WO2021260336A1

WO2021260336A1 - Structure for absorbing impact energy

Info

Publication number: WO2021260336A1
Application number: PCT/FR2021/051170
Authority: WO
Inventors: Yassine BENNANI BRAOULI; Nicolas Freitag
Original assignee: Soletanche Freyssinet
Priority date: 2020-06-25
Filing date: 2021-06-25
Publication date: 2021-12-30
Also published as: CA3188111A1; PE20230541A1; EP4172416A1; FR3097574B1; US20230265623A1; FR3097574A1; CL2022003734A1; JP2023532885A

Abstract

The structure for absorbing impact energy comprises a core (15) having a first surface (10) exposed to impacts, and reinforcements which are distributed inside the core (15) and have frictional interfaces with the core material. The reinforcements comprise first reinforcements (16) that are positioned in a first reinforced region (12) adjacent to the first surface (10) and have main directions of resistance forming an angle of less than 45° with the first surface.

Description

Title: Absorption structure of impact energy

Technical area

[0001] The invention falls within the field of protective structures against the accidental impacts of massive objects, corresponding for example to falling rocks in the mountains, or even to the derailment of a train.

Prior art

[0002] In order to protect roads or buildings from accidental impacts, two types of solutions are traditionally used.

[0003] We first know the protective nets which are arranged so as to intercept impacting objects. These nets, usually metallic, can stop impacts of up to 8 megajoules (MJ) when deforming, and have the advantage of being compact. However, they pose many problems. These structures cannot be stressed several times and they require significant maintenance. After stopping a projectile, the anchor points are damaged and repairs are necessary. Maintaining these structures is expensive and frequent. Maintenance is also necessary due to the corrosion of threads generally laid out in the open air. This constraint is all the more important since these structures are generally located in places that are difficult to access. On the other hand, these unsightly structures tend to degrade the landscapes. In many areas, the establishment of protective nets is not enough to make land exposed to falling objects constructible, the tendency being to save landscapes. These requirements are important in mountainous areas where land pressure is growing.

Finally, these nets have heterogeneous efficiency and cannot absorb impacts over their entire extent. For example, an impact on an anchor post is not absorbed properly. [0005] In FR 3083551 A1, such a protective net is associated with a structure of the merlon type made up of large embankments making it possible to completely block the impacts. These structures can absorb higher energies, up to 30 megajoules, and require low maintenance. However, they occupy a large footprint, and are not always usable in practice.

[0006] Documents WO 2019/091508 A1 and WO 2017/077313 A1 describe gabions, that is to say metal cages filled with stones or sandbags, without necessarily seeking protection against powerful impacts. If, however, such an impact occurs, the metal elements of the cage are stressed in tension. The low deformability of the stone content must be taken into account so that the damage caused is not too great, but the absorption of impact energy by the structure remains quite limited.

[0007] EP 1 520933 A1 describes a technique where facing elements such as gabions are arranged on the front face of a reinforced soil structure and associated with a deformable material, such as recycled tires. Thus, in the event of stone impacts, damaged individual elements of the facing can be replaced.

Technical problem

[0008] There is therefore a need for a durable impact absorption structure that can have a small footprint and good integration into the landscape.

Summary of the invention

[0009] The invention provides a reinforced impact absorption structure for distributing the energy of the impact laterally so as to allow the thickness of the structure to be reduced. If the use of reinforcements is known, they are typically arranged in the depth of an embankment, parallel to the direction in which it is expected to be loaded.

Disclosure of the invention The invention relates to an impact energy comprising a backfill having a first face exposed to impacts and reinforcements distributed inside the backfill and having frictional interfaces with the material of the backfill. The reinforcements comprise first reinforcements placed in a first reinforced region adjacent to the first face and having principal directions of resistance forming an angle of less than 45 ° with the first face.

[0011] The structure may be of the merlon type and arranged orthogonally to a trajectory along which the impacts are anticipated so that the impact against which the protection is sought occurs in a direction having a strong component normal to the first face. It can also be a retaining wall arranged to prevent subsidence of stepped terrain in response to a large impact.

The backfill is preferably made of earth but can also include any type of material capable of absorbing mechanical energy by interacting with the reinforcements. Preferably, the backfill has a certain granularity which allows it to have favorable mechanical behavior.

In one embodiment, suitable for example in sites where strong impacts are likely to occur in opposite directions, the backfill has a second face opposite to the first face. The reinforcements can then comprise second reinforcements placed in a second reinforced region adjacent to the second face and having main directions of resistance forming an angle of less than 45 ° with the second face.

The configuration of the absorption structure allows the friction mobilized at the level of the first (or second, if applicable) reinforcements to have an important contribution to the dissipation of the energy of a powerful impact occurring on the first ( or second) side. This friction results from the deformation of the first (or second) face due to the impact. The location of the first (or second) reinforcements in the breast of the first (or second) reinforced region, which is adjacent to the first (or second) face, and their orientation with respect to this face allows efficient dissipation without requiring a great depth of penetration inside the structure. It is thus possible to obtain an absorption structure the size of which is not too large perpendicular to the faces liable to be struck by objects of high kinetic energy. The footprint is for example less than or equal to 10 m, preferably less than or equal to 5 m, more preferably less than or equal to 3 m.

The reinforcements used are preferably reinforcements of the one-dimensional type, that is to say that the mechanical resistance which they present is exerted essentially according to a single direction of resistance, the mechanical resistance which they present. present in the other directions being negligible in front of this one. These are, for example, bands, and not extended tablecloths or grids. The main direction of strength of the reinforcement is the direction in which the reinforcement tends to propagate mechanical stress when stressed. This is usually the direction of the greatest dimension of the reinforcement.

These reinforcements are arranged so that their main directions of resistance are substantially parallel to each other and to the face (s) of the structure. The main directions of resistance of the first reinforcements can be parallel to the first face of the backfill, and the same for the second face, where appropriate. It is nevertheless possible, in certain cases, for their orientation to deviate a little from the plane of the first face, or from the plane tangent to the latter if the first face is not plane. The angle formed between these main directions and the first face must nevertheless remain an acute angle so that their projection on the first face is longer than their projection in the direction perpendicular to the first face, which gives good dissipation efficiency of energy in the event of impact in the perpendicular direction. [0017] In the case of a non-planar face, reinforcements extending from one another can therefore for example form a polygon matching the shape of the face. A curved face will preferably have a large radius of curvature.

The arrangement of the reinforcements perpendicular to the normal of the front face, and therefore to the direction of the impact in which the energy is to be absorbed, makes it possible to distribute the mechanical energy of the impact laterally in order to reduce the thickness of the requested structure.

In order not to weaken the backfill by creating preferential sliding planes, it is advantageous to avoid as much as possible having the first reinforcements at the heart of it. This is the reason why the reinforcements are mainly placed near the face (s) of the structure liable to receive impacts. This does not exclude the presence of reinforcements in the heart of the embankment, but these will be in the minority. The distribution of reinforcements is heterogeneous in the thickness of the structure. The density of reinforcements is lower in regions far from the flush faces than in the first reinforced region (or the second reinforced region) of the backfill. These are averages and we could possibly find very locally exceptions due for example to construction irregularities or to a deformation of the structure which will cause the bringing together of several reinforcements and therefore a local increase in the density of these reinforcements: reinforcement density is not necessarily continuously decreasing. Preferably, the reinforcements are regularly spaced but only in the reinforced regions close to at least one face of the structure. There may be regions less close to the faces of the structure in which the reinforcements are more spaced or even absent. These regions may however include other types of reinforcements, for example reinforcements oriented according to the thickness of the structure. [0020] The characteristics which follow can, optionally, be implemented. They can be implemented independently of one another or in combination with one another: the first and / or second reinforcements are arranged horizontally; the first face of the backfill is covered with a facing. This facing can be of any type and can make it possible both to improve the mechanical properties of the structure and its integration into the landscape, for example in the case of a vegetated or mineral facing; secondary reinforcements are arranged transversely to the first face. These secondary reinforcements can have any orientation and can, for example, make it possible to reinforce the structure with respect to the forces which it supports in a static regime, in the absence of impact. It is thus possible to imagine zigzag reinforcements connecting the front face and the rear face or reinforcements oriented perpendicularly to the front face and coming to connect the first and / or second reinforcements; the first reinforcements include metal reinforcements, or polymer reinforcements or even reinforcements of the geogrid or geotextile type. at least some of the first reinforcements are arranged in successive segments along their main direction of resistance, with areas of mutual overlap between the segments, with backfill material then being able to lie between successive segments of a first reinforcement, in the overlap areas.

Typically, the structure is capable of absorbing an impact having an energy greater than 2MJ, preferably greater than 5 MJ. These energies correspond to the constraints that can conventionally be subjected to protection walls located in mountains, for example. The dissipation of energy by friction is favored in order to maintain the performance of the structure. The arrangement of the reinforcements is therefore preferably designed to limit as much as possible the rupture of the reinforcements: the plurality of reinforcements comprises reinforcements arranged so as to have a ductile and non-brittle behavior when the front face is stressed by an impact in one direction. normal.

An example of such an arrangement consists in limiting the direct connections between the reinforcements. Two reinforcements arranged in successive segments along their main direction of resistance are for example arranged with a zone of mutual overlap between them, and leaving a layer of the backfill material between the reinforcements, which makes it possible to introduce friction and '' soften the transmission of lateral stress in order to avoid the breakage of the reinforcements. This zone of mutual overlap depends on the stiffness of the reinforcements, the friction surface, and the resistance of the reinforcement at break.

The largest dimension of the reinforcements can also be critical and it is important not to use too large reinforcements in order to prevent their rupture, always with a view to resilience allowing the structure to undergo several impacts without requiring repair.

Brief description of the drawings

[0025] Other features, details and advantages of the invention will become apparent on reading the detailed description below, and on analyzing the accompanying drawings, in which:

Fig. 1

[0026] [Fig. 1] is a sectional side view of a structure according to one embodiment of the invention;

Fig. 2 [0027] [Fig. 2] is a sectional side view of a structure according to another embodiment of the invention;

Fig. 3

[0028] [Fig. 3] is a sectional side view of a structure according to another embodiment of the invention;

Fig. 4

[0029] [Fig. 4] is a sectional side view of a structure according to another embodiment of the invention;

Fig. [0030] [Fig. 5] is a front sectional view of the structure, the section being along the V-V plane indicated in any one of Figures 1 to 4;

Fig. 6

[0031] [Fig. 6] is a top sectional view of a structure according to the embodiment of the invention of Figure 3; Fig. 7

[0032] [Fig. 7] is a top sectional view of a structure according to another embodiment of the invention;

Fig. 8

[0033] [Fig. 8] is a view similar to that of Figure 6 after an energy impact.

Description of the embodiments

The impact energy absorption structure described below by way of example takes the form of a protective fence used to intercept falling rocks that can weigh up to several hundred tons, for example example near mountain roads. Such rock falls can carry energies greater than 6 megajoules (MJ). This protective fence has a first face, or front face, 10 shown on the right in Figures 1 to 4 and a second face, or rear face, 20 shown on the left. These faces 10, 20 can be substantially parallel as in Figures 1 and 3. The rear face 20 can also be inclined relative to the front face 10, as in Figures 2 and 4.

The orientation of the rear face 20 in Figures 2 and 4 allows better dissipation of mechanical energy in the soil but increases the footprint of the structure.

Although the front face 10 is shown vertical in Figures 1 to 4, it can also be inclined, in particular if it is requested to increase the stability of the structure, to modify the footprint or even to adapt to an impact trajectory that we anticipate obliquely. It is indeed interesting that the front face is as much as possible perpendicular to the trajectory of the impact.

The embankment of the exemplary embodiment comprises an earthy backfill 15 delimited by the front and rear faces 10, 20, in which are arranged reinforcements 16 having frictional interfaces with the material of the backfill. These reinforcements 16 are for example bands distributed regularly in the vertical direction and extending horizontally, parallel to the front face 10 and to the rear face 20, in a direction perpendicular to the cutting plane of Figures 1 to 4. This orientation allows to preferentially distribute the mechanical energy of an impact laterally rather than in the thickness of the protective fence.

The reinforcements 16 are arranged in the regions of the backfill 15 which are the most stressed in the event of an impact, the energy of which must be absorbed. In embodiments according to Figures 1 and 2, the reinforcements 16 consist of first reinforcements 16 placed in a first reinforced region 12 adjacent to the front face 10. In those of Figures 3 and 4, besides the first reinforced region 12, a second reinforced region 22 is provided near the rear face 20. This second region reinforced 22 comprises second reinforcements 16. In general, the central region of the fence will not be provided with reinforcements 16 parallel to the faces 10, 20, so as to allow deformation of the fence in the event of impact, so as not to weaken it.

However, secondary reinforcements 18 arranged transversely to the faces 10, 20 can also be incorporated into the backfill

15, to consolidate the whole. The secondary reinforcements 18 can in particular connect the front and rear faces 10, 20.

[0041] The reinforcements 16 can be arranged over the entire width of the fence. Advantageously, use is made of reinforcements 16 arranged in successive segments along their main direction of resistance so as to partially overlap as illustrated in FIG. 5. Each zone 25 of mutual overlap between two successive reinforcements 16 comprises backfill material so that the reinforcements 16 are not in contact with each other. Thus, in the event of an impact, the energy is transmitted from one segment to the next by friction and gradually dissipated while avoiding breaking the reinforcements

16. This can allow the fence to withstand several consecutive impacts without requiring repair.

Ideally, the reinforcements 16 are arranged perfectly parallel to the front and rear faces as illustrated in Figure 6, so as to distribute the mechanical energy as laterally as possible. However, for logistical reasons or in order to particularly reinforce certain portions of the fence and / or to protect certain portions of it, the reinforcements may present a slight angle (which must remain less than 45 °) and sink somewhat into the thickness of the structure, as shown in FIG. 7. It is nevertheless considered that they are substantially parallel to the front face 10 and to the rear face 20 because their orientation remains predominantly lateral. The main directions of resistance of the reinforcements 16 form an angle of less than 45 ° with the face 10 and / or 20 of the backfill 15. Similarly, the reinforcements 16 may have a variation in height and have a slight slope. It is desirable that this slope remains low so as to distribute the energy as sideways as possible. Figure 8 is a representation similar to Figure 6 after it has received a strong impact and localized on its front face 10 shown at the bottom of the figure. It is noted that the energy could have been well dissipated laterally thanks to the reinforcements 16. The reinforcements 16 did not break. They remain arranged in a configuration capable of absorbing other impacts.

The invention is not limited to the examples described above. It encompasses all the variants that a person skilled in the art may consider within the framework of the protection sought.

Claims

[Claim 1] A structure for absorbing impact energy, comprising: an embankment (15) having a first face (10) exposed to impacts; and reinforcements distributed within the backfill (15) and having frictional interfaces with the backfill material, wherein the reinforcements comprise first reinforcements (16) placed in a first reinforced region (12) adjacent to the first face ( 10) and having main directions of resistance forming an angle of less than 45 ° with the first face.

[Claim 2] The structure of claim 1, wherein the main directions of strength of the first reinforcements (16) are parallel to the first face of the backfill (15).

[Claim 3] A structure according to any preceding claim, in which the backfill (15) has a second face (20) opposite the first face (10), and in which the reinforcements comprise second reinforcements (16) placed. in a second reinforced region (22) adjacent to the second face (20) and having main directions of resistance forming an angle of less than 45 ° with the second face.

[Claim 4] A structure according to claim 3, wherein the main directions of resistance of the second reinforcements (16) are parallel to the second face of the backfill (15).

[Claim 5] A structure according to any preceding claim, wherein the reinforcements (16) are arranged horizontally.

[Claim 6] Structure according to any one of the preceding claims, in which the first face (10) of the backfill (15) is covered with a facing.

[Claim 7] A structure according to any one of the preceding claims, further comprising secondary reinforcements disposed transversely to the first face (10).

[Claim 8] A structure according to any preceding claim, wherein the first reinforcements (16) comprise metallic reinforcements.

[Claim 9] A structure according to any preceding claim, wherein the first reinforcements (16) comprise reinforcements of polymeric material.

[Claim 10] A structure according to any one of the preceding claims, in which the reinforcements (16) comprise reinforcements of the geogrid or geotextile type.

[Claim 11] A structure according to any preceding claim, in which at least some of the first reinforcements (16) are arranged in successive segments along their main direction of resistance, with areas (25) of mutual overlap between them. segments.

[Claim 12] The structure of claim 11, wherein backfill material is located between successive segments of a first reinforcement (16), in the overlap areas (25).