EP3336258B1 - End anchorage for a soil and/or rock anchor - Google Patents

Description

The invention relates to an end anchorage for a ground and/or rock anchor, which comprises a tension member made of at least one prestressing strand.

The patent application EP 124 661 A1 discloses an end anchor according to the preamble of claim 1.

The patent application WO 86/00655 A1 discloses an end anchorage having a compressive compression member extended to the surface of the earth.

The patent CH 300 486 A describes a method of creating an upset end of a single wire.

The patent application DE 10 2012 017 704 A1 describes an anchoring of a tendon having a tie rod in a component having a channel. A non-positive connection with the wall of the duct is created by means of a hardenable casting compound.

The utility model DE 20 2008 001 248 U1 relates to a ground or rock anchor with an anchor tension member made of one or more individual elements and with an anchor head design for anchoring the anchor tension member at the air-side end of the borehole.

Advantageously, the tension member is anchored in the end anchorage with as little slippage as possible, so that during displacement measurements during anchor tests and stress tests to determine and check the load-bearing capacity of the subsoil, there is no mixing of reactions in the subsoil and slippage in the end anchorage.

For end anchorages, it is known to anchor the prestressing strands purely mechanically with clamping wedges or with compression sleeves on an anchoring plate. However, this type of anchoring is unfavorable due to the space requirement of the anchoring plate, in which the clamping wedges are fixed or the press sleeves stand up, since the diameter of the drill hole has to be increased compared to the usual diameters used in normal ground anchors without a pressure pipe, which leads to considerable additional costs leads.

An object of the present invention is to propose an end anchorage for a ground and/or rock anchor with a compact structure.

An end anchor that solves this problem is specified in claim 1. The further claims specify preferred embodiments of the end anchorage according to the invention and an anchor with such an end anchorage.

By providing a compressed end of the prestressing strand, the end anchorage can be made compact. It is therefore not necessary to provide a borehole that has an oversized diameter.

Fig. 1

einen Längsschnitt durch die Endverankerung;

Fig. 2

den Schnitt A - A aus Fig. 1;

Fig. 3

den Stauchkopf am Litzenende im Detail;

Fig. 4

den Schnitt B - B durch die Spannstahllitze aus Fig. 3;

Fig. 5

den Schnitt C - C durch den Stauchkopf aus Fig.3 ohne Verfüllung; und

Fig. 6

den Schnitt C - C durch den Stauchkopf aus Fig.3 mit Verfüllung.

The invention is explained further using an exemplary embodiment with reference to figures. Show it:

1

a longitudinal section through the end anchorage;

2

the cut A - A out 1 ;

3

the upsetting head at the end of the strand in detail;

4

cut B - B through the prestressing steel strand 3 ;

figure 5

make the cut C - C through the upsetting head Fig.3 without backfill; and

6

make the cut C - C through the upsetting head Fig.3 with backfill.

1 shows a longitudinal section through the end anchorage 1, z. B. on a pressure pipe of a pressure pipe anchor or generally on a support 11 of a rock and / or ground anchor by means of a transfer plate 3 is supported. The tension member 2 of the anchor is formed from prestressing strands 12, for example prestressing steel strands. These run through bores in the transmission plate 3, then extend along a bonded section and finally pass through bores in an anchor plate 5 (also called “end plate” below). The transfer plate 3 has a bearing surface which bears against the support 11 . The tension strands 12 are provided at their ends with upsetting heads 6 which are supported on the end plate 5 and are pressed against it by means of the pressure plate 10 . For this purpose, the pressure plate 10 is screwed to the end plate 5 or connected to it in some other way.

Between the end plate 5 and the pressure plate 10 the compression heads 6 are surrounded by the cast 8 . This is made, for example, from a material based on cement, plastic and/or metal. The forces of the upsetting heads 6 on the end plate 5 are transmitted to the transmission plate 3 via a steel tube 4 which is arranged between the plates 3 and 5 and surrounds the tension member 2 .

In the steel tube 4 between the end plate 5 and the transmission plate 3, the prestressing steel strands 12 of the tension member 2 are cast in a filling 7, for example grouting mortar, in order to absorb forces from the Tension member 2 to be removed from the transmission plate 3 on the support 11 . Various materials are conceivable for the production of the backfill 7, for example a cement-water mixture with the possible addition of one or more additives, such as e.g. e.g. propellants, liquefiers and setting accelerators, plastic-based mortars, etc.

The one in the 1 shown end anchorage is designed for dismantling the tension member 2. For this purpose, a separating device is provided in order to weaken or cut through the tension strands 12 if necessary. For example, the Separating device an induction coil 16, which surrounds the tension member 2 and this inductively heated during expansion until it breaks. The temperature required for this can be kept below the melting point of the tension member 2 if this is sufficiently prestressed during the heating process, typically with a force that is at least 10%, preferably at least 25% and particularly preferably at least 50% of the breaking strength of the tension member 2 at 0 degrees Celsius.

The induction coil 16 is arranged closer to the plate 3 than to the plate 5, preferably subsequently to the plate 3, and is cast in the filling 7.

A frequency converter (not shown), for example a static frequency converter, is used to energize the induction coil 16 and can be connected to the induction coil 16 via a power supply cable 17 running along the tension member 12 . This is preferably formed by a winding that is one or more layers and consists of a cable. In 1 it can be seen that the power supply cable 17 is passed through an opening in the tube 4 . Alternatively, it is conceivable to guide the cable 17 through the transmission plate 3 from the interior of the support 11 .

The induction coil 16 preferably runs at a distance around the tension member 2 in order to prevent the heat generated in the tension member 2 during the heating process from melting the electrical insulation of the induction coil 16 and thus leading to an electrical short circuit. The induction coil 16 can, for. B. be arranged on or in a piece of pipe, through which the tension member 2 runs and which is embedded in the backfill 7.

2 shows a section through the bonded section with the tension member 2 consisting of the prestressing steel strands 12, which is connected to the steel pipe 4 via the grouting mortar 7. Four prestressing steel strands 12 are shown here. The number can also be different and can be one, two or more. If the number is greater than one, the prestressing steel strands 12 are preferably arranged symmetrically around the center, so that the angle between two adjacent upset heads 6 is the same when viewed in the circumferential direction. It is also conceivable to provide at least one tension strand 12 in the center and to arrange the rest, if any, symmetrically around the center, as just explained.

Furthermore, seven individual wires 13 are shown here for each strand 12 . This number can also be different and can be two, three or more. The respective wire 13 of the stranded wire 12 has a full cross section. Preferably, the respective strand 12 in Center a wire 13 as a core, around which wires 13 are wound, the respective diameter of which is smaller than the diameter of the core.

• zementöser Vergussmörtel,
• Kunststoffvergussmörtel,
• metallischer Verguss, beispielsweise Flüssigmetall wie Wirelock^®.

3 shows in detail the end area of a prestressing steel strand 12 of the end anchorage. The individual wires 13 of the prestressing steel strand 12 are filled in the upsetting head 6 as compressed individual wires 14 with the interstices 15 by the encapsulation 9 and surrounded by the encapsulation 8 . The encapsulation 9 is preferably made from the same material as the encapsulation 8. The following materials are suitable for the encapsulation 8 or 9:

• cementitious grout,
• plastic grout,
• metallic encapsulation, for example liquid metal such as Wirelock ^® .

The pressure plate 10 presses the upsetting head 6 against the end plate 5 in order to eliminate any play. Following the end plate 5, the prestressing steel strand 12 runs in the steel pipe 4, which is filled with the grout 7.

The method according to Birkenmaier, Brandestini, Roš and Vogt is known for producing an upset end of a single wire (BBRV method), see CH 300 486. This method can be transferred here in order to anchor a strand 12 with an upsetting head 6 as a to generate the end. During production, the end of a stranded wire 12 is upset in the cold state with a upsetting machine. The ends 14 of the individual wires 13 of a strand 12 are compressed so that they form a compression head 6 overall, the diameter of which is larger than the diameter of the strand 12 . The upset head 6 is therefore an integral part of the strand 12 and surprisingly has a high load-bearing capacity. This is typically at least 40% of the breaking strength of the strand 12, preferably at least 50%.

The provision of the pressure plate 10 and the encapsulation 8, 9 can prevent the compression heads 6 from yielding under load as a result of the geometry of the compressed individual wires changing from their original shape. As a result, the carrying capacity of the upsetting heads 6 can be increased, as a result of which the upstream composite section can be shortened and the overall slip can be further reduced. Typically, this carrying capacity is at least 70%, preferably at least 90% and particularly preferably 100% of the breaking strength of the strand 12.

4 shows the section through the prestressing steel strand 12 with here the seven individual wires 13 in the area of the end plate 5. The borehole 5a in the end plate 5 can be seen, through which the prestressing steel strand 12 runs.

figure 5 shows the section through an upsetting head 6 before the interstices 15 have been filled and encapsulated.

6 shows the section through the compression head 6 surrounded by the encapsulation 8 with the individual wires 14, the gaps 15 of which are filled with the encapsulation 9.

The end anchorage described here can be used in a variety of ways as part of a ground and/or rock anchor. In use, the anchor's prefabricated end anchorage is inserted into a borehole in the ground or rock. The anchor is z. B. formed as a pressure pipe anchor. In this case, the tension member is free-playing over the entire length of the anchor in a casing, e.g. B. made of PE and anchored in the deepest part of the borehole by means of the end anchorage. To introduce the anchor force into the subsoil, the end anchorage is based on the pressure pipe, which is typically 1.5 to 4 meters long and is connected to the subsoil in a non-positive manner by pouring cement mortar for anchoring purposes. The pressure pipe can be made of one or more materials.

The end anchorage can be used for anchors with retractable tendons or for permanently installed anchors, ie anchors without removable tendons. In the latter case, the separating device for separating or weakening the tension member (cf. e.g. the in 1 elements 16 and 17 shown) may be omitted.

If the end anchorage is designed for dismantling, the tension member can be separated by means of the separating device, which z. B. is designed for heating by induction, weakened so that it tears under the upcoming clamping forces.

Soil and rock anchors with removable tension members are used in particular to secure construction pits. The forces, which are kept in balance by the anchors and are mainly caused by active earth pressure, can usually be taken over by the structures after they have been erected, so that the function of the anchors becomes obsolete. The anchors usually extend under neighboring properties, so that if left in the subsoil they present an obstacle during later construction work. In particular, the tension member made of prestressing steel strands is difficult to cut due to the high strength and toughness of the steel. For this reason, in many cases there is a demand for the anchors to be dismantled.

The end anchorage described here has the following advantages, among others:
The end anchorage has a compact structure.

In this way, the end anchorage can be designed to be slim when viewed transversely to the direction of the borehole. A strand head has a smaller lateral extension than, for example, a strand that is anchored with wedges or a ferrule. Typically, the strand head has a diameter less than 2 times the strand diameter, e.g. B. 1.5 times the wire diameter. It is therefore possible to arrange the strands in a more space-saving manner than usual. Compared to the commonly used ground anchors without a pressure pipe, no larger drill hole diameters are required.

The end anchorage can also be kept short when viewed in the direction of the borehole. The distance between the support 11 and the upsetting head 6 or the upsetting heads 6 is typically less than 1 m, preferably less than 0.50 m.

The tension member can be anchored in the end anchorage with as little slippage as possible, so that during displacement measurements during anchor tests and stress tests to determine and check the load-bearing capacity of the subsoil, there is no mixing of reactions in the subsoil and slippage in the end anchorage. Typically, the slip that occurs in the end anchorage when the tension member is tensioned is less than 0.5 mm, preferably less than 0.2 mm and particularly preferably less than 0.1 mm.

From the foregoing description, numerous modifications are accessible to those skilled in the art without departing from the scope of protection of the invention, which is defined by the claims.

Materials other than those explained above are also conceivable for the manufacture of the individual parts. For example, in addition to steel, other materials are also suitable for providing the tube 4 and/or a tension cord 12 .

Depending on the application, a different number of strands 12 is provided than shown in the figures to form the tension member. In a simple embodiment, a single strand 12 can be provided as a tension member, which has a compression head 6 for anchoring. In general, the number of strands can be one, two or more.

The number of wires 13 of a single strand 12 can also be different than shown in the figures and can be two, three or more.

The length of the bonded section through the backfill 7 depends, among other things, on the load-bearing capacity of the BBRV strand heads, i.e. the higher the load-bearing capacity of the head, the shorter the bonded section can be. It is also conceivable not to provide a composite section and to anchor the upsetting heads directly on the support, for example, so that the anchor plate 5 lies against the support 11 .

Reference sign

1

end anchorage

2

Tension member made of prestressing strands, for example prestressing steel strands

3

transmission plate

4

Pipe, for example steel pipe

5

Anchor or end plate

5a

Hole in the anchor plate

6

compression head

7

Backfilling on composite track, e.g. B. grout

8th

Potting for tying up the compression heads

9

Casting for filling a compression head

10

pressure plate

11

Pressure pipe or support for the end anchorage

12

Individual prestressing strands, for example 7-wire prestressing steel strands

13

single wire of the prestressing strand

14

Compressed individual wires in the upsetting head

15

Gaps between the individual wires in the upsetting head

16

induction coil

17

power supply cable

Claims (9)

1. Prefabricated end anchorage for a soil and/or rock anchor that is insertable into a borehole in the soil or rock, respectively, comprising a tension member (2) including at least one tensioning strand (12), the wires (13) of the tensioning strand (12) being compressed to form an end in the form of a compressed head that is retained on an anchor plate (5), characterised in that the compressed head (14) is embedded in a grouting (8, 9) and a part of the tension member (2) which, seen in the direction toward the compressed head (6), is located in front of the anchor plate, is embedded in a filling (7) and surrounded by a tube (4).
2. End anchorage according to claim 1, which comprises a pressure plate (10) that presses the compressed head (6) against the anchor plate (5).
3. End anchorage according to one of the preceding claims, wherein the mutual spaces (15) of the compressed single wires (14) of the compressed head are also filled.
4. End anchorage according to claim 3, wherein the grouting (8) and the filling (9) in the spaces (15) are produced from at least one of the following materials:

   - cementitious grout,

   - synthetic grout,

   - metallic grout.
5. End anchorage according to one of the preceding claims, comprising a transmitting plate (3) that is arranged at a distance from the anchor plate (5) and serves for the transmission of forces acting upon the tension member (2) to an abutment (11), the tension member (2) extending through the transmitting plate (3), the transmitting plate (3) preferably having a bearing surface intended to rest on a pressure tube serving as an abutment (11).
6. End anchorage according to one of the preceding claims, wherein the tensioning strand (12) has at least one of the following properties:

   - the tensioning strand is made of prestressing steel,

   - the tensioning strand has a single wire (13) as a core around which single wires (13) are wound whose respective diameters are smaller than the diameter of the core,

   - the tensioning strand comprises seven single wires (13).
7. End anchorage according to one of the preceding claims, comprising a separating device (16, 17) for weakening and/or separating the tension member (2) for dismantling.
8. End anchorage according to claim 7, wherein the separating device includes an induction coil (16) by means of which the tension member (2) can be inductively heated.
9. Anchor for anchorage in the soil and/or rock, comprising an end anchorage according to one of the preceding claims and preferably comprising a pressure tube (11) onto which the forces acting upon the anchor plate (5) are transmittable by means of the end anchorage.

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