EP1664463B1 - System for anchoring an object in the ground by means of a peg - Google Patents

Abstract

The stake has anchoring clamps (28) having an end mounted on clamps support for being deployable by an axial traction exerted by an actuating mechanism (66) in a direction opposite to a depression direction. The mechanism is connected with the support by a bayonet connection. A tube (14) has a wall (26) with two openings (30) whose geometry causes the deployment of the clamps along a length of the tube in a traction direction.

Description

INTRODUCTION

The present invention relates to a system for anchoring an object in the ground using a peg, used in particular for anchoring marking terminals, such as those used by surveyors, poles of any kind , including fence posts, support posts for signs.

STATE OF THE ART

Anchorage stakes for marker posts (also known as cadastral markers) have long been known in many variants. These stakes must maintain ground bounds for several decades reliably despite the various attacks that this type of object may suffer, such as ground movements, passages of agricultural vehicles or livestock. Many solutions have already been proposed to increase the peel strength of these pegs. We can globally group them into two classes.

The first class of pegs uses a fixed geometry anchoring system. US-A-4,738,060 has such a peg for anchoring to the ground a permanent marker of an object buried in the ground. The stake comprises a long body terminated at one end by a striking head and at a second end by a plurality of slightly curved, radially disposed, elastic fins facing outwardly of the post in the opposite direction to the tip. so as to form a harpoon. When the stake is driven into the ground, the elastic fins fold back along the body under the thrust of the ground displaced by the penetration of the stake. If the post subsequently undergoes traction, the elastic fins deploy because their part slightly curved tends to become anchored in the surrounding ground under the effect of the elastic force of return of the elastic fins. The practice has unfortunately shown that these harpoons are of limited effectiveness, especially depending on the nature of the soil. Very often, the ground packed in the zone of the elastic fins during the driving of the harpoon prevents them from coming back elastically, so that the fins do not oppose almost any resistance to tearing off the stake.

The second class of pegs provides deployable elements. In EP 0 677 630 B1, such a peg has a longitudinal body of tubular section containing deployable elements. The post is first pressed into the ground, then it receives inside its tubular section a long rod terminated by a mandrel. This rod is supported on the deployable elements and forces out of the body of the stake through guide holes when the mandrel undergoes a substantially axial thrust. The appropriately dimensioned guide orifices and the ground bend the deformable elements in the course of their exit towards the outside in more or less helical trajectories. This type of stake currently has the widest distribution among the surveying anchors market, but it nevertheless has some disadvantages. The deformable elements are generally placed in the axial extension of the post and in the same direction as that of the force required for driving the stake. This geometry does not have optimum capabilities of tear resistance. Indeed, under the effect of traction on the post, the deployable elements tend to give way. It should also be noted that a stake removed from the ground is in principle no longer usable.

WO 01/42569, which discloses the features of the preamble of claim 1, shows in Figs. 17 and 18 an anchor post comprising a tube with two deployable blades as anchoring elements. These blades are mounted with one end on a nut which is movable axially inside the tube. Their free end passes through a slot in the side wall of the tube. A bolt engages the nut in the tube and bears with its head on a closed head of the tube. After breaking down the anchoring pin in the ground, the bolt is rotated to raise the nut, which forces the anchor blades to penetrate through the slots in the ground extending upwardly obliquely along the tube. It will be noted that this anchor post has the advantage of offering improved tear resistance. However, the bolt head, which protrudes from the closed head of the tube, is very troublesome when driving the anchor stake into the ground.

Figs. 20 and 21 of WO 01/42569 show an alternative embodiment which no longer has the aforementioned disadvantage of the anchoring stake of FIGS. 17 and 18. This anchor post comprises a tube and a U-shaped body serving as an anchoring element. A threaded rod with a special head serves as a tool for setting up the anchoring element. The tube is driven into the ground without the anchor. The U-shaped body is then mounted on the threaded rod. For this purpose, a crosshead of the threaded rod is passed through a slot in the base of the U-shaped body and the threaded rod rotated by 90 °. Using the threaded rod, the U-shaped body is pushed into the tube until its lateral arms engage channels arranged in the side wall of the tube. A nut screwed onto the threaded rod pushes the U-shaped body into the tube. Once the lateral arms are engaged in the channels arranged in the side wall of the tube, traction is exerted on the threaded rod, either by means of a lever, or by means of a clamping nut which is lowered on a spacer. This traction forces the side arms of the U-shaped body to penetrate the soil through the channels in the side wall of the tube. When this is complete, the 90 ° threaded rod is rotated to pass its head through the slot in the base of the U-shaped body and to remove the threaded rod from the tube. It will be noted that the subsequent setting operation of the U-shaped anchoring body in the tube is very delicate.

Finally, note that the anchor posts described in WO 01142569 are designed to serve as permanent anchor for poles. Once anchored in the ground, they remain in principle in place. However, for certain applications, in particular for the fixing of marking terminals, it is important to also that we can easily recover the anchor stake if it is no longer used.

OBJECT OF THE INVENTION

An object of the present invention is to provide a system for anchoring an object in the ground with the aid of an anchoring peg providing good resistance to tearing, which allows an easy installation of the anchoring stake and easy recovery of the latter if it is no longer used.

GENERAL DESCRIPTION OF THE INVENTION CLAIMED WITH ITS MAIN ADVANTAGES

According to the invention, this object is achieved in particular by a system for anchoring an object in the ground according to claim 1.

Such a system for anchoring an object in the ground comprises at least one anchoring stake and an actuating mechanism. The anchor post comprises a tube and at least two deformable anchoring claws mounted on a claw holder which is axially movable within the tube. The tube has a tube wall, a driving tip and a head. The anchoring claws are mounted with one end on the claw holder, so that axial traction exerted on the claw holder in the opposite direction to the depressing direction causes the claws to protrude from the tube through openings in the tube wall. These openings have a geometry such that they cause a deployment anchoring claws skew along said tube in the direction of traction. The actuating mechanism is a threaded rod mechanism. An anchoring stake of the system according to the invention further comprises the following features. The claw holder comprises a central support rod which is coaxial with the tube, axially guided and rotatably locked in the tube. The claws are carried by the lower end of this central support rod on the side of the driving tip. On the side of the tube head, a coupling means equips the upper end of the rod support center. The actuating mechanism with threaded rod comprises a nut adapted to bear on the tube head and a threaded rod, on which is screwed said nut, and whose lower end comprises a coupling means adapted to cooperate with the means coupling the upper end of the central support rod to transmit thereto said axial traction when rotating said nut in a first direction.

It will first be appreciated that an anchoring stake of the system according to the invention provides good resistance to tearing. Indeed, the direction of deployment of the claws directly opposes the extraction force, thus obtaining optimum resistance to tearing. The claws being inside the peg during the driving of the post, deformation or claw breakage is excluded. In addition, once the post is depressed, the claws can be deployed in an environment that has not been weakened by the depression of the stake. On the contrary, the depression of the post locally tamped the middle around the stake. This packed medium offers a very good grip for anchoring claws.

It will then be appreciated that with the system according to the invention the setting up of the stake in the ground is particularly simple. Indeed, the depression of the stake in the ground can be done without setting up the actuating mechanism. During this driving operation, the central rod for supporting the claws is completely inserted into the tube, so that there is no element which protrudes with respect to the head of the tube and which would impede the insertion of the tube. percussion anchor post on the tube head. Once the stake is driven into the ground, the actuating mechanism can be coupled to the central support rod of the claws. To this end, it is sufficient to couple the lower end of the threaded rod to the upper end of the central claw support rod. This is a very easy operation because the coupling is done near the head of the tube. To deploy the claws, then turns the nut bearing on the head of the tube in said first direction, which makes up the central rod claw support. When the claws are deployed, the actuating mechanism can be removed and used to anchor other stakes. Reusing the actuating mechanism naturally reduces the costs of the system.

It will still be appreciated that the recovery of a stake anchored in the ground is also very easy. To undo the anchoring, it suffices, for example, to strike the upper end of the central rod for holding claws, which causes the central claw support rod to descend and consequently causes retraction of the claws in the tube. Axial guidance of the central claw support rod will facilitate this operation by avoiding clawing of the claws in the tube.

If it is wished to further reduce the risk of damaging the claws during the recovery of a stake anchored in the ground, an actuating mechanism is advantageously used, which furthermore comprises a locking means connectable to the head of the tube. so as to form a counter-support for the nut when the latter is rotated in a second direction opposite to the first, to thereby cause a translation of said threaded rod to the inside of the tube and to return said claws into the tube. The locking means is advantageously an element that can be removably connected to the tube head. In a preferred embodiment, the actuating nut comprises a base, the tube head comprises a collar and the locking means is a jumper that straddles the base and the collar.

The coupling means advantageously form a coupling with a helical connection or with a bayonet connection. These are couplings that allow quick coupling and decoupling and do not require much space, that is, they do not cause an increase in the section of the tube.

The anchoring claws are preferably deformable rods which, when compared to anchor blades, take up less space in the retracted position and provide better penetration into the ground.

In a particularly compact execution of the anchoring stake, the tube has a square section, the central support rod has a round section and the Anchoring claws are deformable rods of round section which are arranged in the four corners of the square section tube and which pass through openings arranged in the corners of the wall of the tube.

The tube wall includes openings through which the claws exit at different heights. In this way, the anchoring claws deploy in the ground at different depths. In the case of terrain with a very heterogeneous density, this increases the chances of being able to deploy certain claws in a mechanically stable zone. The anchoring claws are also advantageously carried by a plate attached to the lower end of the central support rod and have different lengths.

In order to guarantee good axial guidance, it is preferably provided with axial guidance of the lower and upper end of the central support rod in the tube. Good axial guidance is indeed essential to avoid deformation of the claws when, to retract the claws, one hits on the upper end of the central rod claw support.

To ensure better immobilization of the anchoring stake in the ground, is advantageously arranged on the side of the tube head means for compressing the soil around the tube. Such soil compression means comprise for example a body in the shape of an inverted cone or an inverted pyramid, this body being traversed axially by the tube. Such a soil compression body is advantageously formed of two half-bodies assembled around the tube in a plane which passes through the axis of the tube. It should be noted that the soil compression means may also comprise at least two T-shaped sections which extend obliquely along the upper part of the tube so as to form a "V".

To further facilitate the establishment and recovery of an anchoring stake, the means for the implementation of the anchoring stake advantageously comprise a mandrel provided with a shoulder adapted to bear on a collar surrounding the head tube to drive the tube into the ground, and a central rod with a flexible end adapted to take pressing on the upper end of the central claw support rod in the tube to drive the latter in the tube and thus retract the claws.

It will be appreciated that a system according to the invention is particularly suitable for anchoring a marker terminal in the ground.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1:

une vue schématique en coupe verticale d'un piquet seul après son enfoncement dans le sol;

FIG. 2 :

une vue schématique en coupe verticale d'un piquet après mise en place d'un dispositif servant au déploiement des griffes d'ancrage ;FIG. 3 : une vue schématique en coupe verticale d'un piquet montrant le déploiement des griffes d'ancrage ;

FIG.4:

une vue schématique en coupe verticale d'un piquet après son ancrage définitif ;

FIG. 5 :

une vue schématique en coupe verticale d'un piquet après mise en place d'un dispositif servant à la rétraction du système d'ancrage ;

FIG. 6 :

une vue schématique en coupe verticale d'un piquet montrant la rétraction des griffes d'ancrage ;

FIG. 7 :

une vue schématique de dessus d'un piquet.

FIG. 8 :

une vue schématique en coupe verticale d'un piquet lors de son enfoncement dans le sol à l'aide d'un mandrin spécial ;

FIG. 9 :

une vue schématique en coupe verticale d'un piquet lors de la rétraction des griffes à l'aide du mandrin spécial de la Fig. 8 ; et

FIG. 10 :

une vue schématique en coupe partielle mont rant la fixation d'une borne ou balise à l'aide d'un piquet d'ancrage comprenant un cône de compression de sol ;

FIG. 11 :

une coupe à travers le cône de compression de sol ;

FIG. 12:

une vue schématique en coupe verticale montrant un piquet d'ancrage équipé de profilés de compression du sol;

FIG. 13 :

une coupe horizontale du piquet d'ancrage de la FIG. 12.

Other features and characteristics of the invention will become apparent from the detailed description of some advantageous embodiments presented below, by way of illustration, with reference to the accompanying drawings. These show

FIG. 1:

a schematic view in vertical section of a stake alone after its insertion into the ground;

FIG. 2:

a schematic view in vertical section of a post after placing a device for deploying the anchor claws; 3: a schematic vertical sectional view of a peg showing the deployment of the anchoring claws;

FIG.4:

a schematic view in vertical section of a peg after its final anchoring;

FIG. 5:

a schematic view in vertical section of a peg after setting up a device for retraction of the anchoring system;

FIG. 6:

a schematic vertical sectional view of a peg showing the retraction of the anchoring claws;

FIG. 7:

a schematic top view of a peg.

FIG. 8:

a schematic view in vertical section of a peg when it is driven into the ground by means of a special mandrel;

FIG. 9:

a schematic view in vertical section of a post during retraction of the claws with the special mandrel of FIG. 8; and

FIG. 10:

a schematic view in partial section showing the fixation of a bollard or beacon using an anchor post comprising a soil compression cone;

FIG. 11:

a section through the soil compression cone;

FIG. 12:

a schematic view in vertical section showing an anchor post equipped with soil compression profiles;

FIG. 13:

a horizontal section of the anchor post of FIG. 12.

In the figures, the same references designate identical or similar elements.

DETAILED DESCRIPTION OF A PREFERRED EXECUTION

Fig. 1 illustrates a preferred embodiment of a peg 10 according to the invention, the post 10 being depressed in a medium 12, for example a ground. The stake 10 comprises a tube 14 having at one end a tip 16 and being open at its other end 18. The end 18 of the tube 14 is provided with a head plate 22 (also called tube head) forming a collar . As seen in FIG. 7, the tube 14 has, in the embodiment shown, a square section.

A central support rod 24 is disposed inside the tube 14. This central support rod 24 is provided with a plurality of anchoring claws 28 integral with their lower part of the central rod 24. As can be seen on 1, before deployment, the claws are arranged along the rod 24. The anchoring claws 28 are preferably made of flexible steel, but may be in any other material allowing a plastic or elastic deformation of the claws without breaking when of their deployment.

The tube 14 comprises in its lateral wall 26 a plurality of openings 30. These receive the curved upper ends 32 of the anchoring claws 28 which, before deployment, do not protrude from the side wall 26 of the tube 14 and which are fully housed in tube 14. It will be noticed that the curved upper ends 32 and the openings 30 are spaced not only circumferentially around the tube 14 but also axially along the tube 14. The axial distribution of the points of penetration of the claws 28 in the ground increases the chances of a good anchoring in free from a possible heterogeneity of the medium 12 if it had to present more or less soft areas at different depths. The number of openings 30 and anchor claws 28 may be chosen depending on the nature of the medium 12 or the load to which the present invention will be confronted.

The first phase of implementation of the post 10 is to push it with the aid of a suitable tool, such as a mass or a heavy hammer, in the ground 12. FIG. 1 shows post 10 after this first phase.

Fig. 2 illustrates the second phase of implementation of the stake 10: the establishment of a removable actuating mechanism 33. The actuating mechanism 33 fits on the head 22 of the tube 14 and comprises a threaded rod 36 and a nut 40. This mechanism is installed in practice in the following manner. Through an opening 34 in the head plate 22 is introduced the threaded rod 36 on which is screwed the nut 40. The lower end 42 of the threaded rod 36 has a threaded bore 44 and is screwed on a threaded end 44 'of the central support rod 24, so as to obtain a connection for transmitting a tensile force on the central support rod 24. A possible variant to a helical connection between two threads is for example a bayonet coupling. Other coupling variants, however, are not excluded. Referring to FIG. 7, it will be noted that the central rod 24 is locked in rotation in the tube 14 by means of a square plate 45 fitted in square section of the tube 14. This plate 45 also serves as axial guidance of the central support rod 24 in the tube 14. If the tube 14 had a circular section, it would be necessary for example to provide inside the tube 14 an axial guide which prevents the rotation of the plate 45. In FIG. 7, we also see that the central support rod 24 has a round section and that the anchoring claws 28 are deformable rods of round section which are arranged in the four corners of the tube 14 of square section and which pass through openings arranged in the corners of the wall 26 of the tube 14. This arrangement makes it possible to work with a reduced section tube while ensuring a smooth progression of the deployment, respectively the retraction of the claws 28.

To exert traction on the central support rod 24 in the direction of the arrow 47 of FIG. 3, that is to say in the opposite direction of the driving direction of the stake, the nut 40 is rotated by pressing on the head plate 22 with a wrench in the direction of the arrow 49. Indeed, as the central support rod 24 is locked in rotation in the tube 14, the rotation in the direction of the arrow 47 of the nut 40 bearing on the head plate 22 causes a translation of the central rod support 24 in the direction of the arrow 47, provided naturally that the threads of the nut 40 and the threaded rod 36 have a step to the right. During the translation of the central support rod 24 in the direction of the arrow 47, the anchoring claws 28 are pushed through the openings 30 of the tube 14, to enter the adjacent land 12. The lower and upper edges of the openings 30 are bevelled so that the anchoring claws 28 are guided, starting with the curved upper ends 32, obliquely along the tube 14 in the direction of the arrow 47, it is in the sense of traction. The trajectory of the anchoring claws 28 is determined on the one hand by the geometry of the openings 30, and on the other hand by the resistance to penetration opposite by the medium 12. It will be appreciated that after deployment of the claws 28, the post 10 is firmly anchored in the ground 12 in the manner of a harpoon. Indeed, the anchoring claws 28 then have optimum opposition to any effort tending to extract the stake 10 from the ground 12.

Fig. 4 shows peg 10 anchored in the ground. The threaded rod 36 has been unscrewed from the central support rod 24 and withdrawn together with the nut 40.

Fig. 5 illustrates the first recovery phase of stake 10. Stem The threaded end 36 is again screwed onto the threaded end 44 'of the central support rod 24, in the same manner as during the anchoring phase of the post 10. The nut 40 is brought closer to the head plate 22. tube 14. Next, a rider 50 is placed astride the head plate 22 of the tube 14 and on a base plate 51 of the nut 40. A leg of the rider 50 is supported on the underside of the plate of head 22 and the other leg forms a counter-support for the upper face of the base plate 51 of the nut 40. The nut 40 is then rotated using a key so as to obtain the penetration inside the tube 14 of the threaded rod 36. By this translation, the central support rod 24 is also translated in the direction of the tip 16 of the tube 14. In doing so, it forces the anchoring claws 28 to return by the openings 30 of the tube 14. It will be noted that to push the central support rod 24 towards the tip 16 of the tube 14, the ec rou 40 is supported on the upper leg of the rider 50, which transmits the reaction of this force to the head plate 22 of the tube 14.

Fig. 6 shows the anchoring claws 28 fully retracted inside the tube 14 as a result of the proper rotation of the nut 40 in the direction of the arrow 49 '. The bevelled edges of the openings 30 facilitate the retraction of the anchoring claws 28 and prevent their breaking, so that the post 10 can be reused after its extraction from the ground 12.

FIG. 8 illustrates the depression of an anchor rod 10 in the ground with the aid of a special mandrel 100. This special mandrel 100 comprises a shoulder 102 bearing on the head plate 22 of the tube 14 and a central rod 104. The latter enters the tube 14 to center the mandrel 100 on the tube 14. It will be noticed that in FIG. 8, the end 106 of the central rod 104 is spaced from the upper end of the central support rod 24.

FIG. 9 illustrates the use of the same mandrel 100 for the retraction of the claws 28. When the claws 28 are out of the tube 14, the upper end of the central support rod 24 is very close to the head plate 22 of the tube 14 The central rod 104 of the mandrel 100 can then be supported by the upper end of the central support rod 24 to drive this rod 24 into the tube 14 and thus retract said claws 28. In order not to damage the upper end of the central support rod 24, the end 106 of the rod 104 of the mandrel 100 is advantageously made of a softer material than the upper end of the central support rod 24.

FIG. 10 shows the fixing of a terminal head 110 by means of an anchoring post 10. The terminal head 110, made for example of concrete, is provided with a central channel through which the tube 14 passes. The head plate 22 is housed in a cavity 112 of the terminal head 110. A plastic plug 114 closes this cavity 112 and the opening in the head plate 22 of the tube 14. It is held in place by compression ribs 116 and has a centering cavity 118 for LEDs, milestones or prisms (not shown).

The anchoring post 10 of FIG. 10 further comprises a soil compression body 120 of plastic providing superior stability of the anchoring point in the ground. This body has the shape of an inverted cone or an inverted pyramid provided with a central channel for the passage of the tube 14. In FIG. 11, it can be seen that the soil compression body 120 is formed of two half-bodies 120 ', 120 "which are assembled in a central plane around the tube 14.

The anchoring post 10 of FIGS. 12 and 13 comprises four T-shaped profiles 130 which extend obliquely along the top of the tube 14 towards the upper end thereof, so as to form a "V" in two orthogonal planes. These T-profiles 130 also fulfill the role of soil compression means at the upper end of the tube 14, to ensure better stability of the anchoring point in the ground.

Claims (16)

1. A system for anchoring an object in the ground comprising at least one anchoring stake (10) and means for employing said anchoring stake (10),
   said stake (10) comprising a tube (14) with a drive-in spike (16) and a head (22), and at least two deformable anchoring claws (28) which are mounted with one end on a claw support that can move axially inside said tube (14) so that axial traction exerted on said claw support in the opposite direction to said drive-in direction causes said claws (28) to deploy out from said tube (14) through openings (30) in a wall (26) of the tube (14), said openings (30) having a geometry such that they cause said anchoring claws (28) to deploy at an angle along said tube (14) in the direction of traction; and
   said means for employing said anchoring stake (10) comprise an actuating mechanism (33) involving a threaded rod (36) for exerting said axial traction on said claw support;
   characterized in that
   said claw support comprises a central support rod (24) which is coaxial with said tube (14), axially guided and prevented from rotating in said tube (14), said claws (28) being borne by the lower end of said central support rod (24) at said drive-in spike (16) end, and a coupling means equipping the upper end of said central support rod (24) at said tube head (22) end; and
   said actuating mechanism (33) involving a threaded rod (36) comprises a nut (40) able to bear against said tube head (22) and a threaded rod (36) on to which said nut (40) is screwed and the lower end of which comprises a coupling means able to collaborate with said coupling means at the upper end of said central support rod (24) so as to transmit said axial traction to this upper end when said nut (40) is turned in a first direction
2. The system as claimed in claim 1, characterized in that said means for employing said anchoring stake (10) further comprise a locking means (50) connected to said tube head (22) in such a way as to form a backstop for said nut (40) when the latter is turned in a second direction, the opposite to the first, in order thus to cause a translational movement of said threaded rod (36) toward the inside of said tube (14) and cause said claws (28) to retract back inside said tube (14)
3. The system as claimed in claim 2, characterized in that said locking means (50) is an element that can be connected removably to said tube head (22)
4. The system as claimed in claim 3, characterized in that:

   said nut (40) comprises a base (51);

   said tube head (22) comprises a collar; and

   said locking means (50) is a stirrup piece straddling said base (51) and said collar.
5. The system as claimed in any one of claims 1 to 4, characterized in that said coupling means form a coupling with a helical connection or a bayonet connection
6. The system as claimed in any one of the preceding claims, characterized in that said anchoring claws (28) are deformable rods
7. The system as claimed in claim 6, characterized in that said tube (14) has a square cross section, said central support rod (24) has a round cross section, and said anchoring claws (28) are deformable rods of round cross section which are arranged in the four corners of said square-section tube (14) and which pass through openings arranged in the corners of said wall (26) of the tube (14)
8. The system as claimed in any one of the preceding claims, characterized in that said tube wall (26) comprises exit openings (30) for said claws (28) at different heights
9. The system as claimed in claim 8, characterized in that said anchoring claws (28) are borne by a plate (45) fixed to the lower end of said central support rod (24) and have different lengths
10. The system as claimed in any one of the preceding claims, characterized in that said lower end and said upper end of said central support rod (24) are axially guided in said tube (14)
11. The system as claimed in any one of the preceding claims, characterized by ground-firming means arranged around said tube (14) at said tube head (22) end.
12. The system as claimed in claim 11, characterized in that said ground-firming means comprise a body in the form of an inverted cone or of an inverted pyramid, provided with a central canal through which said tube (14) can pass
13. The system as claimed in claim 12, characterized in that said body is formed of two half-bodies assembled along a central plane.
14. The system as claimed in claim 10, characterized in that said ground-firming means comprise at least two T-sections extending at an angle along the upper part of said tube (14) so as to form a "V".
15. The system as claimed in any one of the preceding claims, characterized in that said means for employing said anchoring stake (10) further comprise a mandrel equipped with a shoulder able to bear against a collar surrounding said tube head (22) in order to drive said tube (14) into the ground, and equipped with a central rod with a flexible end able to bear against the upper end of said central support rod (24) in order to drive the latter into said tube (14) and thus retract said claws (28).
16. Use of a system as claimed in any one of the preceding claims for anchoring a land-survey bench-mark in the ground

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