ZA200102336B - Tubular structure. - Google Patents

Description

o 20012336

Tubular Structure

The invention relates to the field of construction and public works. The object of the invention is an underpass structure, intended more particularly for vehicle traffic.

The invention also covers prefabricated pier elements, specially suited ~ to the design of such a structure.

A roadway for highway traffic and, even more so, for railroad traffic, must have a fairly regular longitudinal profile, avoiding excessive slopes. lt is thus not possible to follow the profile of the terrain constantly, as the roadbed is, in certain sections, either over or under the natural terrain level. Also, it is desirable, at crossings, to have one roadway pass under the other by means of an underpass.

When the difference in level between the laying surface of an underpass and the natural terrain is too great, it is advantageous to provide an open trench whose bottom is placed at the desired level to allow the structure to be : built in the open and then covered with a fill to re-establish the natural terrain level. ‘ : The inventor has in recent years developed a particularly advantageous construction technique for structures of this type, which is described for example in document EP-A-0.081.402 or document US-A-4.836.714.

In this technique, the structure is made up of prefabricated wall elements arranged one after the other on a bed provided at the bottom of the trench. In an embodiment described in particular in document EP-A-0.081.402, the structure comprises, in a section transverse to the centerline, an upper element forming an arch resting on two upright elements forming piers which are placed on either side of a floor. Preferably, the upper longitudinal joints between the arch and the upper edges of the two piers are made up of articulations which give the structure a relative flexibility, in particular during the filling operation.

In addition, the upright elements advantageously have an inwardly curved upper part which connects tangentially to the upper element so as to form a continuous arch.

° 2

Between the bases of the two piers can be placed a floor element, prefabricated or cast in place, which connects to the inner sides of the bases of the piers by means of concreted joints forming a rigid longitudinal bounding, all of which thus forms a flat base allowing the distribution of loads over a large surface area.

In certain cases, however, in particular when the span of the structure is too large, the floor may be eliminated, each pier resting on the ground by : : means of an enlarged base whose dimensions are calculated according to the : loads to be supported and the bearing capacity of the soil. Such an arrangement is described in particular in document US-A-4.836.714. :

In a particular embodiment, it is possible to build structures of very large dimensions, made up of several adjacent passage sections, for example for the construction of an underground expressway with several traffic lanes. In the case of a structure having two passage sections, these are separated by a central pier supporting two arch elements each of which bears, on the outer : ~ side, on a lateral pier. oo IE : Such a technique allows particularly fast and economical construction of structures having very large sections, and has consequently experienced significant development.

Indeed, all elements of the structure may be economically and safely manufactured in a works where it is possible to control manufacturing conditions, for example the position of the reinforcement and the concrete composition.

Thus, comparing with a concrete construction molded on site, prefabricated elements allow a reduced thickness, even for a large span.

Therefore, the elements have a relative flexibility and may yield slightly under the loads applied on the upper element, the side piers bending and thrusting laterally on the fill. :

This technique may be particularly used for bypasses around towns or the passage of a highway or railway through a protected zone, because it allows the structure to be built in a trench, even over a great length, and then to

@ | oo be covered by a fill so as to re-establish the level and the natural appearance of the terrain while moreover providing almost perfect acoustic insulation.

However, it is sometimes difficult to realize on each side of the structure a fill able to take up lateral thrust forces, particularly in urban zones when the roadway is constructed near existing constructions, for example the foundation or basement of a house, or sewers.

The object of the invention is to remedy such drawbacks thanks to a new way of designing such a structure so as to avoid the realization of a fill able to take up lateral thrust forces, particularly in urban zones or when the roadway is constructed above the level of the natural terrain.

The invention thus concerns the construction of a tubular structure consisting of prefabricated wall elements arranged one after the other on a laying platform so as to form a resistant tubular structure having a longitudinal axis and comprising, in a section transverse to the axis, at least three elements, respectively two side elements forming piers and each comprising a substantially vertical wall having a top edge and a base with a flat bottom face a resting on the platform, and at least one upper element with a curved profile resting on the top edges respectively, of the two pier elements along two longitudinal joints and connecting tangentially to the upper parts of said piers so as to form a continuous arch for the transmission of loads on the bases of said piers.

According to the invention, at least some of the pier elements placed on the outer side of the structure are shaped so as to offer sufficient rigidity to take and transmit the loads applied without any lateral support on a fill covering the structure.

According to a preferentiel characteristic of the invention, the pier elements, placed on the outer side of the structure are each provided with at least one stiffening rib extending over at least one face of its lateral wall and capable of opposing its deformation under the effect of the loads applied by the upper element.

Further, according to a particularly advantageous embodiment, each upper element is provided, along at least one lateral side placed on the outside

° 4 of the structure, with a rigid shell extending upwards to stabley maintain a minimum fill thickness over the upper element.

The invention also relates to prefabricated wall elements specially designed for such a structure.

The invention thus constitutes an extension of the known technique employed for the construction of tubular structures which presents many advantages and may be applied to specifical situations.

Indeed, it has been ‘acknowledged up to the present time that the B construction of underpasses was necessary only in the case where, precisely, the roadbed was located under the natural terrain level. When, on the contrary, the terrain is below the roadbed level, the roadbed must be built on an embankment or a viaduct to re-establish the desired level. In urban zones, this then poses the problem of noise caused by vehicle traffic and the disturbance to the environment, and it is often necessary to set up noise-barrier walls that are costly, not very aesthetic and sometimes ineffective.

The new way of designing such a structure according to the present - invention allows to remedy such drawbacks by ensuring the protection of the environment over the entire length of the roadway.

Indeed, according to another characteristic of the invention, the structure is constructed at least partly above the level of the natural terrain which is covered by a first fill embankment having an upper part forming a platform on which the tubular structure is placed.

Then after placing the elements, the whole structure and the first embankment are covered by a second fill which connects to the natural terrain so as to form a artificial hill, the flat base of the structure having a width which is determined according to the bearing capacity of the first embankment for transmitting the loads without risk of excessive settlement.

Other advantageous embodiments of the invention are stated in the claims and will appear from the following description of certain particular embodiments, given by way of non-limiting examples as shown in the appended drawings, in which:

° 5

Figure 1 is a schematic view, in longitudinal section, of a complete structure built according to the invention.

Figure 2 is a cross sectional view along line I-11 of Figure 1.

Figure 3 is a cross sectional view along line lli-1ll of Figure 1.

Figure 4 is an overall schematic view in perspective.

Figure 5 is a detail view of the base of a pier.

Figure 6 shows, in cross section, the design of a structure with two sections placed side by side. E EE

Figure 7 shows a particular embodiment of such a structure.

Figures 8 and 9 show, respectively in a side view and a top view, the exit of a structure obliquely going through a slope.

In Figure 1 has been represented schematically, in longitudinal section, part of a roadway built according to the invention on a relatively uneven terrain whose longitudinal profile is indicated by line 10 which thus corresponds to the crossing of the natural ground 1 by a vertical plane P going through the longitudinal axis of the roadway. The latter is placed on a platform A which 3 comprises a part 11 located under the level of the natural ground and a part 12 oo located above that level.

Consequently, the platform 11 is arranged in a cutting at the bottom of a trench B, whereas the part 12 is arranged on top of an embankment C.

In the cutting part 11, platform A forming the roadway is covered in a classical manner, with a tubular structure D constituting an underpass which is first of all constructed in the open, and then buried under a fill E to re-establish the level 14 of the natural ground.

Such an embodiment is particularly advantageous for the bypassing of urban zones, because it provides perfect acoustic insulation and the restoration of the surroundings, with the possibility of planting on the fill E.

In an embodiment described in patent EP-0.081.402, the tubular wall B is made up of successive sections placed end to end and each comprising, in cross section, at least three elements, respectively an inwardly curved upper element 21 resting on two lateral piers 22, 22' each provided with a flat base enabling them to be placed while standing upright on the ground. The inner

° 6 sides of the bases of the two piers can be connected, by concreted longitudinal joints, to a fourth element forming a floor. In this manner, the entire load applied to the tubular wall is transmitted to a base of very large surface area.

However, it is also possible to eliminate the floor. As shown in Figure 2, each side pier 22, 22' then comprises an enlarged base 23 having two wings, respectively inner and outer, which give the element a sufficient bearing : surface, and a side wall 24 having an upper part 25, curved inwardly, which connects tangentially to the upper element 21 so that the entire arrangement forms, in cross section, a substantially semi-circular arch centered on a longitudinal axis O.

Moreover, the longitudinal joints 26 between the upper element 21 and the upper edges of the two side piers 22, 22' are made up of articulations. centered on planes P1, P'1, in which are placed the centers of curvature of the upper element 21 and of the upper parts 25 of the piers 22, 22'. Preferably, these joint planes are inclined 45 degrees in relation to the vertical.

In this known embodiment, the loads applied on the upper element 21 E oo are transmitted tangentially in the two side piers 22, 22'. The latter bear of the soil via their base 23 but, owning to the flexibility of the structure and to the use of articulated joints 26, the upper element 21 has a tendency to bank slightly, thus spreading the side piers 22, 22' which also bend and bear laterally on the : fill E. The latter must consequently be designed in a particular manner in order to participate in the resistance of the overall structure by taking up lateral thrust forces applied by the two piers 22, 22".

As above indicated, in some cases, it is not possible to lean laterally against the surrounding ground.

According to the invention, it is seen that the side piers, which must then withstand by themselves the loads applied by the upper element, are designed them so that they are quite rigid and do not deflect under the load. For this purpose, each pier element 32 is designed with a stiffening rib 37 placed on the outer side of the wall 34 and extending between the base 33 and the upper joint 36. The pier 32 thus rigidly designed can consequently transmit the loads along a vertical direction without any lateral support on the fill 5.

° 7

Such an embodiment is particularly advantageous in the case of the relatively uneven natural terrain, as represented on figure 1.

Customarily, when the level of the platform 11 corresponds to the natural . terrain level 1, at point 13 of the longitudinal profile 10, the arch structure is stopped, the roadway being constructed in the open over the upper part of an embankment C or even on a viaduct. The result is a disturbance to the surrounding and, in an urban area, one may be required to build noise-barrier walls along the two sides of the roadway. Such an embodiment is costly and not very aesthetic.

According to the invention, instead of being stopped at the exit of trench

B, the tubular structure 2 is extended by a structure of the same nature 3 which is shown in Figure 3, which is a cross section along line IlI-11l of Figure 1.

For this purpose, in the alignment of part 11 of platform A, a first fill embankment is built whose upper part 41 is levelled off so as to form the platform 12 on which tubular structure 3 is placed. : In Figure 4, which is an overall perspective view, is represented, for - simplification, a single section of the tubular structure 3 which comprises, in a section transverse to the axis 0, at least three elements, respectively an inwardly curved upper element 31 resting on two side piers 32, 32' along longitudinal joints 36. These prefabricated wall elements have, preferably, exactly the same profile as the elements 21, 22, 22' of the structure 2 and are consequently placed in the alignment of the latter elements. The longitudinal joints 36 are thus aligned with the longitudinal joints 26 of the structure 2 and constitute, likewise, articulations giving the structure a relative deformability.

Furthermore, each pier 32 is provided with a base 33 bearing on the platform 12. After placing the elements constituting the structure 3 in the alignment of the structure 2, the whole is covered by a second fill 5 having a surface 50 which connects progressively to the natural terrain 1 and to the surface 14 of the fill E for realizing an artificial hill which may advantageously be planted for restoring an aesthetic surrounding.

In this way, a quasi-perfect insulation is provided, even in the parts in which the platform A is at a level higher than the natural terrain.

° 8

In addition, the traffic on the roadway thus covered is no longer visible from neighboring buildings F.

These essential advantages can compensate, in urban zones, for the additional cost due tothe construction of the structure 3 and the second fill 5.

As in the case of -the- structure 2, each side pier 32, 32' comprises, preferably, a footing forming an enlarged base 33 and an inwardly curved side a wall 34 which connects tangentially to the upper element 31. The upper elements 31 and the piers 32 have the same profile as the corresponding elements 21, 22 of the buried structure 2 and can thus be made using the same molds which only have to be adapted for molding the stiffening ribs 37.

Further, the base 33 of each pier 32 can be enlarged inwardly and outwardly to take into account the bearing capacity of the first embankment 4 which is liable to be less that that of the bed 11 provided at the bottom of the trench B, i.e. on the natural ground. “However, as above: indicated, the prefabricated elements of this type, ~~ even for a great span, can be produced in a works far from the worksite and : transported by road, it being possible to place each element lengthwise on a . trailer.

For large dimensions, it is thus desirable to calculate the elements so that their weight is reduced as much as possible. Thus, as a stiffening rib is added to a pier, it can be preferable to reduce the width of the footing 33 by providing the possibility of widening it, after placement, to give it the required bearing surface.

For this purpose, as shown in Figure 5, it is possible to make provision, during the manufacture of the pier elements, for the projection, on both sides, respectively outer 33a and inner 33b, from the footing 33, of stub reinforcement 42a, 42b. Thus, the weight of the pier element can be reduced so as to remain compatible with the transport capacities. After placement of the elements and = by means of appropriate forms, it is possible to pour extensions 44a, 44b on each side of the footing 33 in order to enlarge it so as to reduce the loads applied on the embankment fill 4. By thus reducing the width of the footer 33, it is possible to compensate for the increase in weight due to the rib 37. Also,

[J longitudinal reinforcement bars 45 covering several successive pier elements can be inserted into the stub reinforcements 42 in order to produce a longitudinal girder rigidly connecting the elements, so that they can better withstand differential settlements.

To further increase the bearing surface, it is also possible to pour, between the inner sides of the two pier elements 32, 32', a floor 43 provided with the necessary reinforcement and in which are embedded ‘the stub reinforcements 42b. a

To simplify Figure 3, a structure has been represented which is built on a substantially horizontal natural terrain 1. In practice, however, the slope line of the terrain, along a direction orthogonal to the longitudinal access of the structure, can be more or less inclined in relation to the horizontal, between an uphill slope 16 and a downhill slope 15. As shown by way of example in Figure 6, the result is that, in the zone in which the platform 11 goes above the natural ground level 1, the side of the structure facing downhill must be placed on an . : embankment 61, whereas the side facing uphill bears on the bottom of a cutting

The structure according to the invention is particularly well suited to such a situation. In fact, as indicated above, the use of prefabricated piers 32 bearing on footing of large width and on which rests the upper element 31 via a longitudinal articulation 36 makes it possible to withstand particularly well the differential settlements that may result from such a dissymmetrical bearing.

In Figure 6 has been represented by way of example a structure with two arches of the type described in document EP-A-0.202.256, which is particularly well-suited to the construction of motorways and comprises at least two roadways S1, S2 on each side of a central pier 63 on which rest two upper elements, respectively 64, 64', each of which bears at the outer side on a lateral pier, respectively 65 on the uphill side and 65' on the downhill side.

The fill 5 that covers the entire structure and connects to the natural ground as indicated in Figure 6 is dissymmetrical, but this does not affect the stability of the structure, because the loads are transmitted vertically by the piers 65, 65', made rigid by the ribs 37.

. @

Figures 3 and 6 show another improvement of the invention. Indeed, the second fill 5 which is made over the first fill embankment 4 may slip and it is, thus, advantageous, as indicated in Figure 3, to provide, on the lateral side of. each upper element 31, a concrete plate 38 which extends upward so as to retain the upper part 51 of the fill 5 covering the structure. Thus, the structure is always covered as with a earth cap whose weight increases the overall stability. oo ~~ Preferably, the retaining plate 38 is perpendicular to the lateral side of the wall element 31 and, consequently, parallel to the joint plane P1.

In the case of a single-section structure, as represented in Figure 3, the : upper element 31 may be provided with two plates 38, 38' on each of its sides.

On the other hand, in the case of a two-section structure, each upper element 64, 64' is provided with a retaining plate 38 only on its outer side resting on a lateral pier 65, 65, the inner sides of the two elements 64, 64' resting symmetrically on the central pier 63.

Co . ltisto be noted that the prefabricated element as above described offer many advantages which justify their application to various other situations.

For example, by using such stiffened piers as described above, the fill no longer has to be made in a particular manner and can be re-opened if necessary. lt is thus possible to run pipes 67 through the fill, even after the construction of the structure.

This advantage is of particular value in urban sites because it clears a space on each side of the structure. Such piers can thus be advantageously used, even for a structure built on the bottom of a trench and covered by a fill.

However, in the case represented on Figure 6 of a structure on a dissymmetrical terrain, the part of the fill between the uphill pier 65 and the slope 16 can be designed so as to take up the lateral forces. The pier 65 could thus have been designed without a rib, such as a pier 22 of the structure 2.

Figure 7 shows another embodiment of a structure with two roadways in the case of an exit obliquely going through an inclined natural terrain. It can then be of value to stop first the section S'2 of the structure on the downhill side and to extend the section S'1 located on the uphill side and which alone is

° 11 covered by a fill 51'. The latter is advantageously stopped by an inclined plate 38' provided on the downhill side of the upper element 66 which rests on the central -pier 63'. The latter can consist of a solid wall or a row of pillars over: which is mounted a girder and can have, on the uphill side, a single bearing part 36 for the upper element 66 covering the section S$'1. On the downhill side, the upper part of the central element 63' advantageously constitutes an inclined face 39a against which bears the retaining plate 38a.

Further, rib 37 of each pier 65’ which closes section S'2 towards the outside may be provided, on its upper end, with an inclined face 39 having the same orientation as the plate 38’ which is associated with the upper element 64’ and thus constituting a bearing face for the said plate 38a.

It is to be noted that the lower part 52 of the second fill 5 may be omitted, the slope 51 being stopped by the plate 38’.

The structure is then covered by a simple earth cap and the ribbed piers 65 remain visible from the exterior and assure themselves the phonic ~insultation. An aesthetic effect may be thus obtained. : Furthermore, even in the case of" a structure built in a trench and : covered entirely by a fill, it can be of value to use ribbed piers at the exit of the structure, in particular when it is oblique in relation to the fill that covers it.

As an example, in Figures 8 and 9 is represented the exit of such a structure 7 crossing an embankment E supporting a road 14 whose longitudinal direction forms a non-right angle with the axis 70 of the structure 7.

In its central part, the structure is made up, like the structure 2 in Figure 2, of successive sections each comprising an upper element 21 resting on two lateral piers 22, 22' which can bear laterally on the embankment E covering the structure. However, each side of the embankment E which has been removed in Figure 9 forms an inclined slope E' which is limited along the structure 7 by a line indicated in broken dashes. Usually, at the exit 7 of the structure, the lateral piers 72, 72' of the last section 71 are extended by prefabricated walls 73 having the same inclination as the slope, to maintain the ground.

It is seen that, in particular on the side closest to the lower part of the slope, the pier 72a cannot bear on the filled up ground whose height is

. @ insufficient. In this case, to take up the lateral forces applied by the upper element 71, the two side piers must sometimes be connected by a girder ‘extending between their footings 73, 73". This can present some drawbacks, for example for the construction of a road running within the structure 7, which may be avoided by using, at the two ends of the structure 7 where the height of the filled up ground is insufficient, ribbed piers of the type described above and which take up by themselves the applied loads without requiring any lateral support on the embankment. : -

As represented in Figure 9, the adjacent piers 72a, 72b of the last two sections can be provided with ribs 37 whereas, on the other side, only the end pier 72'a is ribbed, the pier 72'b being of the last but one section bearing on a fill of sufficient height to take up the thrust and being, thus, identical to the normal pier 22’.

It thus appears that the prefabricated elements just described can be used in various ways. Moreover, the invention is of course not limited to the ~ details of the embodiment just described as examples, and other variants, other Co improvements and other uses are conceivable without departing from the protective scope defined by the claims.

In particular, it is advantageous to use, for the construction of the structure, wall elements with an enlarged footing, but it may be preferable to connect the footings of the two piers by a concreted floor allowing the distribution of the load of the single base having a very large bearing surface.

Also, as indicated above, in the embodiments described in the earlier patents, the piers were dimensioned and the reinforcement is designed so as to present a certain flexibility by bearing laterally on the embankment. In the invention, on the other hand, the entire applied load is transmitted by the pier on its footing and this results, for a given passage section, in an increase in the compressive stresses applied on the concrete. Consequently, to avoid being required to increase the thickness of the lateral wall and, consequently, the weight of the piers, it may be of value to make the elements in a high- performance concrete having a substantially improved compressive strength.

The reference signs inserted after the technical characteristics : mentioned in the claims are intended only to facilitate the understanding of said claims and in no way limit their scope.

Claims (13)

° 14 CLAIMS

1. Tubular structure consisting of prefabricated wall elements arranged one after the other on a platform (A) so as to form a resistant tubular structure (D) having a longitudinal axis (0) and comprising, in a section transverse to the axis (0), at least three elements, respectively two side elements (32, 32) forming piers and each comprising a substantially vertical wall (34) having a top edge and a base (33) with a flat bottom face resting on the platform (A), : and at least one upper element (31) with an inwardly curved profile resting on the top edges respectively of two pier elements (32, 32') along two longitudinal joints (36, 36') and connecting tangentially to the upper parts (35, 35') of said piers (32, 32') so as to form a continuous arch for the transmission of loads on the bases (33, 33') of said piers (32, 32), wherein at least some of the pier elements (32, 32') are shaped so as to offer sufficient rigidity to take and transmit the loads applied without any ~~ lateral support on a fill covering the structure.

~ 2. The tubular structure of claim wherein at least some of the pier oo elements (32, 32') are each provided with at least one stiffening rib (37) extending over at least one face of the side wall (34) and capable of opposing its deformation under the effect of loads applied by the upper element (31).

3. The tubular structure of either of claims 1 or 2 wherein each longitudinal joint (36, 36') between a pier element (32) and the upper element (31) constitutes an articulation with a longitudinal axis

4. The tubular structure of claim 3 wherein each longitudinal articulation (36) is centered on a joint plane (P1) inclined in relation to the vertical.

5. The tubular structure of any of the preceding claims wherein each pier element (32) comprises an enlarged base (33) extending on each side of a substantially vertical lateral wall (34) having an upper part (35) inwardly curved on the side of the axis (0) of the structure so as to connect tangentially to the corresponding side of the upper element (31) and at least one stiffening rib (37)

° 15 is provided on the outer side of the lateral wall (34) and extends from the base (33) substantially up to the level of the longitudinal joint (36) .

6. The tubular structure of any of the preceding claims wherein the platform (A) is realized at least in part (12) on the-level of the natual groun (1), the latter being firstly covered with a first fill (4) having an upper part (41) forming a platform (12) to constitute a laying surface for a resistant structure (3) “and after the placing of the elements (31, 32), the whole structure (3) and the : ~ first fill (4) supporting it are covered with a second fill (5) connecting to the natural ground (1) on each side of the structure so as to form an artificial hill, the structure resting on a bearing surface (30) having a width determined by the bearing capacity of the first fill (4) so as to transmit to the latter the loads applied without excessive settlement risk.

7. The underground structure of claim 6 wherein the structure is to built on a natural ground (1) which is inclined as per a transverse direction in relation to the longitudinal axis (O) of the structure (3) between an uphill side (16) and a downhill side (15), the platform (A) being dissymetrical and oo “comprising a part (18) located in a cutting on the bottom of a trench (62) said cutting part (18) supporting and a part (17) provided on fill (61) above the natural ground (1), the piers (65) of the structure oriented to the uphill side (16) and the filled part (17) supporting the piers (65’) of the structure oriented to the downhill side (15), at least said downhill piers (65) being provided with a stiffening rib (37).

8. Tubular structure of any of the preceding claims wherein the base (33) of at least some of the pier elements (32) is provided, on at least one lateral side (33a), with stub reinforcements (42) capable of being embedded in poured concrete after the placing of the element in order to provide an enlargement (44) of the bearing surface (30) of said structure (3).

9. Tubular structure of claim 8, wherein it comprises a floor (43) extending between the bases (33, 33’) of the pier elements (32, 32’) and rigidly attached with the inner sides (33b) o faid bases (33, 33’) so as to constitute a bearing surface (30) of he structure (3).

° 16

10. Tubular structure of any of proceding claims wherein each upper element (31) is provided, along at least of one side oriented to the outside, with a rigid plate (38) extending upwards from said side for maintaining an earth cap (51) having a minimal thickness of fill covering at least partially the structure.

11. Tubular structure of claim 10 wherein the rigid plate (38) arranged on one side of an upper element (31) rests on a supporting face (39) of same orientation provided at an upper end of each stiffening rib (37) with the corresponding pier element. | | : :

12. Tubular structure of either of claim 10 and 11 wherein the fill covering partially the struture is stopped on the level of the rigid plate (38), the ribbed pier elements (65) being visible from the outside.

13. Tubular structure of either of claim 10 to 12, comprising at least two sections (S1, S2) attached on each side of at least one central pier (63), each section comprising an upper element (64) resting, on one side on the central pier (63) and on the other side on an lateral pier (65), wherein at the exit of a Co ground whose surface is inclined in relation to the longitudinal direction of the structure, one of the sections (S'1) is extended in relation to the other (S'2) and covered by an upper element (66) provided, on the side bearing on the central pier (63’), with a rigid plate (38a) extending upwards to maintain a fill (51’) up to the level of the central pier (63'), the upper part of the latter forming, on the uphill side, a support (36) for the upper element (66) and, on the downhill side, an inclined face (39a), supporting the plate (38a) maintaining the fill (51°). .