HARDING PRIZE COMPETITION 2023 | BTS
Flow return to tank
Rear lock nut
Flow to chamber A when extending. TBM advance
TBM advance
Cylinder extends 200mm approx.
when retracting cylinders
Flow to chamber B
Flow return to tank
TBM stopped until all cylinders are retracted
Cylinder retracts Inner lock nut Above, figure 4: Schematic of a hydraulic cylinder cycle
The steel ring had to be located right behind the rear shield/tail skin and bolted to the first concrete ring of the tunnel, previously erected inside the TBM shield. The load applied by the external cylinders would transfer all the way through the steel and concrete rings and ultimately to the cylinders of the TBM thrust system to propel the machine forward. Again, because the constraints within the shaft the
sequence followed pushing the shield approx 2.5m towards the headwall. This left the cutterhead inside the shutter can and room for the crane to lift down the steel ring, landing it over the same launching rails of the TBM shield so this could slide until the final position. With the steel ring in position the rest of the TBM
continued to be assembled, lifting down the gantries as well as the remaining conveyor structures needed to excavate so the final tests and commissioning of the auxiliary elements and equipment could happen before the TBM was launched. As previously mentioned, the steel bars used to
connect the thrust frame and the steel ring were installed as the rest of the components were being prepared for the start of the excavation.
Steel Tension Bars, Hydraulic Equipment As the machine was being prepared, the last items of the launching structure were in the process of being installed.
Steel Tension Bars Four sets of bars were installed across the launching structures to transmit the load from the steel ring to the thrust frame. They were designed as two sets of 5x47mm OD
grade 950/1050 bars installed to each of the top sectors and two sets of larger 6x65mm OD gr 950/1050 installed to each of the bottom sectors. The reason for having a greater number of larger bars is linked to the force that had to be applied at the bottom of the TBM Shield. To cover the distance during the launching, those bars
had to be extended up to 18m that is, two lengths – 6m and 12m per bar – were connected with a coupler.
Hydraulic Equipment To create the required thrust force, one hydraulic cylinder per bar was bolted to the back of the thrust ring to provide a load of 570tonne on each top quadrant and 1,350tonne on each of the bottom quadrants. The cylinders were connected to a hydraulic power
unit so the jacking forces could be limited to 70% of the bar yields by setting a pressure limiting valve.
TBM LAUNCHING The solution of the Pressure Ring to put in motion the TBM was nearly completed by the end of August 2022, and so it was then time to brief the crew for familiarisation and operation of the system in place.
June 2023 | 23
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