Process for obtaining hollow structures such as ducts, grain tanks or shelters.

The present invention relates to a method for obtaining a conduit, having the shape of a cylinder resting on the ground by a base having a transverse curvature overall lower than the rest of the duct wall.

Reference is made to the European divisionaire application 244,890, published on 11 November 1987.

Such structures are typically ducts of large cross section, for example beyond the traditional industrial production of the order of 2 m², buried or not, for the supply of water or other fluid under pressure or without pressure, or to passages of cables and / or other conduits or the movement and parking of people or vehicles.

The invention is also applicable to pipes of smaller section, eg up to 1 m². It is also applicable to the obtaining of similar form structures but relatively short useful as cellars, silos or anti-atomic shelters or other.

Although the invention is primarily described with reference to ducts of large cross section, it is not limited to this technical field.

Various techniques are used for the introduction of conduits for water supply systems, petroleum transportation, cable ducts or other conduits, etc.

The most common technique involves the use of pipe sections with circular section, which are put together and assembled by various methods. This technique has drawbacks which increase with the diameter of the pipe, even if they reduce the length of the sections: manufacturing, transportation, handling and installation. Anyway, in addition to manufacturing problems, congestion problems arise since that approach of an external diameter of 2.50 m which corresponds to the normal limits of road templates. For flow rates, it is necessary to provide several lines in parallel, which is an expensive solution, or build leads on site, according to the techniques of masonry buildings, even also expensive galleries in work and long delays manufacturing or achievement.

In a known process, described for example in FR-A-2030937 and DE-A-2157191 conduit is composed of sections placed end to end and constructed by assembly of longitudinal elements prepared in advance, each corresponding to a portion of the cross section of the wall and bearing on each other along longitudinal seams. The elements are made of corrugated sheet metal, and therefore easy to transport and assemble by simply bolting or riveting.

Moreover, the circular duct is, as we know, the best adapted to the case of high internal pressures. It is furthermore easier to obtain when manufactures sections corresponding to the entire section of pipe. It has however disadvantages in other uses. Creates a circular duct in the floor which supports its weight, the stresses which have a high peak in its central region. It follows that if the soil is loose, significant differential settlements may occur after installation. The circular shape is poorly suited for use in space when it is crowded as is often the case in urban areas. Finally, the weight of the conduit is too high compared; in fact the material is, in the case of unit sections each covering the entire section, evenly distributed over the entire periphery so that the constraints are not.

In FR-A-2030937 and DE-A-2157191 there is provided, in some cases, performing flat section duct, each section comprising in cross section, a lower part forming a base to flat bottom resting on the ground and connected at the sides to an upper curved portion forming arch. But one can scarcely imagine, in the case of large sections, the duct is composed solely of directly buried metal walls because, even if they are corrugated, such elements only have a low resistance to external constraints, which makes uncertain the shape retention of the section and the sealing. Therefore, usually, the metal walls bounding the duct are only lost formwork requiring subsequent concreting. Furthermore, the corrugations increase the strength of the conduit to fluid flow.

Also known by FR-733 098 or US Patent 2,400,071, techniques of assembling a large number of small elements each provided with transverse flanges for assembly with adjacent components. The large number of elements to give them requires an identical shape, resulting in the adoption of a circular section, and in this case, the resistance to stress requires that the junctions are alternated in the longitudinal direction. It was well planned in US Patent 2,400,071 to consider some of the stresses acting on the wall. and to use the upper part of the section of a tunnel element with lower resistance than the lower part, but firstly a staggered joints for assembly of various characteristic elements present an uncertain solidity, and secondly it introduces an additional complication in the assembly by mounting a large number of small elements, while such mounting is difficult to enforce so perfect by unskilled personnel.

Thus, it appears that there is an unsolved need for a method that allows the obtaining of hollow structures, cylindrical, resting on the ground along a generator to form flattened section at the base, in particular ducts important section, or similar structures, this method to achieve structures with high mechanical strength with cost of production, transportation and implementation significantly reduced compared to current techniques.

The present invention therefore provides a process for obtaining a conduit corresponding to the features of claim 1. This conduit is limited by a cylindrical wall that is not of revolution, based on the self by a base having a transverse curvature of lower assembly the rest of the assembly by wall on the spot of longitudinal elements prepared in advance, each corresponding to a part of the cross section of the duct wall and bearing against one another along longitudinal joints, each segment consisting, in cross section, at least two elements, respectively a lower element forming a flat-bottomed base and two connection sides with an upper curved arch member.

According to the invention is carried out a preliminary calculation of the constraints of the entire structure taking into account all the known parameters relating to the installation site, the conditions of use and the intrinsic characteristics of the duct, is determined by depending on the result of this calculation the shape of the longitudinal members so that the longitudinal joints between adjacent elements are in the vicinity of << >> constraints nodes that is to say points where the absolute value of transverse stresses to the wall passes through a minimum and then proceeds to a calculation of stresses element by element and, depending on the result of this calculation, the exact shape of the curvature is determined, the thickness of the section, and the material of each element.

In the majority of cases, the structures of connectors of the invention are not in alternating arrangement. On the contrary the longitudinal seals are in extension of each other on either side of each transverse seal.

The method according to the invention has a first advantage over the prior art namely that transport is facilitated. If one assumes that the maximum dimension is 2.5 m, the current technology only allows the unit transport outer diameter sections at most equal to 2.5 m. If the elements of the invention each correspond to a quarter of the channel section, the latter may have, once completed a diameter of about 3.5 m, a dual surface section, and if the elements correspond to a sixth section, it may have once finished diameter of 4.4 m is about a triple-sectional area. Moreover, for the same height of 2.5 m we will have, in the same volume, a considerable number of unit elements, stacked on each other, so that the same transport vehicle will be used in its payload Max. In contrast, the total length of joints to be made, by welding or other means, is of course increased. It must be observed that it is normally rectilinear joints that are much easier to obtain or perform as circular joints, and the number of these can be reduced to the contrary due to the greater length of unit elements permitted by their smaller unit weight.

Another advantage of the invention results from the non-circular shape of the structure, it was reported above disadvantages of a circular shape.

In addition, thanks to the shape of flattened section at the base, we get a considerable improvement in the distribution of stresses generated in the underlying soil, and the movements of the latter can be reduced dramatically. Another advantage of such forms is equal to a lower section height, hence reducing the search costs (earthworks, shields, drawdown of groundwater, etc.). On the other hand, when the consistency of the soil required bearer (aquifer particular) can be incorporated within a conduit ballast obtained by means of masses of metal or concrete which are hooked by an appropriate bolting under the raft said conduit. Of course, the mass of the weighting is calculated based on data specific to the site concerned and each of the weight members can also be prefabricated. Can also anchor the leads to the ground by the same method of bolting which is made easier from the inside by the flattened shape of the raft.

On the other hand, the preliminary computation of the stresses to which are subject the pipe elements, and using the result of this calculation to determine the thickness of each element, the variation of this thickness from one point to the other of the section, the material of which is made each item and location of longitudinal joints, offer important advantages.

It is common, in fact, that the upper part of a conduit has a protective function and is subject to limited stresses. On the other hand, the weight of the transported fluid, when it is water or another liquid in free flow, obviously more at the bottom than at the top. In addition the seal obtained with assembly joints allows the conduit to withstand internal pressures and, therefore, to be used penstock. Note also that, in its final form, the duct forming a homogeneous and unitary whole, it will not be necessary to make stops to change direction, longitudinal thrusts generators. The possibility of adapting the thickness and material of the element allows significant savings on the cost and transportation.

As mentioned above, the various elements have different thicknesses depending on the calculation result of the stresses. They can also be made of different materials, provided that, if any, precautions were taken to prevent corrosion effect of electrochemical couples.

Preferred materials include, for their low price and their facilities for obtaining and assembly by welding and / or other means, ductile iron, although other materials can be envisaged alone or in combination, such as steel, the alilages aluminum, other metals, reinforced plastics or non-fiber-reinforced or non-concrete, prestressed or not. In the last two cases, it is obvious that the welds that was mentioned above are replaced by appropriate links.

In the case where duct elements are produced by monoblock molding or by continuous profiling section, in particular by extrusion, of materials such as ductile iron, steel, reinforced concrete, resins, etc., is advantageously used a mold or tool whose cross section is shaped to reproduce by acting on the inner surface of the conduit element, the aforementioned variations of optimum profile and likewise the transverse variation in thickness.

The directional changes are achieved by prefabricated curved or canted, especially calculated and adapted to the geometry imposed.

The making of a conduit according to the invention, that is to say by elements that correspond to only a part of the section but which may, for compensation, be of considerable length, raises specific problems when assembly; these problems could be solved by the next assembly process, which is therefore in close contact with the main object of the invention. According to this method, one proceeds to the initial assembly of the elements connecting them both longitudinally and transversely by means allowing limited relative movement of adjacent elements and by interposing between them a flexible material seal, and one proceeds then the final and rigid connection between the elements when the surrounding grounds and all the duct stabilized. Preferably, the initial assembly of the elements to each other is made by means of bolts passing through at least one of a hole extended accordingly.

However, other joining methods may be more advantageous, particularly in joints where strong constraints impose significant wall thickness. In these cases, it is preferred to operate according to one or more of the following modalities.<ul><li>to produce the longitudinal seam and optionally the transverse junction of the conduit elements, forming recessed portions or projecting placed in the zones of corresponding edges and engageable by conjugation of shapes and / or forces to create the longitudinal seals and necessary cross;</li><li>for creating longitudinal joints, forming a rib on each of the edges of two elements to be joined and are distributed along the two ribs thus formed locking means; </li><li>the locking means are rigid or spring clips;</li><li>the stirrups are fastened with rigid or elastic parts-fitted between the inner surface of the clamp and the flank of the corresponding rib or by elastic deformation of the stirrups themselves;</li><li>gaskets, a profile section corresponding to the edges of longitudinal and transverse joints, are interposed between said edges and tight clamp is provided with said stirrups or using clamps, straps, cables or other biasing means;</li><li>in cases where the elements are formed from weldable or sealable materials, the longitudinal and transverse joints are made by adding material welding or corresponding sealing.</li></ul>

According to an interesting modality, to facilitate the establishment and stabilization of the pipe, there are provided stabilizing elements having a triangular longitudinal section, on the sides of the bottom face of the pipe. These elements have a horizontal flat face which is approximately at the bottom of the pipe, a planar face approximately vertical or inclined, and a face that matches that of the pipe. These stabilizing elements are preferably discontinuous and implanted from place to place along the pipe to prevent the lower member to tilt about its longitudinal axis after its establishment.

These stabilizing members may be attached by bolting, welding or other means on the driving structure element. In the case where it is obtained by molding (concrete) can also be integral with it.

Further interest in the stabilization of the whole pipe, the stabilizing elements are advantageous in the case where the pipe is formed of elements some of which constitute the bottom and other side walls with a generally vertical orientation: by providing that the elements stabilizers are set in advance on the side wall elements, or are integral with these elements, they become able to stand upright resting on the ground, which facilitates the obtaining of their function with background elements placed first. Then, the establishment of the elements forming the above can be performed by placing them on the side wall elements.

In the case where the section of the hollow structure, is relatively small, for example a conduit 1 to about 4 square meters, it is expected that the duct section is formed by two components only one of which corresponds to the lower part and alongside the conduit and the other forms a cover. These elements, or at least part of them can be made of concrete or other cast material.

According to another method of obtaining usable seals, in the case where the elements are made of concrete or other cast material, is provided on the edges of the longitudinal elements, angle weldable or bondable material on which is fixed, after establishment and, preferably after stabilization, flat parts for sealing a material compatible with the angle profiles.

In some cases, particularly when it comes to transport or store hazardous fluids, or for the construction of fallout shelters, should get a perfect seal even in case of landslides or explosion nearby, and if the elements are constructed of concrete or other material that may crack or lose its tightness in another way, it is advantageously provided a waterproof coating or inner liner, integral or not the structural elements.

In some cases, this coating may be a lost formwork section for the elements of the structure. If the coating consists of sheet metal or other metallic or non-metallic weldable or bondable material, of the type flat parts mentioned above may be welded or glued to the joints of the coating, or may be welded or paste coating portions directly together at points.

If the structure, duct or shelter, is formed of concrete elements, it provides the crushing strength, while a lining metal sheet or not or plastic welded, adhered or applied by any coating provides absolute tightness contamination or seepage, radioactive or other, even if the movements of the land or explosion due to the distorted structure.

The following examples are mostly related to conduits of large cross section, but it is easy to realize that what is said is true for silos, shelters or similar structures.

In the case of a prefabricated bomb shelter, it implements longitudinal wall elements, which may be constituted in the same way as the large section ducts, and the cover is closed at its ends by walls flat or curved cross. Preferably, gives away a substantially flat bottom, and the base or side members are provided with lateral stabilization elements are integrated during manufacture or subsequently added so as to prevent tilting of the shelter about its longitudinal axis.

Advantageously, there is provided a leakproof lining, particularly if the cover is constructed of concrete.

The shelter can be set up very quickly, because it is formed of separate elements that can be easily transported for assembly on site. It can be placed in an excavation, which is then recapped, or even, in some cases simply be placed on the floor. Note that the base flattened shape provides improved resistance to blast effects, compared to a brick shelter cylindrical or parallelepipedal.

The invention will now be described in more detail using exemplary embodiments, non-limiting, illustrated by the drawings in which:<ul><li>FIGS. 1 to 3 are schematic cross-sections of ducts according to the invention.</li><li>Fig. 4 is a partial section illustrating a method of assembly.</li><li>Fig. 5 is a schematic perspective view of a conduit in which the various sections are formed of longitudinal elements whose longitudinal and transverse seams joining are highlighted.</li><li>Fig. 6 shows an example of pipe elements with a gradual reduction of radial thickness toward the center.</li><li>Fig. 7 shows an example of pipe members having a gradual increase of cross-sectional thickness from left to right.</li><li>Fig. 8 is a cross section of a longitudinal joint showing a mode of joining rib and stirrups.</li><li>Fig. 9 shows an example of profile &amp; interlocking edge of two elements corresponding conduit to form a longitudinal or transverse seal.</li><li>Fig. 10 shows another example of the edge profiling of elements to form a longitudinal or transverse seal.</li><li>Fig. 11 shows yet another example edge profiling of elements to form a longitudinal or transverse seal.</li><li>Fig. 12 shows an embodiment of a transverse spigot of which is ensured by a special profile i'étanchéité annular seal which is compressed using a suitable strapping.</li><li>Fig. 13 is a cross section of the conduit of Figure 12, showing the strap of the seal.</li><li>Fig. 14 shows the establishment of a joint in the case of reinforced concrete elements.</li><li>Fig. 15 is a diagram illustrating the results of stress calculations.</li><li>Fig. 16 is a sectional view of a hollow structure section reinforced concrete corresponding to the calculation of</li><li>Figure 16.</li><li>Fig. 17 shows another embodiment, especially suitable for conduits of small cross section.</li><li>Fig. 18 shows a method of obtaining the seal.</li><li>Fig. 19 shows a fastening of the joint.</li><li>Fig. 20 shows another method of production of the seal.</li></ul>

1 shows, in solid lines, the section of a pipe 1 obtained by the process of the invention, and for comparison by dashes, the section of a circular section 2 same duct. The conduit according to the invention is obtained by assembling five elements of the same length.

Two basic elements 3 are substantially planar; two side 4 elements have a higher variable downward curvature than up a profile is completed by an upper member 5, in section in a circular arc. The example shown is for guidance to a section of 10 m². H The total height is 2.40 m and the width L of 5.00 m, compared with the corresponding diameter D of the circular duct, which is 3.57 m. The excavation necessary for the duct according to the invention is wider at the base than to the circular pipe, but it is shallowest; and in total, the volume to be excavated may be less and work more easy.

2 shows another form of conduit according to the invention, wherein the elements of the bottom 3a are slightly curved, and which comprises two upper elements 5a instead of a.

Figure 3 shows yet another embodiment, which has the feature that the bottom part 3b forms a central cunette 6. It was expected that the culvert is in the middle of the element 3b and is slightly flared so that the elements are identical and stackable for transport, but of course other arrangements are possible. According to the conventional art, the addition of a culvert poses a virtually insoluble problem.

4 illustrates an example of the connection mode between two elements 4, 5 placed as elements 4a and 5a of FIG 2.

The element 4 is in a first stage provided with a connecting plate 7, fixed by a weld 8, which can be run in the factory or on site. This plate 7 has widened holes 9 which, during assembly, are in correspondence with enlarged holes 10 of the element 5. When mounting is interposed between the element 5 and the plate 7 a flexible seal 11 of elastomeric or the like, and then one proceeds to the junction with the aid of a screw 12 and a nut 13.

When the set of elements corresponding to the following section of the duct is mounted, slight relative movements of the elements 4 and 5 can appear, such as the level changes effect the bottom of the excavation. Slight movements can also be a consequence of the settlement of the underlying land. All these movements are made possible by the expansion of the holes 9 and 10. When these movements have stopped happening, we can proceed to the final junction elements by welding 14. The screw 12 and the nut 13 can further be deleted, and the holes 9 and 10 or only one of the two, can be closed by welding.

In Figure 5, there is shown in schematic perspective view a duct obtained by implementing the process according to the invention. This duct comprises longitudinal elements such as A1, B1, C1, etc. for the first section A '1, B' 1, C '1, etc. for the second segment, and so on; these elements are interconnected by longitudinal seams, JL1, JL2, JL3, JL4, etc. and transverse joints JT1, JT2, JT3, JT4, etc.

The method of the invention consists in a first step to determine a known manner by calculating the optimal profile section of the duct according to the parameters known about the installation site, the intrinsic characteristics of the duct itself and its conditions use. In calculating it involves the efforts urging the leads include:<ul><li>the weight of the conduit,</li><li>the weight of the fluid passing through the conduit,</li><li>pressure to build in the conduit (penstock particular)</li><li>the excess pressure resulting from the use of hydraulic equipment (valves, etc.)</li><li>the hydrostatic pressure of a sheet of water in which may be optionally embedded conduit,</li><li>the burden of remplais where is buried conduit,</li><li>existing fixed surcharges possibly on remplais,</li><li>mobile surcharges possibly seeking embankments,</li><li>temperature variations and humidity,</li><li>reactions support, etc.</li></ul>

As indicated in the preamble, it is interesting to arrive at a profile whose lower part is rather flattened and the upper portion corresponds to a curve resulting from the optimization of the calculation of stresses.

The second step is to divide the section of optimum profile thus obtained in adjacent sections each corresponding to a longitudinal element, such as A1, B1, etc., and together providing a substantially continuous inner surface, designated by S in Figure 5.

The third step is to give the cross section of at least some of said elements of varying thickness to suit the stresses exerted at different points of the section of the element considered. Thus, it was demonstrated in Figures 6 and 7 cross sections of duct elements showing how to vary the thickness of material. This feature is extremely important, both for manufacturing and for the transportation and assembly of the element since the amount of material and thus the weight and cost are defined in the most accurate manner possible, based on the parameters governing the implementation of the final pipe. If we consider the application of the invention to the construction of oil pipelines, aqueducts, etc., long lengths, it becomes easy for the influence of weight gain on the final execution profitability of the book.

The duct elements according to the present invention can be made of different materials and be manufactured, in correspondence, by various methods. Thus it is possible to envisage the manufacture of elements such as A1, B1, C1, etc. a metal such as ductile iron, cast iron with spheroidal graphite, steel, aluminum alloys, etc. For such materials, it is possible to apply various processes, for example the cast piece by piece, continuous casting, spinning, forging, differential rolling, etc. All these processes can realize homogeneously from the recesses or projections to be used later, when assembling the elements, the establishment of longitudinal and transverse joints, as will be explained below.

It is also possible to make duct elements in other materials as metals, including reinforced concrete, plastics or resins reinforced or not with fibers, etc. In such conditions, the elements are made by molding using molds or forms that also allow to obtain the projections and hollow above.

All implementation processes of materials defined above for achieving the duct elements according to the invention involve tooling, molds, forms, etc., which must consider the characteristics of the process for obtaining pipes according to the invention under the following conditions:<ul><li>the inner surface of the manufactured pipe section must match the ideal profile section of the pipe, determined by calculation based on known parameters concertante installation type, the conditions of use of leads and its intrinsic characteristics. The expression &lt;&lt; &gt;&gt; optimal profile is meant, in the case of a pipe where the external conditions vary little, an average profile applicable to the conduct of a certain length,</li><li>each item must have the over-all dimensions for assembling with the other elements of the pipe and the different thicknesses of the elements must be calculated to allow them to withstand the stresses to which they are subject.</li></ul>

Sealing finaie is obtained by various means appropriate for each material used, it is created from the interior of the conduit, after definitive stabilization (compression, expansion compensation, compacting, etc.).

will now be described how to perform the assembly of the various elements to form a conduit, with reference to Figures 8 to 12 which show some embodiments of longitudinal joints and transverse joints. And in cross section is shown in Figure 4 a longitudinal seal established between the two conduit elements A1 and B1. In this case there is provided, on either side of the points defined by the two surfaces 71, 72 of the elements A1, B1, respective outer longitudinal ribs 73, 74 which extend over the entire length of the corresponding duct elements . These ribs may be formed during casting, spinning, rolling, or molding or corresponding elements they can also be reported by welding, in which case they can be discontinuous. These two ribs make it possible, as shown in Figure 8, the simple and efficient attachment of a bracket biocage 79, with corners 76, 77 which are fitted in position between the bracket and the corresponding rib by operating by example by marlelage or by any other similar process.

To absorb reéactions acting in a direction perpendicular to the sectional profile of the duct, it is appropriate to give the lateral boundary surfaces of the duct elements A1, B1, etc., forms allowing them to absorb the stresses of best possible way, taking into account all the parameters relating to the conditions of manufacturing and use of the duct, and also the material of which it consists. Thus, by way of non-limiting examples, given in Figures 8, 9 and 10 several profile templates of said side boundary surfaces of the duct elements. In Figure 8, the boundary surfaces 71 and 72 are inclined relative to the plane perpendicular to the profile of the section of the conduit. Such a profiling of the seal surfaces for example suitable when the static loads on the pipe are predominant.

In Figure 9, the two lateral boundary surfaces of the duct elements A1, B1, which are designated by 79 and 80, have corresponding rounded shapes so as to absorb the reactions acting in both directions in said plane perpendicular to the profile section.

In Figure 10, there is shown the boundary faces 82 and 83 which form steps for performing interlocking.

Figures 11, there is shown the profiles 33 and 34 defining a cavity 35 which can be filled by a sealing material for example a casting resin.

It should be noted that all these forms of side surfaces of delimitation of conduit elements can be perfectly performed by any of the above manufacturing processes. To establish a good seal, is provided in each case between the corresponding surfaces of the abovementioned longitudinal seals, coatings, sealants, gaskets or other sealing establishment of agents, including rubber, natural or synthetic, as shown in respectively 8 in Figure 8, in 81 in Figure 9 and 84 in Figure 10.

It should be noted in this regard that these seals provide a pressure seal.

In FIG 14, a longitudinal seal is shown which is established between two duct elements A1, B1 made of reinforced concrete. It has designated 20 and 21, the respective frames of the elements A1, B1. To realize the junction is allowed to exceed the armatures 20, 21 during molding of the elements and, once they have been set up in the positions provided on the place of installation of the duct, it interconnects the end portions projecting respective frames, as indicated at 22, then, using appropriate formwork elements such as 26, is cast a sealing mortar into the gap 23 to achieve the intended longitudinal seam.

In FIG 14, it was revealed at 24 and 25 angular prpfils and recessed elements A1 connecting edges B1. These profiles are intended firstly to facilitate sealing mortar hanging 23 and the other to complete the sealing of the joint, creating gaps for suppressing leakage paths located. Has been designated by 27 and 28 of the formwork of the holding members 26 which is fixed in position by nuts 29, 30.

In Figure 12, an embodiment is shown of a transverse joint between two duct sections respectively constituted by elements such as A1, ..., and elements such as A'1 ... etc. It was designated by 15 and 16 the boundary surfaces of the transverse seal. In the example, there is provided a peripheral seal indicated generally by 17 and comprising firstly a radial bead which fits into the gap between the surfaces 15, 16 and secondly by a peripheral ring whose inner surfaces are applied against the outer surfaces of the respective pipe members, said ring having on its outer peripheral surface of the raised portions 19, intended to be flattened by compression using a strap or necklace 18A, 18B, as shown in Figure 13 which is a cross section of the duct of Figure 12. in the example considered, given as non-limiting, the raised portions 19 may have a dovetail profile and comprise divisions in their slots to create a labyrinth type seal. Flattening the strapping is made in two parts 18A, 18B interconnected by turnbuckles 31, 32 which are actuated for the final tightening.

It should be noted that although all the embodiments of joints between duct elements do not form involves bolting, such a process is not at all excluded and that it is possible to form or fixed on the elements of like portions of the rims and flanges which are then assembled with bolts or similar bodies.

In some applications it is possible, within the scope of the invention, to adopt for the conduit a mixed structure, that is to say to use one hand elements formed of a first material, example of reinforced concrete, in a first portion of the conduit, for example in the lower part between the longitudinal seams and JL1 JL4 in Figure 5, and the other elements formed of a second material, for example a metal or a reinforced plastic or not fibers in the remaining part of the conduit. Such a composite structure may be recommended in a waterworks in open trench, that is to say without high loads on top of the duct, in a remote area where it pays to make the bottom in cast reinforced concrete and the upper part by thin elements, prefabricated in a factory and transported on site.

15 shows, in solid lines in the form of the neutral fiber of a duct section according to the invention (curve I) in indents (curve II) the distribution of the bending moment corresponding to the vertical thrust of the ground and features alternating (curve III) the distribution of the bending moment corresponding to the lateral earth pressure. The complete calculation also includes determining a number of similar curves, corresponding, for example, the internal pressure in the true weight of the pipe, etc. The calculation then includes combining results each corresponding to a type of constraint.

It is observed that the full profile section has four zones &lt;&lt; &gt;&gt; nodes, one located in the lower part of the pipe, the other towards its upper section.

Figure 16 shows the half-section of a duct formed of four elements made of reinforced concrete.

It is observed that the thickness (h₁, h₂) in areas corresponding to the highest stresses of Figure 15, that is to say at the center of the base and on the sides is approximately 50% larger than the thickness h₃ at the top. The junctions JL1, JL2 between elements have been made in the areas of constraint nodes. In this figure the reference f₁ refers to reinforcing bars embedded in the concrete of the elements prepared in advance and f₂ means anchoring irons, which have been folded over each other before being embedded in the concrete during Construction of the structure.

17 shows an embodiment suitable for pipes of relatively small cross section: 1.5 to 4 m². In a simplification, the section of the pipe is divided into two elements that can be carried separately without special difficulties because of their small size. The lower member 40 is made of concrete, and produced by molding, comprising the base with a flat bottom and sides. in addition it is observed includes stabilizing elements 41, which form part of it, and allow its easy installation in a flat-bottom search. These stabilizing elements are volumes to generally triangular cross section, with a horizontal lower face, these stabilizing elements not extending over the entire length of the element 40 for the purpose of relief The upper element 42 of the pipe is simpler form because it has the form of an upturned eaves, low curvature. It can be achieved either by molding or by extrusion. Where the lower member 40 is formed by extrusion, it is clear that the stabilizing members 41 are fixed subsequently, but before the establishment of the pipe, by screwing, welding or any suitable means.

Figure 16 shows in phantom a stabilizing element 41. This figure highlights another benefit of this stabilizer element in the case of a structure whose cross section is formed of more than two elements. We see in fact that the A2 side element, provided with the stabilizing element 41 outside can be alone in the final position. There is therefore no need to provide temporary support for the realization of JL2 junction with the base member A3.

Note also that in the case of a structure resting on the floor, the stabilizing element increases the resistance to lateral forces tending to overturn the structure, which is advantageous in the case of an anti-atomic shelter or otherwise, would be placed on the ground and exposed to blast effects.

18 shows an embodiment of seals in the case where the elements are on or weldable or bondable, for example of concrete:

Each element A1, A2 relates to the edges of ledges 43 of weldable material or bondable, such as ferrous metal, in place during molding if the element is obtained in this manner. Flat elements 44 or other flat connecting elements of weldable or bondable material on the brackets 42 are welded or glued to these, optionally after soil stabilization.

19 shows another assembly of the structures according to the invention.

One of A1, elements comprises a threaded hole 45, which may be provided in an insert 46, this threaded hole being directed approximately perpendicular to the plane of the gasket. The other element A2 has a shoulder 47 with a hole 48 in which is inserted a screw 49 which screws into the hole 45 crossing with the game the hole 48.

20 shows another embodiment of sealing joint, in which the elements A1, A2 in concrete, are provided internally with a sealing coating 50 of sheet metal, forming permanent formwork. An inner plate member 44 is then welded directly to the coating 50. A bracket, similar to that of Figure 18 may be provided on the other edge of the elements A1, A2.

It is observed that a number of assembly arrangements described above are used for setting up the conduit and did not intervene to contain alone in an essential way, the hydrostatic pressure in the case of use penstock, these hydrostatic pressures were partly offset by the surge in embankments.

To better secure the elements of a duct, or other abir and facilitate the implementation by dots, may optionally provide in addition to the prestressing strands forming strapping, cables or rods prestressed interconnecting adjacent longitudinal members in the direction the length of each other. Such cables or rods can interconnect each of at least two consecutive elements, for example, an element may be connected to the element which follows by a set of cables or rods, and to the element which precedes by a similar game , which allows to operate the prestressing progressively as the progress of the installation. One can also provide that each cable or prestressing bar connects three consecutive items or more.