TECHNICAL | SOFT GROUND - BTS LECTURE


The divers had to be trained first, though, for while


they were professional hyperbaric divers used to working in the offshore oil & gas industry they were not specialists in changing disc cutters on a TBM. Teamwork and relationships were also important. The working conditions in the cutterhead were challenging with quite a lot of mud and breathing with masks. A large facility onsite as well as medical teams


supported this strategy and the hyperbaric activities. The divers were transferred in pressurised shuttles from their living habitat on surface and then taken inside the tunnel and connected to the front of the TBM for their daily maintenance operational tasks.


Above:


Saturation technique was employed for cutterhead intervention


Right:


Robotic arm used for some disc cutter removals and replacement


Robotic Arm Doing saturation work is better than daily compression- decompression cycles but it’s still not ideal. Bouygues R&D has been developing a robotic method to avoid human intervention in high pressure conditions to perform some disc cutter replacement work. The method would also help to limit heavy handling, support declogging and cleaning of the cutterhead, and measurement of disc wear. The robotic arm, called TELEMACH, was used for the


first time on TMCLK, where the large diameter TBM had enough space for the system’s movement. Excluding the hyperbaric and muddy environments, the system may seem to have some similarities to robotic arms used in car factories. However, car frames on production lines have known, pre-determined locations - unlike disc cutters, in relation to robotic arms. Despite the challenges, the robotic arm proved


Saturation Technique


Daily interventions would generate daily compression- decompression cycles for the workers changing the disc cutters, which is health and safety concern as there are always risks linked to hyperbaric works. Also, there is also a problem of working time efficiency: working at 5 bar pressure for half an hour would needs decompression for much longer - about four hours. So, to overcome the problem a saturation technique


was developed. The principle of the technique is to increase the duration of the cycles because your body saturated, after a certain period in a hyperbaric environment, you can stay as long as you want. The decompression time may be long, still, but will remain the same. The cycle was increased with divers staying in the


hyperbaric environment, in dedicated chambers, for 28 days, including four days at the end for decompression. A total of 24 days, then, were available for work such as changing disc cutters.


14 | November 2025


successful but in terms of productivity it was perhaps not as efficient as having hyperbaric divers. While not extensively, the robotic arm was only able to reach the external disc cutter cylinders. Further development is needed for the arms to reach all disc cutters. Even though it reused a 14m-diameter TBM from TMCLK, the Trunk Road T2 project had a different intervention strategy. Continued R&D led to an Accessible Cutterhead system, which enables disc cutters to be changed without hyperbaric intervention. The shield on T2 had 72 disc cutters, grouped by two


on cylinders. The cylinders require quite some space and there are fewer on the TBM than conventionally. But you can only see those cylinders being changed. A good monitoring system is vital, therefore, to plan the interventions. During the replacements, sliding gates close at the front of the cylinder holes to seal off the space, and sliding tubes permit the extraction.


TMCLK - CROSS PASSAGES For cross passage construction, the plan was to use artificial ground freezing (AGF). Design development continued, seeking to mitigate risk and save time as there were so many cross passages, each requiring AGF pipes and plant. This was considered to be one of the biggest challenges on TMCLK. A safer, less risky and more industrialised approach was wanted - and development of a system of pipejacking mini-TBMs,


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