BTS | HARDING PRIZE COMPETITION 2023


by a total friction in the tunnel of about 100,000kN


plus 37,500kN that the launching structure could be loaded. This would also unlock the use of the maximum thrust force that the TBM could apply. This short length of tunnel was sufficient to bury the


whole machine in the tunnel and leave the shaft clear to commence the dismantling of the launching structures and prepare the bottom of the shaft to improve the logistics for a rapid construction of the tunnel. The disassembly of the structures was not without


challenges. By this time, the crane capacity was reduced on


site therefore the methodology for dismantling the structures had to be restudied. The different structures had to be split in a sequence, so they were not damaged as they were to be reinstated at Greenwich for the ‘re- launch’ after the rotation of the TBM. The most complicated part was dealing with the


tension created between the thrust frame and the steel ring. To relax that tension from the bars, the cylinders had to be loaded back so the inner lock nut of the stool could be untightened. Then, the pressure in the cylinder was released in a controlled manner letting free the bar and ultimately the structure. During the operation, we understood that a single


bar could not be released, one at a time, but it was necessary to release the whole sector of the ring together, otherwise the tension would be transferred to the adjacent bars and risk overload. With the cylinders and bars dismantled, the removal


of the structures followed. The size of the crane required all the structures had


to be divided into smaller pieces. The sequence started by pushing out the steel ring so the top half of the ring could be unbolted from the bottom half and then lifted. For stability purposes, the bottom quarters were temporarily supported to remove them in singular lifts. After the steel ring was cleared out of the shaft, the


disassembly of the remaining structures continued with no major issues leaving exposed the trailing edge of the first concrete ring built and the entrance of the tunnel.


LESSONS LEARNT FOR THE TBM RELAUNCH I have reviewed the various options that considered to improve the different stages of the operation for the relaunch of the TBM in Greenwich on the Northbound drive once the machine is rotated. One of them is to resolve the redesign of some


of steel structures based on the new conditions for the launch of the TBM and the shaft that is being constructed at the Greenwich site. The main change would be to the steel ring to avoid


any failure during the launch. The ring, therefore, has been stiffened in all the four bolted connections. Also, the opening created at the bottom of the ring has been filled with a new steel panel to give complete continuity around the ring which will also reinforce the bottom bolted joint. With the methodology of the relaunch changed, the installation of the gantry cradles installed at Silvertown


28 | June 2023


would not be required at the rotation chamber. Instead, the same cradle that would be used to transport the gantries around the shaft will also be used to work as a supporting structure for them to run over up to the entrance of the tunnel. From my experience during the assembly of the


launching structures, I understood the potential clashes we might encounter during the installation at Greenwich for the re-launch. Our enhanced understanding of the lifting operations


and how the equipment should be set up to manoeuvre the pieces in a controlled manner would improve the operation to erect the structures. Despite that the excavation during the launch


at Silvertown was well performed, even with the programmed stoppages and unplanned downtimes, the plan includes improvement to communications between the TBM driver and the cylinder operatives. Better control of the operation is implemented by: ● A more intuitive display to show the thrust and elongation parameters on a single screen


● Data collection to be saved every 5 seconds to allow a better understanding of the operation and study any circumstance that can happen


● The elongation sensors being changed to a laser instead to measure the distance advanced and the relative position of the steel ring at each of the sectors. This should minimise any deviation with the mechanical sensor and so enable the squareness of the steel ring to be maintained


CONCLUSION The methodology to launch the TBM can cause significant delays and costs to the project if the decision taken is not well assessed. It is clearly understood that the right decision was adopted by the joint venture upon the conditions studied at the early stages of the project, not only for the launch at the Silvertown site but the possibility of giving a second opportunity to the structures at Greenwich for the relaunch. The solution implemented using the Pressure Ring


System was successfully achieved for the completion of the Southbound tunnel drive, but the team had to examine in detail the design and very complex sequences to minimise and eliminate risks involved during the operation at all levels.


ACKNOWLEDGEMENT I would like to thank to the Riverlinx CJV, the tunnel team, the designer OTB Engineering ltd, PHL Hydraulics, and Herrenknecht AG for their effort and determination invested during the design process and for the understanding of the required solution. A special thanks to the people involved during the


execution that ultimately made this launch possible. It has been an honour to be involved in this


complicated and exciting part of the project and to have this opportunity to acknowledge the team as well as all the people involved on the launching process from the design concept to the performance of the works.


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