US20110299940A1

US20110299940A1 - Resin-anchored bolt with indentations

Info

Publication number: US20110299940A1
Application number: US13/155,504
Authority: US
Inventors: James L. Earl, JR.; Stephen C. Tadolini
Original assignee: MINOVA AMERICAS
Current assignee: MINOVA AMERICAS
Priority date: 2010-06-08
Filing date: 2011-06-08
Publication date: 2011-12-08
Also published as: WO2011156450A2; WO2011156450A3

Abstract

A strata support system that provides support and balance to a rock mass and reacts to movement of the rock mass. The strata support system includes a borehole that is drilled into a surface of the rock mass. A resin is disposed in the borehole to secure a cable within the borehole. An anchor cable bolt assembly having a plurality of strands that are twisted together to form the cable is inserted into the borehole. At least one of the plurality of strands includes an interrupted outer surface that is defined by a plurality of spaced indentations. The plurality of spaced indentations are formed along the length of the strand and provide for a plurality of surface contours to enhance engagement of the anchor cable bolt with the resin.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/352,611 for a RESIN-ANCHORED BOLT WITH INDENTATIONS, filed on Jun. 8, 2010, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an anchor cable bolt assembly, and more particularly, a strata support system utilizing the anchor cable bolt assembly for providing support and balance to a rock mass and reacting to movement of the rock mass in a variety of conditions.
2. Description of the Prior Art
As is well known in the mining industry, there are numerous apparatus and methods used in rock bolting for strata control. An internationally accepted method of strata control is full column resin bolting which provides rapid and effective strata control at relatively lower cost than traditional external set supports.
Resin-anchored cable bolts are generally defined as “active methods” of support. These active reinforcing methods are intended to react to rock mass movement, develop a restraining force and transfer that force back to the rock mass. This counteracts the driving force and eventually results in a balanced condition when the total mobilized resistance within the rock mass is at least equal to the available driving force.
Resin anchored cable bolts can be installed as either passive or post-tensioned supports. In tensioning applications, standard cable heads, low-profile heads, barrels and wedges, can be used to tension the cable.
One form of an anchored bolt is a cable bolt which is made from smooth cable with cable bulbs, cable buttons, bird-cages, or any other “resin interrupting” device. These “resin interrupting” devices are made in a separate step during assembly. Typically, a plurality of strands are formed and then twisted to form the cable. Then a separate step, such as compressing the cable to form a bird cage or bulb, is performed.

SUMMARY OF THE INVENTION

In view of the above, the anchor cable bolt assembly of the present invention includes a plurality of strands that are twisted together to form a cable. Each of the of strands that make up the cable have an interrupted outer surface that is defined by a plurality of spaced indentations fowled along the length of the strands. The spaced indentations disposed in the outer surface of each cable provides for surface contours that enhance engagement of the anchor cable bolt assembly with a resin.
The anchor cable bolt assembly may be used in a strata support system according to the present invention and, is used in the same manner as other resin or grouted bolts. The strata support system includes a borehole that is drilled into a surface of a rock mass. With the anchor cable bolt assembly of the present invention, the borehole to be drilled only has to be slightly larger than the cable so that the anchor cable bolt assembly can be inserted into the drilled hole and rotated. After the borehole is drilled, a package of grout or resin is inserted into the borehole and then the anchor cable bolt assembly of the present invention, with a plate or other attachments if desired, is inserted into the borehole and impacted against the package of resin to rupture the resin package. While the exemplary embodiment discloses the use of a resin package as the source of resin or grout to secure the anchor cable bolt assembly within the borehole, any source of resin or grout known in the art may be used to secure the anchor cable bolt assembly within the borehole. The anchor cable bolt assembly is then rotated to mix the resin and allow the resin to harden to secure the anchor cable bolt assembly within the borehole. It should be noted that the amount of rotation required and set time for the resin to harden varies based on the type of grout or resin used. Once hardened, if desired, the anchor cable bolt assembly can be tensioned against the plate or other attachment by rotating the head portion or barrel with respect to the wedge portion of a tensioning fixture. The anchor cable bolt assembly of the present invention can also be used without tensioning if desired.
In general terms, this invention is relatively simple to make and provides a cost effective anchor cable bolt assembly for strata support in a variety of conditions. The spaced indentations of the present invention provide for sufficient surface contours to engage with the resin, and are much simpler to manufacture than other known anchor cable bolts, such as for example, bulbed or bird-caged cable bolts.
One of the advantages of the anchor cable bolt of the present invention is the reduced cost in manufacturing because of the elimination of the compression step which is normally required in making typical cable bolts with bulbs or birdcages. The other advantage is the time-saving involved in drilling a smaller hole than that which is typically required when bulbed or birdcage cable bolts are employed.
These and other features and advantages of this invention will become more apparent to those skilled in the art from the detailed description of a preferred embodiment. The drawings that accompany the detailed description are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is partial perspective view of an anchor cable bolt assembly according to the present invention;

FIG. 2 is a partial side view of a cable used in the anchor cable bolt assembly according to the present invention;

FIG. 3 is a partial side view of an exemplary strand that is twisted with a plurality of like strands to form the cable used in the anchor cable bolt assembly according to the present invention;

FIG. 4 is a side view of a strata support system with a package of resin prior to rupture and the anchor cable bolt assembly in a partially inserted position according to the present invention;

FIG. 5 is a side view of a strata support system with a package of resin being ruptured and the anchor cable bolt in a fully inserted position according to the present invention;

FIG. 6 is a plane view of a fixture disposed on the end of a cable according to the present invention;

FIG. 7 is a perspective view of an exemplary wedge with serrations used in the fixture according to the subject invention; and

FIG. 8 is a graph showing the anchorage capacity results of an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENTS

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an anchor cable bolt assembly 20, and more particularly, a strata support system 22, utilizing the anchor cable bolt assembly 20, for providing support and balance to a rock mass 24 and reacting to movement of the rock mass 24 in a variety of conditions is generally shown.
The strata support system 22, as shown in FIGS. 4 and 5, includes a borehole 26 that is drilled into a rock mass surface 28. The borehole 26 is defined by a wall portion 30 within the rock mass 24. A cable 32 of an anchor cable bolt assembly 20, as discussed below in greater detail, is inserted into the borehole 26 defined in the rock mass 24. A resin 34 or grout is disposed in the borehole 26 for securing the cable 32 within the borehole 26. The borehole 26 is generally circular and includes a bore diameter d_b. The cable 32 has a cable diameter d_cthat is less than the bore diameter d_b. An annulus 36 is defined between the cable 32 and the wall portion 30 of the borehole 26 to allow for the flow of the resin 34 in the annulus 36. The annulus 36 allows the resin 34 is engage the portions of the cable 32 that are inserted into the borehole 26 and maximize the surface area of the cable 32 that is secured to the mass.
The present invention provides for an anchor cable bolt assembly 20, as shown in FIG. 1, that includes a plurality of strands 38, 40 that are twisted together to form the cable 32. As seen in FIG. 1, the cable 32 as disclosed has 7 strands, but as will be appreciated by those of ordinary skill in the art, the cable 32 could have more or less strands 38, 40, with 5 to 7 strands being typical. Each of the strands 38, 40 has a plurality of indentations 42 which extend along the length of the strand. As shown in FIG. 3, the indentations 42 extend inwardly into the outer surface of the strands 38, 40 that make up the cable 32. In an exemplary embodiment, the indentations 42 may be approximately 0.1 inches wide, 0.025 inches long, and 0.002 inches deep, but these values are merely exemplary and may vary. While in the exemplary embodiment of FIGS. 1-5, the indentations 42 are shown to be generally rectangular, it is noted that the indentations 42 can take any form or geometry. That is, the spaced indentations 42 can be any shape or geometry that extends inwardly into the outer surface of the cable 32 to provide for a surface contour that enhances engagement of the anchor cable bolt assembly 20 with a grout or resin 34.
In the exemplary embodiment, the indentations 42 are formed by running the strands 38, 40 through an indenting station in order to dispose the spaced indentations 42 along each of the strands 38, 40. The indenting station may be any device known in the art for indenting wires. The spaced indentations 42 result in a plurality of surface contours in the anchor cable bolt assembly 20 that improves or enhances engagement of the anchor cable bolt assembly 20 with the grout or resin 34. In the exemplary embodiment, the plurality of strands 38, 40 include a plurality of peripheral strands 38 that are disposed about a longitudinal extending center strand 40. Each of the strands 38, 40 may be coated or uncoated. The coating may be a galvanized coating or any other coating known in the art to protect against corrosion and to facilitate connection to a cable head and wedge assembly 54 or other anchors as desired. The anchor cable bolt assembly 20 may be used in all cable 32 mining applications to increase anchorage bolt anchorage versus smooth cable, without installing cable bulbs, cable buttons, bird-cages, or any other “resin interrupting” device.
The anchor cable bolt assembly 20 may further include a fixture 46, such as a tension fixture 46, secured to an end 48 of the cable 32 to tension the cable 32 relative to the rock mass 24. A plate 50 may be placed between the rock mass 24 and the fixture 46 to assist in tensioning the cable 32 relative to the rock mass 24. The plate 50 may be a flat plate 50, domed plate 50, or any other plate 50 known in the art. In the exemplary embodiment, the plate 50 defines a plate opening 52 for the passage of the cable 32 through the plate 50. The diameter of the plate opening 52 is larger than the cable diameter d_cof the cable 32 such that the cable 32 can be received through the plate opening 52. The fixture 46 has a diameter that is greater than the diameter of the plate opening 52 such that fixture 46 cannot pass through the plate opening 52. The plate 50 is pushed against the rock mass 24 by the fixture 46 which biases the plate 50 towards the rock mass 24 as fixture 46 is tightened, thus creating tension in the anchor cable bolt assembly 20 to secure the anchor cable bolt assembly 20 relative to the rock mass 24.
In the exemplary embodiment, the fixture 46 is a cable head and wedge assembly 54 that is attached to the end 48 of the cable 32 so that the anchor cable bolt assembly 20 may be tensioned. The cable head and wedge assembly 54 in the exemplary embodiment is a low profile cable head and wedge assembly 54 which is manufactured by the applicant. It should be appreciated by those of ordinary skill in the art that standard cable heads, low-profile heads, barrels and wedges, and any other coupler or truss system that is designed for coated or uncoated strands 38, 40 could be used. In the exemplary embodiment, the fixture 46 includes a wedge portion 56 and a corresponding head portion 58 that work together to tension the cable 32 relative to the rock mass 24. The head portion 58 includes an internal bore 60 that is tapered. The wedge portion 56 includes an outer surface 62 that is tapered complementary to the internal bore 60. The wedge portion 56 is received in the internal bore 60 of the head portion 58 to tension the cable 32 relative to the rock mass 24.
The wedge portion 56 engages the cable 32 and secures the cable 32 within the head portion 58 as wedge portion 56 pulled into the corresponding head portion 58. As shown in FIG. 7, the wedge portion 56 has an inner surface 70 that is serrated with a plurality of knurls or serrations 72 for improved engagement with the anchor cable bolt assembly 20. That is, the serrations 72 allow the wedge portion 56 to “bite” into the cable 32 of the anchor cable bolt assembly 20. The wedge portion 56 fits concentrically around the cable 32 of the anchor cable bolt assembly 20, and also nests concentrically within the internally tapered head portion 58. That is, the end 48 of the cable 32 is set between the wedges 44 and pulled into the cable head portion 58 at specified forces to tension and hold the cable 32. The specified forces vary based on the materials used and the tension desired, and as such, these specified forces are determined by the user.
The head portion 58 may include a hexagonal shaped outer surface 64 that receives a driving mechanism to rotate the head portion 58 and tension the cable 32. Although the collar is shown as a hexagonal head, obviously a square head or any other shaped head that accepts a mine roof bolt driver mechanism and boom should function adequately for the intended purpose.
The wedge portion 56 may include a plurality of wedges 44 that are disposed about and secured to the cable 32 portion. The wedge portion 56 is disclosed as a two piece wedge 44 set, but could be a three piece wedge 44 set if desired. When positioned within the head portion 58 and around the cable 32, the individual wedges 44 define a diametric space between each of the wedges 44 to enable the wedges 44 to be urged together tightly when pressed against the cable 32.
Creating this cable head and wedge assembly 54 can be accomplished by pressing the wedges 44 and cable 32 into the head portion 58 as the anchor cable bolt assembly 20 is manufactured. In addition, the cable head and wedge assembly 54 can be created on site by cutting the cable 32 to the desired length, assembling the cable 32, wedges 44, and head portion 58, and then tensioning the cable 32 against the head portion 58, or otherwise pressing the wedges 44 and cable 32 into the head portion 58.
A cap (not shown) may be used to secure the plurality of strands 38, 40 at the inserted end 66 of the anchor cable bolt assembly 20. The inserted end 66 of the anchor cable bolt assembly 20 is the end of the cable 32 that is initially fed into the borehole 26. The cap may be any cap known in the art. The cap may extend outwardly from the inserted end 66 of the anchor cable bolt assembly 20 and assists in rupturing the package of resin 34. In addition, the cap may include at least one wing that extends radially from the cap towards the wall portion 30 of the borehole 26 to mix the resin 34 when the cable 32 bolt assembly is rotated.
The subject invention further provides for a method of forming a strata support system 22. The method begins by forming the interrupted outer surface 68 on at least one of the plurality of strands 38, 40. While in the exemplary embodiment, each of the plurality of strands 38, 40 includes the interrupted outer surface 68, it is not necessary that each strand 38,40 has the plurality of spaced indentations 42 that foil the interrupted outer surface 68. The strands 38, 40 may include a plurality of peripheral strands 38 that are twisted about a center strand 40. In the exemplary embodiment, each of the peripheral strands 38 are passed through an indenting station in order to dispose the spaced indentations 42 along each of the peripheral strands 38. After the strands 38, 40 have been formed, they are twisted together to form the cable 32.
The anchor cable bolt assembly 20 of the present invention is made in a manner similar to the method used to make typical anchor cable bolt assemblies 20 such as bulbed cable bolts, except for two important differences. First, when the individual strands 38, 40 are formed, each strand is passed through an indenting station which forms spaced indentations 42 along the length of the strands 38, 40. Second, during assembly, the step of compressing the cable 32 to form the bulb is eliminated.
A borehole 26 that receives the cable 32 is drilled into the rock mass 24 to a desired bore diameter d_band depth. With the anchor cable bolt assembly 20 of the present invention, the hole to be drilled only has to be slightly larger than the cable 32 so that the anchor cable bolt assembly 20 can be inserted into the drilled hole and rotated. Prior to the cable 32 being inserted into the borehole 26, a package or pouch of grout or resin 34 is placed into the borehole 26. In the exemplary embodiment, the package of resin 34 is inserted all the way to the top of the borehole 26 before the package of resin 34 is broken. The cable 32 is then inserted into the borehole 26 and is used to push the package of resin 34 towards the top of the borehole 26. Once the package of resin 34 engages the top of the borehole 26 the cable 32 is continued to be urged upwardly to rupture the package of resin 34. The resin 34 flows downwardly through the annulus 36 to surround the cable 32. The cable 32 is rotated to mix the resin 34. It should be noted that the amount of rotation required and set time for the grout or resin 34 to harden varies based on the type of grout or resin 34 used. Once hardened, if desired, the anchor cable bolt assembly 20 can be tensioned against the plate 50 or other attachment by rotating the head portion 58 or barrel with respect to the wedge portion 56 of the tensioning fixture 46. As a result of the tensioning, support and balance are provided to the rock mass 24 via the anchor cable bolt assembly 20. The anchor cable bolt assembly 20 of the present invention can also be used without tensioning if desired.
While the exemplary embodiment discloses the use of a package of resin 34 as the source of grout or resin 34 to secure the anchor cable bolt assembly 20 within the borehole 26, any source of grout, resin 34, or other organic or chemical based anchorage formulation known in the art may be used to secure the anchor cable bolt assembly 20 within the borehole 26. For example, the grout or resin 34 could additionally include, but is not limited, to a pumpable grout or resin 34, which is pumped into the annulus 36 that surrounds the cable 32 after the cable 32 has been inserted into the borehole 26.
The anchor cable bolt assembly 20 of the present invention can be installed as either passive or post-tensioned supports, and with any resin type that will provide adequate anchorage to allow for ultimate load capacity, such as for example, polyester, cementious, poly urethane, etc. Additionally, the anchor cable bolt assembly 20, if used as an active support (either vertical, horizontal, or in a truss system), can be tensioned using any of the modes or methods also used to tension smooth (coated or uncoated) strands. The combination of the anchor cable bolt assembly 20 and resin 34 of the present invention provides a stiffer support with less deflection and deformation as load increases.
The strata support system 22 utilizing the anchor cable bolt assembly 20 of the present invention, has been found through testing to exhibit superior anchorage and performance in mining applications. Laboratory testing has indicated that the anchor cable bolt assembly 20 of the present invention is capable of meeting or exceeding the ASTM tensile requirements. The strands 38, 40 having indentations 42 and the interaction the fixture 46 was confirmed to have no adverse reaction to current manufacturing methods.
In addition, field tests have been conducted to confirm anchorage capacity when used with polyester resin 34 products. Ten (10) foot long cables 32 were fitted with a traditional head portion 58 and wedge portion 56. The anchor cable bolt assembly 20 were installed in a 1-inch diameter borehole 26 using a traditional A23 5′ equivalent cartridge. The resin 34 was allowed to cure and pull-tests were performed recording the applied load and displacement. The results were compared with anchor cable bolt assembly 20 that were manufactured with three; 1-inch bulbs located 10, 22, and 33-inches from the bolt end 48. FIG. 8 shows the anchorage capacity test results for the anchor cable bolt assembly 20 of the present invention. All of the tests indicated that the cable 32 of the present invention was brought well into yield and anchorage was adequate for the application, see FIG. 8.
The results were compared to the traditionally bulbed cables 32 (used for anchoring in polyester resin 34), installed in the same geological structure. The data indicated that the anchor cable bolt assembly 20 demonstrated higher system stiffness, which is a support system advantage.
It will be appreciated by those of ordinary skill in the art that the cable 32 can work on any diameter strand and increase anchorage, as compared to smooth cable, in traditional mining applications with polyester resin 34 or other chemical anchorage formulations.
The spaced indentations 42 of the present invention do not adversely affect the tensile strength or yield capacity of the anchor cable bolt assembly 20. The cable 32 results in higher bolting system stiffness when installed in conjunction with the proper borehole 26 diameter and polyester resin 34 and can be used with standard head portions 58, low-profile heads, barrels and wedges 44, and any other coupler or truss system that is designed for coated or uncoated (smooth bright or galvanized) strand.
The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and do come within the scope of the invention. Accordingly, the scope of legal protection afforded this invention can only be determined by studying the following claims.

Claims

1. An anchor cable bolt assembly for providing support and balance to a rock mass and reacting to movement of the rock mass comprising:

a plurality of strands twisted together to faun a cable, at least one of said plurality of strands having an interrupted outer surface defined by a plurality of spaced indentations formed along a length of said at least one strand, and wherein said plurality of spaced indentations provide for a plurality of surface contours for engagement with a resin.

2. The anchor cable bolt assembly as set forth in claim l further including a fixture secured to an end of said cable for tensioning said cable relative to the rock mass.

3. The anchor cable bolt assembly as set forth in claim 2 further including a plate for placement between the rock mass and said fixture for tensioning said cable relative to the rock mass, said plate defining a plate opening for the passage of said cable through said plate.

4. The anchor cable bolt assembly as set forth in claim 2 wherein said fixture includes a wedge portion and a corresponding head portion, wherein said wedge portion engages said cable and secures said cable within said head portion as wedge portion engages said corresponding head portion for tensioning said cable.

5. The anchor cable bolt assembly as set forth in claim 4 wherein said head portion includes an internal bore that is tapered, and said wedge portion includes an outer surface that is tapered and complementary to said internal bore for being received in said internal bore of said head portion for tensioning said cable relative to the rock mass.

6. The anchor cable assembly as set forth in claim 4 wherein said head portion includes a hexagonal shaped outer surface for receiving a driving mechanism to rotate said head portion and tension said cable.

7. The anchor cable assembly as set forth in claim 4 wherein said wedge portion includes a plurality of wedges disposed about said cable for engagement with said cable.

8. The anchor cable bolt assembly as set forth in claim 7 wherein at least one of said wedges includes an inner surface having a plurality of serrations for securing said at least one wedge to said cable.

9. The anchor cable bolt assembly as set forth in claim 1 wherein said plurality of strands include a longitudinally extending center strand and a plurality of peripheral strands spirally wrapped around said center strand.

10. The anchor cable bolt assembly as set forth in claim 9 wherein each of said plurality of peripheral strands includes an interrupted outer surface defined by said plurality of spaced indentations formed along the length of each of said plurality of peripheral strands.

11. The anchor cable bolt assembly as set forth in claim 1 wherein each of said plurality of strands are coated.

12. The anchor cable bolt assembly as set forth in claim 1 wherein each of said plurality of strands are uncoated.

13. A strata support system for providing support and balance to a rock mass and reacting to movement of the rock mass comprising:

a borehole having a bore diameter and being drilled into a rock mass surface;

a plurality of strands, with each of said plurality of strands having a length and being twisted together to form a cable having a cable diameter and capable of being inserted into said borehole; and

a resin disposed in said borehole for securing said cable within said borehole;

wherein at least one of said plurality of strands includes an interrupted outer surface defined by a plurality of spaced indentations formed along the length of said at least one strand for providing a plurality of surface contours to engage with said resin.

14. The strata support system as set forth in claim 13 further including a fixture secured to an end of said cable for tensioning said cable relative to said rock mass.

15. The strata support system as set forth in claim 14 further including a plate for placement between said rock mass and said fixture to tension said cable relative to said rock mass, said plate defining a plate opening for the passage of said cable through said plate.

16. The strata support system as set forth in claim 14 wherein said fixture includes a wedge portion and a corresponding head portion, wherein said wedge portion engages said cable and secures said cable within said head portion as wedge portion engages said corresponding head portion for tensioning said cable.

17. The strata support system as set forth in claim 16 wherein said head portion includes an internal bore is tapered, and said wedge portion includes an outer diameter that is tapered and complementary to said internal bore for being received in said internal bore of said head portion for tensioning said cable.

18. The strata support system as set forth in claim 16 wherein said head portion includes a hexagonal shaped outer surface for receiving a driving mechanism to rotate said head portion and tension said cable.

19. The strata support system as set forth in claim 16 wherein said wedge portion includes a plurality of wedges disposed about said cable for engagement with said cable.

20. The strata support system as set forth in claim 19 wherein at least one of said wedges includes an inner surface having a plurality of serrations for securing said at least one wedge to said cable.

21. The strata support system as set forth in claim 13 wherein said plurality of strands include a longitudinally extending center strand and a plurality of peripheral strands spirally wrapped around said center strand.

22. The anchor cable bolt assembly as set forth in claim 21 wherein each of said plurality of peripheral strands includes an interrupted outer surface defined by said plurality of spaced indentations formed along the length of each of said plurality of peripheral strands.

23. The strata support system as set forth in claim 13 wherein said cable diameter is less than said bore diameter.

24. The strata support system as set forth in claim 23 wherein said borehole is defined by a wall portion within said rock mass, and further includes an annulus defined between said cable and said wall portion of said borehole for the flow of said resin in said annulus.

25. A method of forming a strata support system for providing support and balance to a rock mass and reacting to movement of the rock mass, comprising the steps of:

forming an interrupted outer surface on at least one of a plurality of strands;

twisting together the plurality of strands to form a cable;

drilling a borehole into a surface of a rock mass for receiving the cable;

disposing a resin in the borehole for securing the cable within the borehole; and

inserting the cable into the borehole;

wherein the plurality of indentations provide for a plurality of surface contours for engagement with the resin.

26. The method of forming the strata support system as set forth in claim 25 wherein the forming step is further defined as disposing a plurality of spaced indentations along a length of the at least one strand.

27. The method of forming the strata support system as set forth in claim 25 wherein the forming step is further defined as passing the at least one strand through an indenting station to dispose a plurality of spaced indentations along a length of the at least one strand.

28. The method of forming the strata support system as set forth in claim 25 further including the step of tensioning the cable relative to the rock mass.

29. The method of forming the strata support system as set forth in claim 25 wherein the forming step is further defined as forming an interrupted outer surface on a plurality of strands.