Because of the sheer size and scale of most tunnel boring projects, every single element comes together to ensure the project is completed on time with the help of gigantic, often bespoke machinery and conveyor belt installation.
However, what most tunnel boring machines (TBMs) are not is conventionally speedy, as the tons of earth and stone that they need to move for each metre of progress is substantial, and most of the time taken is ensuring that the debris is safely moved away from the site.
Typically one metre per work hour is considered to be a good pace of progress, and HS2’s extensive TBM fleet is expected to progress at 15m per day on average.
However, exceptionally fortunate geographical circumstances as well as a very effective debris conveyor belt system did lead to an Australian tunnel project in 1995 getting the world record for the fastest progress by a TBM in a single day, according to Guinness World Records.
The project in question, the Katoomba Carrier, is a sewage redirection tunnel initially planned to help redirect waste away from the beautiful Blue Mountains near Sydney, which are a UNESCO Heritage Site and an area of outstanding natural beauty, to much more capable treatment plants.
The tunnel is 3.4m in diameter, and 8.3 miles long, and connects Katoomba with an existing sewer tunnel based at Hazelbrook, where the effluence is funnelled to various different treatment plants close to the city.
The TBM was a custom-made Robbins machine designed to quickly cut through the famously soft sandstone in the Sydney area, which had the benefit of requiring not much shoring up and lining, and being very fast to work with.
This, alongside a very efficient conveyor system, would enable the machine to break three world records, and the machine set an incredible record of 172.4m covered in a single day, which is over 7m per hour.
