Balfour Beatty faced a significant digital accuracy test during its marine and tunnelling works at Hinkley Point C.
Balfour Beatty is responsible for delivering the complex marine and tunnelling works, and constructing the structures for the critical infrastructure needed to supply cooling water to the power station. This project involves the construction of three tunnels under the Bristol Channel, with offshore concrete heads allowing seawater to pass into the tunnels.
Through the delivery stages, from design to offshore execution, precision was vital with very tight construction tolerances required. Once complete, the system will be connected to the seabed via vertical shafts, capped with intake and outfall heads. The intake structures are 44m long and around 8m high, weighing more than 5,000 tonnes each.
The structures were built at a purpose-built facility at Balfour Beatty’s site in Avonmouth, Bristol. Large steel alignment frames were then installed on top of the heads to enable future lifting and piling operations.
Lifting lugs were cast into the reinforced concrete heads and then matched against bespoke handling frames. The accuracy of the fit was critical due to the 5mm tolerance available for alignment, ultimately allowing for the installation of the lifting pins and the subsequent safe offshore lifts.
Verification of works
Tom Bush, digital project delivery coordinator at Balfour Beatty, explained: “It’s no surprise that using cranes to rotate and position the large fabricated structures on to the concrete heads is an incredibly challenging task, and we didn’t have any room for error.
“While we were constructing the concrete heads, fabricators were building the alignment frames. With such a small tolerance on either side of the lifting lugs, we needed to ensure the data and measurements we were giving were accurate. With Topcon’s ClearEdge3D Verity software, we were able to do that.”
The software compares point cloud data with design and fabrication models for verification of work. Balfour Beatty used the software to compare real-time data from the survey team on site against initial drawings. Thus Balfour was able to ensure the lifting lugs were aligned with the tolerance available. Inaccuracies were discovered during the first comparisons, and so changes were fed back to the fabricators and rectified early.
Digital accuracy
Balfour Beatty also used the software to run several scenarios and create a digitally accurate approach that saved time and money, as well as strengthening health and safety precautions. The software translated data collected onsite into a digital model, providing accurate demonstrations of the rotations and twists of the installed lifting lugs on each of the heads, with immediate access to the latest data and digital display models helping to streamline the process.
Bush continued: “Being able to accurately verify the position of each individual lifting lug on each of the concrete heads through Verity allowed us to provide detailed as-built information within a short period of time and remove the risk of expensive or time-consuming errors taking place when it came to fabricating and fitting the alignment frames. This was key to enable the project to keep on programme.”
Adam Box, business development manager for vertical construction at Topcon Positioning Europe, said: “Balfour Beatty had quite the task at hand with this project but, thanks to the software, they’ve been able to verify the work carried out at every stage of the process and ensure a success when it came to installing the frames to the heads.
“We worked closely with Balfour to ensure the software was being used to its full potential, to help reduce the risks of timely and costly errors taking place, and to deliver the project on time.”
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