WO2002073120A1

WO2002073120A1 - Mining method

Info

Publication number: WO2002073120A1
Application number: PCT/IB2002/000684
Authority: WO
Inventors: Marthinus Johannes Potgieter
Original assignee: Brandrill Torrex (Proprietary) Limited
Priority date: 2001-03-09
Filing date: 2002-03-08
Publication date: 2002-09-19

Abstract

A method of breaking an exposed face of hard material such as rock in a mining operation for example comprises making at least one larger hole (2) a predetermined depth into the face; drilling a first set of spaced smaller bore holes (7) near to the larger hole/s a predetermined depth into the face, the axes of the smaller bore holes being arranged in a generally rectilinear configuration and extending generally in the same direction as the axis/es of the larger bore hole/s; using small charge blasting techniques in conjunction with the smaller bore holes to break the material defined between the smaller bore holes and the larger hole/s into the space created by the larger hole/s.

Description

MINING METHOD

INTRODUCTION TO THE INVENTION

This invention relates to a method of breaking a hard material such as rock and particularly but not exclusively to a mining method which is suited for use in continuous or semi-continuous mining.

BACKGROUND TO THE INVENTION

While the invention will be described with reference to its application in mining this should not be considered as restricting its application in any way.

The use of energetic materials such as propellants and explosives for fracturing and breaking of hard materials such as rock is well known and is of prime importance in mining today. In general terms, a hole is drilled or otherwise formed in the rock and the energetic material together with an initiator placed in the hole. In order to maximize efficiency, the hole is stemmed prior to initiation of the energetic material to reduce the amount of pressurized gases escaping from the hole. This method of breaking or fracturing rock and other hard materials is often referred to as "drill and blast method". The drill and blast method is used in both large scale operations such as bench blasting that may for example occur in open cut mining, and small charge blasting and boulder breaking that may occur in underground mines or in heavily populated areas say as part of a civil construction project.

When using the drill and blast method underground it may be necessary to provide free space/s into which the rock can expand when breaking takes place. Various excavating methods such as drilling and blasting, and drilling may be used to create such a space.

In mining and civil excavation work, so-called "small charge" blasting or controlled fracture techniques are being introduced as alternatives to conventional drill-and-blast, mechanical breaking, chemical expansion agent, and in some cases, hand methods. The term "small-charge blasting" as used herein includes any excavation method where relatively small amounts of an energetic substance (typically a few kilograms or less) are consumed for each hole in a rock breaking sequence as well as any method in which a pressurized fluid such as a gas, liquid, or foam, is sealed in the bottom of a drill hole to initiate and propagate a fracture. The term "sealing" refers to the partial or total blockage of the hole to impede the escape of the pressurized fluid from the hole. Examples of small charge blasting devices and methods are described in US Patents 5,765,923; 5,308,149 and 5,098,163.

In many small charge blasting methods, a machine is used to drill a hole into the rock to be broken and then a stemming bar or gun-like barrel is inserted into the hole. A pressurized working fluid, such as a gas, water, or foam, is released rapidly into a portion of the hole, usually the bottom portion. The pressurized fluid is typically generated by combustion of a propellant or explosive source, by electrical discharge into a conductive fluid, by inducing a rapid phase change or by mechanical compression of a working fluid. The stemming bar or barrel seals and stems the pressurized fluid in the hole bottom and thereby causes fracturing of the rock. Small charge blasting can be highly mechanized and automated to increase productivity, can permit excavation machinery to remain near the face due to reduced fly rock discharge, and can have a seismic signature that is relatively small because of the small amount of blasting agent used in the blasting sequence.

OBJECT OF THE INVENTION

An object of the invention is to provide a method of breaking hard material which may be used in a mining method in which rock is mined in a continuous or semi- continuous manner.

SUMMARY OF THE INVENTION

According to the invention a method of breaking an exposed face of hard material comprises:

(a) making at least one larger hole a predetermined depth into the face;

(b) drilling a first set of spaced smaller bore holes near to the larger hole/s a predetermined depth into the face, the axes of the smaller bore holes being arranged in a generally rectilinear configuration and extending generally in the same direction as the axis/es of the larger bore hole/s; and;

(c) using small charge blasting techniques in conjunction with the smaller bore holes to break the material defined between the smaller bore holes and the larger hole/s into the space created by the larger hole/s.

Further according to one aspect of the invention the larger holes may be drilled or cut using a suitable saw device.

Still further according to the invention where the larger holes have been drilled and have a circular bore and there are a plurality of larger bore holes the axes of the larger bore holes being generally parallel configuration with the adjacent bores intersecting with each other along their lengths.

Still further according to the invention the method includes the further steps of

(d) drilling a further set of spaced smaller holes the set being adjacent to the position originally occupied by the previous set; and

(e) using small charge blasting techniques to sequentially break the material defined between the further and previous sets of smaller holes into the space previously occupied by broken material.

Still further according to the invention steps (d) and (e) may be repeated.

Still further according to the invention the method includes the step of removing broken material from adjacent the face.

Still further according to the invention the small charge blasting technique utilizes a propellant change in each smaller hole and the technique is of the type known as penetrating cone fracture or PCF (Trade mark).

Still further according to the invention the method is a mining method and the hard material is rock.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention described by way of example only follows with reference to the accompanying drawings in which:

FIG 1 to 3 are front elevations of a working face including larger and smaller holes drilled in accordance with the method of the invention and showing sequential stages of a continuous mining method; and FIG 2 is an enlarged view of several larger and one smaller hole.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION WITH REFERENCE TO THE DRAWINGS

In this embodiment of the invention a continuous mining method utilizing small charge blasting techniques in the form of penetrating cone fracture (PCF) techniques is provided.

The mining method is intended for use in underground mines where rock (1) must be removed for example in stoping or developing operations.

The first step according to the method of this embodiment is to drill a plurality of generally parallel larger bore holes (2) with their axes in a generally rectilinear configuration extending in a generally upright manner.

As may be seen from figure 1 of the drawings the larger bore holes (2) are drilled such that the sides (3) of adjacent holes (2) intersect at 4, in this way providing a substantially continuous slot (5) of a predetermined depth.

Drilling of the holes (4) is effected using a drill rig and known technology. The drill rig hammer is pneumatically or hydraulically operated. Once the first of the larger holes (2) has been drilled the second and subsequent holes are drilled using the first and then the preceding hole as a guide for a guide assembly associated with the drill rig. In this way a reasonable degree of accuracy is achievable.

Adjacent to and spaced from the slot (5) made by the larger holes (2) a first set (6) of smaller diameter holes (7) is drilled. These holes are spaced substantially equally from each other and their axes are positioned to lie on a straight line which is spaced a predetermined distance from slot (5) and generally parallel thereto.

Further sets (8) of smaller holes (7) are drilled with each set being generally parallel to each other and to the first set (6). The sets (8) and (6) may have an equal spacing or a different spacing depending on the characteristics of the rock to be broken. They may also have a converging configuration.

It will be appreciated that sets (8) of smaller holes (7) can be continued to be drilled during the operations as described below.

When sufficient numbers of sets (6) and (8) of holes (7) had been drilled they are charged in known manner with a propellant cartridge and stemmed in known manner by utilizing particulate stemming, a stemming bar or the like. Charging of the holes (7) can form part of an ongoing procedure as new holes (7) are drilled.

Initiation of the propellant charges is sequentially by a set with the first set (6) being initiated first and the adjacent sets (8) being initiated sequentially thereafter.

Initiation of the propellant of the first set (6) of holes (7) breaks the rock associated with the first set (6) and particularly that located between the first set

(6) of smaller holes (7) and the slot (5). Because of the space provided by the slot (5) it is possible for the propellant to break the adjacent rock into that space whereafter removal of the rock can commence immediately.

Sequential initiation of the propellant located in the sequential sets (8) of holes

(7) in each instance breaks off the rock bounded by adjacent sets of parallel holes into the space created by the previous break. This space is maintained largely free by the continuous or intermittent removal of broken rock therefrom. This sequence of breaking steps is shown in figures 1, 2 and 3 with figure 2 indicating the effect of breaking using the first set (6) of smaller holes (7) and figure 3 indicating the effect of breaking using the next set (8) of holes (7).

It will be appreciated that with substantially continuous or semi-continuous drilling, charging, breaking and rock removal operations the invention provides for a continuous or semi-continuous mining method. Because of the nature of small charge blasting and particular PCF it is not necessary to clear the area where breaking is effected and this may thus be done on a substantially continuous basis.

Other embodiments are envisaged within the scope of the invention including other breaking methods and applications such as applications in tunneling and the breaking of other hard substances such as concrete.

Claims

1. A method of breaking an exposed face of hard material comprises:

(a) making at least one larger hole a predetermined depth into the face;

(a) drilling a first set of spaced smaller bore holes near to the larger hole/s a predetermined depth into the face, the axes of the smaller bore holes being arranged in a generally rectilinear configuration and extending generally in the same direction as the axis/es of the larger bore hole/s; and;

(b) using small charge blasting techniques in conjunction with the smaller bore holes to break the material defined between the smaller bore holes and the larger hole/s into the space created by the larger hole/s.

2. A method as claimed in claim 1 which includes the further steps of (d) drilling a further set of spaced smaller holes the set being adjacent to the position originally occupied by the previous set; and (e) using small charge blasting techniques to sequentially break the material defined between the further and previous sets of smaller holes into the space previously occupied by broken material.

3. A method as claimed in claim 2 in which steps (d) and (e) are repeated.

4. A method as claimed in any of the preceding claims in which the larger holes are cut using a suitable saw-type of device.

5. A method as claimed in any of claims 1 to 3 in which the larger holes are drilled.

6. A method as claimed in claim 5 in which there are a plurality of larger bore holes the axes of the larger bore holes being generally parallel with the adjacent bores intersecting with each other along their lengths.

7. A method as claimed in any of the preceding claims which includes the step of removing broken material from adjacent the face.

8. A method as claimed in any of the preceding claims in which the small charge blasting technique utilizes a propellant change in each smaller hole.

9. A method as claimed in any of the preceding claims in which the hard material is rock.

10. A mining method including a method as claimed in any of the preceding claims.

11. A method substantially as herein described with reference to the accompanying drawings.