TECHNICAL | SHAFTS, CAVERNS - BTS HARDING PRIZE COMPETITION
3.1. Vortex coupler installation One of my principal responsibilities was setting out the position and angle of nearly 500 couplers cast into the secondary lining, Figure 7. All data were uploaded onto the EDM and a clear mark-up was produced in advance, ensuring efficient installation and reducing the risk of accidents caused by rushed work. I mounted a large, laminated drawing adjacent to the installation area, allowing installed couplers to be ticked off and enabling all shifts to track progress consistently. Occasionally couplers clashed with the slipform
climbing tubes. It was essential to understand the connecting structures to relocate them appropriately. Recognising that the external couplers were most critical in terms of cover, I adjusted the positioning of inner couplers where necessary to maintain compliance. Couplers were protected with foam and subsequently
Above:
Worst case scenario showing the rig ovalising. Red areas (negative values) is where the cast lining was thicker than design, blue areas (positive values) where thinner
Figure 6. Although a longer shutter could theoretically permit a faster rise rate, it would also increase the rig’s weight, requiring additional bracing and jacks. Another key limiting factor in jacking the rig was
the need to balance steel fixing, carpentry, slipform movement, and concrete placement. At different stages of the operation, each discipline became the critical activity, making collaborative working and clear communication essential. I maintained constant dialogue with all gangs to ensure the slipform progressed as planned. At the start of each shift, I met with the chargehands to outline my setting out plan and to identify any urgent requirements, which was particularly important when I was the sole engineer on site. By monitoring the arrival of concrete wagons, I
identified suitable gaps in supply to land reinforcement onto the deck, improving efficiency and continuity of work. In the fast paced environment, where multiple activities were occurring simultaneously, clear and coherent communication was vital. For the slipform to operate successfully, the rig had to function as a well coordinated system, with stoppages used productively to address outstanding tasks. The most challenging aspect was ensuring a consistent supply of reinforcement for the fixers. As the rig could not be overloaded, reinforcement had to be landed in a controlled, ‘drip fed’ manner between concrete wagons to maintain workflow continuity.
Right:
Slipform alterations to form corbels used to support the primary trusses for the cover slab
exposed on the hanging deck, which also served as the location for concrete repairs. To streamline repair documentation, I devised a clock-face system referenced to the tunnel portals. This provided a simple and reliable method of recording repair locations, which proved particularly valuable when working on the rig as you would lose track of where you were.
3.2. Movement of the rig At the end of each shift, I used the TunnelBeamer to record an as built survey in order to monitor how the slip finished concrete was deviating from the design profile. The survey data were presented in a clear diagram, Figure 8, and the number of survey points was increased whenever readings indicated potential concern. The results quickly highlighted that the rig was
ovalising. This deformation was likely influenced by the two tunnel portal openings, where the forces acting on the rig differed, or by the slower placement of the initial wagons, which caused uneven filling of the shutter. However, the primary factor appeared to be the widened section of the deck used for landing reinforcement. This additional loading increased the cantilever effect, effectively pulling the rig outward. The affected area is highlighted in red in Figure 8 and Figure 9. To realign the rig with the design position, the
climbing tubes were relocated from being cast within the concrete to installation on the inside face of the completed secondary lining, as illustrated in Figure 10. This modification was intended to reduce the effective cantilever length. A simplified calculation, carried out from first principles, confirmed that the adjustment would have a beneficial effect. The deflection of a cantilever is directly proportional
to the cube of its length (L3). Therefore, reducing the cantilever length significantly decreases deflection. Calculation showed that shortening the cantilever length by 0.4m, from 3.2m to 2.8m, reduced the maximum deflection by approximately 33%, from 33P/3EI to 22P/3EI (where P is the load, E is Young’s Modulus, and I is Moment of Inertia of the Cross Section). The relocated climbing tubes were supported on
24 | April 2026
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
