Tunnel formwork is used for the lining of waterways, culverts, diversion tunnels, and shafts. From the perspective of opening and closing mechanisms, tunnel formwork systems are generally classified into two main categories:

• Hydraulic tunnel formwork
• Mechanical tunnel formwork

In hydraulic tunnel formwork systems, the opening and closing of the formwork segments are carried out by means of hydraulic jacks. In mechanical tunnel formwork systems, this operation is performed using manual or oil‑operated screw jacks. Hydraulic systems are typically employed in large cross‑sections due to the considerable weight of the formwork segments. In contrast, the use of hydraulic mechanisms in small‑scale tunnel formwork is technically challenging and may cause spatial constraints within the internal area of the tunnel formwork.

The lining of a conduit is usually executed in two stages. First, the invert lining (floor lining) is carried out using a bottom formwork or invert template. Subsequently, the lining of the walls and the crown (roof) is completed.