EP0638689B1 - Method for facilitating the extraction of the reinforcement of a prestressed ground-anchor and corresponding anchor - Google Patents

Abstract

The invention relates to a prestressed ground anchor. The longitudinal reinforcement (6) in the anchor is sealed into the ground by a hardened sealing slurry in which there is, around the armature, a tube (2) designed to resist the prestressing tension but which is broken by a tension exerted on the reinforcement which is greater than the prestressing tension but insufficient to break the reinforcement. <IMAGE>

Description

The invention relates to an anchor of the type comprising a longitudinal reinforcement, one end of which is pressed into the ground and sealed to the ground by a hardened mass of a grout of sealing and the opposite end of which is stressed by means of tension to prestress the tie rod and which has a tube around the frame.

The publications DE-B- 2 606 095 and CH-A-5 09476 describe anchors as defined above.

In the case of a tie rod used temporarily, it is advantageous to be able to remove the reinforcement after service to avoid that it does not cause discomfort in the field and / or for the reuse.

Publication DE-B- 2 606 095 provides for this purpose to fix the armature to an anchor body capable of being destroyed by a force of shear exerted transversely. The tube placed around the frame is a tube intended to ensure sealing.

The present invention aims to facilitate the extraction of the armature by simple tensile forces.

This is achieved by the process according to the invention by incorporating the tube into the grout of sealing before setting so that this tube ensures continuity of sealing between the reinforcement and the ground, this tube being chosen to resist prestressing traction and to be broken by a traction exerted on the reinforcement greater than the traction of prestressed but insufficient to break the reinforcement.

However, we can prestress the reinforcement without danger for the tube and you can, if desired, pull the frame with a sufficient force to cause the tube to rupture and release the reinforcement which can then be extracted from the ground, because the tube which linked it to the land was broken.

The tube used according to publication CH-A-5 09476 is also incorporated into the concrete grout before setting and able to withstand prestressing traction.

The tie rod of the present invention differs from the tie rod described in this publication in that the tube is constructed in such a way that its wall be put in tension without breaking under the effect of prestressing of the reinforcement, ensuring the transition of the tensile force from the tie rod to land during the service phase, and is capable of being broken by a traction exerted on the reinforcement greater than the prestressing traction but insufficient to break the frame.

The frame is for example constituted by a bar or a bundle of strands.

The sealing tube is advantageously a fiber tube glass which ensures continuity of the seal between the reinforcement and the ground and thus, ensure the transition of the effort of pulling the tie rod to the ground during the service phase.

The tensile force of the tie rod goes from the reinforcement to the tube in glass fibers by covering, pulling the latter by a value close to that of the force applied in the reinforcement.

The tensile force exerted on the glass fiber tube is subsequently disseminated in the field by the sealing bulb created around the tube.

The fiberglass tube is thus the weak link of a sealing chain whose continuity can be broken by destruction of the material of which it is composed.

When the tie rod is no longer in service, it suffices the armature of the tie rod to reach the tensile strength of the tube fiberglass sealing and, following rupture, to extract by pulling this frame. Only remain in the field, once the operation completed, the disintegrated fiberglass tube and the grout sealing placed outside of the latter.

The armature is dimensioned so that the value of the traction of the reinforcement is greater than that of the fiber tube glass.

The two figures in the accompanying drawing illustrate two modes of embodiment of the invention, in axial section.

With reference to these two figures, the phases will be described below which allow the installation of a tie rod, in accordance with the present invention.

• on réalise dans le terrain un forage 1 ayant la longueur voulue pour l'ancrage ;
• on met en place dans ce forage un tube 2 en fibres de verre, sur tout ou partie de la longueur du forage. En fait, ce tube n'est nécessaire que dans la région prévue pour le scellement au terrain de l'extrémité inférieure de l'armature du tirant. Dans l'exemple considéré, le tube en fibres de verre ne s'étend pas sur toute la longueur du forage mais seulement sur la partie inférieure du forage et il est prolongé vers le haut par un tube de protection 3 ;
• on injecte un coulis de ciment dans le tube 2 en sorte que ce coulis traverse le tube par une série de manchettes 4 et remplisse l'espace 5 compris entre le tube et le forage.
• avant cette injection ou avant que le coulis n'ait fait sa prise, on enfonce l'armature 6 dans le forage 1 jusqu'à ce que l'extrémité inférieure 6a de l'armature ait pénétrée dans le tube 2 sur une longueur suffisante. Le coulis d'injection assure d'une part la fixation du tube 2 à la paroi du forage et, d'autre part, la fixation de l'armature à ce tube, en sorte que tout se passe comme si l'armature était fixée au forage par l'intermédiaire d'un bloc de ciment comportant autour de l'armature un cylindre de moindre résistance à la traction constitué par le tube en fibres de verre. On met en place autour de l'autre extrémité 6b de l'armature, un dispositif de précontrainte traditionnel constitué, par exemple par une plaque de répartition 7 appuyée sur le terrain et un écrou 8 coopérant avec une partie filetée de cette extrémité.

The following operations are carried out:

• a borehole 1 is made in the ground having the desired length for anchoring;
• a tube 2 made of glass fibers is placed in this borehole over all or part of the length of the borehole. In fact, this tube is only necessary in the region provided for sealing the terrain of the lower end of the frame of the tie rod. In the example considered, the glass fiber tube does not extend over the entire length of the borehole but only over the lower part of the borehole and is extended upwards by a protective tube 3;
• a cement grout is injected into the tube 2 so that this grout passes through the tube through a series of cuffs 4 and fills the space 5 between the tube and the borehole.
• before this injection or before the grout has set, the frame 6 is pushed into the borehole 1 until the lower end 6a of the frame has penetrated into the tube 2 over a sufficient length. The injection grout ensures on the one hand the fixing of the tube 2 to the wall of the borehole and, on the other hand, the fixing of the reinforcement to this tube, so that everything happens as if the reinforcement was fixed during drilling by means of a cement block comprising around the frame a cylinder of lower tensile strength constituted by the glass fiber tube. Is placed around the other end 6b of the frame, a traditional prestressing device consisting, for example by a distribution plate 7 supported on the ground and a nut 8 cooperating with a threaded portion of this end.

In the variant of FIG. 2, the glass fiber tube 2 has been fixed to the frame 6 prior to the introduction of the tube and the reinforcement in the borehole. In this case, the grout for fixing the tube to the ground can no longer be introduced from inside the tube and it is introduced by an injection tube 9 outside the tube 2.

In variants, the glass fiber tube is replaced by plastic tubes with equivalent properties for the use considered.

Claims (8)

1. Method for facilitating, after service, the extraction of the reinforcement of an anchoring tension rod comprising a longitudinal reinforcement (6), one end of which is pushed into the ground and bedded in the ground by a hardened mass of a bedding grout and the opposite end of which is stressed by tensioning means in order to prestress the tension rod, the tension rod including a tube (2) around the reinforcement, characterized in that the tube is incorporated into the bedding grout, before it sets, so that the tube ensures continuity of the seal between the reinforcement and the ground, the said tube being chosen to withstand the prestressing tension and able to be broken by a tension greater than the prestressing tension but insufficient to break the reinforcement (6).
2. Method according to Claim 1, characterized in that the said tube (2) is installed in a hole (1) in the ground before inserting the reinforcement (6) into the tube.
3. Method according to Claim 2, characterized in that the tube (2) is bedded in a hole (1) by a bedding grout injected from the inside of the tube.
4. Method according to Claim 1, characterized in that the tube (2) is fixed to the reinforcement (6) by means of a hardened bedding grout before inserting the tube and the reinforcement into a hole (1) in the ground.
5. Method according to one of the preceding claims, characterized in that a glass-fibre tube (2) is used.
6. Anchoring tension rod comprising a longitudinal reinforcement (6) to be pushed into a hole (1) in the ground and to be bedded in the ground by a bedding grout, the opposite end (6b) of the reinforcement being able to be stressed by tensioning means (7, 8) in order to prestress the tension rod, and a tube (2) to be arranged around the reinforcement in the bedding grout, the said tube (2) being able to withstand the prestressing tension, characterized in that the tube (2) is constructed in such a way that its wall is put in tension without it breaking due to the effect of prestressing the reinforcement (6), ensuring the transition of the tensile load from the tension rod to the ground during the service phase, and is able to be broken by a tension exerted on the reinforcement which is greater than the prestressing tension but insufficient to break the reinforcement.
7. Tension rod according to Claim 6, in which the said tube (2) is made of glass fibres.
8. Tension rod according to Claim 6 or 7 in service in the ground, the lower end (6a) of the reinforcement being bedded in the ground by the hardened grout containing the said tube (2) around the reinforcement and the upper end (6b) of the reinforcement being stressed by a prestressing tension.

Images