At its own production facility, Autostrada is manufacturing precast reinforced concrete tunnel lining segments for the left-hand running tunnel between Syrets and Mostytska metro stations. This marks an important stage in preparations for the launch of the tunnel boring machine (TBM) and the subsequent construction of the underground section of the metro extension.

Tunnel lining segments are high-strength precast reinforced concrete elements assembled into the permanent tunnel lining as excavation progresses. Once connected, they form a continuous structural system designed to withstand loads imposed by the surrounding ground and groundwater pressure, ensuring the tunnel's strength, stability and long-term durability.

The production process begins with the fabrication of a reinforcement cage — the steel framework of each segment. Its design is determined by structural engineers based on the site's geotechnical conditions, tunnel depth, ground loads and groundwater pressure. The reinforcement provides the concrete element with the structural capacity required to resist the design forces.

The completed reinforcement cage is placed into a precision-engineered steel mould that defines the exact geometry of the finished segment. These specialised moulds were manufactured by the German company Herrenknecht AG specifically for the Vynohradar metro extension project. They ensure a high degree of dimensional accuracy, as even minor deviations can affect the alignment and fit of segments during assembly.

The mould is then filled with concrete. The segments are manufactured using B40 strength-class concrete, with a specified characteristic compressive strength of 40 MPa. Following placement, the concrete is thoroughly compacted to eliminate entrapped air and ensure uniform distribution throughout the mould, producing a dense and homogeneous reinforced concrete structure.

Each mould is identified by a letter from A to G. This designation reflects the configuration of the tunnel lining: each ring consists of seven reinforced concrete segments, each with its own specified geometry and position within the assembly. Segment A serves as the key segment, completing and closing the ring during installation.

Another important engineering consideration is the tunnel alignment. Metro tunnels do not follow an entirely straight path; their alignment changes along certain sections. To accommodate these curves, specially designed segment geometries and ring configurations are used, including segment D, identified in the project as a turning segment. This enables the required tunnel alignment to be achieved in accordance with the design parameters.

Precision is critical throughout this process. All seven segments must fit together accurately to form a structurally sound ring. Even the moulds at the production facility are arranged in a sequence corresponding to the order in which the segments will be installed by the tunnel boring machine.

The planned rate of tunnelling requires extensive advance preparation. The TBM is expected to install 8–10 tunnel lining rings per day, equivalent to approximately 10–12 metres of completed tunnel, or 56–70 reinforced concrete segments daily. As the TBM is planned to operate around the clock, the production facility must ensure a continuous supply of segments. We are therefore building up a sufficient stock of finished segments ahead of the start of excavation of the left-hand running tunnel between Syrets and Mostytska stations.

Autostrada is delivering the Vynohradar metro extension using its own resources and capabilities. To undertake projects of this scale and technical complexity, the company has established Ukraine's largest dedicated metro construction division, bringing together leading industry specialists. Combining the expertise of its professional team, advanced technologies and a fully integrated production and construction process, Autostrada delivers all key stages of the project in accordance with stringent international quality and safety standards.