TECHNICAL | SHAFTS, CAVERNS - BTS HARDING PRIZE COMPETITION
Left:
Preparatory works included steel fixing and portal shutters
Right:
Looking up to the top of the shaft
rig once the concrete at the base of the shutter had adequately cured. In total, 24No. equally spaced climbing tubes were installed, each capable of carrying 500kg, giving a combined live load capacity of 12 tonnes. These tubes were cast into the middle of the secondary lining and provided structural support during the slipforming operation. The rig’s top deck was used primarily for steel fixing
and preparatory works, the working deck facilitated the pouring of concrete into the shutter, and the hanging deck beneath the shutter provided access for finishers to carry out concrete repairs. Access to the rig was primarily via a lift, with a manrider available as a secondary means of egress. During my shift, I served as the lead engineer on the
slipform rig. My responsibilities included managing the workforce across all decks and coordinating the continuous supply of concrete required to maintain uninterrupted movement of the rig. Effective communication was essential to the success of the operation, ensuring that each stage of the process was executed safely and efficiently. As this was my first experience working with a slipform, the project provided a significant learning opportunity and valuable exposure to complex construction techniques.
2.4. Slipform preparation works Prior to starting the slipform, extensive preparatory works were required. A key element involved the installation of two drum shutters around the tunnel
Right:
Slipform rig setup before concreting
portals that the shaft secondary lining would be formed around, Figure 3. I was responsible for setting out the position of the C24 timbers and marking the angles at which they were to be cut, given that the tunnels entered the shaft at an angle. Accurate setting out was critical to ensure the slipform rig could pass the portals without obstruction, while also providing sufficient structural depth for the concrete lining to be formed around. Additional boxouts were installed higher in the shaft to accommodate the mid-level connection tunnel, which tied into the primary lining. Careful attention was given to the setting out of these features to avoid potential issues during later stages of construction. To achieve the required watertightness, all leaks in the
primary lining were injected prior to the slip, maximising the likelihood of sealing the shaft. The shaft was jet washed to remove dust and all fixings were cleared. I managed this process across shifts, ensuring no areas were overlooked through effective handovers and by delegating specific sections of the shaft to different teams. I sprayed reference levels every 2m up the shaft, providing clear markers once the slipform commenced. These levels were essential for identifying changes in reinforcement, scheduling the installation of cast-in items, and monitoring daily progress. Reinforcement zones were also marked directly on the rig to assist steel fixers as well as the locations that required rig alterations at the top of the shaft. By maintaining a proactive approach to preparation, the slipform was able to progress smoothly, with all
Far Right:
Spillage from the base of the shutter
20 | April 2026
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