Elongated enclosure of large cross-section, and process for its manufacture

Elongated enclosure (1) designed to withstand internal pressure capable of exceeding 10 bars, and resting on a ground, said enclosure comprising:

• (a) a rigid concrete slab (2) capable of withstanding flection and comprising a lower face (21) resting on the ground, an upper face (22) and two lateral faces (23) parallel to said longitudinal axis;
• (b) a water-tight sealed parallel tubular space (A) having a truncated transverse section extending along a longitudinal axis and constituted by thin metal wall elements welded together and forming closed sections laid end to end, each section comprising an upper part forming a curved arch (3) between two lateral ends (31, 31') extended tangentially by two flat plates (4, 4') and at least one thin horizontal plate (32) having two parallel longitudinal edges attached rigidly and in watertight fashion respectively along each lateral end of said arch (3) for sealing said tubular space (A);
• (c) said upper face (22) having a width substantially equal to the space separating said two lateral ends (31, 31') of said curved arch (3);
• (d) said at least one horizontal plate (32) covering at least one of said upper (22) and lower (21) faces of said slab (2);
• (e) said flat plates (4, 4') extending respectively along said lateral faces (23) of said slab (2);
• and
• (f) means for attaching said flat plates (4, 4') respectively to the corresponding lateral faces (23) of the slab (2) with a pressure at least sufficient to prevent shifting of each of said plates (4 4') long said corresponding lateral face (23, 23') of said slab (2) under the effect of stresses (15) generated by internal pressure and to prevent detachment of said plates (4, 4') under the effect of external stresses.