Tunnel forms come basically in two different shapes: full and half. Full-tunnel systems are all-steel formwork used for rooms that are relatively square in shape. Half tunnel is an L-shaped all-steel formwork system that is set by crane, then another half-tunnel form set separately adjacent to the previous half (Figure 4.9). The two halves are then connected together to form an inverted U-shaped tunnel form. The half-tunnel system allows for greater flexibility in room sizes by simple addition or replacement of center fill panels. Half tunnels are simpler, lighter and faster in use than full tunnels.
The tunnel formwork system consists of:
1. Deck panel. The thick steel skin used to form the ceiling and floor of each module
2. Wall panel. Also made of a thick steel skin, used to form the walls between two adjacent modules
3. Waler and waler splices. Stiffer deck and wall panels to minimize deflection due to concrete lateral pressure
Diagonal strut assembly. Used to provide additional support for the floor slab and keep walls and floors perpendicular
5. Taper tie. Wall tie between forms of two adjacent tunnel, keeps forms in place while concrete is being placed
6. Wheel jack assembly. Allows laborers to move tunnel forms over short distances, and also allows cranes to pull out a collapsed form after concrete has cured