US20230265623A1

US20230265623A1 - Structure for absorbing impact energy

Info

Publication number: US20230265623A1
Application number: US18/003,004
Authority: US
Inventors: Yassine BENNANI BRAOULI; Nicolas Freitag
Original assignee: Soletanche Freyssinet SA
Current assignee: Soletanche Freyssinet SA
Priority date: 2020-06-25
Filing date: 2021-06-25
Publication date: 2023-08-24
Also published as: EP4172416A1; CA3188111A1; FR3097574A1; PE20230541A1; JP2023532885A; WO2021260336A1; CL2022003734A1; FR3097574B1

Abstract

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

Description

TECHNICAL FIELD

The invention relates to the field of structures for protection against accidental impacts of massive objects, corresponding for example to falling rocks in the mountains, or to the derailment of a train.

PRIOR ART

In order to protect roads or buildings from accidental impacts, two types of solutions are traditionally used.
First of all, protective nets are known that are disposed so as to intercept the impacting objects. These nets, which are generally metallic, can stop impacts of up to 8 megajoules (MJ) by deforming, and have the advantage of being compact. However, they entail numerous problems. These structures cannot be acted upon a plurality of times and they require significant maintenance. After having stopped a projectile, the anchoring points are damaged and it is necessary to carry out repairs. Maintenance of these structures is costly and frequent. Maintenance is also necessary due to the corrosion of the nets, which are generally disposed in the open air. This constraint is all the more important since these structures are generally situated in places that are difficult to access. On the other hand, these unattractive structures tend to degrade the landscape. In numerous territories, putting protective nets in place is not sufficient to make land exposed to falling objects constructible, the trend being to safeguard landscapes. These requirements are important in mountainous areas where land pressure is increasing.
Finally, these nets have heterogeneous effectiveness and cannot absorb impacts over their entire extent. For example, an impact on an anchoring post is not absorbed properly.
In FR 3 083 551 A1, such a protective net is associated with a structure of the merlon type constituted of substantial embankments making it possible to completely block the impacts. These structures make it possible to absorb higher energies, up to 30 megajoules, and require little maintenance. However, they occupy a large footprint on the ground, and are not always usable in practice.
Documents WO 2019/091508 A1 and WO 2017/077313 A1 describe gabions, i.e. metallic cages filled with stones or sandbags, without necessarily seeking protection against powerful impacts. If such an impact nevertheless occurs, the metallic elements of the cage are acted upon in tension. It is necessary to rely on the low deformability of the stony content so that the damage caused is not too great, but the absorption of the impact energy by the structure remains quite limited.
EP 1 520 933 A1 describes a technique in which facing elements such as gabions are disposed 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

There is therefore a need for a durable impact absorption structure that can be compact and have good landscape integration.

SUMMARY OF THE INVENTION

The invention proposes a reinforced impact absorption structure that makes it possible to distribute 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 conventionally disposed in the depth of an embankment, parallel to the direction in which it is expected to be acted upon.

SUMMARY OF THE INVENTION

The object of the invention is a of impact energy, comprising an embankment having a first face exposed to impacts and reinforcements distributed within the embankment and having frictional interfaces with the material of the embankment. The reinforcements comprise first reinforcements placed in a first reinforced region adjacent to the first face and having main strength directions forming an angle of less than 45° with the first face.
The structure can be of the merlon type and can be disposed orthogonally to a trajectory along which impacts are anticipated such that the impact against which protection is sought occurs in a direction having a strong component normal to the first face. It can also be a retaining wall disposed so as to prevent subsidence of stepped terrain in response to a substantial impact.
The embankment is preferably constituted of earth but can also have any type of material that is liable to absorb mechanical energy by interacting with the reinforcements. Preferably, the embankment has a certain granularity that allows it to have favorable mechanical behavior.
In one embodiment, suitable for example for sites where powerful impacts are likely to occur in opposite directions, the embankment has a second face opposite the first face. The reinforcements can then comprise second reinforcements placed in a second reinforced region adjacent to the second face and having main strength directions forming an angle of less than 45° with the second face.
The configuration of the absorption structure allows the friction mobilized at the first (or second, if applicable) reinforcements to have a significant contribution to the dissipation of the energy of a powerful impact occurring on the first (or second) face. This friction results from the deformation of the first (or second) face due to the impact. The location of the first (or second) reinforcements within the first (or second) reinforced region, which is adjacent to the first (or second) face, and their orientation relative to this face allows effective dissipation without requiring a great depth of penetration into the structure. It is thus possible to obtain an absorption structure that is not too bulky perpendicular to the faces likely to be struck by objects of high kinetic energy. The footprint on the ground is for example less than or equal to 10 m, preferably less than or equal to 5 m, even more preferably less than or equal to 3 m.
The reinforcements used are preferably reinforcements of the one-dimensional type, i.e. the mechanical strength that they exhibit is for the most part exerted in a single strength direction, the mechanical strength that they exhibit in the other directions being negligible compared to this one. They are, for example, strips, and not sheets or extended gratings. The main strength direction of the reinforcement corresponds to the direction in which the reinforcement tends to propagate a mechanical stress when it is acted upon. It is generally the direction of the largest dimension of the reinforcement.
These reinforcements are disposed such that their main strength directions are substantially parallel to each other and to the one or more faces of the structure. The main strength directions of the first reinforcements can be parallel to the first face of the embankment, and likewise for the second face, if 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 planar. The angle formed between these main directions and the first face nevertheless has to remain an acute angle so that their projection onto the first face is longer than their projection in the direction perpendicular to the first face, and this gives good energy dissipation effectiveness in the event of impact in the perpendicular direction.
In the case of a non-planar face, reinforcements in the extension of one another could therefore for example form a polygon matching the shape of the face. A curved face will preferably have a large radius of curvature.
The disposition of the reinforcements perpendicular to the normal of the front face, and therefore to the direction of the impact of 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 structure acted upon.
In order not to weaken the embankment by creating preferential slip planes, it is advantageous to avoid as far as possible disposing the first reinforcements in the center of it. This is the reason why the reinforcements are predominantly disposed close to the one or more faces of the structure that are likely to receive impacts. This does not exclude the presence of reinforcements in the center of the embankment, but these will be in the minority. The distribution of the reinforcements is heterogeneous in the thickness of the structure. The density of reinforcements is lower in regions that are remote from the flush faces than in the first reinforced region (or the second reinforced region) of the embankment. These are averages and it may be possible to find, very locally, exceptions that are due, for example, to construction irregularities or to deformation of the structure that will cause a plurality of reinforcements to move closer together and therefore a local increase in the density of these reinforcements: the density of reinforcements 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 widely spaced or even absent. These regions can however have other types of reinforcements, for example reinforcements oriented along the thickness of the structure.
The following features may, optionally, be implemented. They may be implemented independently of one another or in combination with one another:

- the first and/or second reinforcements are disposed horizontally;
- the first face of the embankment is covered with a facing. This facing can be of any type and can make possible both the improvement of the mechanical properties of the structure and its landscape integration, for example when it is a green or mineral facing;
- secondary reinforcements are disposed transversely to the first face. These secondary reinforcements can have any orientation and can for example make it possible to reinforce the structure against forces that it withstands under static conditions, in the absence of impact. It is thus possible to imagine zigzag-shaped reinforcements connecting the front face and the rear face or reinforcements oriented perpendicular to the front face and connecting the first and/or second reinforcements;
- the first reinforcements comprise metallic reinforcements or reinforcements made of polymer material or reinforcements of the geogrid or geotextile type.
- at least some of the first reinforcements are arranged in successive segments along their main strength direction, with zones of mutual overlap between the segments, it then being possible for embankment material to be between the successive segments of a first reinforcement, in the overlap zones.

Typically, the structure is capable of absorbing an impact having an energy greater than 2 MJ, preferably greater than 5 MJ. These energies correspond to stresses that protective merlons disposed in the mountains, for example, can conventionally suffer.
The dissipation of the energy by friction is favored in order to preserve the performance of the structure. The arrangement of the reinforcements is therefore preferably designed to limit as far as possible the breaking of the reinforcements: the plurality of reinforcements comprises reinforcements arranged so as to have ductile and not brittle behavior when the front face is acted upon by an impact in a normal direction.
An example of such an arrangement consists in limiting the direct connections between the reinforcements. Two reinforcements arranged in successive segments along their main strength direction are for example disposed with a zone of mutual overlap between them, and leaving a layer of the material of the embankment between the reinforcements, and this makes it possible to introduce friction and to soften the transmission of lateral stress in order to avoid the reinforcements breaking. This zone of mutual overlap is a function of the stiffness of the reinforcements, of the friction surface, of the breaking strength of the reinforcement.
The largest dimension of the reinforcements can also be critical and it is important not to use reinforcements of too large a dimension in order to prevent their breaking, still with a view to resilience allowing the structure to suffer a plurality of impacts without requiring repair.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics, details and advantages of the invention will become apparent upon reading the detailed description below, and upon analyzing the appended drawings, in which:

FIG. 1 is a cross-sectional side view of a structure according to one embodiment of the invention;

FIG. 2 is a cross-sectional side view of a structure according to another embodiment of the invention;

FIG. 3 is a cross-sectional side view of a structure according to another embodiment of the invention;

FIG. 4 is a cross-sectional side view of a structure according to another embodiment of the invention;

FIG. 5 is a cross-sectional front view of the structure, the cross section being on the plane V-V indicated in any one of FIGS. 1 to 4 ;

FIG. 6 is a cross-sectional top view of a structure according to the embodiment of the invention in FIG. 3 ;

FIG. 7 is a cross-sectional top view of a structure according to another embodiment of the invention;

FIG. 8 is a view similar to that of FIG. 6 after an energy impact.

DESCRIPTION OF THE EMBODIMENTS

The structure for absorbing impact energy described below by way of example takes the form of a protective merlon used to intercept falling rocks that can weigh up to several hundred metric tons, for example close to mountain roads. Such falling rocks can carry energies in excess of 6 megajoules (MJ).
This protective merlon has a first face, or front face, 10 shown on the right in FIGS. 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 FIGS. 1 and 3 . The rear face 20 can also be inclined relative to the front face 10, as in FIGS. 2 and 4 .
The orientation of the rear face 20 in FIGS. 2 and 4 allows better dissipation of the mechanical energy in the ground but increases the footprint of the structure on the ground.
Although the front face 10 is depicted as vertical in FIGS. 1 to 4 , it can also be inclined, in particular if increasing the stability of the structure, modifying the footprint on the ground or adapting to an impact trajectory that is anticipated to be oblique is required. Specifically, it is advantageous for the front face to be as far as possible perpendicular to the trajectory of the impact.
The merlon of the exemplary embodiment comprises an earthen embankment 15 delimited by the front and rear faces 10, 20, in which reinforcements 16 are disposed that have frictional interfaces with the material of the embankment. These reinforcements 16 are, for example, strips that are regularly distributed in the vertical direction and extend horizontally, parallel to the front face 10 and to the rear face 20, in a direction perpendicular to the section plane in FIGS. 1 to 4 . This orientation makes it possible to preferentially distribute the mechanical energy of an impact laterally rather than in the thickness of the protective merlon.
The reinforcements 16 are disposed in the regions of the embankment 15 that are acted upon the most in the event of an impact of which the energy has to be absorbed. In embodiments according to FIGS. 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 in FIGS. 3 and 4 , in addition to the first reinforced region 12, a second reinforced region 22 is provided near the rear face 20. This second reinforced region 22 comprises second reinforcements 16. In general, the central region of the merlon will not be provided with reinforcements 16 parallel to the faces 10, 20, so as to allow deformation of the merlon in the event of impact, so as not to weaken it.
However, secondary reinforcements 18 disposed transversely to the faces 10, 20 can also be incorporated into the embankment 15, so as to consolidate the whole. The secondary reinforcements 18 can in particular connect the front and rear faces 10, 20.
The reinforcements 16 can be disposed over the entire width of the merlon. Advantageously, reinforcements 16 are used that are disposed in successive segments along their main strength direction so as to partially overlap as illustrated in FIG. 5 . Each zone 25 of mutual overlap between two successive reinforcements 16 has embankment material such 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 dissipated gradually while at the same time avoiding causing the reinforcements 16 to break. This can allow the merlon to withstand a plurality of consecutive impacts without requiring repair.
Ideally, the reinforcements 16 are disposed perfectly parallel to the front and rear faces as illustrated in FIG. 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 merlon and/or to protect certain portions thereof, the reinforcements can have a slight angle (which has to remain less than 45°) and be somewhat sunken into the thickness of the structure, as shown in FIG. 7 . They are nevertheless considered to be substantially parallel to the front face 10 and to the rear face 20 because their orientation remains predominantly lateral. The main strength directions of the reinforcements 16 form an angle of less than 45° with the face 10 and/or 20 of the embankment 15.
Similarly, the reinforcements 16 can vary in height and have a slight slope. It is desirable for this slope to remain shallow so as to distribute the energy as laterally as possible.
FIG. 8 is a depiction similar to FIG. 6 after it has received a powerful and localized impact on its front face 10 shown at the bottom of the figure. It can be seen that the energy was able to be properly dissipated laterally by virtue of the reinforcements 16. The reinforcements 16 did not break. They remain disposed in a configuration capable of damping other impacts.
The invention is not limited to the examples described above. It encompasses all the variants that a person skilled in the art can envision within the scope of protection desired.

Claims

1. A structure for absorbing impact energy, comprising:

an embankment having a first face exposed to impacts; and

reinforcements distributed within the embankment and having frictional interfaces with the material of the embankment,

wherein the reinforcements comprise first reinforcements placed in a first reinforced region adjacent to the first face and having main strength directions forming an angle of less than 45° with the first face.

2. The structure as claimed in claim 1, wherein the main strength directions of the first reinforcements are parallel to the first face of the embankment.

3. The structure as claimed in claim 1, wherein the embankment has a second face opposite the first face, and wherein the reinforcements comprise second reinforcements placed in a second reinforced region adjacent to the second face and having main strength directions forming an angle of less than 45° with the second face.

4. The structure as claimed in claim 3, wherein the main strength directions of the second reinforcements are parallel to the second face of the embankment.

5. The structure as claimed in claim 1, wherein the reinforcements are disposed horizontally.

6. The structure as claimed in claim 1, wherein the first face of the embankment is covered with a facing.

7. The structure as claimed in also having secondary reinforcements disposed transversely to the first face.

8. The structure as claimed in claim 1, wherein the first reinforcements comprise metallic reinforcements.

9. The structure as claimed in claim 1, wherein the first reinforcements comprise reinforcements made of polymer material.

10. The structure as claimed in claim 1, wherein the reinforcements comprise reinforcements of the geogrid or geotextile type.

11. The structure as claimed in claim 1, wherein at least some of the first reinforcements are arranged in successive segments along their main strength direction, with zones of mutual overlap between the segments.

12. The structure as claimed in claim 11, wherein embankment material is between the successive segments of a first reinforcement, in the overlap zones.