System and method for underground blasting

Abstract

A simplified blasting system enables utilization of electronic delay detonators (23e) and pyrotechnic delay detonators (23p) in a simplified blasting set up. Both the electronic time delay detonators (23e) and the pyrotechnic delay detonators (23p) have shock tube fuses (32) which enables both types of detonators to be initiated by a common trunkline such as a low energy detonating cord trunkline (38). This system eliminates the need for separate firing systems, an electric firing system for electrically-initiated electronic delay detonators and a detonating cord trunkline for the non-electrically-initiated pyrotechnic delay detonators.

Claims

1. A system for blasting a geological formation to form therein a tunnel having a perimeter wall enclosing an interior space, the system comprising: a series of perimeter boreholes disposed in such geological formation in a pattern corresponding to such perimeter wall, with explosive charges disposed in respective ones of the perimeter boreholes; a series of interior boreholes disposed in such geological formation interiorly of the perimeter boreholes, with explosive charges disposed in respective ones of the interior boreholes; electronic delay perimeter detonators having shock tube fuses are disposed only in respective ones of the perimeter boreholes in signal-transfer communication with the explosive charges contained in the associated perimeter boreholes, and pyrotechnic delay interior detonators having shock tube fuses are disposed only in respective ones of the interior boreholes in signal-transfer communication with the explosive charges contained in the associated interior boreholes; the fuses of both the perimeter detonators and the interior detonators being connected in signal-transfer communication with a non-electric trunkline, whereby to initiate both the perimeter detonators and the interior detonators by an initiation signal transmitted via the trunkline.

2. The system of claim 1 comprising a single non-electric trunkline to which the fuses of the electronic delay detonators and the pyrotechnic delay detonators are connected.

3. The system of claim 2 wherein the non-electric trunkline comprises detonating cord.

4. The system of claim 1 wherein the non-electric trunkline comprises detonating cord.

5. A method for blasting a geological formation to form therein a tunnel having a perimeter wall enclosing an interior space, the method comprising the following steps: drilling a series of perimeter boreholes into the geological formation in a pattern corresponding to such perimeter wall; placing explosive charges in respective ones of the perimeter boreholes; drilling a series of interior boreholes into the geological formation interiorly of the perimeter boreholes; placing explosive charges in respective ones of the interior boreholes; emplacing electronic delay perimeter detonators having shock tube fuses only into respective ones of the perimeter boreholes in signal-transfer communication with the explosive charges contained in the respective perimeter boreholes; emplacing pyrotechnic delay interior detonators having shock tube fuses only into respective ones of the interior boreholes in signal-transfer communication with the explosive charges contained in the respective interior boreholes; connecting the fuses of both the perimeter detonators and the interior detonators in signal-transfer communication with a non-electric trunkline; and initiating both the perimeter detonators and the interior detonators by sending an initiation signal via the trunkline to the detonator fuses.

6. The method of claim 5 further comprising connecting the fuses of the perimeter detonators and the interior detonators to the same single, non-electric trunkline.

7. The method of claim 6 comprising utilizing detonating cord as the non-electric trunkline.

8. The method of claim 5 comprising utilizing detonating cord as the non-electric trunkline.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic elevation view showing a blasting system in accordance with the prior art for tunneling into a face;

(2) FIG. 2 is a schematic elevation view showing a blasting system in accordance with an embodiment of the present invention for tunneling into the same face illustrated in FIG. 1;

(3) FIG. 2A is a schematic cross-sectional view, with part broken away, taken parallel to a typical perimeter borehole of FIG. 2; and

(4) FIG. 2B is a view identical to that of FIG. 2A except that it is taken parallel to a typical interior borehole of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION AND SPECIFIC EMBODIMENTS THEREOF

(5) While efficient blasting operation is of course always important, in the case of underground mining operations it is especially critical during periods of relatively low prices for the ore, coal or mineral being mined. Whether in tunnel roadway construction or under-ground mining, efficient tunnel blasting operations depend in part on the quality of the perimeter profile of the tunnel (cavity) created by the explosion. That is, the perimeter of the cavity left by blasting the geological formation should not be excessively fractured or weakened, but desirably should be a clean void profile, one without excessive cracking or irregularities along the walls of the tunnel to be created by the blast. Other factors impacting efficiency include control of blast fragmentation to provide a desirable range of sizes in the muck pile resulting from the blast, and reduction of the cycle time between successive blasts. The cycle time includes the time required to set up each blast, including connecting fuses to the detonators to be emplaced within the boreholes, as well as removing the muck pile generated in an earlier blast, drilling and loading new boreholes, etc.

(6) As is well known in the art, electronic delay detonators (sometimes herein referred to simply as electronic detonators) provide much more accurate timing of initiation of the detonator than do pyrotechnic delay detonators (sometimes herein referred to simply as pyrotechnic detonators). Timing of explosions between different boreholes is desirably controlled within milliseconds of each other over a range of pre-selected delay periods. For example, it may be desired to have a 25 millisecond delay between detonations in certain boreholes, a 60 millisecond delay between detonations in other boreholes and, in some circumstances, a 1,500 millisecond, i.e., 1.5 seconds, delay between detonations in other boreholes. The range of deviation from the target detonation times of a series of detonators is referred to as the scatter range. Testing of long delay time pyrotechnic detonators such as LP16 pyrotechnic detonators revealed a scatter range of 150 milliseconds. In contrast, testing of comparable detonators, such as a SmartShot electronic LP16 detonator manufactured by DetNet South Africa Pty Ltd., demonstrated a scatter range of only 1 millisecond.

(7) In blasting a geological formation, detonators are respectively disposed in explosive charges contained in respective perimeter and interior boreholes drilled into the geological formation, for example, into a rock or ore formation, coal seam or the like. It is known to utilize electronic delay detonators disposed in the explosive charges contained in the perimeter boreholes and to use pyrotechnic delay detonators disposed in the explosive charges contained in the interior boreholes. The use of pyrotechnic delay detonators in the interior boreholes reduces the overall cost of the detonators without adversely affecting the formation of a clean, i.e., regular, profile of the cavity generated by the blast.

(8) Reducing to the extent possible the scatter range in the perimeter boreholes will minimize or at least reduce back breakage and overbreak and preserve the contour of the design profile of the cavity created by the blast (the blast cavity). The advantage provided by the orders of magnitude improvement in scatter range of electronic delay detonators as compared to the scatter range of pyrotechnic delay detonators is especially pronounced when poor ground conditions are encountered.

(9) A typical environment of use of an embodiment of the present invention is disclosed in the John Kovacs article Mine Development OptimisationAn Evolutionary Process published in connection with the 12.sup.th AUSIMM Underground Operator's Conference, Adelaide South Australia, Australia, 24-26 Mar. 2014. The entirety of this article is incorporated by reference herein and made part of this application. The author, John Kovacs, is a Senior Technical Consultant of DynoConsult, a company related to the assignee of this application, and authored the article based in part on information supplied to him by the inventor.

(10) In conducting blasting operations to form tunnels in mining operations and the like, it is desired that the resulting blast cavity have no or reduced back breakage and no or reduced overbreak while avoiding or minimizing underbreak. Underbreak is the failure to attain the desired diameter of the blast cavity in parts of the cavity and is problematic as it may require a second operation to remove unwanted rock protruding into the blast cavity. (As used herein, the term rock has its broadest meaning as comprising a geological formation which may be rock, an ore body, a coal seam, etc.) Overbreak is the unwanted removal of rock beyond the planned diameter of the blast cavity in parts of the cavity and is problematic as it often requires reconstitution of the planned diameter with concrete or the like. Obviously, the occurrence of overbreak or underbreak is a serious problem as it slows production and requires additional work to rectify the situation. Back breakage is cracking of the rock adjacent to the perimeter of the blast cavity and is also problematic as it weakens the structure around the blast cavity. Reducing back breakage by largely confining the effect of the blast to the desired profile of the resulting blast cavity reduces the amount of ground support structure which may be required to reinforce the geological formation surrounding the blast cavity. Ground support structure includes installation of timber or steel support columns, or designing the blast to leave behind support columns of the rock being blasted. Avoiding the need to supply ground structure, as well as the attainment of more closely controlled size range of the rock in the muck pile, are advantages of using electronic detonators in the perimeter boreholes.

(11) The use of pyrotechnic delay detonators in the interior boreholes provides a significant cost savings as compared to using electronic detonators throughout. However, the use of both electronic and pyrotechnic detonators in the same blast set-up complicates the fuse system because the prior art systems required that the electronic detonators be shot with electric wire fuses and the pyrotechnic detonators be shot with shock tube fuses. The resulting hybrid wire/shock tube fuse system complicates installation, requires more extensive training of personnel and increases the chances of error during se-up of the blast.

(12) FIG. 1 schematically shows a prior art blasting system installed through face 20 of a geological formation g in which a tunnel 22 (which may, but need not, be a substantially horizontal tunnel) is to be blasted. Face 20 may be, for example, an underground mine face. Tunnel 22 may be a prospective tunnel or it may be an extension of an already existing tunnel. In any case, the blast cavity resulting from the blast will define a tunnel 22 having a nearly flat floor 22a, opposite sidewalls 22b, 22c and a concave arched roof 22d. The boreholes of FIGS. 1 and 2 are numbered to correspond to the delay Period Number of the detonators emplaced in the boreholes. The following Table shows the delay period in milliseconds (ms) for various delay detonators.

(13) TABLE-US-00001 TABLE Period No. Delay Time (ms) 1 500 2 800 3 1100 4 1400 5 1700 6 2000 7 2300 8 2700 9 3100 10 3500 11 3900 12 4400 13 4900 14 5400 15 5900 16 6500 17 7200 18 8000

(14) A plurality of perimeter boreholes 15, 16, 17 and 18 have respective electronic delay detonators disposed therein. The delay periods of the detonators respectively disposed in the perimeter boreholes 15, 16, 17 and 18 are, as shown (in milliseconds) in the above Table, 5.9, 6.5, 7.2 and 8.0 seconds. The perimeter boreholes 15, 16, 17 and 18 are positioned to approximately define the desired profile of tunnel 22. The perimeter boreholes (and the interior boreholes as well) are substantially parallel to the longitudinal axis of the blast cavity, i.e., the tunnel 22, and so are substantially horizontal in a horizontal tunnel. As is conventional, face 20 has drilled into it a burn/cut hole B to provide, as is well known, a point of relief, that is, to provide room for shifting of rock during the initial stage of detonation.

(15) A plurality of interior boreholes 1-8 and 10-14 are numbered to correspond to the delay Period Numbers of the detonators disposed in the interior boreholes. Thus, the delay periods of the detonators disposed in the interior boreholes vary, as shown (in milliseconds) in the above Table, from 0.5 seconds (Period No. 1) to 5.4 seconds (Period No. 14). The interior boreholes are positioned within the perimeter defined by the perimeter boreholes. The selected delay periods of detonators emplaced in the boreholes as described above is of course specific to a given case. Obviously, different delay periods and combinations of delay periods may be selected depending on the nature of the geological formation being blasted to form a tunnel of prescribed dimensions.

(16) Each of the perimeter boreholes contains an explosive charge having embedded within it one or more electronic delay detonators whereas each of the interior boreholes contains an explosive charge and one or more pyrotechnic delay detonators. A harness wire 24 is connected via electric fuse wires 26 to electronic detonators respectively disposed within the perimeter boreholes. A relay electronic detonator 28 is connected via one of the electric fuse wires 26 to harness wire 24 and is detonated in order to initiate the detonating cord trunkline 30 which itself is connected by a plurality of shock tube fuses 32 to respective pyrotechnic delay detonators embedded within the explosive charges respectively disposed within the interior boreholes. In order to initiate the blasting sequence, a firing signal from an electric blasting generator (not shown) sends an appropriate electric current through harness wire 24 thence via electric fuse wires 26 to the electronic detonators respectively disposed in each of the perimeter boreholes and to relay detonator 28. Initiation of relay detonator 28 initiates detonating cord trunkline 30 which in turn initiates each of shock tube fuses 32 to initiate the pyrotechnic detonators respectively disposed in the interior boreholes.

(17) The prior art scheme illustrated in FIG. 1 is seen to require two separate firing systems respectively comprising electric harness wire 24 and detonating cord trunkline 30, as well as the extension of electric harness wire 24 to fire a relay electronic delay detonator 28. The latter must be connected in signal transmission relationship to detonating cord trunkline 30. Setting up this complex wiring scheme is time-consuming, requires maintaining in stock electric wire for electric harness wire 24 and detonating cord for detonating cord trunkline 30, electronic detonators having electric fuse wires 26 and pyrotechnic detonators having shock tube fuses 32. In addition, the relatively complex nature of the arrangement requires well trained personnel and is nonetheless more susceptible to connection errors, and therefore failures, than is the simplified and improved system of the present invention, an embodiment of which is described below in connection with FIG. 2.

(18) FIG. 2 schematically shows the same face 20 of geological formation g illustrated in FIG. 1, and so the description of structures identically numbered to those of FIG. 1 is not repeated. The face 20 of FIG. 2 is drilled identically as in FIG. 1, with interior boreholes 1-8 and 10-14, perimeter boreholes 15, 16, 17 and 18, and burn/cut hole B. As is the case in the prior art arrangement of FIG. 1, the perimeter boreholes 15-18 are respectively loaded with explosive charges within which are embedded electronic delay detonators, and the interior boreholes similarly have therein explosive charges within which are embedded one or more pyrotechnic delay detonators. However, the embodiment of the present invention illustrated in FIG. 2 differs from the prior art arrangement of FIG. 1 in that the electronic delay detonators have shock tube fuses 40 instead of electric wire fuses. Electronic delay detonators suitable for use in the present invention and having shock tube fuses are sold under the trademark DigiDet by DetNet South Africa (Pty) Ltd. A signal-transmitting detonator 34 has a fuse 34a connected to a signal-initiating device (not shown). Fuse 34a may be a shock tube fuse. Signal-transmitting detonator 34 is connected in signal-transmitting relationship with a detonating cord trunkline 38 which is connected by shock tube fuses 40 both to electronic delay detonators in the perimeter boreholes, as well as to pyrotechnic delay detonators in the interior boreholes. The electronic delay detonators are embedded in respective explosive charges disposed in respective ones of the perimeter boreholes as exemplified by FIG. 2A, and the pyrotechnic delay detonators are embedded in respective explosive charges disposed in respective ones of the interior boreholes as ex-emplified in FIG. 2B. Initiation of detonating cord trunkline 38 by signal-transmitting detonator 34 initiates all shock tube fuses 40 to initiate the detonators contained in both the perimeter and interior boreholes.

(19) FIG. 2A shows a typical perimeter borehole n formed in geological formation g and containing an explosive charge c within which is embedded an electronic delay detonator 23e from which extends a shock tube fuse 32. Shock tube fuse 32 exits from perimeter borehole n at face 20 and is connected to detonating cord trunkline 38.

(20) FIG. 2B shows a typical interior borehole n which is substantially identical to the perimeter borehole of FIG. 2A except that a pyrotechnic delay detonator 23p is utilized. Pyrotechnic delay detonator 23p is embedded within an explosive charge c and its shock tube fuse 32 exits from interior borehole n at face 20 and is connected to detonating cord trunkline 38.

(21) The blasting system of FIG. 2 is seen to be greatly simplified relative to the prior art system illustrated in FIG. 1. Instead of having to wire both electrical and detonating cord systems, only a single detonating cord trunkline is required. This reduces the items which must be kept in stock and greatly simplifies the set-up procedure, thereby both lessening training requirements and greatly reducing the prospects for error. Set-up time is also reduced.

(22) When utilizing electronic delay detonators in the perimeter boreholes, control of the perimeter of the void created by the blast was so precise that half-barrel markings were noticeable in the walls of the resulting blast cavity. These markings are the longitudinal half of perimeter boreholes and their presence at the edge of the void created by the blast shows how accurately the void perimeter was formed. This accuracy was attained despite the use of pyrotechnic delay detonators in the interior boreholes.

(23) While the invention has been described in detail with reference to a specific embodiment, it will be appreciated that numerous variations may be made to the described embodiment, which variations nonetheless lie within the scope of the present invention.