CA2653307C - Improved rock bolt with ploughing anchors - Google Patents
Improved rock bolt with ploughing anchors Download PDFInfo
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- CA2653307C CA2653307C CA2653307A CA2653307A CA2653307C CA 2653307 C CA2653307 C CA 2653307C CA 2653307 A CA2653307 A CA 2653307A CA 2653307 A CA2653307 A CA 2653307A CA 2653307 C CA2653307 C CA 2653307C
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- Prior art keywords
- stem
- borehole
- anchor
- grout
- anchors
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- 239000011435 rock Substances 0.000 title claims abstract description 112
- 239000011440 grout Substances 0.000 claims abstract description 60
- 238000000926 separation method Methods 0.000 claims abstract description 6
- 239000000463 material Substances 0.000 claims description 10
- 238000005452 bending Methods 0.000 claims description 7
- 239000003822 epoxy resin Substances 0.000 claims description 5
- 238000000034 method Methods 0.000 claims description 5
- 229920000647 polyepoxide Polymers 0.000 claims description 5
- 239000011347 resin Substances 0.000 claims description 5
- 229920005989 resin Polymers 0.000 claims description 5
- 239000004848 polyfunctional curative Substances 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 claims description 2
- 238000006073 displacement reaction Methods 0.000 description 7
- 238000009826 distribution Methods 0.000 description 5
- 238000005065 mining Methods 0.000 description 5
- 238000010586 diagram Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000035939 shock Effects 0.000 description 3
- 238000004873 anchoring Methods 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- 239000004568 cement Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 229920000728 polyester Polymers 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 239000011378 shotcrete Substances 0.000 description 1
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
- E21D21/0026—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection characterised by constructional features of the bolts
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D21/00—Anchoring-bolts for roof, floor in galleries or longwall working, or shaft-lining protection
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- Engineering & Computer Science (AREA)
- Mining & Mineral Resources (AREA)
- Structural Engineering (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Geochemistry & Mineralogy (AREA)
- Geology (AREA)
- Piles And Underground Anchors (AREA)
Abstract
A rock bolt for being grouted to set in grout (g) in a borehole in a rock, said bolt comprising - an elongate massive stem (1) with a surface anchor (3); - said stem (1) comprising two or more extensive lengths of stem portions (1a, 1b, ..., 1i), - each stem portion followed by a borehole anchor (2a, 2b, ..., 2i) for setting in said grout (g), said borehole anchors distributed with separations (La, Lb, ..., Li) along the length of said stem (1); - said stem portions (1a, 1b, ..., 1i) arranged for slipping relative to said grout of said borehole, so as for each of said stem portions (1a, 1b, ..., 1i) to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor (3, 2a, 2b, ...) and a consecutive anchor (2a, 2b, 2c, ..., 2i); characterized in that - one or more of said borehole anchors (2a, 2b, 2c, ..., 2i) being arranged for having a bearing capacity in said grout (g) being less than a failure strength of an adjacent stem portion ((1a or 1b), (1b or 1c), ... (1i), to enable one or more of said borehole anchors (2a, 2b, ..., 2i) to move during rock deformation so as for redistributing strain between stem portions (1a, 1b, ..., 1i).
Description
Improved rock bolt with ploughing anchors Introduction The present invention relates to an improved deformable rock bolt with anchors arranged for ploughing in the hardened grout in the borehole in which the bolt is arranged for reinforcing the rock.
General background In mined underground cavities, the lithostatic pressure which balanced the rocks before the mining process excavated the mining cavity, a significant imbalance arises from the moment the mining cavity is formed. This particularly relates to tunnels and mines with an overburden of often more than 1000 m of rocks. The lithostatic pressure is thus of considerable magnitude, and the rock may deform by rock bursts or slow, but significant rock deformation depending on the lithology and mechanical properties of the rock.
In general, the maximum accumulated rock deformation occurs at the tunnel walls where the pressure gradient is high, and which is also the only available underground space to receive the deforming rock. The accumulated deformation becomes smaller with the distance from the wall, please see an illustration in Fig. 1.
When the displacement increments are taken into account, the displacement increments may look like what is illustrated in Fig. 2. The displacement increment is large in the incremental range nearest to the cavity wall, and the displacement increment decreases with increasing distance from the wall.
Background art The so-called deformable bolt or "D-bolt" described in the applicant's international patent application PCT/N02007/000461 filed 22.12.2007, describes a rock bolt for being grouted in a borehole in a rock. Essential of the D-bolt are the following features:
- An elongate cylindrical massive stem with a preferably threaded bolt head comprising a nut and a washer arranged for pre-tensioning the rock bolt in the borehole. A face plate for the bolt head is usually required.
- The stem comprising three or more extensive lengths of stem portions. Each stem portion is followed by an integrated anchor. Each anchor is of short extent compared to the extent of the stem portions, and the anchors are distributed with separations along the length of the stem.
- The anchors are arranged for being locally anchored relative to their corresponding local borehole wall portions. This is for taking up load arising due to rock deformation.
- The stem portions are more or less slick so as for enabling slipping relative to the grout or the borehole. Thus each of the elongate, slick stem portions may constrain local rock deformation through elongation, the stem portions being free to extend between pairs of a locally anchored, fixed, preceding anchor and a locally anchored consecutive anchor which is also fixed.
Two significant features of the above-mentioned deformable bolt are: Firstly, it has the ability to take up both shock deformation such as rock bursts. A
rock burst may incur damage to bolts used in the prior art. A commonly used rib bar of the prior art may break when cracks suddenly open in the rock, due to the short available portion of the rib bar to take up deformation. Secondly, the above-mentioned deformable bolt has the ability to take up long-term deformation which occurs when the rock steadily creeps, and distribute the local rock deformation on a relatively long bar segment between two consecutive anchors fixed in the grout but relatively moving.
One significant advantage of the D-bolt is due to the fact that if one fixed anchor should loose its grip during deformation, a consecutive anchor will probably hold. A
second significant advantage of the D-bolt is, that contrary to rib bars which are held firmly by the grout throughout their length and thus vulnerable to break due to large local extensional deformation, long sections of the deformable bolt may slide longitudinally in the borehole grout, and distribute any longitudinal deformation of the
General background In mined underground cavities, the lithostatic pressure which balanced the rocks before the mining process excavated the mining cavity, a significant imbalance arises from the moment the mining cavity is formed. This particularly relates to tunnels and mines with an overburden of often more than 1000 m of rocks. The lithostatic pressure is thus of considerable magnitude, and the rock may deform by rock bursts or slow, but significant rock deformation depending on the lithology and mechanical properties of the rock.
In general, the maximum accumulated rock deformation occurs at the tunnel walls where the pressure gradient is high, and which is also the only available underground space to receive the deforming rock. The accumulated deformation becomes smaller with the distance from the wall, please see an illustration in Fig. 1.
When the displacement increments are taken into account, the displacement increments may look like what is illustrated in Fig. 2. The displacement increment is large in the incremental range nearest to the cavity wall, and the displacement increment decreases with increasing distance from the wall.
Background art The so-called deformable bolt or "D-bolt" described in the applicant's international patent application PCT/N02007/000461 filed 22.12.2007, describes a rock bolt for being grouted in a borehole in a rock. Essential of the D-bolt are the following features:
- An elongate cylindrical massive stem with a preferably threaded bolt head comprising a nut and a washer arranged for pre-tensioning the rock bolt in the borehole. A face plate for the bolt head is usually required.
- The stem comprising three or more extensive lengths of stem portions. Each stem portion is followed by an integrated anchor. Each anchor is of short extent compared to the extent of the stem portions, and the anchors are distributed with separations along the length of the stem.
- The anchors are arranged for being locally anchored relative to their corresponding local borehole wall portions. This is for taking up load arising due to rock deformation.
- The stem portions are more or less slick so as for enabling slipping relative to the grout or the borehole. Thus each of the elongate, slick stem portions may constrain local rock deformation through elongation, the stem portions being free to extend between pairs of a locally anchored, fixed, preceding anchor and a locally anchored consecutive anchor which is also fixed.
Two significant features of the above-mentioned deformable bolt are: Firstly, it has the ability to take up both shock deformation such as rock bursts. A
rock burst may incur damage to bolts used in the prior art. A commonly used rib bar of the prior art may break when cracks suddenly open in the rock, due to the short available portion of the rib bar to take up deformation. Secondly, the above-mentioned deformable bolt has the ability to take up long-term deformation which occurs when the rock steadily creeps, and distribute the local rock deformation on a relatively long bar segment between two consecutive anchors fixed in the grout but relatively moving.
One significant advantage of the D-bolt is due to the fact that if one fixed anchor should loose its grip during deformation, a consecutive anchor will probably hold. A
second significant advantage of the D-bolt is, that contrary to rib bars which are held firmly by the grout throughout their length and thus vulnerable to break due to large local extensional deformation, long sections of the deformable bolt may slide longitudinally in the borehole grout, and distribute any longitudinal deformation of the
2 rock, whether the deformation is due to a shock burst or due to long-term creep. The deformable bolt of the above prior art is to be deformed by extension through the elastically recoverable range, and stop there if mounted in a sufficient number in the rock, but, if too few bolts are arranged there is a risk that some bolts may locally pass the yield limit and eventually pass the failure strength. The anchors of the prior art bolt are designed to be solidly fixed in the borehole grout, for never to move to any significant degree.
German patent DE3504543C1 describes a slick single stem anchor with an inner anchor and an outer anchor by a fixed bolt head. The anchors are arranged as bends of increasing amplitude away from the stem axis and are arranged to lose their grip consecutively, and to lose their grip at the anchor end facing the slick stem first.
As such it resembles the cone bolt mentioned below, but it can not be pre-tensioned.
Another bolt in common use, particularly in South African mines, is the so-called "cone bolt", which comprises a bolt with a surface head and associated face plate, a slick stem of required length, and an inverted cone which presents a significant widening from the stem diameter to a larger diameter at the inner end of the bolt. The cone bolt's inner end is designed to cooperate with the shear resistance presented by the borehole grout and shall have an anchor bearing capacity not exceeding the failure strength of the slick stem. However, if the cone bolt's head breaks, which it may be susceptible of doing first as the surface deformation is larger than the rock deformation deeper from the wall surface, the entire purpose of the cone bolt is lost: neither shock bursts nor creep may be counteracted.
Further, any previously restrained deformation held back by the cone bolt will accelerate after the cone bolt tension is lost due to the head being lost.
However, even though the above-mentioned D-bolt has its significant advantages, for some mining conditions there is a need for even further extending the operating range of the rock bolt. For any deformable rock bolt of the prior art the longitudinal rock extension deformation may either eventually break the bolt, the bolt head may eventually be pulled into the borehole, or the inner end of the bolt may
German patent DE3504543C1 describes a slick single stem anchor with an inner anchor and an outer anchor by a fixed bolt head. The anchors are arranged as bends of increasing amplitude away from the stem axis and are arranged to lose their grip consecutively, and to lose their grip at the anchor end facing the slick stem first.
As such it resembles the cone bolt mentioned below, but it can not be pre-tensioned.
Another bolt in common use, particularly in South African mines, is the so-called "cone bolt", which comprises a bolt with a surface head and associated face plate, a slick stem of required length, and an inverted cone which presents a significant widening from the stem diameter to a larger diameter at the inner end of the bolt. The cone bolt's inner end is designed to cooperate with the shear resistance presented by the borehole grout and shall have an anchor bearing capacity not exceeding the failure strength of the slick stem. However, if the cone bolt's head breaks, which it may be susceptible of doing first as the surface deformation is larger than the rock deformation deeper from the wall surface, the entire purpose of the cone bolt is lost: neither shock bursts nor creep may be counteracted.
Further, any previously restrained deformation held back by the cone bolt will accelerate after the cone bolt tension is lost due to the head being lost.
However, even though the above-mentioned D-bolt has its significant advantages, for some mining conditions there is a need for even further extending the operating range of the rock bolt. For any deformable rock bolt of the prior art the longitudinal rock extension deformation may either eventually break the bolt, the bolt head may eventually be pulled into the borehole, or the inner end of the bolt may
3 eventually loose its hold in the grout. The latter problem is a particular problem to the cone bolt. Further, for some national regulations, utilizing bolts to their failure strength may not be allowed.
A significant mechanical problem is that even though each long bolt section of the prior art D-bolt is able to slide in the grout while the anchors are fixed, for unevenly distributed rock deformation one section may become loaded past its failure strength, thus the integrity of the original bolt and thus the local rock mass is only partly preserved through the remaining sections being fixedly anchored in the borehole.
Short figure captions The invention and some features of the invention in relation to features of the prior art are illustrated in the accompanying drawing figures:
Fig. 1 illustrates the accumulated distribution of rock displacement in a tunnel wall as a function of the distance from the tunnel wall. Please notice that the derivative of the function is largest near the wall.
Fig. 2 illustrates in increments (corresponding to a rock bolt's sliding sections) the displacement of three sections in a tunnel wall.
Fig. 3 shows distribution of the load in the bolt sections in case of fixed anchors. The right hatched, left hatched and vertical hatched columns in the diagram refer to the loads induced by the elongations in the corresponding bolt sections, respectively. All anchors are fixed. Fig. 3 illustrates the resulting incremental distribution of load in bolt sections of a rock bolt of the prior art as illustrated, such as the D-bolt using fixed anchors. Here, the outer long section is loaded to very near the yield load, and may pass over the yield load limit upon further deformation.
Fig. 4 shows load transfer between sections and the distribution of loads in the sections in case of movable anchors. The right hatched, left hatched, and vertical hatched columns in the diagram refer to the loads induced by the elongations in the
A significant mechanical problem is that even though each long bolt section of the prior art D-bolt is able to slide in the grout while the anchors are fixed, for unevenly distributed rock deformation one section may become loaded past its failure strength, thus the integrity of the original bolt and thus the local rock mass is only partly preserved through the remaining sections being fixedly anchored in the borehole.
Short figure captions The invention and some features of the invention in relation to features of the prior art are illustrated in the accompanying drawing figures:
Fig. 1 illustrates the accumulated distribution of rock displacement in a tunnel wall as a function of the distance from the tunnel wall. Please notice that the derivative of the function is largest near the wall.
Fig. 2 illustrates in increments (corresponding to a rock bolt's sliding sections) the displacement of three sections in a tunnel wall.
Fig. 3 shows distribution of the load in the bolt sections in case of fixed anchors. The right hatched, left hatched and vertical hatched columns in the diagram refer to the loads induced by the elongations in the corresponding bolt sections, respectively. All anchors are fixed. Fig. 3 illustrates the resulting incremental distribution of load in bolt sections of a rock bolt of the prior art as illustrated, such as the D-bolt using fixed anchors. Here, the outer long section is loaded to very near the yield load, and may pass over the yield load limit upon further deformation.
Fig. 4 shows load transfer between sections and the distribution of loads in the sections in case of movable anchors. The right hatched, left hatched, and vertical hatched columns in the diagram refer to the loads induced by the elongations in the
4 corresponding bolt sections, respectively. Some or all anchors are ploughing.
Fig. 4 illustrates resulting incremental distribution of load in bolt sections of a rock bolt according to the present invention, in which the anchors are designed for having a bearing capacity in the grout being less than the failure strength of an adjacent stem portion. Thus when the outer, left section has been heavily loaded and has approached the yield load, the first anchor's (2a) bearing capacity limit has been exceeded and the anchor has moved in the direction of the outer section as illustrated. Thus load has successively been transferred from the outer stem section to the intermediate stem section without exceeding the yield strength of the outer stem section. Likewise, as load has successively been transferred from the outer section to the intermediate section, the load at the intermediate section has exceeded the bearing capacity of the second anchor (2b) which has slid outwards in the direction of the surface, and thus part of the load has been transferred to the third stem section, which, in this illustration, has not reached the yield load yet.
Fig. 5a illustrates embodiments of the prior art D-bolt which have been modified to the present invention so as for having movable anchors relative to the grout, according to the present invention.
Fig. 5b illustrates two embodiments of the present invention represented by a rock bolt with a bolt head, and optional near-surface anchor and paddle-shaped anchors arranged consecutively between slick stem portions. The upper rock bolt has single paddle anchors and the lower rock bolt illustrated has double paddle anchors.
Fig. 6 illustrates an embodiment of an integrated single bending paddle anchor according to a preferred embodiment of the invention. The single bending paddle anchor is shown in a first side view and a second side view orthogonal to said first side view, and in section view.
Fig. 7 illustrates corresponding views of an integrated double bending paddle anchor along the lines of Fig. 6.
Fig. 4 illustrates resulting incremental distribution of load in bolt sections of a rock bolt according to the present invention, in which the anchors are designed for having a bearing capacity in the grout being less than the failure strength of an adjacent stem portion. Thus when the outer, left section has been heavily loaded and has approached the yield load, the first anchor's (2a) bearing capacity limit has been exceeded and the anchor has moved in the direction of the outer section as illustrated. Thus load has successively been transferred from the outer stem section to the intermediate stem section without exceeding the yield strength of the outer stem section. Likewise, as load has successively been transferred from the outer section to the intermediate section, the load at the intermediate section has exceeded the bearing capacity of the second anchor (2b) which has slid outwards in the direction of the surface, and thus part of the load has been transferred to the third stem section, which, in this illustration, has not reached the yield load yet.
Fig. 5a illustrates embodiments of the prior art D-bolt which have been modified to the present invention so as for having movable anchors relative to the grout, according to the present invention.
Fig. 5b illustrates two embodiments of the present invention represented by a rock bolt with a bolt head, and optional near-surface anchor and paddle-shaped anchors arranged consecutively between slick stem portions. The upper rock bolt has single paddle anchors and the lower rock bolt illustrated has double paddle anchors.
Fig. 6 illustrates an embodiment of an integrated single bending paddle anchor according to a preferred embodiment of the invention. The single bending paddle anchor is shown in a first side view and a second side view orthogonal to said first side view, and in section view.
Fig. 7 illustrates corresponding views of an integrated double bending paddle anchor along the lines of Fig. 6.
5 Fig. 8a illustrates an installed rock bolt according to the invention which shall illustrate the bolt newly arranged in grout in a borehole.
Fig. 8b illustrates a taut, deformed, slid rock bolt. Fig. 8b illustrates the same bolt after significant longitudinal expansion of the rock itself, and a significant longitudinal extension of the rock bolt while still fixed at least at the inner anchor. At least two anchors have slid.
Fig. 9 is a graph of pull load (in kN) as a function of joint opening (in mm) in a pull test using twin-paddle anchor bolts with 0 22 mm, 0.3 m segment. Fig. 9 illustrates a force versus length diagram for a pull test using a double paddle anchor and a 0.3 m segment for two test samples of 0 22 mm. For Sample B, the load increased steeply to over 250 kN (a stress of approximately 660 MPa) at slightly less than 40 mm joint opening, and failed at about 52 mm. For Sample A, for which the resin was accidently mixed to an unsatisfactory degree, the anchor had a lower bearing capacity of about 200 kN in that particular grout (a stress in the stem of approximately 525 MPa), the tension built up slower and the anchor started ploughing at about 35 mm but maintained its resistance at about 200 kN, and did not loose its grip until a total movement of 200 mm when the test was terminated.
Brief summary of the invention and advantages of the invention A solution to several of the above-mentioned problems is presented by the present invention which is a rock bolt for being grouted to set in grout in a borehole in a rock, comprising the following features:
- an elongate massive stem with a surface anchor the stem having two or more extensive lengths of stem portions;
- each stem portion followed by a borehole anchor for setting in the grout, the borehole anchors distributed with separations along the length of the stem;
Fig. 8b illustrates a taut, deformed, slid rock bolt. Fig. 8b illustrates the same bolt after significant longitudinal expansion of the rock itself, and a significant longitudinal extension of the rock bolt while still fixed at least at the inner anchor. At least two anchors have slid.
Fig. 9 is a graph of pull load (in kN) as a function of joint opening (in mm) in a pull test using twin-paddle anchor bolts with 0 22 mm, 0.3 m segment. Fig. 9 illustrates a force versus length diagram for a pull test using a double paddle anchor and a 0.3 m segment for two test samples of 0 22 mm. For Sample B, the load increased steeply to over 250 kN (a stress of approximately 660 MPa) at slightly less than 40 mm joint opening, and failed at about 52 mm. For Sample A, for which the resin was accidently mixed to an unsatisfactory degree, the anchor had a lower bearing capacity of about 200 kN in that particular grout (a stress in the stem of approximately 525 MPa), the tension built up slower and the anchor started ploughing at about 35 mm but maintained its resistance at about 200 kN, and did not loose its grip until a total movement of 200 mm when the test was terminated.
Brief summary of the invention and advantages of the invention A solution to several of the above-mentioned problems is presented by the present invention which is a rock bolt for being grouted to set in grout in a borehole in a rock, comprising the following features:
- an elongate massive stem with a surface anchor the stem having two or more extensive lengths of stem portions;
- each stem portion followed by a borehole anchor for setting in the grout, the borehole anchors distributed with separations along the length of the stem;
6 - the stem portions arranged for slipping relative to said grout of said borehole, so as for each of the stem portions to constrain local rock deformation through elongation of the stem portions between pairs of a locally anchored preceding anchor and a consecutive anchor;
- one or more of said borehole anchors is arranged for having a bearing capacity in said grout being less than a failure strength of an adjacent stem portion, to enable one or more of said borehole anchors to move during rock deformation so as for redistributing strain between stem portions.
Advantages of the invention Redistribution of stress:
A first advantage of the invention is that by enabling one or more of the borehole anchors to move during rock deformation will allow for redistribution of stress and strain from a more stressed stem portion to a less stressed stem portion, given that the stress difference between the unevenly stressed stem portions is higher than the bearing capacity of the anchor. This will enable the rock bolt of the invention to stay in operation for an extended deformation length and thus for an extended time compared to rock bolts of the prior art, without exceeding its failure strength. In other words, the rock bolt of the invention allows elastic strain redistribution without exceeding the yield limit of the rock bolt.
High pull force during ploughing:
A second advantage of the invention is that even though some the anchors may slowly plough through the hardened grout in the borehole when the bearing capacity of the anchors exceeded, this ploughing action occurs at a pull load near to but below the failure strength of the rock bolt stem (please see Fig. 9), thus the work required to make the anchor plough through the hardened grout is very high, thus the work required to plough the anchor through a given distance is very high and restricts rock displacement to a significant degree without exceeding the failure strength of the rock
- one or more of said borehole anchors is arranged for having a bearing capacity in said grout being less than a failure strength of an adjacent stem portion, to enable one or more of said borehole anchors to move during rock deformation so as for redistributing strain between stem portions.
Advantages of the invention Redistribution of stress:
A first advantage of the invention is that by enabling one or more of the borehole anchors to move during rock deformation will allow for redistribution of stress and strain from a more stressed stem portion to a less stressed stem portion, given that the stress difference between the unevenly stressed stem portions is higher than the bearing capacity of the anchor. This will enable the rock bolt of the invention to stay in operation for an extended deformation length and thus for an extended time compared to rock bolts of the prior art, without exceeding its failure strength. In other words, the rock bolt of the invention allows elastic strain redistribution without exceeding the yield limit of the rock bolt.
High pull force during ploughing:
A second advantage of the invention is that even though some the anchors may slowly plough through the hardened grout in the borehole when the bearing capacity of the anchors exceeded, this ploughing action occurs at a pull load near to but below the failure strength of the rock bolt stem (please see Fig. 9), thus the work required to make the anchor plough through the hardened grout is very high, thus the work required to plough the anchor through a given distance is very high and restricts rock displacement to a significant degree without exceeding the failure strength of the rock
7 bolt stem anywhere along the stem. This provides a higher overall deformation capacity and deformation work resistance than the prior art.
Part functionality after break:
A third advantage of the invention is that given the not very likely event that one of the stem sections should break (e.g. due to combined longitudinal extension and shear faulting across the borehole) the anchors at either side of the fault would still be intact and the entire function of the rock bolt would not be lost, as would be the case with the cone bolt.
Extended effective range:
A fourth advantage of the invention is that if the rock bolt of the invention is strained so far that the inner anchor starts ploughing, the rock bolt of the invention does not break but it still works while the inner anchor continues to plough under very high pull load near to, but below the failure strength of the rock bolt stem. Thus the restricting work length of the rock bolt according to the invention is extended as compared to the prior art D-bolt, and the work required to deform and displace the inner anchor and the remaining anchors of the rock bolt of the invention with several ploughing anchors far exceeds the work required to deform and move the single anchor cone bolt.
In other words, the rock bolt of the present invention extends the work length of the entire bolt to exceed the total longitudinal extension of rock surrounding the borehole.
Unidirectional anchor stamping:
A fifth advantage of the rock bolt according to an embodiment of the invention shown in Figs. 6 & 7 is that the anchors may be manufactured by stamping the stem from one side only, forming the single or twin-paddle anchors in one operation without turning the stem. This may reduce the number of operations for each bolt produced and is a significant advantage during manufacture of the several tens of thousands of rock bolts required for some mines.
Part functionality after break:
A third advantage of the invention is that given the not very likely event that one of the stem sections should break (e.g. due to combined longitudinal extension and shear faulting across the borehole) the anchors at either side of the fault would still be intact and the entire function of the rock bolt would not be lost, as would be the case with the cone bolt.
Extended effective range:
A fourth advantage of the invention is that if the rock bolt of the invention is strained so far that the inner anchor starts ploughing, the rock bolt of the invention does not break but it still works while the inner anchor continues to plough under very high pull load near to, but below the failure strength of the rock bolt stem. Thus the restricting work length of the rock bolt according to the invention is extended as compared to the prior art D-bolt, and the work required to deform and displace the inner anchor and the remaining anchors of the rock bolt of the invention with several ploughing anchors far exceeds the work required to deform and move the single anchor cone bolt.
In other words, the rock bolt of the present invention extends the work length of the entire bolt to exceed the total longitudinal extension of rock surrounding the borehole.
Unidirectional anchor stamping:
A fifth advantage of the rock bolt according to an embodiment of the invention shown in Figs. 6 & 7 is that the anchors may be manufactured by stamping the stem from one side only, forming the single or twin-paddle anchors in one operation without turning the stem. This may reduce the number of operations for each bolt produced and is a significant advantage during manufacture of the several tens of thousands of rock bolts required for some mines.
8 Description of preferred embodiments of the invention The invention is a rock bolt for being grouted to set in grout (g) in a borehole in a rock. The grout (g) may be a two-component epoxy resin for being mixed while in the borehole, or a cement, a polyester, or masses for filling part or all of the annulus between the borehole wall and the rock bolt. The rock bolt according to the invention comprises the following features:
- an elongate massive stem (1) with a surface anchor (3), the stem (1) comprising two or more extensive lengths of stem portions (1 a, 1 b, ..., 1 i), in which each stem portion is followed by a borehole anchor (2a, 2b, ..., 2i) for setting in the grout (g), said borehole anchors distributed with separations (La, Lb, ..., L;) along the length of the stem (1). The stem portions (1 a, 1 b, ..., 1 i) are arranged for slipping relative to the grout of said borehole, so as for each of the stem portions (1 a, 1 b, ..., 1 i) to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor (3, 2a, 2b, ...) and a consecutive anchor (2a, 2b, 2c, ..., 2i). So far, the rock bolt of the invention is rather similar to the D-bolt of the prior art. One of the essential novel features of the present invention over the D-bolt is that one or more of the borehole anchors (2a, 2b, 2c, ..., 2i) are arranged for having a bearing capacity in said grout (g) being less than a failure strength of an adjacent stem portion ((1 a or 1 b), (1 b or 1 c), ... (1 i). This will enable one or more of the borehole anchors (2a, 2b, ..., 2i) to move during rock deformation so as for redistributing strain between stem portions (1 a, 1b, ..., 1i). Please see embodiment in Fig. 5a and 5b. Preferably, two or more consecutive anchors separating consecutive sections of the rock bolt stem are movable in the grout, as illustrated in Fig. 8b. In Fig. 5a, even the last anchor (2c) slips. The strength of the last anchor is designed less than the failure strength of the last long segment so that the segment never fails rather than the last anchor slips when it subjects to a high load.
The bearing capacity of the borehole anchors (2) in the grout (g) may be adapted to be less than the failure strength of the adjacent stem portions. (1) in several ways:
- an elongate massive stem (1) with a surface anchor (3), the stem (1) comprising two or more extensive lengths of stem portions (1 a, 1 b, ..., 1 i), in which each stem portion is followed by a borehole anchor (2a, 2b, ..., 2i) for setting in the grout (g), said borehole anchors distributed with separations (La, Lb, ..., L;) along the length of the stem (1). The stem portions (1 a, 1 b, ..., 1 i) are arranged for slipping relative to the grout of said borehole, so as for each of the stem portions (1 a, 1 b, ..., 1 i) to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor (3, 2a, 2b, ...) and a consecutive anchor (2a, 2b, 2c, ..., 2i). So far, the rock bolt of the invention is rather similar to the D-bolt of the prior art. One of the essential novel features of the present invention over the D-bolt is that one or more of the borehole anchors (2a, 2b, 2c, ..., 2i) are arranged for having a bearing capacity in said grout (g) being less than a failure strength of an adjacent stem portion ((1 a or 1 b), (1 b or 1 c), ... (1 i). This will enable one or more of the borehole anchors (2a, 2b, ..., 2i) to move during rock deformation so as for redistributing strain between stem portions (1 a, 1b, ..., 1i). Please see embodiment in Fig. 5a and 5b. Preferably, two or more consecutive anchors separating consecutive sections of the rock bolt stem are movable in the grout, as illustrated in Fig. 8b. In Fig. 5a, even the last anchor (2c) slips. The strength of the last anchor is designed less than the failure strength of the last long segment so that the segment never fails rather than the last anchor slips when it subjects to a high load.
The bearing capacity of the borehole anchors (2) in the grout (g) may be adapted to be less than the failure strength of the adjacent stem portions. (1) in several ways:
9 - Adjusting the size or shape of the anchors (2) to the mechanical properties of the hardened grout so as for the anchors to lose their bearing capacity at a given load, i.e. modifying the anchors in order to adapt their bearing capacity in a given, perfectly mixed and hardened grout to be sufficiently less than the failure strength of the bolt stem so as for allowing the anchors to plough above a given pull load.
- By controlling the mechanical properties of said grout (g) to get desired mechanical properties when eventually hardened, during the preparation of said grout (g), say, using a two component epoxy resin, controlling the ratio of resin to hardener.
- By designing the anchors to deform mechanically at a given load in order to reduce the bearing capacity at a given load.
In a preferred embodiment of the invention, one or more of said borehole anchors (2a, 2b, 2c, ..., 2i) being arranged for having a bearing capacity in said grout (g) being not only less than a failure strength, but also less than a yield strength of an adjacent stem portion ((1 a or 1 b), (1 b or 1 c), ... (1 i)).
In a preferred embodiment of the invention, the borehole anchors (2a, 2b, ..., 2i) are materially integrated with the stem portions, i.e. the anchors are formed from a same smooth bar material blank (0) as the stem portions (1 a, 1 b, ..., 1 i) are formed from.
This is an advantage from a manufacturing point of view. Further manufacturing advantages are described below.
In a preferred embodiment of the anchors of the bolt according to the invention, please see the embodiment illustrated in Fig. 6, the bolt comprises one or more paddle-shaped anchors (2, 22) formed from said smooth bar material blank (0) by bending a first short portion (20) of said smooth bar (0) to a first side of said smooth bar's (0) axis, the length of said first short portion (20) corresponding to a length of said borehole anchor, and clamping said first short bent portion (20) to a desired thickness less than, and to a desired width greater than, a diameter of said smooth bar material blank (0).
In another preferred embodiment of the anchors of the bolt according to the invention, please see the embodiment illustrated in Fig. 7, the bolt comprises double paddle-shaped anchors (24) formed from said smooth bar material blank (0) by bending a first short portion (20) of the smooth bar (0) to a first side, and a second small portion (23) adjacent to said first short portion (20), to a second side of said smooth bar's (0) axis, the combined length of said first and second short portions (22, 23) corresponding to a length of said borehole anchor, and clamping said first and second short bent portions (20, 23) to desired thicknesses less than, and to desired widths greater than, a diameter of said smooth bar material blank (0).
The outer bar section of long extension may have the surface anchor (3) as its outer anchoring point, but in an embodiment shown in Fig. 5b, the rock bolt of the invention comprises a short outer stem portion (1 o) adjacent to said surface anchor (3) and an auxiliary borehole anchor (20) similar to said borehole anchors (2a, 2b, ..., 2i) adjacent to said first stem portion (1a). The auxiliary outer borehole anchor (2o) may be arranged not to slip in the grout. In other words, the auxiliary borehole anchor (20), which is arranged adjacent to the surface anchor (3) and arranged between the short outer stem portion (10) and the first stem portion (1 a), may be arranged for having a bearing capacity in the grout (g) being higher than a failure strength of the main stem portion (1a). With such an embodiment of the invention, one or more of the anchors (2a, 2b, ... ) further inside the borehole may be displaced in the grout and transfer load in order not to exceed the failure load of the stem portions (1a, 1b, ...).
In an embodiment of the invention the innermost anchor (2i) may be arranged with a bearing capacity in the grout (g) being higher than a failure strength of the innermost stem portion (1 i). This situation may be envisaged such as in Fig. 8b where the innermost anchor (2i) is fixed in place relative to the borehole wall and the grout.
It is also possible to combine the two above embodiments in that the auxiliary anchor (2o) and the innermost anchor (2i) being arranged to have a bearing capacity in the grout (g) exceeding the failure strength of the stem (1, 10, 1 a, 1i). In such a bolt, when the rock expands, the outer, auxiliary anchor (20) near the surface anchor (3), and the inner anchor (2i) will reside generally fixed in the grout (g) while the anchors (2a, 2b, ...) lying between the outermost and innermost anchors (2o, 2i) are allowed to slide in the grout to redistribute strain along the stem when the rock expands.
The desired ploughing properties may be achieved by controlling/designing the shape of the anchors, or by designing some or all the anchors to plough through the given resin given a certain axial load, being less than the failure strength of the stem portion.
Alternatively the outer borehole anchor (20) may be arranged to slip in the grout so as for the auxiliary outer stem portion to be slightly extended (or contracted) under varying load during rock deformation.
The pattern of lengths of the stem portions may be varied according to the requirements presented by the local geological conditions and/or mining regulations.
According to an embodiment of the rock bolt of the invention, one or more of said stem portions (1 a, 1 b, ...) may have a longer initial length than a consecutive stem portion (1 b, 1 c, ..., 1 i) , please see the embodiment illustrated in Fig.
5b. In another embodiment of the invention, one or more of the stem portions (1 a, 1 b, ...) may generally the same length as a consecutive stem portion (1 b, 1 c..., 1 i).
In an embodiment of the invention the stem portions (1) have a higher deformation capacity per unit length as compared to said anchors (2), i.e. the stem portions are elastically extendible, and the anchors are hard and resilient, but slip before the stem portions exceed their yield limit.
In a preferred embodiment of the invention two or more of the stem portions (1 a, 1 b, ..., 1 i) have essentially the same failure strength, particularly this relates to consecutive stem portions.
In preferred embodiments of the invention, the borehole anchors (2a, 2b, ..., 2i) are of short extent, say between 5 and 20 per cent length compared to the length of said stem portion (1 a, 1b, ..., 1i).
In one preferred embodiment of the invention, the surface anchor (3) of the rock bolt comprises a threaded portion (3a) at the borehole surface portion of the stem (1), the threaded portion (3a) provided with one or more nuts (3b) and one or more washers or sheaves (3c). This allows pre-tensioning of the bolt (1) when mounted in the borehole. Alternatively, the rock bolt may have a surface anchor (3) comprising a fixed head (3f) at the borehole surface portion of the stem (1). Anyway, in order to transfer load to the wall and maintain the integrity of the rock surface with possible shotcrete and metallic nets, the surface anchor (3) may be provided with a face plate (3d). The rock bolt of the present invention may be used with several kinds of face plates of the background art.
A simple example of use of the rock bolt according to the invention is illustrated in Fig. 8. The rock deformation in the present example is according to Fig. 1.
The surface anchor (3) moves outward to a larger degree than the first main anchor (2a).
The generally outer, first main stem portion (1a) will thus be strained most of all stem portions, please see Fig. 4. The novel features of the rock bolt according to the invention resides in the ratio of the anchoring properties of the anchors (2a, 2b, ..., 2i) with respect to the grout, preferably an epoxy resin, compared to the failure strength of the stem portions (1 a, 1b, ..., 1i) of the rock bolt. The result of anchor (2a) having a bearing capacity less than the failure strength of stem portion (1a) is that anchor (2a) will move outwards when stem portion (1 a) is strained over the bearing capacity of anchor (2a), please see Fig. 8 and Fig. 4. The result of anchor (2a) having a bearing capacity which is also less than the failure strength of the consecutive stem portion (1b) will result in anchor (2a) to move outward while straining consecutive stem portion (1 b). This will unload some of the strain from the more heavily stressed stem portion (1 a) and strain stem portion (1 b). When approaching the yield load of section (1 b), the consecutive anchor (2b) will start ploughing outward and transfer load to the consecutive section (1 c).
- By controlling the mechanical properties of said grout (g) to get desired mechanical properties when eventually hardened, during the preparation of said grout (g), say, using a two component epoxy resin, controlling the ratio of resin to hardener.
- By designing the anchors to deform mechanically at a given load in order to reduce the bearing capacity at a given load.
In a preferred embodiment of the invention, one or more of said borehole anchors (2a, 2b, 2c, ..., 2i) being arranged for having a bearing capacity in said grout (g) being not only less than a failure strength, but also less than a yield strength of an adjacent stem portion ((1 a or 1 b), (1 b or 1 c), ... (1 i)).
In a preferred embodiment of the invention, the borehole anchors (2a, 2b, ..., 2i) are materially integrated with the stem portions, i.e. the anchors are formed from a same smooth bar material blank (0) as the stem portions (1 a, 1 b, ..., 1 i) are formed from.
This is an advantage from a manufacturing point of view. Further manufacturing advantages are described below.
In a preferred embodiment of the anchors of the bolt according to the invention, please see the embodiment illustrated in Fig. 6, the bolt comprises one or more paddle-shaped anchors (2, 22) formed from said smooth bar material blank (0) by bending a first short portion (20) of said smooth bar (0) to a first side of said smooth bar's (0) axis, the length of said first short portion (20) corresponding to a length of said borehole anchor, and clamping said first short bent portion (20) to a desired thickness less than, and to a desired width greater than, a diameter of said smooth bar material blank (0).
In another preferred embodiment of the anchors of the bolt according to the invention, please see the embodiment illustrated in Fig. 7, the bolt comprises double paddle-shaped anchors (24) formed from said smooth bar material blank (0) by bending a first short portion (20) of the smooth bar (0) to a first side, and a second small portion (23) adjacent to said first short portion (20), to a second side of said smooth bar's (0) axis, the combined length of said first and second short portions (22, 23) corresponding to a length of said borehole anchor, and clamping said first and second short bent portions (20, 23) to desired thicknesses less than, and to desired widths greater than, a diameter of said smooth bar material blank (0).
The outer bar section of long extension may have the surface anchor (3) as its outer anchoring point, but in an embodiment shown in Fig. 5b, the rock bolt of the invention comprises a short outer stem portion (1 o) adjacent to said surface anchor (3) and an auxiliary borehole anchor (20) similar to said borehole anchors (2a, 2b, ..., 2i) adjacent to said first stem portion (1a). The auxiliary outer borehole anchor (2o) may be arranged not to slip in the grout. In other words, the auxiliary borehole anchor (20), which is arranged adjacent to the surface anchor (3) and arranged between the short outer stem portion (10) and the first stem portion (1 a), may be arranged for having a bearing capacity in the grout (g) being higher than a failure strength of the main stem portion (1a). With such an embodiment of the invention, one or more of the anchors (2a, 2b, ... ) further inside the borehole may be displaced in the grout and transfer load in order not to exceed the failure load of the stem portions (1a, 1b, ...).
In an embodiment of the invention the innermost anchor (2i) may be arranged with a bearing capacity in the grout (g) being higher than a failure strength of the innermost stem portion (1 i). This situation may be envisaged such as in Fig. 8b where the innermost anchor (2i) is fixed in place relative to the borehole wall and the grout.
It is also possible to combine the two above embodiments in that the auxiliary anchor (2o) and the innermost anchor (2i) being arranged to have a bearing capacity in the grout (g) exceeding the failure strength of the stem (1, 10, 1 a, 1i). In such a bolt, when the rock expands, the outer, auxiliary anchor (20) near the surface anchor (3), and the inner anchor (2i) will reside generally fixed in the grout (g) while the anchors (2a, 2b, ...) lying between the outermost and innermost anchors (2o, 2i) are allowed to slide in the grout to redistribute strain along the stem when the rock expands.
The desired ploughing properties may be achieved by controlling/designing the shape of the anchors, or by designing some or all the anchors to plough through the given resin given a certain axial load, being less than the failure strength of the stem portion.
Alternatively the outer borehole anchor (20) may be arranged to slip in the grout so as for the auxiliary outer stem portion to be slightly extended (or contracted) under varying load during rock deformation.
The pattern of lengths of the stem portions may be varied according to the requirements presented by the local geological conditions and/or mining regulations.
According to an embodiment of the rock bolt of the invention, one or more of said stem portions (1 a, 1 b, ...) may have a longer initial length than a consecutive stem portion (1 b, 1 c, ..., 1 i) , please see the embodiment illustrated in Fig.
5b. In another embodiment of the invention, one or more of the stem portions (1 a, 1 b, ...) may generally the same length as a consecutive stem portion (1 b, 1 c..., 1 i).
In an embodiment of the invention the stem portions (1) have a higher deformation capacity per unit length as compared to said anchors (2), i.e. the stem portions are elastically extendible, and the anchors are hard and resilient, but slip before the stem portions exceed their yield limit.
In a preferred embodiment of the invention two or more of the stem portions (1 a, 1 b, ..., 1 i) have essentially the same failure strength, particularly this relates to consecutive stem portions.
In preferred embodiments of the invention, the borehole anchors (2a, 2b, ..., 2i) are of short extent, say between 5 and 20 per cent length compared to the length of said stem portion (1 a, 1b, ..., 1i).
In one preferred embodiment of the invention, the surface anchor (3) of the rock bolt comprises a threaded portion (3a) at the borehole surface portion of the stem (1), the threaded portion (3a) provided with one or more nuts (3b) and one or more washers or sheaves (3c). This allows pre-tensioning of the bolt (1) when mounted in the borehole. Alternatively, the rock bolt may have a surface anchor (3) comprising a fixed head (3f) at the borehole surface portion of the stem (1). Anyway, in order to transfer load to the wall and maintain the integrity of the rock surface with possible shotcrete and metallic nets, the surface anchor (3) may be provided with a face plate (3d). The rock bolt of the present invention may be used with several kinds of face plates of the background art.
A simple example of use of the rock bolt according to the invention is illustrated in Fig. 8. The rock deformation in the present example is according to Fig. 1.
The surface anchor (3) moves outward to a larger degree than the first main anchor (2a).
The generally outer, first main stem portion (1a) will thus be strained most of all stem portions, please see Fig. 4. The novel features of the rock bolt according to the invention resides in the ratio of the anchoring properties of the anchors (2a, 2b, ..., 2i) with respect to the grout, preferably an epoxy resin, compared to the failure strength of the stem portions (1 a, 1b, ..., 1i) of the rock bolt. The result of anchor (2a) having a bearing capacity less than the failure strength of stem portion (1a) is that anchor (2a) will move outwards when stem portion (1 a) is strained over the bearing capacity of anchor (2a), please see Fig. 8 and Fig. 4. The result of anchor (2a) having a bearing capacity which is also less than the failure strength of the consecutive stem portion (1b) will result in anchor (2a) to move outward while straining consecutive stem portion (1 b). This will unload some of the strain from the more heavily stressed stem portion (1 a) and strain stem portion (1 b). When approaching the yield load of section (1 b), the consecutive anchor (2b) will start ploughing outward and transfer load to the consecutive section (1 c).
Claims (21)
1. A rock bolt for being grouted to set in grout in a borehole in a rock, said bolt comprising - an elongate massive stem with a surface anchor;
- said stem comprising two or more extensive lengths of stem portions, - each stem portion followed by a borehole anchor for setting in said grout, said borehole anchors distributed with separations along the length of said stem;
- said stem portions arranged for slipping relative to said grout of said borehole, so as for each of said stem portions to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor and a consecutive anchor;
wherein - one or more of said borehole anchors being arranged for having a bearing capacity in said grout being less than a failure strength of an adjacent stem portion, to enable one or more of said borehole anchors to move during rock deformation so as for redistributing strain between stem portions.
- said stem comprising two or more extensive lengths of stem portions, - each stem portion followed by a borehole anchor for setting in said grout, said borehole anchors distributed with separations along the length of said stem;
- said stem portions arranged for slipping relative to said grout of said borehole, so as for each of said stem portions to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor and a consecutive anchor;
wherein - one or more of said borehole anchors being arranged for having a bearing capacity in said grout being less than a failure strength of an adjacent stem portion, to enable one or more of said borehole anchors to move during rock deformation so as for redistributing strain between stem portions.
2. The rock bolt of claim 1, said borehole anchors being integrated, formed from a same smooth bar material blank as the stem portions are formed from.
3. The rock bolt of claim 2, comprising a paddle-shaped anchor formed from said smooth bar material blank by bending a first short portion of said smooth bar to a first side of said smooth bar's axis, the length of said first short portion corresponding to a length of said borehole anchor, and clamping said first short bent portion to a desired thickness less than, and to a desired width greater than, a diameter of said smooth bar material blank.
4. The rock bolt of claim 2, comprising a double paddle-shaped anchor formed from said smooth bar material blank by bending a first short portion of said smooth bar to a first side, and a second short portion adjacent to said first short portion, to a second side of said smooth bar's axis, the combined length of said first and second short portions corresponding to a length of said borehole anchor, and clamping said first and second short bent portions to desired thicknesses less than, and to desired widths greater than, a diameter of said smooth bar material blank.
5. The rock bolt of claim 1, comprising a short outer stem portion adjacent to said surface anchor and an auxiliary borehole anchor similar to said borehole anchors adjacent to said first stem portion.
6. The rock bolt of claim 1, one or more of said stem portions having a longer initial length than a consecutive stem portion.
7. The rock bolt of claim 1, one or more of said stem portions having generally the same length as a consecutive stem portion.
8. The rock bolt of claim 1, said stem portions having a higher deformation capacity per unit length as compared to said anchors.
9. The rock bolt of claim 1, two or more of said stem portions having essentially the same failure strength.
10. The rock bolt of claim 1, said borehole anchors being of short extent compared to the length of said stem portion.
11. The rock bolt of claim 1, said surface anchor comprising a threaded portion at the borehole surface portion of said stem, said threaded portion provided with one or more nuts and one or more washers or sheaves, so as for enabling pre-tensioning of said bolt.
12. The rock bolt of claim 1, said surface anchor comprising a fixed head at the borehole surface portion of said stem.
13. The rock bolt of claim 11 or 12, said surface anchor comprising a face plate.
14. The rock bolt of claim 1, said grout being two-component epoxy resin for being mixed while in the borehole.
15. The rock bolt of claim 1, one or more of said borehole anchors being arranged for having a bearing capacity in said grout being less than a yield strength of an adjacent stem portion.
16. The rock bolt of claim 5, said auxiliary borehole anchor adjacent to said surface anchor and arranged between said short outer stem portion and said first stem portion being arranged for having a bearing capacity in said grout being higher than a failure strength of said main stem portion.
17. The rock bolt of claim 1, said innermost anchor arranged with a bearing capacity in said grout being higher than a failure strength of said innermost stem portion.
18. A method for installing a rock bolt to set in grout in a borehole in a rock, said bolt comprising - an elongate massive stem with a surface anchor;
- said stem comprising two or more extensive lengths of stem portions, - each stem portion followed by a borehole anchor for setting in said grout, said borehole anchors distributed with separations along the length of said stem;
- arranging said stem portions for slipping relative to said grout of said borehole, so as for each of said stem portions to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor and a consecutive anchor;
characterized by - arranging one or more of said borehole anchors with a bearing capacity in said grout being less than a failure strength of an adjacent stem portion, enabling one or more of said borehole anchors to move during rock deformation so as for redistributing strain between stem portions.
- said stem comprising two or more extensive lengths of stem portions, - each stem portion followed by a borehole anchor for setting in said grout, said borehole anchors distributed with separations along the length of said stem;
- arranging said stem portions for slipping relative to said grout of said borehole, so as for each of said stem portions to constrain local rock deformation through elongation of said stem portions between pairs of a locally anchored preceding anchor and a consecutive anchor;
characterized by - arranging one or more of said borehole anchors with a bearing capacity in said grout being less than a failure strength of an adjacent stem portion, enabling one or more of said borehole anchors to move during rock deformation so as for redistributing strain between stem portions.
19. The method of claim 18, controlling said bearing capacity in said grout by controlling the mechanical properties of said grout to get desired mechanical properties when eventually hardened, during the preparation of said grout.
20. The method of claim 19, using a two component epoxy resin, controlling the ratio of resin to hardener.
21. The method of claim 18, controlling the mechanical properties of the anchors by designing the shape of the one or more of said anchors to have a desired bearing capacity and to plough through the given resin above said bearing capacity being less than the failure strength of said stem portion.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NONO20085384 | 2008-12-23 | ||
| NO20085384A NO332912B1 (en) | 2008-12-23 | 2008-12-23 | Improved rock bolt with plowing anchors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2653307A1 CA2653307A1 (en) | 2010-06-23 |
| CA2653307C true CA2653307C (en) | 2012-05-01 |
Family
ID=42101537
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2653307A Active CA2653307C (en) | 2008-12-23 | 2009-02-09 | Improved rock bolt with ploughing anchors |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA2653307C (en) |
| CL (1) | CL2011001581A1 (en) |
| NO (1) | NO332912B1 (en) |
| WO (1) | WO2010074584A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105928649A (en) * | 2016-04-15 | 2016-09-07 | 长江水利委员会长江科学院 | System and method for measuring stress relief time lag characteristics of deeply-buried high-energy-storage rock mass |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CL2014001002A1 (en) * | 2013-12-12 | 2014-11-28 | Ncm Innovations Pty Ltd | Rock anchor bolt including an elongated cylindrical body having, a first distal end and a second opposite proximal end, a threaded portion at the second end, a first anchor located at or at least partially located at a first end portion of the body, a second anchor, a first stem portion between the first and second anchor. |
| WO2019023719A1 (en) * | 2017-07-26 | 2019-01-31 | Ncm Innovations (Pty) Ltd | Paddle adapted rock bolt with improved installation properties |
| CN110219687B (en) * | 2019-06-21 | 2020-08-21 | 安徽理工大学 | Method for monitoring stress distribution of full-length anchoring bolt body |
| CN111911209B (en) * | 2020-08-17 | 2022-02-08 | 河北工程大学 | Accurate targeted anchor grouting control method suitable for deep soft rock roadway |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3326428A1 (en) * | 1983-07-22 | 1985-02-07 | HLS-Verwaltung GmbH, 4630 Bochum | Sliding anchor |
| DE3504543C1 (en) | 1985-02-11 | 1986-05-15 | Bochumer Eisenhütte Heintzmann GmbH & Co KG, 4630 Bochum | Resin-bedded roof bolt |
| US5511909A (en) * | 1994-06-07 | 1996-04-30 | Jennmar Corporation | Cable bolt and method of use in supporting a rock formation |
| AU747261B2 (en) * | 1999-09-14 | 2002-05-09 | Fci Holdings Delaware, Inc. | Grit surface cable products |
| WO2007000461A1 (en) | 2005-06-27 | 2007-01-04 | Etilux S.A. | Unit comprising a metallic support and an emitter-receiver device |
| SE532203C2 (en) * | 2006-12-22 | 2009-11-10 | Dynamic Rock Support As | A deformable rock bolt |
-
2008
- 2008-12-23 NO NO20085384A patent/NO332912B1/en unknown
-
2009
- 2009-02-09 CA CA2653307A patent/CA2653307C/en active Active
- 2009-12-23 WO PCT/NO2009/000443 patent/WO2010074584A1/en active Application Filing
-
2011
- 2011-06-23 CL CL2011001581A patent/CL2011001581A1/en unknown
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105928649A (en) * | 2016-04-15 | 2016-09-07 | 长江水利委员会长江科学院 | System and method for measuring stress relief time lag characteristics of deeply-buried high-energy-storage rock mass |
| CN105928649B (en) * | 2016-04-15 | 2018-11-02 | 长江水利委员会长江科学院 | Buried high energy storage rock mass stress release time lag characteristic measurement system and method |
Also Published As
| Publication number | Publication date |
|---|---|
| NO20085384L (en) | 2010-06-24 |
| WO2010074584A1 (en) | 2010-07-01 |
| CA2653307A1 (en) | 2010-06-23 |
| NO332912B1 (en) | 2013-01-28 |
| CL2011001581A1 (en) | 2012-05-11 |
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