the cutterhead. It was very important to survey the installation of this
first structure to understand the clearance left between this ring and the TBM Shield. The scanner showed that an average of 180mm gap around the shield was achieved after the installation of the ‘shutter can’ with the TBM shield sitting on the cradle.
Seal Can Another circular structure is the ‘seal can’, which was assembled on surface and lifted down the shaft as one piece to be bolted onto the exposed flanged connection of the embedded ‘shutter can’. The special feature of this ring is the installation of
two internal rows of rubber that would act as a seal to isolate the TBM shield and the tunnel from any potential ingress of soil and water that could happen during the excavation through the headwall and into the ground. Thanks to the rubber, we could also maintain the earth pressure in front of the cutterhead as required by the designer during the first stages of the excavation.
Shield actual position
Profiles Above, figure 2: Scanner of the shutter can and TBM shield during the assembly June 2023 | 21
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