TBM launch shaft works advance for Poland’s high-speed rail tunnel

Preparation for Poland’s high-speed rail tunnel beneath Lodz has reached an important stage, with the launch cradle completed inside the Retkinia launch chamber and assembly of the tunnel boring machine now progressing.

The underground tunnel will form a key section of the planned high-speed rail route through Lodz, providing a new connection beneath the dense urban fabric of the city. The main bored tunnel section is expected to be around 4.6 km long, running from the Retkinia area toward the city centre and Lodz Fabryczna station.

The launch shaft is one of the most critical interfaces in the project. It is where surface construction, temporary works, shaft support, TBM assembly and the start of underground excavation all come together. Before the machine can begin its drive, the shaft must provide enough space, stiffness, support and alignment control for safe assembly and launch.

The completed cradle is a semi-circular concrete structure that supports the TBM shield during assembly and launch. Although it may appear as a temporary element, its role is essential. It controls the starting position of the machine, supports heavy shield components and helps ensure that the TBM begins excavation on the correct alignment.

For a large urban tunnel, small errors at launch can become significant over distance. The cradle therefore needs to be built with tight geometric control, sufficient bearing capacity and reliable load transfer into the base of the shaft. It must also resist the concentrated loads from TBM components, hydraulic thrust forces and installation activities.

Assembly of the TBM shield is now under way, with major sections being lowered into the chamber. Individual shield elements reportedly weigh between 50 t and 65 t and contain the hydraulic thrust cylinders that will drive the machine forward during excavation. Once assembly and testing are complete, the machine will be moved into its final launch position.

The tunnel is planned beneath a densely developed urban area, where surface disruption, settlement and interaction with existing buildings and infrastructure must be carefully controlled. TBM excavation is well suited to this type of environment because it allows continuous underground construction while limiting open excavation at the surface.

However, the success of the tunnelling operation depends strongly on the preparation works. Launch and receiving shafts must be designed for deep excavation stability, groundwater control, base heave resistance, wall movements, temporary access, lifting operations and safe emergency arrangements.

Work is also progressing on intermediate shafts, which will later provide ventilation and emergency evacuation functions. At the K6 shaft, excavation support using diaphragm walls has started, showing the wider ground engineering effort needed before the main tunnel drive begins.

Excavation is targeted for early 2027. The current milestone shows that for urban rail tunnels, the visible breakthrough moment is only the final part of a much longer geotechnical sequence. Before the TBM moves, the project depends on shaft stability, accurate cradle construction, groundwater control, lifting logistics and careful management of ground movement below the city.