TECHNICAL | MECHANISED TUNNELLING/HS2


Above:


Chiltern Tunnel looking south towards London


“We’re in chalk and these are naturally occurring


phenomenon across the Chiltern Hills, so it’s not unusual to have indentations,” says Clapp. Jacques adds that the tunnelling operations activated


existing dissolution features; it did not create them. Looking at the TBMs’ output and the material in the


slurry treatment plant, Align and HS2 developed a ground movement risk assessment that was carried out each day, and it helped to remove any surprises. “The accuracy of that enabled us to identify each of


those movement locations prior to anybody else, so we were out on site and in two cases witnessed the ground movements starting,” says Clapp. Tunnelling through flint was abrasive on the


cutterhead, but working in a SPZ 1 also presented challenges for maintenance, whether planned otherwise. Safe areas for tool changes were established around each of the shaft locations but outside those areas it had to be assessed whether water could be kept out of the head for long enough to carry out the work. “There were some locations where, ideally, we could


have changed tools sooner, but the machines were being well looked after and they delivered what they needed to,” says Clapp. The C1 contract brought many new aspects to


tunnelling in the UK – a variable density TBM, continuous boring, the TBM technology, and, the length of the Chiltern Tunnel to name a few, so there is a lot to learn from this project. Jacques believes the TBM innovations will become established on future projects.


14 | July 2024


“We are the first site on HS2 to have an IPT, constantly


sharing with the HS2 tunnelling working group. Through this group, our legacy will be not just to HS2, but to the wider industry,” he says. For Clapp, one of the legacies will be the apprentices


and graduates employed who are now skilled in their disciplines. “We’ve seen people who started with us with no


construction experience, leaving as fully competent and experienced individuals to join projects elsewhere. That’s a really positive legacy,” says Clapp. Jacques adds that many operatives now have


enhanced skills through using the robots on the TBMs, and new skills and expertise gained from the automatic slurry process. Align still has plenty of work to do, including


completing the 38 cross passages and five adits, which are currently 75% complete, and fitting-out the five shafts, but the team and HS2 are still taking time to acknowledge what Clapp describes as a “fantastic milestone” in completing tunnel boring. The two 16.1km-long drives were challenging but,


completing them “safely and on plan”, was a great achievement. “The result speaks for itself – and that’s not by


luck. It’s come from hard work and team effort, and we all have massive pride in that achievement,” says Clapp. “The scale of what we have here is unusual and the


challenges we’ve overcome are unusual so why would you not be proud?”


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