IN Brief:
- PORR has lowered the first 215-tonne TBM support sections into the 45m-deep Retkinia shaft.
- The 4.6km, 14m-diameter tunnel will carry two tracks beneath Łódź at speeds up to 160km/h.
- Excavation is scheduled for early 2027, followed by railway fit-out and testing through 2029.
PORR has started assembling the tunnel boring machine that will excavate a 4.6km high-speed rail tunnel beneath Łódź, lowering the first major support sections into the 45m-deep Retkinia launch shaft. Excavation is scheduled to begin during the first quarter of 2027.
The machine will be approximately 14m in diameter and weigh around 3,200 tonnes when fully assembled. Its trailing sections are about 19m long and weigh roughly 215 tonnes each, requiring a 450-tonne gantry crane to place them within the shaft before underground connection and testing.
These support sections contain the power, control, hydraulic, ventilation, and conveyor systems that allow the cutterhead to operate continuously. Their installation establishes the working sequence behind the shield, where segment handling, spoil removal, utilities, and operator access must remain coordinated throughout the drive.
The tunnel will run from Retkinia towards a reception shaft near Łódź Fabryczna station. It is designed to carry two tracks beneath the city at speeds of up to 160km/h, forming a central part of Poland’s planned high-speed railway network and the wider Port Polska transport programme.
Assembly fixes the machine to the programme
A tunnel boring machine of this scale does not arrive as a complete unit. Major components are delivered separately, lowered in a prescribed order, and connected within the restricted geometry of the launch shaft. Crane capacity, lifting points, temporary works, access routes, and assembly tolerances must therefore be coordinated with the permanent structure before excavation can begin.
The support systems are as important as the cutterhead. Conveyor equipment must remove spoil at the rate generated by the machine, while electrical and hydraulic systems control cutting, thrust, steering, and segment installation. Any interruption to those functions can stop the entire operation, regardless of the condition of the face.
Once commissioned, the TBM will install precast concrete lining rings as it advances. The machine braces against the completed lining to generate forward thrust, excavates the face, and places the next ring within the shield. A failure in segment supply, spoil handling, grout delivery, or critical plant can therefore affect several linked operations at once.
Urban tunnelling beneath Łódź also requires close control of ground movement. Buildings, roads, utilities, and rail infrastructure above the alignment must be monitored as the face passes, with operating parameters adjusted to the encountered geology. Instrumentation data will guide face pressure, advance rate, grout injection, and intervention decisions throughout the drive.
PORR’s package covers the tunnel between Retkinia and Łódź Fabryczna, together with launch, reception, and intermediate infrastructure. Five supply and intervention shafts are included along the route, providing access for logistics, emergency arrangements, ventilation, and later railway systems.
The machine is expected to break through in 2028, after which the programme will move into track, power, signalling, communications, safety systems, and testing. Final acceptance is planned for 2029, leaving a substantial fit-out period after civil excavation rather than treating breakthrough as the end of the job.
The route forms part of Railway Line No. 85 and the proposed high-speed “Y” network. The corridor is intended to connect Warsaw, the planned central airport, and Łódź before branching towards Wrocław and Poznań, placing the city tunnel within a national programme rather than a standalone urban scheme.
That wider programme has already generated road, airport, and programme-management procurements, but the Łódź tunnel presents a distinct engineering risk. Its performance will influence how quickly the railway can be integrated through the city and how reliably later systems contractors can gain access to a completed civil asset.
Large-diameter tunnelling also concentrates supply-chain demand. Cutter tools, seals, bearings, drives, pumps, conveyors, lining segments, grout, and monitoring equipment must remain available over a multi-year programme. Many components are specialised and carry long manufacturing lead times, so maintenance and spares planning must be settled before the machine begins its first sustained drive.
The launch shaft itself becomes a critical logistics point once assembly accelerates. Deliveries have to arrive in the right sequence, heavy lifts must avoid clashes with temporary works, and testing teams need access to each installed system before the next section restricts it. A delay in one component can quickly affect the wider commissioning plan.
The first lowered sections may look modest beside the eventual cutterhead, but they mark the point at which the machine becomes tied to the project’s physical sequence. From here, every assembly stage and systems test must be completed inside the shaft before excavation can start.
The planned 2027 launch will begin the most visible phase of the tunnel. The less visible equipment now being installed will determine whether the TBM can sustain the advance rates required for a 2028 breakthrough and a 2029 handover.