BTS | HARDING PRIZE COMPETITION 2023
Shutter can Seal can Thrust frame Steel ring
Right, figure 3: 3D model of the launching structures
Thrust Frame
The ‘thrust frame’ is the structure that receives the loads imposed during the TBM launch and transfers them to the ground. The structure was composed of a main frame where the last item of the launching structures, the ‘steel ring’ (described below), was tied to, and also several props that would strengthen the structure and help transmit the loads to the slab. Because the dimensions of its main frame, the
structure had to be assembled on the ground surface and kept in the right position, level, and dimensions as per the base plates cast previously into the concrete at the bottom of the shaft. All the cast-in elements were fixed to the slab using
steel bars M47mm OD (Outer Diameter) 950/1050 that had to be meticulously positioned by the surveying team, so that all connections matched when placing the base of the structure. The total weight of the thrust frame structure was
about 90tonne and, therefore, the positioning was a big challenge for the team due to the small clearances within the walls of the shaft. In fact, the shaft wall at the pit bottom had to be
slightly broken out to place the base plates of the main columns. Once the thrust frame was installed and checked
for the correct inclination, the auxiliary props and rear columns were connected to it.
22 | June 2023
Steel Ring The ‘steel ring’ is big circular structure of almost 100tonne weight. The ring is designed to transfer the external loads
applied by four groups of cylinders to the TBM thrust cylinders. These external loads were transmitted to the ‘thrust frame’ by means of connecting steel bars in tension. The steel structure also had to be assembled on the
surface due to its size. The ring was composed of four circular sectors
although it was not completely symmetric for two reasons: differences in thrust forces and launching arrangements, respectively. ● The working conditions given to the designer of the structures were based on the weight of the TBM as well as the inclined position of the machine and the excavation parameters. Therefore, the force to be applied was expected to be higher on the bottom sectors rather than the top ones. In addition, the bottom half of the ring had to be more reinforced to transmit this higher thrust to the shield.
● Due to the sequence studied for the launching as well as the design of the TBM back-up gantries, the bottom sector had an opening, losing part of the structure to allow the installation of the gantry cradles required for the bogies of the gantries to run over them as the machine advanced.
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