This casing voussoir is of the type comprising a metallic frame 1, 2, 3.sup.a, 3.sup.b, 9 and a mass 12 of concrete or other like material strong in compression and anchored to that frame, the assembly having the shape of a cylindrical ring sector, characterized in that the frame 1, 2, 3.sup.a, 3.sup.b, 9 comprises two plates 1, 2, arranged along radial faces of the voussoir and interconnected by bars 3.sup.a, 3.sup.b, constituted by distinct parts of these plates 1, 2 and fixed to these latter by means of a filler material 8. A particular applications can be found for this voussoir in the lining of tunnels or similar underground works.