FR2672937A1 - UNDERGROUND TUBULAR STRUCTURE AND ITS MANUFACTURING METHOD. - Google Patents

Abstract

The subject of the invention is an underground tubular structure (1) of large dimensions built by assembling superimposed prefabricated longitudinal elements (2, 2') each having the shape of a box of U-shaped cross section, the said elements being laid one over the other and one after the other along a longitudinal axis, then covered with backfill (13). Each prefabricated element (2) is divided by a central wall (24), the structure (1) thus consisting of two tubular sections (S1, S2) placed side by side, on either side of a partition consisting of the central walls (24, 24'), which are superimposed and aligned, of the two elements (2, 2') of each pair. The height of at least one of the lateral and central walls of at least one of the superimposed elements may be adjusted depending on the applied loads and expected deformations in such a way that, in service, the loads are equally distributed over the three supports. The invention applies particularly to the building of roadways under backfill.

Description

The subject of the invention is a buried tubular structure produced by

  assembly of longitudinal elements

  prefabricated and having a large width relative to its height, such a structure may have large dimensions and, for example, provide two parallel lanes of road traffic.

  The invention is more particularly suited to the

  realization of rectangular section structures.

  Various methods are known for producing buried structures of large cross section for the circulation of fluids at high flow rates, or else underground passages serving, for example, for the circulation of people, of cattle.

  or vehicles below a road or railroad.

  Often such passages are buried at a relatively small height and are therefore made on the bottom

  a trench which is then backfilled.

  The need for passages of this type being very important, in particular for the improvement of the road or rail network, we have been led to develop industrialized processes making it possible to reduce costs and very significantly reduce the exposure time. To this end, the inventor has already proposed different methods of making, from prefabricated longitudinal elements, buried structures

  under backfill which may have large sections.

  European patent EP 081 402, in particular, describes a process for producing tubular structures which may have very large sections and made up of adjacent sections each comprising, in a preferred embodiment, two side elements with vertical side wall, placed on either side of a raft, and

  on which is placed a curved element in the shape of a vault.

  Even for very large sections, such elements remain transportable if their width is limited to the road gauge because they can be stacked, lengthwise, on a road trailer. However, at least two molds must be available, one for the side elements and the other for the vault elements, and possibly a mold to erase it. In another embodiment described in European patent 0188 487, each section of the conduit consists of two elements, respectively a lower element forming a raft which rises on its edges to provide two longitudinal supports and an upper element in the form of a vault resting by its lateral edges on said supports. Such a method makes it possible to economically produce either conduits for circulation of a fluid possibly under pressure, or underground passages for pedestrians,

cattle or even vehicles.

  The use of an upper arch-shaped element makes it possible to transfer part of the supported forces to the sides and, consequently, to reduce the thickness of the upper wall. However, this results in a total height

  with the key relatively important compared to the width.

  However, in certain cases, the height of the passage must be limited when the upper level, for example that of a road or a railway, is determined and the level of the excavation is not to be lowered too low , for example to stay above the water table It may be preferable, in this case, to use structures with rectangular section or, in any case, whose upper part is

relatively flattened.

  To this end, it is possible, for example, in the case of patent EP 081 402, to replace the arch element with a flat slab or, in the case of patent EP 188 487, to give the upper element the shape of an inverted U-shaped box with a flat central part and two wings

  lateral bearing on the raft.

  However, when it is made up of a flat slab and a fortiori when it has a rectangular section, the upper element works on bending, since one no longer benefits from the arch effect and the part flat central unit forming the ceiling of the duct must therefore be reinforced This leads to thicknesses and reinforcement which, for large sections, can make the elements untransportable In practice, it is hardly possible to exceed a width of four meters which corresponds to that of a traffic lane. Furthermore, to reduce the cost of the prefabricated elements, it is advantageous to produce them in series in different dimensions, and to give the upper part and the lower part, identical shapes so as to

make in the same mold.

  The subject of the invention is a provision making it possible to economically solve all of these problems and to produce tubular structures of large dimensions, having a flattened section, preferably rectangular, and made up of elements of a single type, which can be made

in the same mold.

  In general, such a structure is produced by assembling prefabricated longitudinal elements and comprising, for each cross section, a pair of superimposed elements each having the shape of a box with U-shaped section comprising an extended flattened central part. by two side walls, respectively a lower element open at the top and resting on the ground by its central part, and an upper element open at the bottom and whose side walls bear at their ends on the ends of the side walls of the lower element, said elements being placed on the ground one on top of the other and following one another along a longitudinal axis,

then covered with an embankment.

  According to the invention, each prefabricated element is shared by a central wall substantially parallel to the two side walls and, when the elements are placed one on the other, the central wall of the upper element is supported by its end. on the end of the

  central wall of the lower element, so that the structure thus produced comprises two contiguous tubular sections, on either side of a partition formed by the 5 superimposed and aligned central walls of the two elements of each pair.

  In a particularly advantageous manner, each upper element bears at least temporarily on the corresponding lower element by means of at least one intermediate support device, of adjustable thickness, interposed between the ends opposite 'at least one of the three longitudinal supports constituted by said side and central walls superimposed, for the adjustment, at least temporarily, of the distance between said opposite ends and of the height of said longitudinal support. Preferably, each intermediate support device consists of at least one hydraulic or mechanical jack, comprising two parts which are movable axially with respect to one another and which bear respectively one on the lower element and the other on the upper element of the structure But it is also possible to use an elongated inflatable envelope extending at least over part of the length of the joint between the ends opposite the walls

of the two overlapping elements.

  By virtue of such arrangements, after the upper elements have been placed on the lower elements, the distance between the ends facing the two walls can be adjusted so as to obtain a determined distribution of the support pressures between the three supports. longitudinal and, after assembly of the elements, realization of the embankment and stabilization of the whole of the conduit and the distribution of the stresses, a final blocking of the ends is carried out opposite the longitudinal height support

  adjustable and the intermediate support device is removed.

  According to another equally advantageous characteristic, the two superimposed elements, respectively lower and upper, have substantially identical profiles and are made of concrete in the same mold, and two of the longitudinal supports have ends with inverted profiles, respectively in hollow and in projection, capable of engaging one another when the upper element is placed on the lower element, the opposite ends constituting the third longitudinal support being symmetrical with respect to a passing median plane by the other two

longitudinal supports.

  For example, the end of the wall constituting the third symmetrical support may have a crenellated longitudinal profile comprising at least two longitudinal parts respectively placed at two levels symmetrical with respect to the median plane and having in cross section inverted hollow and projecting profiles , the upper element being offset longitudinally at installation with respect to the lower element so that the crenellated ends facing the two elements of each pair engage one in the other. In another embodiment, at least one of the three longitudinal supports formed by the superimposed side and central walls has an intermediate bar interposed between the ends of the corresponding walls, the latter being shorter than the other two walls so as to leave between the said ends when the elements are installed, a space in which the bar is placed, the latter having a height equal to or slightly greater than that of the said space, that is to say double the distance between the end of the wall and the plane passing through

lateral supports.

  Advantageously, such an intermediate bar can be limited by two longitudinal edges with a convex profile, the end of the central wall having a corresponding concave longitudinal profile which allows,

  to admit slight displacements or deformations of the two elements with respect to each other, for example as a result of differential settlements.

  But the invention also has many

  other advantages which will appear in the description which follows

  follow certain embodiments given as

  example and shown in the accompanying drawings.

  Figure 1 is a cross-sectional view of a

structure according to the invention.

  Figure 2 is a schematic view of a mold for

the realization of an element.

  Figure 3 is a detail view showing a

variant.

  Figure 4 is an elevational view, partially in longitudinal section, of a structure provided with a device

adjustable intermediate support.

  Figures 5 and 6 are detailed views, respectively in longitudinal section and in cross section of a variant of the intermediate support device. Figure 7 and Figure 8 show, respectively in longitudinal section and in cross section, another mode

for carrying out the invention.

  Figure 9 shows schematically, in perspective,

  the installation of the elements of Figures 7 and 8.

  Figure 10 shows, in perspective, another mode

for carrying out the invention.

  Figures 11 and 12 show still other modes

of the central support.

  Figure 13 shows a face structure

upper inclined.

  In Figure 1, there is shown, in cross section, a structure according to the invention comprising two

  adjoining sections for the passage of vehicles.

  -7 The structure 1 is placed on the bottom 11, flattened and packed, a trench 12 and covered with an embankment 13 on which one can pass below a track 14 of road or rail traffic. 5 The structure 1 can, as shown in Figure 1, be used for the passage of vehicles or a

  river, for example in the valley, for the evacuation of floods.

  Structure 1 is made up of prefabricated reinforced concrete elements, produced in an industrialized manner and assembled on site, and comprises, for each cross section, a pair of superimposed elements, respectively a lower element 2 and an upper element 2 'These two elements have identical shapes, the upper element 2' being simply turned over before being placed on the element

lower 2.

  Each element 2 is molded in one piece and has a flat central part 21 bordered on its two sides by two vertical side walls 22, 23, and in the middle of which rises a central wall 24, the whole of the box having thus a double U section which opens upwards for the lower element 2 resting on the ground 11 by its base 21, and which opens downwards for the upper element 2 'turned over, and therefore comprises a flat central part 21 'bordered by two side walls 22', 23 ', and

  shared in two by a central wall 24 '.

  The two elements 2, 2 ', having identical sections, after turning over, the upper element 2' rests at the ends 4 ', 3', of its side walls 23 ', 22', respectively on the ends 3, 4, side walls 22, 23, of the lower element 21, the central walls 24 ', 24, bearing one on the other by their ends 5', 5. Each pair of superimposed elements 21, 21 ', therefore constitutes a gallery section comprising two contiguous sections Sl, 52, and, by placing one after the other, along a longitudinal axis x'x, a certain number of pairs

  of elements A, A '; B, B '; C, C ';, a tubular structure can be formed comprising two contiguous sections Sl, 52, and having a rectangular section the width L of which may be large relative to the height H and, for example, exceed twice that. this.

  For a specific passage section, necessary, for example, to ensure a certain flow in the case of a

  fluid transport pipe, it is possible to reduce the height H of the structure.

  It is thus possible to pass two separate traffic lanes under a motorway or a railway track by reducing to a minimum the height HI of the trench while limiting the range between supports of the flat parts 21 ′ to the value just necessary for the passage of a lane , i.e. do not

not exceeding four meters.

  Thus, it is possible to produce, in a single mold, as shown very diagrammatically in FIG. 2, elements comprising a flat central part, two lateral walls and a central wall, and capable of constituting the upper element and the lower element of a

double gallery section.

  To ensure the centering of the two superposed elements on each other, it is advantageous to provide on the ends 3, 4, side walls 22, 23, parts, respectively hollow and projecting, for example a longitudinal boss 31 and a groove 41 of corresponding shapes, the arrangement of which is reversed on the inverted element, and which can therefore engage one into the other in the manner of a tenon and mortise interlocking It is preferable, however , to leave, between the nested parts 31, 41, a certain clearance which allows the deformations of the elements under the action of the loads applied, the two extreme supports 3, 4 'and 4, 3', being able to admit slight pivotings around 'axes

horizontal.

  As indicated schematically in Figure 2, the two superimposed elements 2 and 2 'can be cast in the same mold 14, easy to design, and consisting for example of a fixed base on which are fixed formwork walls 15 making it possible to give the element 2 the desired shape and dimensions, inserts 16 being provided for the shuttering of the ends 3, 4, 5, of the vertical walls 22, 23, 24. To allow the molding of the two superimposed elements in the same mold, the latter must have a symmetry allowing the inversion This is why the end 5 of the central wall 24 must be symmetrical by

  relative to the plane passing through the two lateral supports 3, 4.

  In the simplest embodiment shown in Figure 1, the end 5 has a flat bearing face 50 which

is placed in this plane.

  To ensure a good distribution of the load on the three supports, shims possibly made of elastic material can be interposed between the ends 5, 5 ', bearing one on the other However, taking into account the loads applied, provision has been made some more elaborate provisions

  which will be described in detail later.

  It will be noted, moreover, that, even using a single mold 14, it is possible to admit slight differences between the two superimposed elements 2 and 2 ′ insofar as these differences result in limited modifications of the mold Thus, in the example shown in Figure 3, there is provided at the base of the lower element 2, an outward enlargement of the planar portion 21 which increases the seating surface and can be achieved by means of a simple auxiliary formwork Similarly, it is possible, without significant modification of the mold, to vary the heights h,

  h ', of the lower element 2 and of the upper element 2'.

  Figure 4, which is a longitudinal section of a gallery made up of several adjacent cells A, A '; B, B '; C, C ';, shows a first embodiment,

  particularly advantageous, central support.

  As can be seen, in fact, on cell B, B ', which has been represented in section by a longitudinal plane, the central walls 24, 24', of the two elements 2, 2 ', have a height slightly less than that of the side walls 22, 23, such that the ends 5, 5 'of the central walls 24, 24' are separated by a space e when the upper element 2 'is placed on the lower element 2 Furthermore , recesses 51 are arranged along the end 5 of the central wall 24 so as to form, when the upper element 2 ′ is turned upside down, a housing consisting of two vis-à-vis recesses 51, 51 ', and in which a hydraulic cylinder 52 can be placed, the two elements of which bear, in opposite directions, on the ends 5, 5', of the two

walls 24, 24 '.

  Depending on the length d of the elements 2, it is possible to provide either a single cylinder 52 placed in the transverse median plane of the element, or several cylinders distributed over the length of

the wall 24.

  The cylinders 52 thus constitute, between the central walls 24, 24 ', of the two elements 2, 2', superimposed, an intermediate support device of adjustable thickness which allows, after having placed the upper element 2 'on the lower element 2, to act on the distance e between the ends 5, 5 ', of the central walls so as to modify the distribution of the stresses on the three supports 3, 4'; 5.5 '; 4, 3 ', for example to ensure equal distribution or, if preferred, to increase the stresses applied on

  the central support by unloading the lateral supports.

  When the desired distribution of forces has been obtained, the intermediate support 5, 5 ′ can be locked in this position, for example by interposing shims between the ends 5, 5 ′, or, simply, by carrying out concrete concreting. , the ends 5, 5 ′, which can optionally be provided, as shown in FIG. 5, with reinforcements 53 which are embedded in a mortar using suitable shuttering elements. After setting or blocking, the jacks 52 can

be withdrawn.

  This adjustment of the distribution of the stresses on the three supports can be carried out either at the installation of each cell, or after the installation of several cells covering a significant length and, possibly, of the whole of the structure For example, one can carry out this adjustment after completion of the embankment 13 so as to take account of the differential settlements which have occurred and,

possibly correct them.

  The intermediate support device can be produced in different ways. For example, as shown in FIGS. 5 and 6, the jacks 52 can be replaced by an elongated inflatable envelope 54 interposed between the ends 5, 5 ′, and extending over almost the entire length of the central wall 24, 24 ′, leaving at the two ends of the parts 55, possibly provided with waiting frames 53 which can be wedged and concreted after adjusting the height of the support , the inflatable envelope 54 then being removed and the corresponding space

possibly concreted.

  In the examples which have just been described, the intermediate supports 5, 5 ', are perfectly symmetrical and therefore make it possible to produce the two elements 2, 2', of each

cell in the same mold.

  However, other embodiments can be envisaged, in particular when, to simplify the structure, it is not desired to use an adjustable intermediate support. Thus, in the example shown in Figures 7, 8, 9, the central wall 24 has a crenellated profile, its end 5 being made up of two longitudinal parts 56, 57, placed at different levels symmetrical with respect to to the plane P passing through the two lateral supports 3, 4, the part 56 being below this plane and the part 57 above. In addition, the two parts 56 and 57 are provided, respectively, at their end, with a longitudinal boss 25 and a groove 26 having corresponding projecting and recessed profiles. As before, to make a cell, two identical elements 2, 2 ′, superimposed in the same mold, are superimposed, the lateral supports 3, 4, and 4 ′, 3 ′, being inverted and their recessed portions 31 and projecting 41

committing to each other.

  However, the upper element 2 'must be offset longitudinally by a distance corresponding to the length of the parts 56, 57, so that the short part 56' of the central wall 24 'of the upper element 2' is superimposed on the long part 57 of the central wall 24 of the lower element 2, their recessed 26 and projecting ends 25

s engaging each other.

  Generally, the length of the elements being fairly short compared to their width L, only two parts 56, 57 will be provided on the central wall 24, of different levels. However, it would also be possible, for a longer length, to provide several offset parts. 56, 57, in

  even number, constituting a crenellated profile.

  In FIG. 10, another example of a symmetrical intermediate support is shown. In this case, the central wall 24 is, over at least part of its length, shorter than the side walls 22, 23 Thus, when the two elements 2, 2 ', are superimposed, the ends 5, 5', of the two central walls 24, 24 ', are separated by a space in which can be placed an intermediate bar 6 ensuring the transfer of forces and of height equal to that of said space, that is to say twice the distance between the end 5 of the central wall 24 and the plane P passing through the lateral supports 3, 4 The height of the bar 6 can also be slightly greater that after installation,

  the central support is more loaded than the lateral supports.

  To facilitate the positioning of the bar 6, the two longitudinal edges 61, 62 of the latter have a transverse profile forming a projection 25 and engage, when laying, in the ends 5, 5 ′, of the walls 24, 241, these being provided with grooves 26 having a corresponding hollow profile. In the case shown in Figure 11, the bar 6 is given an olive shape bounded by two longitudinal edges 61, 62, having a convex circular profile, the ends 5, 5 ', of the central walls 24, 24', having a

  concave circular profile with the same curvature.

  In this way, the olive bar 6 can be oriented slightly relative to the two superimposed elements 2, 2 ', which makes it possible to take into account displacements or deformations due, for example, to differential settlements and to avoid stress concentrations that could

cause cracking.

  We see that the invention can be the subject of many variants and is not limited only to the details

  embodiments which have just been described.

  For example, to obtain a good distribution of the stresses between the supports, the jacks constituting an intermediate support of adjustable height could be interposed between the ends of the side walls, the central support

being fixed.

  One could also imagine other ways of achieving an intermediate central support having a

  symmetry allowing the prefabricated element to be turned over.

  For example, as shown in FIG. 12, the end 5 of the central wall 24 could be provided with a lateral boss 27 giving it, in cross section, a staircase profile. After turning, the two lateral bosses 27, 27 ', are placed on either side of the longitudinal median plane and engage with one another, ensuring the centering of the end 5' on the end 5 of the

lower wall 24.

  The bosses 27 may extend over the entire length of the wall 24 or else over a part of the latter, alternately on either side of the median plane, which

  provides a better centering effect.

  Furthermore, the invention applies, in general, to the production of structures of large width relative to their height and having a section

  flattened but it is not necessarily rectangular.

  Thus, in the case of fluid circulation conduits, it would be advantageous to give each passage section a rounded profile in the corners,

  as shown in Figure 1.

  In addition, if it is preferable to give the elements 2 a rectangular section, this could also be, for example, trapezoidal, the side walls 22, 23,

  being inclined with respect to the bottom 21.

  It should also be noted that, if the central support 5, ', is theoretically placed in the plane P passing through the two lateral supports 3, 4'; 4, 3 ', which is normally horizontal, this arrangement is not imperative As we have seen, in fact, it may be interesting to slightly raise the central support 5, 5', so that it is more loaded and, even in the case where there are no intermediate cylinders 52, it is possible to obtain such a result by simply giving the central wall 24 a greater height so that the support 5 is located a little above the

  plane P passing through the lateral supports 3, 4.

  It is also possible to advantageously interpose between the faces bearing one on the other a damping strip of slightly compressible material, for example neoprene or lead. Such a strip can play the role of a seal against infiltration but also allows, when the central support 5, 5 ', is raised, to absorb vibrations and to remove hard spots for vehicles passing over the structure on a traffic lane 5 14 which, most often is very close to the upper side

21 'of structure 1.

  The invention also makes it possible, thanks to the use of two superimposed double U elements, to optionally adapt the inclination of the upper face 21 ′ to that of the track 14 passing over the structure 1 Indeed , if it is preferable that the lower face 21 resting on the ground be horizontal, one can however play on the relative heights of the lateral supports 3, 4 '; 4, 3 ', by slightly pivoting the upper element 2' around the central support 5, 5 ', which, as we have seen, has been provided for this purpose As shown in the Figure 13, it suffices, for example, to give different heights to the damping strips 27 interposed between the two lateral supports so that the upper face 21 'is inclined relative to the lower face 21, this inclination corresponding to that of

track 14.

  The reference signs, inserted after the characters-

  technical aspects mentioned in the claims, have

  for the sole purpose of facilitating the understanding of these

  and in no way limit its scope.

Claims (14)

  1 buried tubular structure (1) produced by assembling prefabricated longitudinal elements and comprising, for each cross section, a pair of superimposed elements (2, 2 ′) each having the shape of a box with a U-shaped section comprising a part flattened central (21) extended by two side walls (22, 23), respectively a lower element (2) open upwards and resting on the ground by its central part (21), and an upper element (2 ') open towards the bottom and whose side walls (23, 23 ') bear by their ends (4' 3 ') on the ends (3, 4) of the side walls (23, 24) of the lower element (2), said elements being placed one on top of the other and one after the other along a longitudinal axis, then covered with an embankment (13), 15 characterized in that each prefabricated element (2) is shared by a central wall (24) substantially parallel to the two side walls (22), (23), and that, when the elements are placed one on the other, the central wall (24 ') of the upper element (2') is supported by its end (5 ') on the end (5) of the central wall (24) of the lower element (2), so that the structure (1) thus produced comprises two contiguous tubular sections (SI, 52), on either side of a partition constituted by the central walls (24, 24 ') superimposed and   aligned of the two elements (2, 2 ') of each pair.   2 buried tubular structure (1) according to claim 1, characterized in that each upper element (2 ') bears at least temporarily on the corresponding lower element (2) by means of at least one device for intermediate support (52), of adjustable thickness, interposed between the ends (5 5 ') facing at least one of the three longitudinal supports (3, 3'; 4, 4 '; 5, 5 ') constituted by said side and central walls superposed, for the adjustment, at least temporarily, of the distance between said ends (5, 5') facing each other   and the height of said longitudinal support.   3 buried tubular structure (1) according to claim 2, characterized in that each pair of elements, respectively upper (2 ') and lower (2), resting on one another, is associated with a device d '' intermediate support (52) (6) interposed between the ends   (5, 5 ') of the central walls (24, 24').   4 buried tubular structure (1) according to claim 2, characterized in that each pair of elements, respectively upper (2 ') and lower (2), resting on one another, is associated with at least one intermediate support device (52) (6) interposed between the ends of at least one pair of side walls (22, 23),   on at least one side of the structure (1).   5 Buried tubular structure (1> according to one of   Claims 2 to 4, characterized in that each   intermediate support device consists of at least one hydraulic or mechanical jack (52), comprising two parts movable axially with respect to one another and bearing respectively on one of the lower element (2) and   the other on the upper element (2 ').   6 Buried tubular structure (1) according to one of   Claims 2 to 4, characterized in that each   intermediate support device consists of an elongated inflatable envelope (54) extending at least over part of the length of the joint between the ends (5, 5 ') facing each other   walls (24, 24 ') of the two superimposed elements (2, 2').   7 Buried tubular structure (1) according to one of   Claims 2 to 6, characterized in that, after the   poses upper elements (2 ') on the lower elements   (2), the distance between the ends (5, 5 ') is adjusted by screw-   opposite the walls associated with an intermediate support device (52 54), so as to obtain a determined distribution of the support pressures between the three longitudinal supports (3, 4 '; 5, 5'; 4, 3 ' ) and that, after assembly of the elements, completion of the embankment and stabilization of   the entire duct and the distribution of stresses, a permanent blocking of the ends (5, 5 ′) is carried out opposite the longitudinal support of adjustable height and the intermediate support device is removed5 (52, 54).   8 Buried tubular structure (1) according to one of   previous claims, characterized in that the   two elements, respectively lower (2) and upper (2 '), of each pair, have substantially identical profiles and are made of concrete in the same mold, that two of the longitudinal supports have ends (3, 4) with inverted profile recessed (31) and projecting (41), capable of engaging one another in the installation of the upper element (2 ') on   the lower element (2) and that the ends (5, 5 ') facing each other   opposite the third longitudinal support are symmetrical with respect to a plane (P) passing through the two   other longitudinal supports (3, 4 '; 4, 3').   9 buried tubular structure (1) according to claim 8, characterized in that the end (5) of the wall (24) constituting the third symmetrical support has a crenellated longitudinal profile comprising at least two parts (56, 57) including the longitudinal edges (26 25) are placed respectively at two levels symmetrical with respect to the plane (P) passing through the other two supports and having in cross section inverted hollow and projecting profiles, the upper element (2 ') being offset longitudinally at installation with respect to the lower element (2) so that the crenellated ends facing the two elements (2, 2 ') of each pair engage one in the other.   Buried tubular structure (1) according to claim 8, characterized in that at least one of the three longitudinal supports (3, 3 '; 4, 4'; 5, 5 ') constituted by the superposed side and central walls comprises an intermediate bar (6) interposed between the ends (5, 5 ') of the corresponding walls (24, 24'), the latter being shorter than the other two walls (22, 23) so as to leave between said ends ( 5, 5 '), at installation   elements, a space in which is placed the bar (6), the latter having a height at least equal to that of said space.   11 buried tubular structure (1) according to claim 10, characterized in that the bar   intermediate (6) has a height slightly greater than double the distance between the end (5) of the central wall and the plane (P) passing through the lateral supports (3, 4).   12 buried tubular structure (1) according to claim 10, characterized in that the bar (6) is limited by two longitudinal edges (61, 62) with convex profile and that the end (5) of the central wall (24 ) has a corresponding concave longitudinal profile so as to allow slight displacements or deformations of the two   elements (2, 2 ') relative to each other.   13 Buried tubular structure (1) according to one of   previous claims, characterized in that the end (5) of the central wall (24) is placed at a   height slightly greater than the level of plane P passing through the two lateral supports so that the central support (5, 5 ') is more loaded than the two lateral supports (3, 4') (4.25 3 ').   14 buried tubular structure (1) according to one of the preceding claims, characterized in that one   interpose a strip 27 of slightly compressible material between at least the lateral supports (3, 4 ') (4, 3'). 30 15 Buried tubular structure (1) according to claim 13, characterized in that, at least by   wedging, the two lateral supports (3, 4 ') (4, 3') are given different heights so that the central part (21 ') of the upper element (2') is slightly inclined relative to the part central (21) of the lower element (2) resting on the ground.