Abstract: Two adjoining voussoirs 1, 2 in a tunnel shield are assembled by sandwiching a wedge 12 between their adjacent sides 7, 8. The wedge extends over the entire length and width of the voussoir sides, and has concave surfaces 12a of equal curvature radius to the convex surfaces of the voussoir sides. The angle .alpha. between the adjacent outer surfaces of the voussoirs may be adjusted by varying the radial disposition of the wedge before tightening the assembly. The full mating contact between the voussoir sides and the wedge evenly distributes the applied stress.

Abstract: A manhole cover plug (1A) contains three helical ribs (5A) whose profile, in transverse cross-section, has two lateral quarter-circular parts (11A, 12A). These lateral parts cooperate with helical grooves of the frame with a quarter-circular profile of a greater radius.

Abstract: A grating (1) is composed of a series of transversal elements (2) which each have a central hole (11) and, at each end and on each surface, a planar surface (5) for abutting an adjacent transversal element. These elements are clamped one against the other by a central crosspiece (3) traversing their central holes. During the passage of rolling loads, the surfaces (5) slide one on the other to ensure at least four effective seat points for the grating, preventing its rocking.

Abstract: The manhole has a frame 1 with a flange 4 to be embedded in the road and a movable cover 2 to fit in the cylindrical wall 3 of the frame. On its inside the wall 3 has three support surfaces 9 each downwardly sloping at an angle .alpha. to the horizontal in the circumferential direction and at an angle .beta. to the horizontal in the radial direction. Between the surfaces 9 the frame has three undercut surfaces 11 extending radially. On its underside the cover 2 has six surfaces 14, 15. When the cover is on the frame three surfaces 14 are parallel to the corresponding surfaces 9 and the three surfaces 15 are parallel to the corresponding surfaces 11. The surfaces 9, 11 on the frame abut the surfaces 14, 15 by which the cover is held against rocking.

Abstract: Casing voussoir of the type comprising a web in the general shape of a sector of a cylindrical ring and at least two juxtaposition walls substantially perpendicular to said web and parallel to each other, wherein the voussoir has guide means for the juxtaposition of said walls between two neighboring voussoirs of the casing, said guide means being constituted by at least two elements of conjugate shape, one being a hollow in one of the walls and the other being a projection on the other wall, said elements having a clearance therebetween when the two voussoirs are juxtaposed along said walls.

Abstract: Casing panel comprising voussoirs of the type comprising a web and juxtaposition walls which are substantially perpendicular to the web, wherein two juxtaposed walls, pertaining to two adjacent voussoirs of this panel, define therebetween a cavity for receiving a filling material and have, between said cavity and the outer surface of the webs of the voussoirs, bearing surfaces which are substantially parallel to the direction of the web and bear against each other so as to result in a high pressure drop in the flow of material between the exterior of the webs and the cavity.

Abstract: A manhole assembly includes a cover rotatable within a frame to lock the cover therein, the cover being formed with at least one projection extending outwardly of its periphery. The frame is formed with at least one anchorage, and a rod is threaded at one end thereof and has an anchoring formation at the other end thereof. The rod may be engaged between the projection and the anchorage and a nut may be screwed on the threaded end of the rod to move the projection towards the anchorage and lock the cover in the frame.

Abstract: A man-hole assembly includes a man hole cover, a surrounding frame, a housing in the frame, a projection provided in the cover and extending into the housing when the cover is mounted in the frame to close the man hole and a key for locking the projection in the housing. The key includes an upper plate and a parallelopipedic foot connected to the plate by a stem, the plate being provided on its short sides with downwardly-extending flanges.