WO2007066186A1 - Brittle material fracturing system - Google Patents

Brittle material fracturing system Download PDF

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Publication number
WO2007066186A1
WO2007066186A1 PCT/IB2006/003393 IB2006003393W WO2007066186A1 WO 2007066186 A1 WO2007066186 A1 WO 2007066186A1 IB 2006003393 W IB2006003393 W IB 2006003393W WO 2007066186 A1 WO2007066186 A1 WO 2007066186A1
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WO
WIPO (PCT)
Prior art keywords
compressive
pulses
pulsed
compressive pulses
rigid body
Prior art date
Application number
PCT/IB2006/003393
Other languages
French (fr)
Inventor
Johannes Stanislaus Kuijpers
Original Assignee
Csir
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Csir filed Critical Csir
Publication of WO2007066186A1 publication Critical patent/WO2007066186A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21C—MINING OR QUARRYING
    • E21C37/00—Other methods or devices for dislodging with or without loading

Definitions

  • THIS invention relates to a brittle material fracturing system.
  • the invention relates to a method and apparatus for fracturing rock.
  • rock In broad terms rock is conventionally broken using one of two methods.
  • the primary rock breaking mechanism is compressive crushing with the necessary crushing action being achieved by means of devices such as pneumatic hammers, drills, saws or the like. It is recognised that the crushing method is highly inefficient.
  • tension is induced in the rock by, for instance, blasting or by means of an expansion device of some kind.
  • blasting or by means of an expansion device of some kind.
  • these techniques require a hole to be drilled into the rock to allow the blasting explosive or expansion device to be placed within the body of rock.
  • the drilling of the hole itself involves crushing and is inefficient, time-consuming, inconvenient and costly.
  • a method of fracturing brittle material for example rock, which comprises applying compressive pulses to a selected area of a surface of the material which is to be fractured, the amplitude, frequency and/or duration of the compressive pulses and the area over which the pulses are applied to the surface being selected such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and interact with each other, within the material, to cause the material to fracture.
  • the compressive pulses are applied to the surface of the material by means of a rigid body acting against the surface.
  • the rigid body may for instance be reciprocated against the surface.
  • the body may be held in contact with the surface and a pulsed force be applied to the body such that the body, by transmission of the pulsed force, applies compressive pulses to the material.
  • the rigid body has a depth dimension, measured transverse to the surface, which is less than the lateral dimension of the body, measured parallel to the surface, and that body has a circular shape when viewed in a direction transverse to the surface.
  • compressive pulses are applied to the surface of the material by means of a pulsed liquid jet directed against the surface.
  • the liquid jet has a circular shape when viewed in a direction transverse to the surface and is composed of liquid drops.
  • a brittle material fracturing apparatus comprising pulse applying means for applying compressive pulses to a selected area of a surface of the material which is to be fractured, and control means for controlling the amplitude, frequency and/or duration of the compressive pulses such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and combine with each other, within the material, to cause the material to fracture.
  • the invention is based upon the recognition that materials such as rock are hard and brittle in nature and that, while such materials are strong in compression, they can be fractured by tensile forces.
  • the present invention seeks to provide for the generation of tensile stresses in such materials.
  • the numeral 10 indicates the surface of a rock mass 12 which is to be fractured.
  • the numeral 14 indicates a rigid body which is placed and held against the surface 10.
  • the body 14 is preferably circular in shape with the numeral 16 indicating the diameter of the body. As illustrated the body has fairly squat proportions with the depth 18 of the body, measured transverse to the surface 10, being substantially less than the lateral dimension of the body represented by the diameter 16.
  • the numeral 20 indicates a device for driving the body 14 against the surface in a pulsed manner. For the duration of each pulse, the body applies compression to the mass 12 over the area of the surface contacted by the body. The compressive stresses pulsed into the mass 12 are indicated by the numeral 22.
  • the compressive force which is applied to the surface 10 is sufficient to compress it slightly over the area to which the force is applied.
  • the boundary of the compression area i.e. at the boundary of the body 14, there will be a slight curvature or deformation of the surface material as shown in a somewhat exaggerated manner in the enlargement in the drawing, indicated by the numeral 24.
  • This curvature of the material results in the generation of tensile stresses in the material at the boundary surface.
  • the tensile stresses generated at the boundary of the compression area, i.e at the boundary of the body 14, are also transmitted into the rock in a pulsed manner as diagrammatically indicated by the numeral 26.
  • the applied compressive force is selected such that, at a certain depth within the rock mass 12, the tensile pulses interact with each other, typically by converging on and reinforcing each other to create, in combination, sufficient tensile stress to cause the rock mass to fracture.
  • Other relevant factors will be the pulse duration, i.e. the period of time for which compression is applied to the rock face at each pulse, and/or the pulse frequency, i.e. frequency with which compressions are applied to the face.
  • correct selection pulse frequency and/or duration can be used to limit the time- related interference of the compressive and tensile stresses, permitting the tensile stresses to dominate in the zone, within the rock mass, where they are operative to cause fracturing of the rock.
  • the inventor has established that the higher the frequency of pulse application, the higher the ratio of tensile stress to compressive stress and accordingly the better the chance of achieving sufficient combined tensile stress to achieve fracturing.
  • the body 14 It is considered desirable for the body 14 to have squat dimensions, i.e. a small ratio of depth to lateral dimension, because this can to some extent eliminate vibrational effects in the body itself as the pulses are applied, i.e. shorter duration pulses can be applied through a body with a small depth to lateral dimension ratio, leading to less interference between the compressive and tensile stresses.
  • Mathematical models also indicate that higher levels of tensile stress are achievable with higher pulse frequencies and that it is preferable to transmit the pulses to the rock mass through a solid body rather than one which only contacts the face about the perimeter of the body, as would be the case with, say, a hollow cylindrical body arranged with its axis transverse to the face.
  • the required compressive pulses can be applied to the body by any suitable mechanical or other means, for example a vibratory motor capable of acting at appropriate frequencies with appropriate force.
  • the body 14 is held against the surface 10 while pulsed force is applied to it.
  • a coupling medium between the body and the surface This could for instance be provided by a film of water or other liquid capable of transmitting the compressive forces while maintaining intimate contact with both the body and the surface.
  • the body 14 itself may be reciprocated against the surface by a suitable reciprocating drive acting on the body, as indicated by the arrows 30. It will be understood that in this version of the invention the body is effectively impacted at an appropriate frequency and with appropriate force against the surface.
  • pulsed compression is applied to the surface 10 by means of a pulsed, high pressure liquid jet, typically a water jet.
  • a pulsed, high pressure liquid jet typically a water jet.
  • the jet may be in the form of a solid stream of the liquid. It is however preferred that the jet, at each pulse, be composed of discrete liquid drops. With a view to ensuring appropriate interaction of the tensile stresses which are generated and transmitted into the rock mass it is also preferred that the jet have a circular cross-section so as to impinge on the surface 10 over a circular area.

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  • Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Geology (AREA)
  • Earth Drilling (AREA)

Abstract

The invention concerns a method and apparatus for fracturing brittle material such as rock (12). In the method, compressive pulses are applied to a selected area of the surface (10) of the material which is to be fractured. The amplitude, frequency and/or duration of the compressive pulses and the area over which the pulses are applied to the surface are selected such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses (26) induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and interact with each other, within the material, to cause the material to fracture.

Description

"BRITTLE MATERIAL FRACTURING SYSTEM"
BACKGROUND TO THE INVENTION
THIS invention relates to a brittle material fracturing system. In one application the invention relates to a method and apparatus for fracturing rock.
In broad terms rock is conventionally broken using one of two methods. In the first method, the primary rock breaking mechanism is compressive crushing with the necessary crushing action being achieved by means of devices such as pneumatic hammers, drills, saws or the like. It is recognised that the crushing method is highly inefficient.
In the second method tension is induced in the rock by, for instance, blasting or by means of an expansion device of some kind. However these techniques require a hole to be drilled into the rock to allow the blasting explosive or expansion device to be placed within the body of rock. The drilling of the hole itself involves crushing and is inefficient, time-consuming, inconvenient and costly.
It is an object of the present invention to provide a method and means whereby a brittle material such as rock can be fractured by tensile forces without the need to drill a hole into the material and by avoiding compressive crushing of the material. SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a method of fracturing brittle material, for example rock, which comprises applying compressive pulses to a selected area of a surface of the material which is to be fractured, the amplitude, frequency and/or duration of the compressive pulses and the area over which the pulses are applied to the surface being selected such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and interact with each other, within the material, to cause the material to fracture.
In some embodiments, the compressive pulses are applied to the surface of the material by means of a rigid body acting against the surface. The rigid body may for instance be reciprocated against the surface. Alterantively the body may be held in contact with the surface and a pulsed force be applied to the body such that the body, by transmission of the pulsed force, applies compressive pulses to the material. In such arrangements it is preferred that the rigid body has a depth dimension, measured transverse to the surface, which is less than the lateral dimension of the body, measured parallel to the surface, and that body has a circular shape when viewed in a direction transverse to the surface.
In another version of the invention, compressive pulses are applied to the surface of the material by means of a pulsed liquid jet directed against the surface. Preferably the liquid jet has a circular shape when viewed in a direction transverse to the surface and is composed of liquid drops.
According to another aspect of the invention there is provided a brittle material fracturing apparatus comprising pulse applying means for applying compressive pulses to a selected area of a surface of the material which is to be fractured, and control means for controlling the amplitude, frequency and/or duration of the compressive pulses such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and combine with each other, within the material, to cause the material to fracture.
Other features of the invention are defined in the appended claims.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawing which diagrammatically illustrates embodiments of the invention.
SPECIFIC DESCRIPTION
The invention is based upon the recognition that materials such as rock are hard and brittle in nature and that, while such materials are strong in compression, they can be fractured by tensile forces. The present invention seeks to provide for the generation of tensile stresses in such materials.
In the drawing, the numeral 10 indicates the surface of a rock mass 12 which is to be fractured. The numeral 14 indicates a rigid body which is placed and held against the surface 10. The body 14 is preferably circular in shape with the numeral 16 indicating the diameter of the body. As illustrated the body has fairly squat proportions with the depth 18 of the body, measured transverse to the surface 10, being substantially less than the lateral dimension of the body represented by the diameter 16. -A-
The numeral 20 indicates a device for driving the body 14 against the surface in a pulsed manner. For the duration of each pulse, the body applies compression to the mass 12 over the area of the surface contacted by the body. The compressive stresses pulsed into the mass 12 are indicated by the numeral 22.
At each pulse the compressive force which is applied to the surface 10 is sufficient to compress it slightly over the area to which the force is applied. In the present example, some compression of the rock face accordingly takes place over the area of the body 14. At the boundary of the compression area, i.e. at the boundary of the body 14, there will be a slight curvature or deformation of the surface material as shown in a somewhat exaggerated manner in the enlargement in the drawing, indicated by the numeral 24.
This curvature of the material results in the generation of tensile stresses in the material at the boundary surface. The tensile stresses generated at the boundary of the compression area, i.e at the boundary of the body 14, are also transmitted into the rock in a pulsed manner as diagrammatically indicated by the numeral 26. The applied compressive force is selected such that, at a certain depth within the rock mass 12, the tensile pulses interact with each other, typically by converging on and reinforcing each other to create, in combination, sufficient tensile stress to cause the rock mass to fracture.
The inventor recognises that achievement of the desired result, i.e. fracturing of the rock, will be dependent on a number of factors including the magnitude of the compressive pulses, i.e. the compressive pressure or force which is applied to the rock face and which will in turn determine the magnitude of the tensile stresses achieved in the rock mass. Other relevant factors will be the pulse duration, i.e. the period of time for which compression is applied to the rock face at each pulse, and/or the pulse frequency, i.e. frequency with which compressions are applied to the face. Although the tensile stresses which are generated in the rock mass will generally be smaller in magnitude than the compressive stresses, correct selection pulse frequency and/or duration can be used to limit the time- related interference of the compressive and tensile stresses, permitting the tensile stresses to dominate in the zone, within the rock mass, where they are operative to cause fracturing of the rock.
The inventor has established that the higher the frequency of pulse application, the higher the ratio of tensile stress to compressive stress and accordingly the better the chance of achieving sufficient combined tensile stress to achieve fracturing.
It is considered desirable for the body 14 to have squat dimensions, i.e. a small ratio of depth to lateral dimension, because this can to some extent eliminate vibrational effects in the body itself as the pulses are applied, i.e. shorter duration pulses can be applied through a body with a small depth to lateral dimension ratio, leading to less interference between the compressive and tensile stresses. Mathematical models also indicate that higher levels of tensile stress are achievable with higher pulse frequencies and that it is preferable to transmit the pulses to the rock mass through a solid body rather than one which only contacts the face about the perimeter of the body, as would be the case with, say, a hollow cylindrical body arranged with its axis transverse to the face.
The required compressive pulses can be applied to the body by any suitable mechanical or other means, for example a vibratory motor capable of acting at appropriate frequencies with appropriate force.
In the example described above, the body 14 is held against the surface 10 while pulsed force is applied to it. For better coupling of the body with the rock surface, which may be uneven, to ensure efficient transmission of the compressive pulses, it is proposed to provide a coupling medium between the body and the surface. This could for instance be provided by a film of water or other liquid capable of transmitting the compressive forces while maintaining intimate contact with both the body and the surface.
In another version of the invention, the body 14 itself may be reciprocated against the surface by a suitable reciprocating drive acting on the body, as indicated by the arrows 30. It will be understood that in this version of the invention the body is effectively impacted at an appropriate frequency and with appropriate force against the surface.
In yet another version of the invention, pulsed compression is applied to the surface 10 by means of a pulsed, high pressure liquid jet, typically a water jet. At each pulse the jet may be in the form of a solid stream of the liquid. It is however preferred that the jet, at each pulse, be composed of discrete liquid drops. With a view to ensuring appropriate interaction of the tensile stresses which are generated and transmitted into the rock mass it is also preferred that the jet have a circular cross-section so as to impinge on the surface 10 over a circular area.
Although specific mention has been made of the fracturing of brittle materials such as rock, it should be noted that the method and apparatus of the invention can be used to fracture other brittle materials, for instance concrete, as well.

Claims

1.
A method of fracturing brittle material which comprises applying compressive pulses to a selected area of a surface of the material which is to be fractured, the amplitude, frequency and/or duration of the compressive pulses and the area over which the pulses are applied to the surface being selected such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and interact with each other, within the material, to cause the material to fracture.
2.
A method according to claim 1 wherein the brittle material is rock.
3.
A method according to either one of the preceding claims wherein compressive pulses are applied to the surface of the material by means of a rigid body acting against the surface.
4.
A method according to claim 3 wherein the rigid body is reciprocated against the surface.
5.
A method according to claim 3 wherein the body is held in contact with the surface and a pulsed force is applied to the body such that the body, by transmission of the pulsed force, applies compressive pulses to the material.
6.
A method according to any one of claims 3 to 5 wherein the rigid body has a depth dimension, measured transverse to the surface, which is less than the lateral dimension of the body, measured parallel to the surface.
7.
A method according to claim 6 wherein the rigid body has a circular shape when viewed in a direction transverse to the surface.
8.
A method according to either one of claims 1 or 2 wherein compressive pulses are applied to the surface of the material by means of a pulsed liquid jet directed against the surface.
9.
A method according to claim 8 wherein the liquid jet has a circular shape when viewed in a direction transverse to the surface.
10.
A method according to claim 9 wherein the liquid jet is composed of liquid drops.
11.
A brittle material fracturing apparatus comprising pulse applying means for applying compressive pulses to a selected area of a surface of the material which is to be fractured, and control means for controlling the amplitude, frequency and/or duration of the compressive pulses such that compressive stresses induced in the material by the compressive pulses are not adequate to fracture the material but are such that tensile stresses induced in the material, around the boundary of the selected area, by the compressive pulses are transmitted into the material and combine with each other, within the material, to cause the material to fracture.
12.
An apparatus according to claim 11 wherein the pulse applying means comprises a rigid body arranged to apply compressive pulses to the surface of the material.
13.
An apparatus according to claim 12 wherein the pulse applying means comprises means for reciprocating the rigid body against the surface.
14.
An apparatus according to claim 12 wherein the pulse applying means comprises means for applying a pulsed force to the body while the body is held in contact with the surface such that the body, by transmission of the pulsed force, applies compressive pulses to the material.
15.
An apparatus according to any one of claims 12 to 14 wherein the rigid body has a depth dimension, measured transverse to the surface, which is less than the lateral dimension of the body, measured parallel to the surface.
16.
An apparatus according to claim 15 wherein the rigid body has a circular shape when viewed in a direction transverse to the surface.
17.
An apparatus according to claim 11 wherein the pulse applying means comprises means for generating a pulsed liquid jet and for directing the pulsed jet against the surface.
18.
An apparatus according to claim 17 wherein the pulsed liquid jet has a circular shape when viewed in a direction transverse to the surface.
19.
An apparatus according to claim 18 wherein liquid jet is composed of liquid drops.
PCT/IB2006/003393 2005-12-08 2006-11-29 Brittle material fracturing system WO2007066186A1 (en)

Applications Claiming Priority (2)

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ZA2005/09976 2005-12-08
ZA200509976 2005-12-08

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WO2007066186A1 true WO2007066186A1 (en) 2007-06-14

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111335861A (en) * 2020-03-20 2020-06-26 中煤科工集团重庆研究院有限公司 Safety protection method for ultrahigh-pressure hydraulic slotting device
CN111472740A (en) * 2020-04-22 2020-07-31 中煤科工集团重庆研究院有限公司 Ultrahigh-pressure water jet remote control system and method

Citations (10)

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Publication number Priority date Publication date Assignee Title
GB1195862A (en) * 1967-05-30 1970-06-24 Hughes Tool Co Well Drilling Methods and Apparatus Employing Pressure Variations in a Drilling Fluid.
US3708121A (en) * 1971-04-19 1973-01-02 Exotech Apparatus for forming pulse jets of liquid
US4074858A (en) * 1976-11-01 1978-02-21 Institute Of Gas Technology High pressure pulsed water jet apparatus and process
DE2752225A1 (en) * 1976-11-24 1978-06-01 Atlas Copco Ab METHOD AND DEVICE FOR BREAKING HARD, SPRODLE MATERIAL, e.g. ROCK
US4190202A (en) * 1978-07-03 1980-02-26 Institute Of Gas Technology High pressure pulsed water jet
US4610321A (en) * 1985-03-25 1986-09-09 Whaling Michael H Cavitating jet device
EP0221730A1 (en) * 1985-10-22 1987-05-13 Electric Power Research Institute, Inc Abrasive entrained high pressure fluid jet apparatus and method of use
US5291957A (en) * 1990-09-04 1994-03-08 Ccore Technology And Licensing, Ltd. Method and apparatus for jet cutting
US5927329A (en) * 1997-05-30 1999-07-27 Jetec Company Apparatus for generating a high-speed pulsed fluid jet
US5950736A (en) * 1997-09-26 1999-09-14 Apti Inc. Method and apparatus for improving drilling efficiency by application of a traveling wave to drilling fluid

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1195862A (en) * 1967-05-30 1970-06-24 Hughes Tool Co Well Drilling Methods and Apparatus Employing Pressure Variations in a Drilling Fluid.
US3708121A (en) * 1971-04-19 1973-01-02 Exotech Apparatus for forming pulse jets of liquid
US4074858A (en) * 1976-11-01 1978-02-21 Institute Of Gas Technology High pressure pulsed water jet apparatus and process
DE2752225A1 (en) * 1976-11-24 1978-06-01 Atlas Copco Ab METHOD AND DEVICE FOR BREAKING HARD, SPRODLE MATERIAL, e.g. ROCK
US4190202A (en) * 1978-07-03 1980-02-26 Institute Of Gas Technology High pressure pulsed water jet
US4610321A (en) * 1985-03-25 1986-09-09 Whaling Michael H Cavitating jet device
EP0221730A1 (en) * 1985-10-22 1987-05-13 Electric Power Research Institute, Inc Abrasive entrained high pressure fluid jet apparatus and method of use
US5291957A (en) * 1990-09-04 1994-03-08 Ccore Technology And Licensing, Ltd. Method and apparatus for jet cutting
US5927329A (en) * 1997-05-30 1999-07-27 Jetec Company Apparatus for generating a high-speed pulsed fluid jet
US5950736A (en) * 1997-09-26 1999-09-14 Apti Inc. Method and apparatus for improving drilling efficiency by application of a traveling wave to drilling fluid

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111335861A (en) * 2020-03-20 2020-06-26 中煤科工集团重庆研究院有限公司 Safety protection method for ultrahigh-pressure hydraulic slotting device
CN111472740A (en) * 2020-04-22 2020-07-31 中煤科工集团重庆研究院有限公司 Ultrahigh-pressure water jet remote control system and method

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