Abstract: An improved collapsible fixture for fabrication of tunnel modules and tunnel sections for building underwater tunnel tubes is provided. The fixture has a series of shell-like support members along its length, each member having a stationary base portion, two rotatable side portions and a connecting foldable linkage portion. A common truss is connected to each of the foldable linkage portions and is activated by a plurality of hydraulically operated cylinders connected to the wheel core member of the fixture. In order to collapse the fixture, moveable radial spoke members in the shell-like support members are connected to sliding plate members which are moveably attached to hub plates on the wheel core member.