EP2550404B1 - Device for an at least partially removable anchor and method for at least partially removing an anchor - Google Patents

Description

The present invention relates to a device for an at least partially removable anchor and a method for at least partially removing an anchor.

Temporary prestressed anchors are often used to anchor the vertical walls of excavations.

Such prestressed anchors are composed for example of a bundle of parallel extending Siebendrähtiger prestressing steel strands, which serve as tension members. On the air side, the strands are fixed by means of clamping wedges in an anchor head. Behind this, the strands run individually or in a collective PE tube, without any bond with the foundation ground and freely stretchable via the so-called "free anchor length" L _fr up to an anchoring body. In the subsequent so-called "anchoring length" L _v the bare strands are connected in the anchoring body by means of injected cement mortar with the ground, in order to transmit the forces applied to the anchor head forces in the ground.

Also anchors without anchoring length L _v , so-called pressure tube anchors are used, in which the free anchor length L _fr extends to the anchor end, from where the anchor force is introduced via a pressure member enclosing the draft tube in the ground.

Depending on the quality of the ground, conventional anchors have a breaking load of 400 to 2500 kN and a setting force of 240 to 1500 kN, which are offset in lateral and vertical distances of 2 to 4 m.

The anchors are composed according to the depth of the pit and the forces acting on the anchored structure forces typically from a free anchor length L _fr of 7 to 25 m and - if available - an anchoring length L _v of 4 to 8 m together and depending on the depth of the Excavation in several, staggered in depth layers installed. Here, especially in urban areas, the majority of anchors come to lie beneath neighboring properties.

As soon as the forces absorbed by the anchored supporting structure can be released in the course of the construction progress on the building erected in the excavation pit, the anchors lose their function. If the whereabouts of the tension members in the ground e.g. is undesirable because of later proposed in this area, the anchors must be as far as possible, i. at least their over the free anchor length extending part are removed.

To remove the anchor, the method is known to produce predetermined breaking points at the transition L _fr - L _v by mechanical or thermal weaknesses of the tension members and to remove the free anchor length, the tension members at the predetermined breaking point by applying appropriate forces on the anchor head demolish (see, eg DE 195 00 091 C1 ). This method has serious disadvantages. Thus, the lost through the weakening of the tension members cross section must be compensated by additional, also weakened tension members. Also, the weakened tension members have a relatively rigid behavior, so that the break occurs abruptly and does not announce itself by a previous stretching. An abrupt failure of an anchor is undesirable in particular with regard to system security.

Furthermore, processes are known which effect the separation of the tensile members by heating or melting by means of an aluminothermic reaction mixture (cf., for example, US Pat DE 34 00 350 A1 ). A disadvantage is, inter alia, that a uniform heating of the tension member is difficult and not always a complete separation takes place. For example, if several strands are present, they are not heated due to their different location in the hole exactly at the same time and thus not at the same time to break against. The first broken wires can lead to premature release of the anchoring on the anchor head, whereby the voltage on the not yet broken wires is eliminated and they do not break.

From the patent CH 603 919 A5 It is known to inductively heat the tension members by means of an induction coil until they are severed and can be pulled out of the wellbore. The induction coil is located between a flat thermal insulation and an asbestos hose. This is movable and thus protects the induction coil insufficient against displacement relative to the tension members. When using the armature, especially if it remains longer in the ground, it can lead to damage of the induction coil when moving, so that it is no longer functional.

Furthermore, the cable runs to the power supply of the induction coil between serving as tension members strands and can also be easily damaged. In addition, the cavities between the strands and the collecting duct are not sealed air-side in the region of the separation point, so that in the free anchor length L _fr penetrating water can accumulate in the region of the separation point. As a result, the heating of the strands due to continuous cooling by the heating and evaporation of the Water practically impossible or at least delayed until the water has evaporated completely. (The strands thus function in a similar way to the heating rods of an immersion heater to heat water.)

Also from the European patent application EP 0 583 725 A1 the separation of the tension members by means of inductive heating is known. Between the induction coil and the tension members an electrically conductive metal tube is additionally provided, which is also heated inductively to heat the tension members beyond the Curie temperature to the melting point. This leads to a complex and expensive construction. Furthermore, it has been shown that in the heating of tension members made of stranded strands, the individual wires are not heated at the same time, which leads to a non-simultaneous tearing of the wires. The impulse of the wires first breaking off in a stranded strand loosens the wedge anchorage of the strand at the anchor head, whereby the wires, which have not yet cracked, are relaxed and thus their tearing off is prevented. A generic device is also made JP 2007 262880 A known.

The Applicant has referred to the prior patent CH 702926 B1 voluntarily restricted and separate claims submitted for Switzerland and Liechtenstein.

Object of the present invention is to improve the known devices and methods so that the tension member of an anchor is separable in a simpler and more reliable manner.

This object is achieved by a device according to claim 1 and a method according to the independent method claim. The further claims give preferred embodiments of the inventive device and the inventive method and a prestressable anchor with an inventive device.

The invention is based on the finding that contrary to the teaching of the EP 0 583 725 A1 no additional electrically conductive metal tube is required in order to heat a tension member beyond the Curie temperature to the melting point can. If the tension member is sufficiently biased during the heating process, a reliable separation at temperatures below the melting point is possible.

• Fig. 1 einen schematischen Schnitt durch eine Baugrube mit einem Anker ausgestattet mit einer Trennvorrichtung zum Trennen der Zugglieder an einer vorbestimmten Trennstelle;
• Fig. 2 einen Längsschnitt der Trennvorrichtung gemäss Fig. 1, die gemäss einem ersten Ausführungsbeispiel am Ende des Sammelhüllrohres der freien Ankerlänge L_fr angebracht ist;
• Fig. 3 eine Vorderansicht einer Distanzscheibe für eine Trennvorrichtung gemäss Fig. 1;
• Fig. 4 einen Querschnitt der Trennvorrichtung gemäss Fig. 1 in der in Fig. 2 mit I-I bezeichneten Schnittebene;
• Fig. 5 den Verlauf der relativen Festigkeit von Spannstahldraht in Funktion der Temperatur;
• Fig. 6 einen Längsschnitt der Trennvorrichtung gemäss Fig. 1, bei welchem gemäss einem zweiten Ausführungsbeispiel das Ende des Sammelhüllrohres der freien Ankerlänge L_fr als Trägerrohr dient;
• Fig. 7 einen Schnitt durch die Trennvorrichtung in der in Fig. 6 mit II-II bezeichneten Schnittebene;
• Fig. 8 die Ansicht des Distanzzapfenes für die Trennvorrichtung gemäss Fig. 6, der die Verfüllung im Bereich der Trennstelle beidseits abschliesst;
• Fig. 9 einen Längsschnitt der Trennvorrichtung gemäss Fig. 1, die gemäss einem dritten Ausführungsbeispiel am Ende des Sammelhüllrohres der freien Ankerlänge L_fr angebracht ist und mit Injektionsmaterial verfüllt ist; und
• Fig. 10 einen Schnitt durch die Trennvorrichtung in der in Fig. 9 mit III-III bezeichneten Schnittebene.

The invention is further preferred
Embodiments explained with reference to figures. Show it:

• Fig. 1 a schematic section through a pit with an anchor equipped with a separator for separating the tension members at a predetermined separation point;
• Fig. 2 a longitudinal section of the separator according to Fig. 1 , which is mounted according to a first embodiment at the end of the collecting duct of the free anchor length L _fr ;
• Fig. 3 a front view of a spacer for a separator according to Fig. 1 ;
• Fig. 4 a cross section of the separator according to Fig. 1 in the in Fig. 2 sectional plane designated II;
• Fig. 5 the course of the relative strength of prestressing steel wire as a function of temperature;
• Fig. 6 a longitudinal section of the separator according to Fig. 1 in which according to a second embodiment, the end of the collecting tube of the free anchor length L _fr serves as a carrier tube;
• Fig. 7 a section through the separator in the in Fig. 6 sectional plane designated II-II;
• Fig. 8 the view of the spacer pin for the separator according to Fig. 6 , which closes the filling in the area of the separation point on both sides;
• Fig. 9 a longitudinal section of the separator according to Fig. 1 , which is mounted according to a third embodiment at the end of the collecting duct of the free anchor length L _fr and filled with injection material; and
• Fig. 10 a section through the separator in the in Fig. 9 III-III cutting plane.

Fig. 1 shows an excavation 1, the vertical Baugrubenabschluss is secured with an anchored structure 19. The anchoring is ensured by prestressed armature 5, which are connected via an anchor head 6 to the structure 19. Each anchor 5 is installed in a previously drilled in the ground 3 hole 4 and extends below a neighboring plot. 2

The tension members 9 of each armature 5 are each designed, for example, as a seven-stranded prestressing steel strand and have a free anchor length (L _fr ) 7 guided by a collecting duct 10 and an anchoring length (L _v ) 8 joined to the ground 3 by cement mortar 11 in a force-transmitting manner.

At the separation point 12 at the transition of the free anchor length (L _fr ) 7 to the anchoring length (L _v ) 8, a separator 13 for separating the tension members 9 in the armature 5 is integrated.

A cable 18 for powering the separator 13 extends outside of the collecting tube 10 and is attached thereto. The injection line, through which the cement mortar is passed for anchoring, also runs outside the collecting duct 10 (not shown). When attaching the anchor injection line and cable 18 are secured together on the collecting tube 10 and inserted into the borehole 4.

Fig. 2 shows the structure of a first embodiment of the separation device 13 for separating the tension members 9 at the separation point 12. For energy transfer, the separation device 13 with an induction coil in the form of a single-layer winding 16 (inductor) of thermally insulated copper wire, wound on a support tube 15, equipped. The winding 16 has a number of turns which is in the range of 5 to 50, preferably 10 to 30. The cable 18 for powering the winding 16 is connected to the two ends of the winding 16 and extends outside of the support tube 15. Thus, the cable 18 is protected against damage during pretensioning of the tension members 9.

The support tube 15 is rigid to prevent displacement of the induction coil 16 relative to the tension members 9 and any resulting damage thereto, and is made of a material that is electrically insulating and non-ferromagnetic. Due to the rigidity of the support tube 15, inter alia, it is prevented that the forces occurring after the installation of the armature deform the support tube 15 at least over the region of the induction coil 16. As a material for the support tube 15 is eg glass fiber material, PE, PP or PVC.

The separating device 13 is arranged substantially centrally in the borehole 4 and the cavity between the rear end of the separating device 13 and the ground 3 is filled with cement mortar 11.

The induction coil 16 is supplied in operation via the electric cable 18 with higher frequency power to heat the tension members 9 inductively to breakage.

The cavities between the support tube 15 and the tension members 9 are filled with a filling 17. Et al The following materials are suitable as backfilling 17: Cement-water mixture with the possible addition of one or more additives, e.g. Propellant, plasticizer and setting accelerator, plastic-based mortar with thermally insulating additives, putty, etc.

• Die Verfüllung 17 bewirkt eine thermische Isolation jedes einzelnen Zuggliedes 9, sodass die gleichmässige Erwärmung ohne Abstrahlung oder Aufnahme von Anstrahlungsenergie benachbarter Zugglieder 9 sichergestellt ist. Sind die Zugglieder 9 als Litzen 14 ausgebildet, ist gewährleistet, dass die Drähte der einzelnen Litzen 14 und die Litzen 14 insgesamt gleich schnell erwärmt werden.
• Die Verfüllung 17 bewirkt eine minimale Verankerung der Zugglieder 9 luftseits der Trennstelle 12. Bei Litzen 14 als Zugglieder 9 werden die zuerst abreissenden Drähte der einzelnen Litzen 14 sich leicht verzögert erst dann in Bewegung setzen, wenn mehrere bzw. alle Drähte und Litzen 14 getrennt sind. Die Verankerung ist insbesondere dann wirksam, wenn sich ein möglichst grosser Teil des Trägerrohrs 15 luftseits der Trennstelle 12 befindet. Wie in Fig. 2 ersichtlich, ist zu diesem Zweck die Wicklung 16 seitlich versetzt zur Mitte des Trägerrohrs 15 angeordnet.
• Durch das Distanzelement 20 sowie die Verfüllung 17 ist das Trägerrohr 15 abgedichtet, sodass eine Ansammlung von Wasser bei der Trennstelle 12 vermieden ist. Wasser ist nebst einer Verhinderung einer etwaigen Korrosion u.a. auch deshalb zu vermeiden, weil es die Zugglieder 9 beim Erwärmungsvorgang derart kühlen kann, dass diese für eine Trennung nicht mehr genügend erhitzt werden.
• Durch das Distanzelement 20 sowie die Verfüllung 17 des Trägerrohres 15 ist die freie Ankerlänge L_fr 7 gegen das Eindringen von Zementmörtel 11 während dem Ausinjiziern der Verankerungsstrecke L_v 8 abgedichtet. Dadurch ist verhindert, dass sich in die freie Ankerlänge 7 eindringender Zementmörtel 11 an den Litzen festsetzen und deren Herausziehen nach der Trennung erheblich erschweren oder ganz verunmöglichen kann.

The filling 17 has different effects:

• The backfilling 17 causes a thermal insulation of each individual tension member 9, so that the uniform heating without radiation or absorption of radiation energy of adjacent tension members 9 is ensured. Are the tension members 9 formed as strands 14, it is ensured that the wires of the individual strands 14 and the strands 14 are heated at the same speed.
• The backfilling 17 causes a minimal anchoring of the tension members 9 on the air side of the separation point 12. In strands 14 as tension members 9, the first tearing wires of the individual strands 14 are only slightly delayed then set in motion when several or all wires and strands 14 are separated , The anchoring is particularly effective when the largest possible part of the support tube 15 is located on the air side of the separation point 12. As in Fig. 2 can be seen, the winding 16 is laterally offset from the center of the support tube 15 for this purpose.
• By the spacer 20 and the filling 17, the support tube 15 is sealed, so that an accumulation of water at the separation point 12 is avoided. Water is to be avoided in addition to preventing any corrosion, inter alia also because it can cool the tension members 9 during the heating process so that they are not heated enough for a separation.
• By the spacer element 20 and the filling 17 of the support tube 15, the free anchor length L _fr 7 is sealed against the penetration of cement mortar 11 during the Ausinjiziern the anchoring section L _v 8. This prevents that in the free anchor length 7 penetrating cement mortar 11 settle on the strands and their extraction after separation can considerably complicate or completely impossible.

Due to the thermal insulation of the individual tension members 9 and the anchoring of the tension members 9 on the air side of the separation point 12, a synchronous tearing off of the individual wires is ensured, in particular in tension members 9 made of strands 14.

As Fig. 2 further shows, the air-side end of the support tube 15 is inserted into the collecting duct 10. Spacers 20 are inserted at the end of the support tube 15 and have passages through which the tension members 9 extend. The spacers 20 are made of a solid or relatively solid material, such as metal or plastic. They ensure, in particular during assembly of the separating device 13, that the part of the tension members 9, which runs inside the carrier tube 15, comes to lie in a predetermined position with respect to the induction coil 16. Advantageously, this position is chosen symmetrically, so that the tension members 9 as uniform as possible generated by the induction coil 16 magnetic field are penetrated and thus the most uniform and simultaneous heating is achieved.

• Durchgang 20.1 bei N=1,
• Durchgang 20.2 und 20.5 bei N=2,
• Durchgang 20.3, 20.5 und 20.7 bei N=3,
• Durchgang 20.3, 20.4, 20.6 und 20.7 bei N=4,
• Durchgang 20.1, 20.2, 20.4, 20.5 und 20.7 bei N=5,
• Durchgang 20.2-20.7 bei N=6,
• Durchgang 20.1-20.7 bei N=7.

Fig. 3 shows a front view of a single spacer 20, which is designed for a maximum of seven tension members 9 and thus provided with seven passages 20.1 - 20.7. The outer passages 20.2 - 20.7 are arranged uniformly distributed around the central passage 20.1. Depending on the number N of the tension members 9 used, the respective passage 20.1 - 20.7 is either penetrated by a tension member 9 or sealed by the backfilling 17. A symmetrical arrangement of the tension members 9 can be achieved, for example, by passing a tension member 9 through the following passages:

• Passage 20.1 at N = 1,
• Passage 20.2 and 20.5 at N = 2,
• Passage 20.3, 20.5 and 20.7 at N = 3,
• Passage 20.3, 20.4, 20.6 and 20.7 at N = 4,
• Passage 20.1, 20.2, 20.4, 20.5 and 20.7 at N = 5,
• Passage 20.2-20.7 at N = 6,
• Passage 20.1-20.7 at N = 7.

Each number N gives a rotational symmetry, i. with a rotation through the angle 360 ° / n, the passages penetrated by a tension member come back to coincide, where n = 2 for N = 2, 4 or 5; n = 3 for N = 3; n = 6 for N = 6 or 7 and n = infinite for N = 1.

Of course, the number of passages in the spacer 20 is arbitrarily adaptable to the number N of the tension members provided at the anchor. For example, the spacer 20 may be designed for anchors with 8 - 12 strands or 13 - 19 strands as tension members.

Fig. 4 shows the cross section through the separator 13 at the separation point 12. The separator 13 is arranged substantially centrally in the borehole 4 in the ground 3 and outside filled with cement mortar 11. In the example shown here seven tension members are provided, which are each formed as a strand 14 with seven wires and enclosed by the wound on the support tube 15 induction coil 16. This has an outer diameter D _a and an inner diameter Di, wherein the ratio D _a to D _{i is} at most 1.5 and preferably at most 1.25. This ensures that the lateral extent of the separating device 13 corresponds approximately to the diameter of the collecting duct 10 and that no enlargement of the borehole 4 is required.

Fig. 6 shows a longitudinal section through a structure of a separating device 13 according to a second embodiment for separating the tension members 9 at the separation point 12. For energy transfer, the separation device 13 with an induction coil in the form of a single-layer winding 16 (inductor) of a single or two-wire electric cable 18, wound directly on the collecting duct 10, equipped. The electric cable 18, which leads along the collecting duct 10 to the outside, thus serves directly to form the winding 16. A transition between the electric cable and winding is thus eliminated.

The winding 16 has a number of turns, which is in the range of 5 to 50, preferably 10 to 30. The winding is fixed on the collecting tube 10 by a shrink tube 23. The electric cable 18 extends outside the collecting duct 10 to the anchor head 6 and is thereby protected against damage during pretensioning of the tension members 9.

The cavities between the collecting duct 10 and the tension members 9 are filled with a filling 17.
The filling 17 is bounded on both sides by spacer pins 21, which are made of an elastically deformable material, such as rubber.

The collecting duct 10 is locally compressed by means of steel strips 22, which are tensioned with a sufficiently large force, so that the play between the tension members 9 and the collecting duct 10 closes with respect to the spacer pin 21.

Fig. 7 shows the cross section through the separator 13 at the separation point 12th

Fig. 8 shows the distance pin 21 for a tension member consisting of 4 prestressing steel strands 14 with the passages 21.1 to 21.4. The spacer pin 21 has a length which is at least equal to the width of the steel strip 22nd

Fig. 9 shows a longitudinal section through a structure of a separating device according to a third embodiment, which is mounted after the bitumen filling 24 at the end of the collecting duct of the free anchor length L _fr .

For the purpose of sealing the free anchor length 7, the end of the collecting sleeve 10 is poured out against the cement mortar 11 injected into the anchoring length 8 with a hot-filled bitumen filling 24, which is fixed with steel bands 22 opposite the collecting sleeve 10.

The winding 16 consisting of turns of the electric cable 18 is seated on a support tube 15, which with a shrink tube 23 against the collecting tube 10 and the anchoring length 8 forming part of the tension members 14th is fixed. The cavities between the support tube 15 and the tension members 9 are filled directly by the cement mortar 11 injected into the anchoring length 8. When installing the armature 5, therefore, the support tube 15 is sealed at the air-side end, but open at the mountain end, so that the injection material 11 can penetrate during injection into the support tube 15 and this can fill.

Fig. 10 shows the cross section through the separator 13 at the separation point 12th

As well as by the backfill 17 and the spacer elements 20, 21 in the first and second embodiment is here by the backfilling 24, the support tube 15 is sealed on the biasing part of the tension members 9 side facing the separation point 12, on the one hand, a passage of water and on the other a passage of injection material 11 are prevented. This ensures that, on the one hand, the injection material 11 does not reach the prestressable part of the tension members 9 during injection and, on the other hand, no water can penetrate from the outside to the separation point 12, thus enabling efficient heating of the tension members 9.

In the following, further explanations are given, which do not relate specifically to a single embodiment.

Advantageously, the respective strand 14 of the tension member 9 has a core around which wires are wound whose diameter is smaller than the diameter of the soul. This ensures that during the heating process, the soul, which is additionally heated by the surrounding wires, not the first rips, but all the wires of the strand 14 are separated simultaneously.

The tension members 9 of the prestressed ground and rock anchors 5 are usually biased to about 60% of the breaking force. Since an anchor 5 can be embedded in the ground for a long time, it must be ensured for the removal by means of the separating device 13 that the tension members 9 are still sufficiently prestressed. The bias voltage is selected so that during the heating process by the induction coil 16, the respective tension member 9 is biased with a force corresponding to at least 10%, preferably at least 25% and more preferably at least 50% of the breaking force of the tension member 9 at 0 degrees Celsius.

Due to sufficient preload it is possible to separate the tension members 9 at relatively moderate temperatures, which are below the melting point and typically below 700 degrees Celsius and even below 600 degrees Celsius. If the strength of the tension member 9 is lowered by heating below the voltage applied in the tension member 9, this tears. Due to the tension of the torn-off part of the tension member 9 will jump out of the anchor head. For safety reasons, therefore, the anchor head is covered during the heating process with a hood to catch the tension members 9 after the break.

Fig. 5 shows the curve of the strength F as a function of the temperature T for a drawn prestressing steel wire, where F is normalized to the value of the strength at 0 degrees Celsius. As can be seen, the strength at temperatures above 600 ° C falls below 10% of the original value. Accordingly, the higher the bias voltage during the heating operation, the lower the temperatures are sufficient to cause the tension member 9 to crack.

Thus, the separator 13 need not be designed to allow heating above the Curie temperature (for Fe 768 ° C) to the melting point as in the apparatus of FIG EP 0 583 725 A1 the case is. In particular, no electrically conductive metal tube is required, which is arranged in the region between the induction coil 16 and the separation point 12 and the tension members 9 heated by heat conduction and heat radiation. The magnetic field generated by the induction coil 16 can therefore freely penetrate into the tension members 9 and heat them.

As a power supply to the power supply of the induction coil 16 is a static frequency converter having a load circuit with the winding 16 as induction. The load oscillating circuit is constructed as a parallel resonant circuit, which has power condensers as elements and the winding 16 connected via the cable 18. Capacitance and inductance of these elements determine the working frequency. The load circuit is connected to a power source, which includes a connectable to the usual power grid main transformer, a rectifier, a chopper and a smoothing part. The load circuit is connected to an H-bridge, which is controlled by the chopper.

The design of the power supply in the form of a circuit with electronic components allows a compact and relatively lightweight construction. Thus, the static frequency converter is much lighter than a dynamic frequency converter can be built and typically weighs less than 100 kg, and preferably less than 50 kg. Also, by the integration of the respective used induction coil 16 and the cable 18 used in the Oscillating circuit, the magnetic field optimized, which is used to heat the tension members 9.

By means of the static frequency converter, the induction coil 16 can be acted upon by a current which is above 2.5 A, preferably above 5 A and particularly preferably above 10 A, and which has a frequency f of more than 1 kHz and preferably more than 10 kHz. Typically, the frequency is in the range of 30-50 kHz. The power delivered by the frequency converter is greater than 1 kW and preferably greater than 3 kW, e.g. at 5 kW.

The heating power, which is induced by means of the induction coil 16 in the tension members 9, increases with increasing frequency f of the flow. On the other hand, due to the skin effect, the penetration depth of the current decreases as the frequency f increases.

The cable 18 is at least 5 m and preferably at least 10 m long and is a commercially available cable, for example one with more than two wires and / or with wires each having a cross section of at least 1.5 mm ² . The respective core can be designed either as a single wire or as a stranded wire. If a cable 18 is used with four wires, so the two opposite wires are advantageously connected together.

Surprisingly, it has been found that a commercial cable 18 does not appreciably heat when passing the current at high frequency. There are thus no expensive special cable for the power supply of the winding 16 is required.

The separation device 13 shown here is for removal (deconstruction) at least the free anchor length of the tension members of prestressed floor and rock anchors, as described, for example, in the Swiss standard "SIA 267 geotechnics" and "EN 1537 ground anchors".

Starting from the foregoing description of preferred embodiments, modifications adapted to those skilled in the art are obtainable without departing from the scope of the invention as defined in the claims.

Instead of a filling 17, which completely fills the support tube 15, it is also possible to provide a seal at each of the two ends of the support tube 15 and to leave the cavity between the two seals unfilled. The air in the cavity then acts thermally insulating for the individual tension members. As a seal, for example, an element in the form of in Fig. 6 shown spacer pin 21 are used.

Instead of a single-layer winding 16, a two-layer winding is also conceivable, with the separation device remaining slender in its lateral extent, even in this embodiment.

The separator is in addition to anchor with an anchoring length u.a. also suitable for those without anchoring length, in particular pressure tube anchor.

Claims (15)

1. Device for an at least partially removable anchor (5) that is anchorable in a foundation ground (3) by injecting cement mortar, comprising

   at least one tension member (9) with a pretensionable part (7) and

   an induction coil (16) surrounding the tension member for separating the tension member at a separating point (12) by induction heating, wherein

   as seen in cross-section, the area between the induction coil (16) and the separating point (12) is free from an electrically conducting metal tube, and wherein the induction coil (16) is arranged on a carrier tube (15), characterised in that

   the carrier tube (15) is sealed on the side of the separating point (12) facing towards the pretensionable part (7) of the tension member by a seal (17, 20, 21; 24), which is located at a distance from the free end of the pretensionable part (7), so that the seal is located in the foundation ground (3) when the anchor is built in, and which seals the pretensionable part (7) against the ingress of cement mortar while the latter is being injected.
2. Device according to claim 1, wherein the carrier tube (15) is rigid and preferably made of a synthetic material, in particular PE, PP, or PVC, or of glass fibre material.
3. Device according to one of the preceding claims, comprising a common sheath (10), in which the pretensionable part (7) of the tension member (9) extends, one of the ends of the sheath (10) preferably serving as the carrier tube for the induction coil (16).
4. Device according to one of the preceding claims, wherein the carrier tube (15) is sealed (17, 20, 21; 11, 24) on both sides of the separating point (12) in order to avoid an accumulation of water.
5. Device according to one of the preceding claims, wherein the carrier tube (15) is provided with a filling (17; 11) that seals the separating point (12) and preferably insulates the tension member (9) thermally and/or anchors it to the carrier tube (15).
6. Device according to one of the preceding claims, wherein the ratio of the external diameter (D_a) of the induction coil (16) to the internal diameter (D_i) of the induction coil is equal to at most 1.5 and preferably to at most 1.25 and/or the winding of the induction coil (16) is at most two-layered and preferably single-layered.
7. Device according to one of the preceding claims, comprising a cable (18) for the energy supply of the induction coil (16), which cable runs outside the carrier tube (15) in order to avoid damages of the cable (18) when the tension member (9) is pretensioned.
8. Device according to claim 7, wherein the cable (18) is seamlessly wound around the carrier tube (15) to form the induction coil (16).
9. Device according to one of claims 7 to 8, wherein the cable (18) has more than two conductors and/or conductors having a cross-sectional area of at least 1.5 mm² each.
10. Device according to one of the preceding claims, comprising a frequency converter for supplying the induction coil (16) with current, which frequency converter allows the generation of a frequency of more than 1 kHz and/or is a static frequency converter.
11. Device according to claim 10, wherein, for generating an alternating current, the frequency converter includes an oscillating circuit, in which the induction coil (16) can be integrated.
12. Device according to one of the preceding claims, comprising multiple tension members (9), wherein at least one spacer (20; 21) is received in the carrier tube (15), which spacer has passages (20.1 - 20.7; 21.1 - 21.4) through which the tension members (9) extend, and wherein the passages (20.1 - 20.7; 21.1 - 21.4) are preferably arranged such that a rotational symmetry results when seen in the cross-section of the spacer (20; 21).
13. Device according to one of the preceding claims, wherein the at least one tension member (9) is in the form of a strand (14) having a core around which wires are wound whose diameter is smaller than the diameter of the core.
14. Pretensionable anchor (5) comprising a device according to one of the preceding claims.
15. Method for at least partially removing an anchor (5) according to claim 14 including at least one tension member (9) which is heated by means of an induction coil (16) in order to be separated, characterised in that
    the tension member (9) is pretensioned during the heating procedure with a force that corresponds to at least 10 %, preferably at least 25 %, and particularly preferably at least 50 % of the breaking force of the tension member (9) at 0 degrees Celsius.

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