GROUND ANCHOR SYSTEM AND METHOD

Abstract

A ground anchor system configured for introducing into a borehole, and comprising a plurality of straps each having a length dimension extending along a central longitudinal axis of the ground anchor system. Each of said straps has a width dimension taken along a major axis and a thickness dimension taken along a minor axis. The major axis and the minor axis are disposed at a transverse plane of the ground anchor system and intersect at a middle point. The middle point of each of said straps is intersected by an imaginary line extending through the longitudinal axis at the transverse plane. The imaginary line forms an angle smaller than 90 with the major axis of the respective strap.

Claims

1. A ground anchor system configured to be introduced into a borehole, the ground anchor system comprising: a plurality of straps each having a length dimension extending along a central longitudinal axis of the ground anchor system between a distal end and a proximal end, each of the plurality of straps having a width dimension taken along a major axis and a thickness dimension taken along a minor axis, the major axis and the minor axis being disposed at a transverse plane of the ground anchor system and intersect at a middle point; and an anchor sleeve configured for enveloping the plurality of straps therein; wherein each of the plurality of straps includes a middle point intersected by an imaginary line extending through the longitudinal axis at the transverse plane, the imaginary line forms an angle smaller than 90 with the major axis of the respective strap; and wherein said anchor sleeve has a sleeve length that is shorter than said length dimension of the straps, so that when said anchor sleeve envelopes the straps, said distal end of the plurality of straps is free of said anchor sleeve.

2. The ground anchor system according to claim 1, wherein said distal end of the plurality of straps is configured for directly contacting a grouting agent when being at least partially grouted within the borehole.

3. The ground anchor system according to claim 1, wherein said proximal end of the plurality of straps is free of said anchor sleeve to be axially stressed by a pre-stressing system after being at least partially grouted within the borehole.

4. The ground anchor system according to claim 1, wherein the plurality of straps are substantially equally spaced from the longitudinal axis.

5. The ground anchor system according to claim 1, wherein the plurality of straps are disposed substantially symmetrically with respect to the longitudinal axis.

6. The ground anchor system according to claim 1, wherein the plurality of straps are disposed substantially equally angularly with respect to each other.

7. The ground anchor system according to claim 1, wherein each of the plurality of straps at the transverse plane has a cross-sectional area exhibiting a rectangular shape.

8. The ground anchor system according to claim 1, wherein each of the plurality of straps are made of polymeric material.

9. The ground anchor system according to claim 1, wherein the width dimension is smaller than a radius of an inscribed circle of the borehole in which the ground anchor system is introduced.

10. The ground anchor system according to claim 1, wherein the width dimension is defined between an innermost edge and an outermost edge of each of the plurality of straps, and the innermost edge is disposed closer to the longitudinal axis than the outermost edge.

11. A ground anchor system configured to be introduced into a borehole, the ground anchor system comprising: a plurality of straps each having a length dimension extending along a central longitudinal axis of the ground anchor system between a distal end and a proximal end, each of the plurality of straps having a width dimension and a thickness dimension smaller than the width dimension, the width dimension and the thickness dimension being taken at a transverse plane of the ground anchor system; and an anchor sleeve configured for enveloping the plurality of straps therein; wherein the width dimension is defined between an innermost edge and an outermost edge of each of the plurality of straps; wherein the innermost edge of each of the plurality of straps is disposed closer to the longitudinal axis than the outermost edge; and wherein said anchor sleeve has a sleeve length being shorter than said length dimension of the straps, so that when said anchor sleeve envelopes the straps, said distal end of the straps is free of said anchor sleeve.

12. The ground anchor system according to claim 11, wherein said distal end of the plurality of straps is configured for directly contacting a grouting agent when being at least partially grouted within the borehole.

13. The ground anchor system according to claim 11, wherein said proximal end of the plurality of straps is free of said anchor sleeve to be axially stressed by a pre-stressing system after being at least partially grouted within the borehole.

14. The ground anchor system according to claim 11, wherein the innermost edges of the plurality of straps define a central gap therebetween, and the longitudinal axis extends substantially coaxially with the central gap.

15. The ground anchor system according to claim 11, wherein a middle point at the width dimension of each of the plurality of straps is intersected by an imaginary line extending through the longitudinal axis at the transverse plane, the imaginary line forms an angle smaller than 90 with the width dimension of the respective strap.

16. The ground anchor system according to claim 11, wherein the plurality of straps are substantially equally spaced from the longitudinal axis.

17. The ground anchor system according to claim 11, wherein the plurality of straps are disposed substantially symmetrically with respect to the longitudinal axis.

18. The ground anchor system according to claim 11, wherein the plurality of straps are disposed substantially equally angularly with respect to each other.

19. The ground anchor system according to claim 11, wherein each of the plurality of straps at the transverse plane has a cross-sectional area exhibiting a rectangular shape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0060] FIG. 1A is a perspective view of a strap having a cross section with a rectangular shape, configured for use in conjunction with a ground anchor system according to the prior art;

[0061] FIG. 1B is a perspective view of a strap having a cross section with an oval shape, configured for use in conjunction with a ground anchor system according to the prior art;

[0062] FIG. 1C is an isometric view of a ground anchor system known in the art in which one of the straps is disconnected from the ground anchor system for illustration purposes;

[0063] FIG. 1D is a cross sectional view taken along line I-I in FIG. 1C, with the upper strap connected to the ground anchor system;

[0064] FIG. 2A is a perspective view of a ground anchor system according to one example of the presently disclosed subject matter;

[0065] FIG. 2B is a cross sectional view, taken along line II-II in FIG. 2A;

[0066] FIG. 3 is a cross sectional view of a ground anchor system according to another example of the presently disclosed subject matter;

[0067] FIG. 4A is a front view of a wedging device according to an aspect of the present disclosure, the wedging device configured with four straps;

[0068] FIG. 4B is a sectioned planner view taken along line in FIG. 4A;

[0069] FIG. 5 is an exploded perspective view of the sectored wedges of the wedging device of FIGS. 4A and 4B;

[0070] FIG. 6 is a perspective view of a spacer-disc used in conjunction with the presently disclosed subject matter;

[0071] FIGS. 7A to 7F illustrate sequential steps of a method for applying a ground anchoring system according to the present disclosure;

DETAILED DESCRIPTION OF EMBODIMENTS

[0072] Attention is first directed to FIGS. 1A and 1B of the drawings, illustrating a perspective view of two example of known in the art straps, generally designated 10 and 20, configured for use in conjunction with a ground anchor system. The straps 10 and 20 are flat tendons made of a polymeric material. In particular, the straps 10 and 20 are made of Carbon Fiber Reinforced Polymers (CFRPs), belonging to a group of Fiber Reinforced Polymers (FRPs) and composites thereof. The CFRPs are used in the field of ground anchoring since they are able to bear high axial loads, to resist to corrosion (as opposed to metal tendons) and to be easily trimmed or cut when required.

[0073] As seen in the drawings, the straps 10 and 20 are examples of flat tendons having a different cross-sectional shape, as detailed below.

[0074] As seen in FIG. 1A, the strap 10 has a length dimension L.sub.1, a width dimension W.sub.1 and a thickness dimension T.sub.1, so that L.sub.1>>W.sub.1>T.sub.1. The strap 10 is substantially straight along its length dimension L.sub.1. The width dimension W.sub.1 and thickness dimension T.sub.1 refer to dimensions of a cross section of the strap 10, taken at a plane that is transverse to an axis along which the length dimension L.sub.1 is taken. The cross section of the strap 10 is characterized by a major axis X.sub.1 and a minor axis Y.sub.1, being perpendicular to each other. The cross section of the strap 10 has a rectangular shape. The width dimension W.sub.1 is taken along the major axis X.sub.1 between an innermost edge 14 and an outermost edge 15 and the thickness dimension T.sub.1 is taken along the minor axis Y.sub.1. The major axis X.sub.1 is centered with respect to the thickness dimension T.sub.1, and the minor axis Y.sub.1 is centered with respect to the width dimension W.sub.1. The major and the minor axes X.sub.1 and Y.sub.1 intersect at a middle point 12.

[0075] As seen in FIG. 1B, the strap 20 that is shown from a perspective view, has a length dimension L.sub.2, a width dimension W.sub.2 and a thickness dimension T.sub.2, so that L.sub.2>>W.sub.2>T.sub.2. The strap 20 is substantially straight along its length dimension L.sub.2. The width dimension W.sub.2 and thickness dimension T.sub.2 refer to dimensions of a cross section of the strap 20, taken at a plane that is transverse to an axis along which the length dimension L.sub.2 is taken. The cross section of the strap 20 is characterized by a major axis X.sub.2 and a minor axis Y.sub.2, being perpendicular to each other. The cross section of the strap 20 has an oval shape. The width dimension W.sub.2 is taken along the major axis X.sub.2 between an innermost edge 24 and an outermost edge 25 and the thickness dimension T.sub.2 is taken along the minor axis Y.sub.2. The major axis X.sub.2 is centered with respect to the thickness dimension T.sub.2, and the minor axis Y.sub.2 is centered with respect to the width dimension W.sub.2. The major and the minor axes X.sub.2 and Y.sub.2 intersect at a middle point 22.

[0076] Attention is now directed to FIGS. 1C and 1D of the drawings, illustrating a known in the art ground anchor system 1 having a longitudinal axis A and a transverse plane A, being perpendicular thereto. The ground anchor system 1 comprises: three of the straps 10, a central tube 3 and spacers 5. The straps 10 are positioned in the ground anchor system 1 in accordance with a specific orientation with respect to each other, as detailed below.

[0077] The three straps 10 extend along the longitudinal axis A and are radially disposed with respect thereto. The straps 10 are mounted on the central tube 3 by the spacers 5.

[0078] As can be seen in FIG. 1D, each one of the straps 10 is disposed in such a manner that its middle point 12 is intersected by an imaginary line 16, extending through the longitudinal axis A at the transverse plane A. Each one of the imaginary lines 16 forms with the major axis X.sub.1 of the respective strap 10 an angle a that is equal to 90.

[0079] It is further seen in FIG. 1D that a distance K.sub.1, extending between the innermost edge 14 of the strap 10 and the longitudinal axis A is equal to the distance K.sub.2, extending between the outermost edge 15 of the strap 10 and the longitudinal axis A.

[0080] Reference is now made to the ground anchor system 1 of FIG. 1D in order to explain its limitations with respect to a particular example of straps and borehole having particular dimensions. As can be seen in FIG. 1D, the ground anchor system 1 is configured to be installed within a borehole having a diameter D which is equal to 110 mm On the other hand, the width dimension W.sub.1 of the strap 10 is equal 40 mm and the thickness dimension T.sub.1 is equal to 9 mm. Each of the three straps 10 has a tensile strength of 360 KN. This means that the ground anchor system 1 is configured to withstand a tensile strength of 1,080 KN (3*360 KN). It is well known in the field of ground anchoring that sometimes there is a need to provide a ground anchor system which is able to withstand much higher tensile strength (e.g., 2,000 KN, 3,000 KN) for a given borehole (e.g., having a diameter D of 110 mm). In order to provide such a system, it is possible to use straps having other characteristics (e.g., thickness, width, structure, material, etc.), but this can be expensive or even non-feasible. Alternatively, it is possible to increase the number of the straps within the system. However, the arrangement of the straps within the system, such as the arrangement of FIGS. 1C and 1D, would limit or even not allow that.

[0081] This problem can be solved by arranging the straps in accordance with a more compact arrangement as provided by the system of the presently disclosed subject matter, and as explained below with respect to particular examples.

[0082] Reference is now made to FIGS. 2A and 2B, illustrating an example of a ground anchor system 100 according to the presently disclosed subject matter.

[0083] The ground anchor system 100 is accommodated within a round borehole 101 having by a diameter D which is equal to 110 mm. The ground anchor system 100 is configured with eight of the straps 10, the length dimension of which extends along a central longitudinal axis B. The longitudinal axis B is perpendicular to a transverse plane B of the system. The straps 10 are accommodated within a sleeve 103. As can be seen, free ends of the straps 10 extend from a surface 102 of the ground, while the remaining portions of the straps 10 are fully accommodated within the borehole.

[0084] The ground anchor system 100 comprises a grouting tube 105 extending along the longitudinal axis B. The grouting tube 105 has a distal end that is connected to a distributer 106. The grouting tube 105 is configured to receive a grouting agent via its proximal end, and to deliver the grouting agent into the borehole 101 via the distributer 106. The grouting tube 105 is disposed along a central gap 107, best seen in FIG. 2B, which is defined by the innermost edges 14 of the straps 10, and extends substantially coaxially with the longitudinal axis B.

[0085] As aforementioned, one of the alternatives for increasing the tensile strength of a ground anchor system is by increasing the number of the straps within the system. Since the system is configured for introducing into a given borehole with a given diameter D, its external dimensions have to be preserved while straps are added thereto. Increasing the number of straps, without changing the external dimensions of the system can be obtained by the arranging the straps within the system in a different and more compact manner. One example of such an arrangement is shown in FIGS. 2A and 2B, and another example, is shown in FIG. 3, the description of which is provided below.

[0086] Reference is now made to FIG. 2B, in which the disposition of the straps 10 within the system and their orientation with respect to the longitudinal axis B is shown.

[0087] The straps 10 are radially disposed with respect to the longitudinal axis B and radially extend therefrom. According to the present example, the straps 10 are disposed in a star polygon fashion, and in particular of a star polygon having eight vertices, wherein each one of the straps 10 is associated with its respective vertex of the star polygon. According to other examples, the ground anchor system can be provided with a different number of the straps 10, which are disposed in a star polygon fashion, i.e.: a Y-like shape in case of three straps, a +-like shape in case of four straps, a -like shape in case of five straps, etc. The straps 10 are equally spaced from the longitudinal axis B so that the innermost edge 14 of each strap is disposed closer to the longitudinal axis B than its outermost edge 15. According to this arrangement, the innermost edge 14 of each one of the straps 10 is distant from the longitudinal axis B to a distance K.sub.3 and the outermost edge 15 is distant from the longitudinal axis B to a distance K.sub.4 (K.sub.3<K.sub.4). In addition, the straps 10 are disposed symmetrically with respect to the longitudinal axis B, and equally angularly with respect to each other, with an angle therebetween. In the specific example of eight straps 10, the angle is equal to 45, but can vary depending on the number of straps 10, according to the formula 360/n, for a system having n of the straps 10.

[0088] As can further be seen in FIG. 2B, each one of the middle points 12 of the straps 10 is intersected by an imaginary line 116 that extends through the longitudinal axis B. The imaginary lines 116 extend at the plane B and are provided for explaining the angular orientation of the straps 10 within the ground anchor system 100.

[0089] The arrangement of the straps 10 is such that the imaginary lines 116 coextend with their major axis X.sub.1 so that the angle of 0 is formed therebetween.

[0090] The arrangement of the straps according to the example of FIGS. 2A and 2B provided a ground anchor system with eight of the straps 10. Since each one of the straps 10 has a tensile strength of 360 KN, the entire system can withstand a tensile strength of 2,880 KN (8*360 KN). While the ground anchor system 100 is able to withstand such a tensile strength, it still can be mounted within a borehole having a diameter D of 110 mm.

[0091] Referring now to FIG. 3, which is a cross section of another example of a ground anchor system according to the presently disclosed subject matter, generally designated 200. A perspective view of the ground anchor system 200 is not presented in the drawings. The ground anchor system 200 includes an arrangement of the straps 10 in accordance with the general concept of the presently disclosed subject matter, as detailed below.

[0092] Similarly to ground anchor system 100, the ground anchor system 200 is accommodated within a substantially round borehole generally designated 201 and characterized by a diameter D. Furthermore, the ground anchor system 200 has components that are similar to those of the ground anchor system 100, but has another arrangement of straps therein.

[0093] The ground anchor system 200 is configured with six of the straps 10, the length dimension of which extends along a central longitudinal axis C. The longitudinal axis C is perpendicular to a transverse plane C of the system. The straps 10 are accommodated within a sleeve 203.

[0094] The straps 10 of FIG. 3 are equally spaced from the longitudinal axis C so that the innermost edge 14 of each strap is disposed closer to the longitudinal axis C than its outermost edge 15. According to this arrangement, the innermost edge 14 of each one of the straps 10 is distant from the longitudinal axis C to a distance K.sub.5 and the outermost edge 15 is distant from the longitudinal axis C to a distance K.sub.6 (K.sub.5<K.sub.6). In addition, the straps 10 are disposed symmetrically with respect to the longitudinal axis C, and equally angularly with respect to each other, with an angle therebetween. In the specific example of six straps 10, the angle is equal to 60.

[0095] As can further be seen in FIG. 3, each one of the middle points 12 of the straps 10 is intersected by an imaginary line 216 that extends through the longitudinal axis C. The imaginary lines 216 extend at the plane C and are provided for explaining the angular orientation of the straps 10 within the ground anchor system 200.

[0096] The arrangement of the straps 10 in FIG. 3 is such that the each one of the imaginary lines 216 forms an acute angle , i.e. an angel smaller than 90.

[0097] It is appreciated that the example of FIG. 3 is a general example of an arrangement of the straps 10, which allows increasing the number of the straps within the system 10, while preserving the external dimensions of the system.

[0098] According to example, the angle can vary within a spectrum of all acute angles, i.e. can be any angle smaller than 90, in accordance with the engineering requirements of the system, e.g., the tensile strength of the system.

[0099] The arrangement of the straps according to the example of FIGS. 3 provided a ground anchor system with six of the straps 10. Since each one of the straps 10 has a tensile strength of 360 KN, the entire system can withstand a tensile strength of 2,160 KN (6*360 KN). While the ground anchor system 200 is able to withstand such a tensile strength, it still can be mounted within a borehole having a diameter D of 110 mm.

[0100] The ground anchor systems 100 and 200 can be assembled in accordance with a method of the presently disclosed subject matter, which can be performed prior to applying it into the borehole, and can be performed at a construction site or at any other location remote therefrom.

[0101] The method for assembling the ground anchor system 100 includes at least the following steps: [0102] providing eight of the straps 10; and [0103] disposing the straps 10 so that their major axis X.sub.1 coextends with the imaginary line 116 and their innermost edge 114 is distant from the longitudinal axis B to the distance K.sub.3.

[0104] The method for assembling the ground anchor system 200 includes at least the following steps: [0105] providing eight of the straps 10; and [0106] disposing the straps 10 so that their major axis X.sub.1 coextends with the imaginary line 216 and their innermost edge 214 is distant from the longitudinal axis B to the distance K.sub.5.

[0107] Referring now to FIGS. 4A and 4B, illustrating a wedging device 400, configured for use in conjunction with the ground anchor system according to the presently disclosed subject matter. The wedging device 400 comprises a wedging-ring 426 (typically made of steel) configured with a cylindrical bore 428 tapering along a longitudinal axis E thereof. The wedging device 400 further comprises a plurality of sectored wedges typically made of steel (four in the illustrated example; designated 430a, 430b, 430c and 430d; said sectored wedges best seen in FIG. 5), each configured with two side walls 432 and 434, and an arched wall 436. The arrangement is such that the side walls 432 and 434 extend substantially parallel to the longitudinal axis D and the arched walls 436 axially taper at an extent similar to the tapering cylindrical bore 428.

[0108] Accordingly, when the sectored wedges 430a, 430b, 430c and 430d are disposed within the wedging-ring 426 four wedging-gaps 440a, 440b, 440c and 440d extend between adjoining side walls 432 and 434 of two neighboring sectored wedges 430a, 430b, 430c and 430d, respectively. The wedging-gaps 440a, 440b, 440c and 440d are each configured, as far as size and shape, for receiving a strap 10 radially disposed therein, said straps designated 10a, 10b, 10c and 10d, respectively.

[0109] As can best be seen in FIG. 4A, the straps 10a, 10b, 10c and 10d are disposed at a radial orientation, i.e. extending along the radius of the wedging device 400. Furthermore, the sectored wedges 430a, 430b, 430c and 430d, and likewise the straps, are disposed symmetrically within the wedging device 400, i.e. are substantially equally angularly disposed therein. As a result of the structure disclosed, a central gap 441 extends between innermost edges of the straps, said central gap 441 extending substantially coaxially along axis E between the sectored wedges within the wedging-ring, i.e. between the vertexes of the sectored wedges.

[0110] The arrangement is such that axial tensioning the straps designated 10a, 10b, 10c and 10d in direction of arrow 443 (FIG. 7D) whilst retaining the wedging device 400 or pulling it at a sense opposed to direction of arrow 443, results in clapping the sectored wedges 430a, 430b, 430c and 430d about the straps 10a, 10b, 10c and 10d, so as to prevent their detaching from the wedging device 400.

[0111] FIG. 6 illustrates a spacer disk 450 used in conjunction with an anchoring system according to the present disclosure. The spacer disk 450 serves on the one hand for retaining the plurality of straps at their respective radially disposed position as discussed hereinabove, along the borehole into which the ground anchor system is introduced as will be hereinafter discussed with reference to FIGS. 7A to 7F, and on the other hand the spacer disk 450 facilitates flow of fluid grouting material therethrough, i.e. so as not to constitute a barrier for flow of the grouting agent throughout the entire depth of the bore of the ground anchor.

[0112] Spacer disk 450 is configured with a plurality (four in the particular example) of radially extending slots 452a, 452b, 452c and 452d, which when mounted in the ground anchor system (see hereinafter) are disposed substantially in register with the a four wedging-gaps 440a, 440b, 440c and 440d extending between neighboring sectored wedges 430a, 430b, 430c and 430d. The spacer disk 450 is further configured with a plurality of openings 456 and a central opening 458 (coinciding with the longitudinal axis E and with the central gap 441, facilitating flow of fluid grouting material therethrough.

[0113] As can further be seen in FIG. 6, the spacer-disc can have a diameter smaller than that of the circumcircle defined by the radially remote edges of the radially disposed straps 10a, 10b, 10c and 10d, such that fluid grouting agent can flow therethrough.

[0114] Turning now to FIGS. 7A to 7F, there are illustrated sequential steps of a method for applying a ground anchor system according to the present disclosure. It is however appreciated that the method is similar to methods performed insofar, with the exception of using ground anchor systems in accordance with the present disclosed subject matter, configured for use with radially disposed straps.

[0115] The method comprising the following steps:

[0116] a) providing a ground anchor system 100;

[0117] b) introducing the ground anchor system 100 into the borehole 101 in the ground, such that free ends of the straps 100 extend from a surface 102 of the ground (FIG. 7A);

[0118] c) applying a grouting agent into the borehole via the grouting tube 105 and allowing the grouting agent to cure, thereby fixing the ground anchor system 100 to the borehole 101 (FIG. 7B);

[0119] d) disposing a wedging device 400 over the free ends of the straps 10 (FIG. 7C).

[0120] e) mounting a pre-stressing system, e.g. tensioning mechanism such as jack 488, over said free ends of the straps 100 (FIG. 7D);

[0121] f) axially stressing the straps. In the illustrated example the axial stressing is performed by jack 488 (FIG. 7D);

[0122] g) mounting a second wedging device 400 according to the disclosure behind the tensioning mechanism 488 (FIG. 7D);

[0123] h) axially stressing the ground-anchor system as indicated by arrow 443 (FIG. 7D)

[0124] i) axially fixing the straps 10 by the second wedging device 400, allowing setting of the first wedging device 400 (FIG. 7E); and

[0125] j) disassembling the pre-stressing system from the straps while preserving them in a stressed position.