Abstract: The present invention relates to improvements in U-shaped tunnel shutterings or framing for poured concrete constituted by two half shells in the form of a right-angled dihedron, of which the edges of upper horizontal panels are connected by clamping locks and each of said edges is connected to the bottom of a vertical panel by braces of adjustable length, the reduction in length of the braces determining a reduction in the angle of the dihedron; said shutterings may be used either in the form of a complete "U" with the two half-shells connected, in which case lower parts of the two vertical panels are connected by removable horizontal bars of adjustable length, or as half-shells in which case props are used which are articulated on the free edge of the horizontal panel and rest on the ground.