U.S. patent number 3,877,373 [Application Number 05/422,656] was granted by the patent office on 1975-04-15 for drill-and-blast process.
This patent grant is currently assigned to E. I. du Pont de Nemours and Company. Invention is credited to Oswald R. Bergmann, David L. Coursen.
United States Patent |
3,877,373 |
Bergmann , et al. |
April 15, 1975 |
Drill-and-blast process
Abstract
Working, e.g., excavating, a geological mass by a succession of
substantially continuous drill-load-blast sequences, each sequence
comprising drilling a hole in the mass, placing a charge of
condensed secondary explosive in the hole, and initiating the
charge by projecting propagative energy, e.g., the kinetic energy
of a high-velocity projectile, through an inactive medium, e.g.,
the atmosphere, to the charge from a location which confronts, and
is separated from, the hole in a manner such that energy is
released into the charge at a rate sufficiently high to cause
detonation thereof. An apparatus including drilling means,
explosives-delivery means, and means for projecting energy, e.g., a
gun, mounted on support means that preferably can be moved so as to
position the drilling means, explosives delivery means, and
energy-projection path sequentially on substantially a common
axis.
Inventors: |
Bergmann; Oswald R. (Cherry
Hill Township, NJ), Coursen; David L. (Newark, DE) |
Assignee: |
E. I. du Pont de Nemours and
Company (Wilmington, DE)
|
Family
ID: |
27025704 |
Appl.
No.: |
05/422,656 |
Filed: |
December 7, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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878005 |
Nov 19, 1969 |
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Current U.S.
Class: |
102/312; 102/201;
299/13 |
Current CPC
Class: |
F42D
1/045 (20130101); F42D 3/04 (20130101); E21C
37/00 (20130101); E21C 41/00 (20130101); F42D
1/04 (20130101); E21D 9/006 (20130101) |
Current International
Class: |
E21C
37/00 (20060101); F42D 3/00 (20060101); E21D
9/00 (20060101); F42D 1/00 (20060101); E21C
41/00 (20060101); F42D 3/04 (20060101); F42D
1/04 (20060101); F42D 1/045 (20060101); F42d
003/04 () |
Field of
Search: |
;102/21-24 ;42/1R ;89/1R
;86/2C ;299/13 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Dept. of Army Technical Manual, TM9-1910, Military Explosives, pp.
47-49 relied on, April, 1955 UF523A51 1955 C.4..
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Primary Examiner: Pendegrass; Verlin R.
Parent Case Text
This is a continuation, of application Ser. No. 878,005 filed Nov.
19, 1969, and now abandoned.
Claims
We claim:
1. A process for advancing an underground rock face which comprises
performing a plurality of substantially continuous drill-load-blast
sequences substantially concurrently as a group at different
locations in the rock, followed by other such groups of sequences
in a manner such as to produce a substantially continuous
succession of groups of sequences, the number of said sequences
carried out substantially concurrently as a group being less than
about 35% of the total number of sequences in said succession, each
substantially concurrent group of sequences producing a portion of
a new face and said succession of groups producing an entire new
face, each of said sequences comprising the steps of (a) drilling a
hole in the rock from the face to be advanced, (b) placing a charge
of condensed, exclusively secondary explosive in the hole, and (c)
initiating the explosive charge in the hole by causing energy to be
released into the charge by the impact of a projectile with the
charge, by the impingement of a focussed laser beam onto the
charge, or by the discharge of a spark from an electrode to the
charge, said energy being projected to the charge from a location
which is separated from the hole by a distance of less than about
30 feet and being released into the charge at a rate sufficiently
high to cause detonation thereof, and a separate pulse of energy
being released for the initiation of each charge.
2. A process of claim 1 wherein said plurality of sequences in a
group are synchronized in a manner such that Steps (a) and (b) are
completed in all of the sequences in said group before Step (c) is
begun in any of said sequences.
3. A process of claim 1 wherein said condensed secondary explosive
is dynamite.
4. A process of claim 1 wherein said condensed secondary explosive
is a water-bearing explosive.
5. A process of claim 1 wherein said energy is released into the
charge by the impact of a projectile therewith.
6. A process of claim 5 wherein said projectile is inert.
7. A process of claim 5 wherein the velocity of said projectile
upon impact is at least about 1,500 feet per second.
8. A process of claim 1 wherein the energy is released into the
charge by impingement of the focussed output of a laser on said
charge.
9. A process of claim 1 wherein the compressive strength of the
rock is at least about 15,000 psi.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved drill-and-blast process
wherein a secondary explosive charge is loaded into a drill hole
and then initiated therein by the rapid release of energy projected
to the charge through an inactive medium, e.g., the atmosphere, and
to a drill-and-blast module useful for carrying out the process in
a rapid, cyclic manner.
Drill-and-blast processes have long provided man with a powerful
tool for performing useful work, affording the energy required, for
example, for excavation operations of various kinds, i.e.,
operations in which material is dug out and removed at or below the
earth's surface either to form a useful cavity, e.g., in tunneling,
or to derive profit from the removed material, e.g., in mining. The
explosive energy afforded by drill-and-blast processes also has
been utilized for other purposes, e.g., in seismic prospecting to
provide information regarding the location of useful geological
strata, such as gas- or oil-bering strata. At the present time
there is an ever-increasing need for prospecting and excavation
operations, and especially for underground excavations, e.g., for
constructing water and vehicle tunnels, parking spaces, and
military defense sites, and for exploiting very large mineral
deposits under conservation constraints. However, significant
reductions in cost and increases in the sustained rate of working,
e.g., tunnel advance, are needed if prospecting and excavation are
to be utilized effectively to meet the challenges of urbanization
and natural resource conservation.
In the conventional drill-and-blast method of working a geological
mass such as rock for excavation thereof, holes are drilled in a
predetermined pattern in the rock; after all of the holes have been
drilled, a secondary explosive charge is loaded therein, usually by
hand; an initiating device, i.e., a blasting cap or primer, is
placed in contact with the charge in each hole, or with detonating
cord leading to the charge, and connected to a remotely located
common actuating device such as a blasting machine; and the charges
thereafter are initiated by energizing of the actuating device. In
underground excavation, after a ventilation period or "smoke time,"
which is necessary to clear the airborn fumes and dust produced as
a result of such a blast, the round is concluded with the mucking
operation, i.e., the loading and transporting of the disintegrated
material (muck) from the excavation to a disposal area. This cycle
is then repeated.
In recent years, mechanical excavators, or "moles," have been
developed which are capable of boring a tunnel or shaft, or mining
out ore, by means of a rotating cutterhead driven by electric or
hydraulic motors, the muck being picked up by a wheel which
discharges it onto a belt conveyor that carries it back behind the
machine. At their present respective levels of technological
development, mechanical excavators have a greater driving
capability per day in weak and medium-strength rock than the
drill-and-blast method. This is due chiefly to the fact that the
mechanical method involves a near-continuous operation, although
delays are encountered because of changes in geological conditions,
mechanical and electrical failures, the need for frequent cutter
changes, etc.
There are serious limitations to the use of mechanical excavators,
however. One of these is that mechanical excavators cannot be used
effectively in hard and/or abrasive rock, e.g., rock having a
compressive strength of more than about 15,000 psi or a Moh's Scale
hardness greater than about 5. Rock of this nature is presently
encountered in about one-third of the excavation projects, and it
is expected that this percentage will increase as future public
construction demands force excavations to be made at greater depths
and in areas of known hard-rock conditions. A second limitation is
that the initial investment in mechanical excavators is high, and
consequently their use in many short tunnels cannot be economically
justified even though the excavator would be technically capable of
driving the tunnel. Furthermore, investment in a new excavator
usually is necessary in each mechanical tunnel-driving project
because the different diameter requirements and geological
conditions encountered from project to project necessitate the
designing of a machine for each individual tunnel, even though
machines which have been used in completed projects may still have
some useful life. With respect to mining operations, continuous
mining machines sometimes are too large and inflexible to permit
the efficient mining of narrow ore seams. For reasons such as
these, the drill-and-blast method of excavation is the method of
choice in many operations at the present time.
As now practiced, however, the drill-and-blast method of excavation
has inherent delays in each cycle which cause the rate of heading
advance, or driving capablity per day, to be low. The low rate of
advance, requirement of large labor crews, and costs of expended
materials make the total excavation costs high. Cycle delays and
high manpower requirements are inherent in the procedures presently
employed to prepare the formation for the disintegration step,
i.e., the blast, and by the condition of the environment in the
work area during and after blast. The preparative operations
include moving the drilling equipment up to the face, drilling the
holes, moving back the drilling equipment, charging the holes with
secondary explosive, placing assemblies (i.e., blasting caps)
containing primary explosive charges in contact with the secondary
explosive, or in contact with detonating cords leading to the
secondary explosives in the holes, and connecting the assemblies
that contain primary explosive charges to a source of energy so
that a continuous energy-storing, as well as energy-transmitting,
circuit is formed from a remotely located common energy source,
e.g., a blasting machine or power line, to the secondary explosive
charges. The initial energy, e.g., an electrical pulse emitted by
the common energy source, thus is transmitted to the secondary
explosive through an active medium, i.e., one containing stored
energy (the primary explosive), which is used in turn to initiate
the secondary explosive.
Because of the time required to drill, load, and otherwise prepare
the holes for blasting, it has been necessary, in the interest of
efficiency, to design the rounds (the drill hole arrangement at the
face) to pull large cross-sectional areas of the face in one blast,
e.g., the full cross-sectional area (full-face method), or a large
part of it (top heading and bench method). Rounds of this size
require a large number of drill holes and consequently the
detonation of a large number of explosive charges. For example, for
a full-face round in a typical railroad tunnel 28 feet high and 21
feet wide, about 900 pounds of explosive may be detonated per
round. Because of the pressure and rock-throw effects resulting
from blasts of this magnitude, the immediate blast area must be
cleared of personnel and equipment. This is the reason why remote
emission of the initiation pulse, and therefore connection of all
of the charges into an energy-transmitting circuit, have been
necessary.
Large single blasts such as have been employed heretofore can
produce strong ground vibrations which may be detrimental to
surrounding structures. In addition, such blasts produce large
quantities of airborn fumes and dust which must be exhausted before
personnel can move in with mucking equipment. Usually fans must be
operated for a period of at least about twenty minutes to clear the
area so that work can be resumed. After the "smoke time," the
mucking machine is moved in, the round is mucked out, and the
mucker is moved out.
Drilling procedures have been made more efficient in recent years
with the introduction of modern drilling machines, such as
pneumatic percussive drills mounted on a drill jumbo (a mobile work
platform), and drill hole loading time has been reduced
considerably with the availability of such devices as a pneumatic
cartridge loader havng a semiautomatic breech-piece for feeding
cartridges into a loading tube continuously, and a robot loader for
moving the tube in the drill hole. However, the efficient use of
equipment and manpower still has necessitated large-round blasts,
and delays therefore have remained considerable owing to the time
required for moving the drilling equipment up to the face to be
blasted; moving it back before the blast; moving the loading
personnel and equipment in and out; performing the manual
operations of connecting the blasting leads (cap leg wires, or
lengths of detonating fuse or safety fuse) to form a blasting
circuit to the remote actuating device; and "smoke time."
The use of blasting caps in a remotely actuated large blasting
circuit to initiate the charges in the drill holes in
drill-and-blast processes thus can be seen to be uneconomical from
the viewpoint of expenditure of time and manpower. In addition,
since the caps are consumed in the blast, their cost also is a
factor to be considered. Also, with respect to safety
considerations, the use of blasting caps is not entirely without
risk since they contain a primary (highly sensitive) explosive
charge adjacent to a less-sensitive secondary explosive base
charge, thereby forming a continuous reaction train from the
primary explosive in the cap to the secondary explosive charge in
the drill hole when the cap has been placed in initiating position.
Thus it is most important to guard against accidental ignition of
the ignition charge, adjacent to the primary explosive charge, in
the positioned cap as well as in caps located in a storage area or
in transit to the charge in the drill hole. Also, because of the
interdependency of all of the charges in a round with respect to
electrical initiation, once they have been connected, accidental
generation of voltage at any one location in the electric circuit
is likely to set off all of the charges. Apart from considerations
of safety and materials cost, however, another serious drawback to
the initiation methods now employed in blasting is that they are
not amenable to mechanization and efficient operation in small
blast cycles and, consequently, represent a formidable barrier to
the performance of drill-and-blast operations on a rapid,
near-continuous basis, i.e., in a substantially continuous cyclic
succession of uninterrupted drill-load-blast sequences, a manner of
operation which obviously is the most reasonable approach to
decreasing cost and time. Such mechanization and small-blast-cycle
operation not only would greatly increase the efficiency of
drill-and-blast excavation operations, but also would provide an
efficient means of utilizing the drill-and-blast technique for the
common-depth-point method of seismic prospecting. Particularly in
areas where the surface layer (e.g., fractured rock, coral,
unconsolidated ice or frozen ground) strongly absorbs seismic
energy, the use of explosives in drill holes in the latter method
would provide higher-energy signals and information concerning
deeper layers than the gas exploders currently in use.
SUMMARY OF THE INVENTION
This invention provides an improved drill-and-blast process in
which secondary explosive charges confined in drill holes in a
geological mass to be worked, e.g., rock, are initiated by the
rapid release therein of energy projected to the charges in the
drill holes through an inactive medium, e.g., the atmosphere,
rather than via a continuous reaction train containing a primary
explosive. More specifically, the process of this invention
comprises performing a succession of substantially continuous
drill-load-blast sequences, each sequence at a single location in
the mass different from the locations where other sequences are
performed, and each sequence comprising the steps of (a) drilling a
hole in the mass; (b) placing a charge of condensed secondary
explosive in the hole so that the explosive is confined and
supported by the wall of the hole; and (c) initiating the explosive
charge in the hole by projecting propagative energy, e.g., the
kinetic energy of a high-velocity projectile, through an inactive
medium, e.g., the atmosphere, to the charge from a location which
confronts, and is separated from, the hole in a manner such that
energy is released into the charge at a rate sufficiently high to
cause detonation thereof. Preferably, and especially when the
process is an excavation process, the succession of sequences is
also substantially continuous, i.e., the process is comprised of
substantially continuous drill-load-blast sequences in
substantially continuous succession.
"Propagative energy" is energy which derives from the intensity and
time dependence of the dynamic physical phenomena utilized to
transport it from one place to another, e.g., the energy which
derives from the intensity and time dependence of an
electromagnetic field or of shock wave pressure, the velocity of a
projectile, etc.
The term "inactive medium," as used herein to describe the
environment through which the propagative energy is projected to
the charge, denotes a medium, e.g., the atmosphere, which contains
no stored energy of its own, thus making no energy contribution to
the initiation process. Thus, the energy is projected into the
charge in the absence, or without the intervention, of a primary
explosive in a physically continuous reaction train with the
charge, or, more specifically, in the absence of a blasting
cap.
A "sequence" as used herein denotes a drill-load (charge
placement)-blast (charge initiation) operation at a given location
(drilling a hole, loading the same hole with explosive, and
initiating the explosive in the same hole). The sequence is
followed by one or more other such sequences at different
locations, thereby producing a "succession" of sequences or
cycles.
The term "substantially continuous," when used herein to describe
the drill-load-blast sequences, means that the steps of the
sequence follow closely one upon the other without the intervention
of additional steps which are not directly concerned with
operations performed on the mass being worked. For example, the
sequences are not interrupted for the length of time required to
move vehicular equipment back away from the formation and move
different equipment up, connect blasting leads to the explosive
charges, and move all equipment and personnel out of the area to a
remote position. A "substantially continuous" sequence in the
present process typically is one in which the total "dead time,"
i.e., the time between drilling and charge placement steps plus the
time between charge placement and charge initiation steps, is only
on the order of five minutes or less.
The term "substantially continuous" when used herein to describe
the succession of sequences in a preferred embodiment, has
generally the same connotation as described above for continuity of
sequence steps. That is, sequence follows closely upon sequence,
either before or after completion of the previous sequence, from
the first to the last in the succession, without delays or
interruptions between the last step of one sequence (blast) and the
first step of the next (drill) to exhaust the area of fumes or move
equipment up to the mass from a remote position. A "substantially
continuous" succession of sequences in the present process
typically is one in which the "dead time," i.e., time between
sequences, is less than about 10 minutes, dead time between
sequences in the present process, when used for excavating, usually
being much less, i.e., less than about 1-2 minutes.
In a most efficient embodiment of the process, a number of
sequences are carried out substantially concurrently as a group or
set of sequences, followed by one or more other such groups in,
usually substantially continuous, succession. In this case, each
"cycle" of the cyclic process or succession is a cycle of groups of
sequences. The term "substantially concurrently" as applied herein
to the performance of the sequences in a group denotes that all of
the sequences are begun and completed over a selected time period
after which another cycle begins. The term is not used to imply
that the same step is carried out in every sequence of the group at
precisely the same time.
All drill-load-blast sequences, and preferably also cyclic
successions of sequences or groups of sequences, are carried out
substantially continuously, as explained above. However, the
specific time employed per sequence and succession, and the time
pattern in which the sequences are performed relative to other
sequences can vary depending on such factors as the equipment
available, working space available, etc. One or more drills, one or
more explosive loaders, and one or more energy-projecting devices
can be employed.
For carrying out the process more rapidly and efficiently,
especially in constricted areas, a novel drill-and-blast module
also is provided by the present invention, the module comprising,
in combination,
a. drilling means comprising an elongated member, e.g., a drill
steel, having a bit at one end, and positioned on support means in
axially movable relationship therewith;
b. explosives-delivery means for delivering explosive into a hole
made by the drilling means, the explosives-delivery means being
positioned on support means in axially movable relationship
therewith and in predetermined alignment with respect to the
drilling means, the explosives-delivery means comprising a tube
having one discharge end and an explosives feed end; and
c. means for projecting energy, e.g., a gun, for initiating
explosive delivered into a hole by the explosives-delivery means,
the energy-projecting means being positioned on support means in
predetermined alignment with the drilling means and
explosives-delivery means; the drilling means, explosives-delivery
means, and energy-projecting means being (1) supported in a manner
such that the bit of the drilling means, discharge end of the
explosives-delivery means, and energy-exiting end of the
energy-projecting means, e.g., a gun muzzle, are located near a
common, operating end, and (2) positioned, or adapted to be
positioned, in a manner such that the energy-projecting means
projects energy on a path that leads into an explosive charge
delivered by the explosives-delivery means into a hole drilled by
the drilling means; the movable relationship of the drilling means
and explosives-delivery means with the support means being such
that the bit of the drilling means and the discharge end of the
explosives-delivery means extend sequentially beyond all other
components of the module in an axial direction at the operating
end.
The module, when positioned near a mass of material to be blasted,
e.g., a rock face or the earth's surface, and suitably energized,
in rapid sequence drills a hole in the material, loads explosive
into the hole, and initiates the explosive by the projection and
release of energy into the explosive, preferably by projectile
impact, and can repeat the sequence at any desired number of other
locations. For this reason, the three working components, i.e., the
drilling means, explosives-delivery means, and energy-projecting
means, are positioned, or adapted to be positioned, in a manner
such that the explosives-delivery means delivers explosive into a
hole made by the drilling means, and the energy-projecting means
projects energy on a path that leads into the explosive in the
hole. In other words, the longitudinal axes of the drilling means,
explosives-delivery means, and energy-projecting means pass,
simultaneously or sequentially, through substantially a common
point in space located a desired distance outside the module near
the operating end corresponding to the location at which the drill
bit initially penetrates the formation, i.e., at the mouth of the
drill hole. By "substantially a common point" we mean that at the
desired location outside the module, i.e., at the mouth of the
drill hole, on a normal to the drill axis the three longitudinal
axes all pass through the same point, or the axes of the
explosives-delivery means and energy-projecting means pass through
points which are within one drill hole radius from the point
through which the drill passes (i.e., on the axis of the drill
hole). This passage through substantially a common point may be
accomplished by positioning the three working components on axes
which converge at the desired point, or by providing positioning
means, e.g., and indexing mechanism, to cause the axes
substantially to coincide sequentially. The converging
non-coincidable design, while feasible, is not preferred, however,
since it requires a precise positioning of the module with respect
to distance from a point on the mass to be worked and precise
maintenance of the same distance through the entire drilling,
loading, and initiation sequence. Therefore, in a preferred
embodiment, the support means cooperate(s) with a positioning means
adapted to sequentially position, e.g., by pivoting and/or sliding,
the drilling means, explosives-delivery means, and
energy-projecting means on substantially a common longitudinal
axis.
The "longitudinal axes" of the drilling means, explosives-delivery
means, and energy-projecting means which sequentially coincide or
converge as described are the longitudinal axis of the elongated
member, e.g., the drill steel, to which the bit is attached, the
longitudinal axis of the bore of the delivery tube, and the axis
along which the energy is projected from the energy-projecting
member, e.g., the longitudinal axis of a gun bore.
The term "module" is used herein to denote an apparatus which is a
functional unit or assembly of components adapted to be operative
as a unit within a larger assembly in which it can be interchanged
with another such unit and, if desired, operated together with
other such units.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing, which illustrates specific embodiments
of the invention,
FIGS. 1 through 4 are longitudinal cross-sectional views of a
typical module of this invention through a given, substantially
vertical plane (with respect to the horizon) at different
times;
FIGS. 1A through 4A are cross-sectional views of the module shown
in FIGS. 1 through 4, respectively, as observed through a given
vertical plane substantially normal to the plane of view of FIGS. 1
through 4 and intersecting said plane at the location indicated by
dotted line A-A' and viewed in the direction of the arrows;
FIG. 5 is a longitudinal cross-sectional view of a portion of a
module of this invention in which the energy-projecting means
differs from that shown in FIGS. 1 through 4; and
FIG. 6 is a front, partially plan, view of a face in a geological
mass being worked in small blast cycles according to the process of
this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present process, charges of condensed secondary explosive
are confined in drill holes and thereafter are initiated, each by
rapidly releasing energy into the charge by projecting propagative
energy to the charge through an inactive medium, e.g., the
atmosphere. This mode of initiation is differentiable from those
which employ a primary explosive in a continuous reaction train
with the charge, and from that which is employed in drill-and-blast
processes as commonly practiced, i.e., the initiation of the
charges in all of the drill holes by a common energy emission i.e.,
an electrical pulse or flame, generated remote from the drill
holes, the multiple charges having previously been joined together
in a single energy-transmitting circuit. Use of the method of
initiation employed in the present process eliminates the
time-consuming operations required to prepare conventional
electrical or non-electrical blasting circuits, reduces manpower
requirements, and permits excavation processes to be effected with
considerably smaller blast cycles than heretofore. In addition, the
hazards of accidental detonation which are encountered when
sensitive primary explosive compositions, as in blasting caps, are
present in continuous reaction trains with the charges are
avoided.
An efficient drill-and-blast process requires that as much as
possible of the available explosive energy be manifest in the form
of high pressure working on the formation surrounding the drill
hole, e.g., to break the formation. This is accomplished by having
as much of the explosive as possible surrounded by the formation
with avoidance of any substantial intervening compressible layer,
e.g., an air annulus, between the explosive and the formation. For
this reason, the explosive charge is positioned within a drill hole
so that it is confined by the formation and contacts the walls of
the hole sufficiently to be supported thereby. In each
drill-load-blast sequence, the hole is drilled at the selected
location, and then the explosive is loaded into the drilled hole,
by any of the various ways that are suitable for the type of
explosive charge employed, and the length and direction of the
hole. For example, if the charge consists of one or more explosive
cartridges or packages, or a solid explosive in bulk, pneumatic
loading may be employed. Water gel explosives can be pumped in. The
velocity of loading should be low enough that the explosive does
not detonate spontaneously by impact with the formation or with a
previously loaded cartridge. Such spontaneous detonation during
loading is avoided since it can destroy the loading equipment.
The selection of the explosive to be used in the present process is
made, as in any blasting process, on the basis of safety,
performance, convenience, and economics. To provide the pressures
required in hard rock, the explosive should be a condensed, e.g.,
solid (cast or packed powder), semisolid, or liquid, detonating
explosive, and it should be relatively insensitive to heat and mild
shock, i.e., it is a secondary explosive rather than a primary
explosive. A primary explosive is one which detonates when brought
in contact with a flame or incandescent wire, whereas secondary
explosives require, at least in practical commercial application,
the use of a detonator and frequently a booster for initiation of
detonation (Melvin A. Cook, The Science of High Explosives,
Reinhold, 1958, pp. 1-4). Representative secondary explosives
include dynamites, ammonium nitrate/fuel oil mixtures, TNT, PETN,
nitrostarch, and the currently popular water-bearing explosives as
exemplified in U.S. Pat. Nos. 3,202,556, 3,355,336, 3,431,155 and
3,444,014. The ingredients of the explosive composition can be
pre-mixed and the mixture loaded into the holes, or, where
feasible, as in the case of ammonium nitrate prills and fuel oils,
the ingredients can be mixed during loading by feeding into a
common stream, or loaded separately and mixed in the holes. The
explosive charge in a given drill hole can be uniform in
composition and/or density throughout its length; or different
compositions, or the same composition at different densities, can
be employed. If a particular selected composition is insufficiently
sensitive to a given energy-projecting system, successful
detonation can be achieved by adding a small amount of a
sensitizing ingredient, e.g., a finely divided metal fuel, to the
composition, or making the charge more sensitive only in the
portion thereof where the energy is initially released, e.g., the
portion where projectile impact occurs, care being taken, however,
to avoid sensitizing the charge to the levels characteristic of the
primary explosives (e.g., lead styphnate or lead azide), which are
unsafe to handle in bulk under field conditions. Special
sensitizing measures may be avoided, however, by altering
conditions in the energy-projecting system, such as projectile
velocity, area of impact, nose configuration, etc., as will be
described hereinafter.
After the drill holes has been loaded, the charge of secondary
explosive therein is initiated by means of propagative energy
projected to the charge through an inactive medium from a location
which confronts, and is separated from, the hole, the energy being
released into the charge at a high rate per unit volume of charge
in the vicinity of energy release. High rate of release is required
to achieve a high local pressure and thereby to initiate
detonation. Various types of propagative energy can be so projected
and released to produce the required detonation. For example,
kinetic energy of motion (e.g., via a projectile), electromagnetic
radiation (e.g., via a focussed pulse of light from a laser), or
electrical energy (e.g., via a high-energy electrical discharge
through an electrode) can be used. The medium through which the
energy travels to the charge from the point of projection or
emission, e.g., a gun chamber, a laser, or a source of electrical
energy such as a capacitor, is inactive (i.e., contains no stored
energy), and in most instances will simply be the atmosphere in the
vicinity of the mass being worked. In the case of electrical
energy, the energy is transmitted at least in part through an
electrode. Since the energy is projected locally and a pulse of
energy is projected for each of the charges, the initiation step
can be performed after loading without the delays required to
connect the charges to each other and to a common energy source.
This permits efficient blasting in small blast cycles.
Of the various ways of projecting and releasing energy that can be
used in the present process, propulsion of a high-velocity
projectile and impact thereof with the charge are preferred from
the standpoint of ease of operation and availability and cost of
equipment. Various kinds of projectiles and ways of propelling the
projectile can be employed, provided the impact velocity is
sufficiently high and the mass of the projectile sufficiently great
to release the energy at a sufficiently high rate, i.e., to subject
the charge to high enough pressure over a sufficient area and time
that it is caused to detonate completely at its expected velocity
under the conditions prevailing in the drill hole. Complete,
high-order detonation is required so that the maximum potential of
the explosive, e.g., for fragmenting, or introducing seismic energy
into, the surrounding formation may be utilized. Thus, as used
herein, the term "initiation" refers to the supplying of an impluse
which brings the explosive charge in the drill hole to complete
detonation at a rate which falls within a range commonly
encountered with the particular explosive composition in question
when initiated by conventional means. Generally, propagative energy
is projected from a location which is less than about thirty feet
from the portion of the mass being worked.
In the preferred case of projectile impact initiation, the chief
factors determining whether or not such detonation will occur in a
given explosive are the velocity of the projectile on impact, the
shock impedance of the projectile, and its mass and shape. The
minimum projectile velocity is higher as the sensitivity of the
explosive to impact and the shock impedance of the projectile are
less. For a given explosive and projectile material, the minimum
impact velocity required to produce detonation usually is lower as
the mass of the projectile is greater (up to a certain maximum) and
the area of the projectile nose, i.e., the area of the projectile
surface which impacts squarely against the explosive, is larger.
Also, for a given system and with a blunt-nose projectile, the
required detonation may be achieved at lower impact velocities if
the trajectory of the projectile is substantially on the drill hole
axis (head-on or non-glancing impact). As will be seen from the
subsequent examples, certain dynamites are initiated reliably by
0.22-caliber bullets (3.5 grams; pointed nose) at impact velocities
as low as 1,500 feet per second, while certain water-gel explosives
require higher impact velocities, e.g., about 2,800 feet per
second, with the same ammunition. On the basis of wider
applicability with respect to explosives with which the projectile
system is useful, therefore, a system in which bullets are
propelled to at least about 3,000 feet per second muzzle velocity
(about 2,800 feet per second impact velocity at a distance of 15
feet from the muzzle) is preferred.
The projectile is a body of material propelled to high velocity. It
can be a unitary solid, e.g., a bullet, or solid particles, e.g.,
shot. A high-velocity fluid jet, such as a water jet, also can be
used. Since the required impact velocity and high projectile shock
impedance can be attained more readily with solid projectiles,
solids are preferred, and particularly unitary solids. Unitary
solid projectiles should be made of materials, preferably metals,
which are strong enough to withstand the pressure and heat applied
during propulsion. Their configuration is generally cylindrical
with their forward end pointed or blunt, or spherical. For
explosives which are initiated readily by projectile impact, e.g.,
gelatin dynamites, the pointed-nose bullet found in commercial
ammunition rounds can be employed. For less-sensitive explosives,
it may be helpful to use a blunt-nose bullet, or one which has a
conical cavity in the nose surface. Although the nose of the
projectile may carry a secondary explosive charge thereon to assist
in the initiation, inert projectiles are preferred since they are
safer to store and deliver, and cheaper. When the projectile is
propelled, the gun can be in substantial axial alignment with the
drill hole, or positioned at a small angle thereto. Substantial
axial alignment is preferred to assure accuracy of impact and
complete detonation. However, especially if the projectile has a
pointed nose, the projectile can come in at an angle, e.g., up to
about 15.degree. to the hole axis, the allowable misalignment in
any given case depending on the nature of the mass being worked and
impact conditions.
The type of gun employed to propel the projectile is not critical
provided it is capable of affording the required muzzle and impact
velocities with the type of projectile and propellant, or
ammunition, used. Any small arms, e.g., rifles, shotguns, and
pistols, can be used. Air guns also can be employed.
Another suitable way of initiating the explosive charge in the
drill hole is to impinge the focussed output of a pulsed laser onto
the charge. In such an embodiment, the ease of initiation of a
given explosive charge can be enhanced by increasing the power of
the laser, e.g., by use of a Q-switched rather than a free-running
laser, and by having the end of the charge nearest the mouth of the
drill hole under suitable confinement. For example, a transparent
plastic layer can be employed over the end of the charge, either as
a separate unit, or as an end of a cartridge unit, and the focussed
laser beam allowed to pass through the plastic to the charge. While
the specific amount of energy required to initiate an explosive
reliably by a laser beam varies with the particular explosive
composition, for the more sensitive secondary explosives such as
pentaerythritol tetranitrate, gelatin dynamites, etc. about 0.025
joule/sq mm or more of incident energy is capable of causing
initiation when a Q-switched laser beam is focussed on the surface
of the charge. Often the charge can be made more sensitive to
initiation by incorporating in it a small amount of material having
a high light-absorption coefficient, e.g., carbon black. This
increases the rate of release of the energy per unit volume.
In still another method of initiating the explosive charge in the
drill hole, one or more expendable electrodes are positioned in, or
in close proximity to, the charge, e.g., by means of a wire-feeding
mechanism, such as those that have been developed for feeding
welding wire off a roll, and energy is projected through and along
the electrode by electrically discharging a capacitor bank through
the electrode.
A great advantage of the present process is derived from the fact
that all of the process steps, including initiation of the charges,
are performed locally, with the necessary equipment operating close
to the mass being worked on. Thus, the energy to be released into
the charges is projected from a location which confronts the mass,
although being separated from it. The minimum distance between the
energy-projecting device, e.g., a gun, and the drill holes will
depend chiefly on the total weight of explosive detonated in one
blast cycle (i.e., in holes detonating within milliseconds of each
other), the nature of the rock breakage produced (direction and
velocity of missiles), and the impact- and shock-resistance of the
device. As a general rule, the energy-projecting device will be
separated from the mass by a distance which is approximately
proportional to the cube root of the weight of explosive detonated
per cycle. Although large separation distances can be employed,
e.g., up to about one to two tunnel or shaft diameters, it is
preferred to work as close to the mass as is feasible with the
equipment used. This is especially true when the drill-and-blast
module of the invention is employed. In such a case, the module is
positioned close enough to the face for the drill to make the
desired size hole, e.g., within a few feet, and it is more
efficient to perform the blast step, e.g., fire the gun, with the
module in about the same position, or at any rate to avoid having
to move the module back from the face before blasting.
The length of the explosive charge with respect to the length of
the drill hole will vary depending on the type of work being
performed. In excavation, it normally will be more efficient to
substantially fill the hole with explosive. A layer of gas or
liquid, e.g., air or water, or a solid layer, e.g., carboard or
plastic, between the mouth of the drill hole and the end of the
charge where the energy is to be released does not preclude
satisfactory initiation of the charge under certain circumstances,
although the nature and maximum depth of such a layer, beyond which
initiation becomes impossible or erratic, varies with the
particular type of propagative energy used for initiation, the
explosive composition, and the magnitude of the energy. Any
material between the mouth of the drill hole and the end of the
charge where energy is to be released, as well as between the
energy-projection location and the mouth of the drill hole, should
be a material which, in the amount present, does not absorb a major
fraction of projected energy. For example, a light-absorptive,
light-scattering or light defocusing environment should be avoided
between a laser device and the charge, and an electrically
conductive environment should be avoided around an electrode. With
laser initiation, any optically transparent material can be
present. In the case of initiation by projectile impact, gases can
be present, as well as liquids or solids to a certain depth. For
example, explosives such as certain dynamites (GELEX 2), when
wrapped in a paper cartridge (cartridge end about three-eighths
inch thick, for example) and covered by a layer of water up to
about four inches thick in a 1.75-2.00-inch-diameter drill hole,
can be initiated reliably by the impact of a commercial fully
jacketed 0.22-caliber bullet (3.5 grams) impacting the water at a
velocity of about 2,800-3,600 feet per second. In practice, any
layer of liquid or solid material present over the end of the
charge usually will be due to conditions encountered in the area to
be blasted, e.g., water, or to the condition of the explosive
charged, e.g., a cartridge end.
The location pattern of the sequences (hole pattern), the time
pattern in which the drill-load-blast sequences are performed, the
number of sequences carried out concurrently (holes per cycle), and
the amount of explosive detonated per sequence or concurrent group
of sequences are all conditions that can vary widely, depending on
many factors such as the nature of the work to be performed, the
overall size and physical properties of the mass being worked, the
number of drill-and-blast modules (or separated components)
available, the impact- and shock-resistance of the equipment (since
it confronts the mass during blast), the degree of constriction of
the working area, ventilation and noise abatement requirements and
capability, etc. For operations such as in seismic prospecting,
secondary blasting, etc., one vehicle-mounted module may be moved
along the surface as required and employed to perform a succession
of single rapid drill-load-blast sequences at desired locations in
a desired time pattern. In operations such as trenching or
underground excavation, the use of multiple modules to perform
multiple sequences concurrently in groups is more efficient, more
modules (or more sequences per group or cycle) giving faster
advance. The specific number of sequences employed per concurrent
group (i.e., holes per cycle) depends on the number of modules, and
the space, available, the impact- and shock-resistance of the
modules, and mounting assembly employed, how close to the face the
modules are employed, the size of the charges, and the time
interval between blasts. Considering all of these factors, in most
cases the size of the cycles will be less than about one-half the
size of the entire round, most often up to about 35% of the total
number of holes required, or such that no more than about 100
pounds, usually up to about 30 pounds, of explosive detonates per
cycle.
The angle of the drill holes with respect to the face also will
depend on the type of work desired. In some instances, the holes
will need to be drilled non-normal to a face because of space
restrictions at the sides, roof, and floor of a tunnel. In other
instances, oblique holes will be used to provide a special type of
cut. Any of the patterns commonly employed in drill-and-blast
operations can be employed in the present process.
The present process can be used for excavating in any geological
mass, but is particularly advantageous when used in hard abrasive
rock, e.g., rock having a compressive strength of more than about
15,000 psi or a Moh's Scale hardness greater than about 5, where
mechanical excavators are presently ineffective. Moreover, since
the application of the process is applicable to a wide range of
geological conditions, the process offers the important advantage
of being adaptable to use with changing conditions as are commonly
encountered, i.e., major differences in rock types and arrangements
occurring within relatively small vertical and horizontal
distances. Naturally, the process can be employed in excavating for
construction purposes, as well as for mineral recovery, e.g.,
ferrous and nonferrous metal ore mining, stone mining and
quarrying, etc., and in seismic prospecting operations.
The drill-and-blast module of the present invention incorporates
three basic working components within its structure, i.e., drilling
means, means for delivering explosive comprising an
explosives-delivery or drill-hole-loading tube, and
energy-projecting means, e.g., a gun, as well as support means on
which the three other components are mounted and which maintain(s)
the required positions of the three components relative to one
another. Any mounting scheme which is convenient can be employed
provided the working end of each component, i.e., the drill bit,
discharge end of the delivery tube, and energy-exiting end of the
energy-projecting member, e.g., the gun muzzle, are located near a
common end, i.e., the operating end of the module, and provided the
components are capable of moving as required, i.e., the drill and
delivery tube movable axially with respect to the support means,
and, in the preferred embodiment, a support means movable, e.g.,
pivotally and/or slidably, so as to permit the three basic
components to be positioned sequentially on a common axis. With
these basic components and motions, the module can, in rapid
sequence, drill a hole in a geological mass, load explosive into
the drill hole, and initiate the explosive, and rapidly repeat the
sequence, thereby performing the desired work on the mass.
The general configuration and dimensions of the module will be
determined on the basis of economic factors as well as on the range
of drill hole depths it will be required to produce and load, the
number and types of constructional elements and types of driving
mechanisms employed in the module, the positions of the basic
components relative to one another, etc. Considering the relative
dimensions of drill holes commonly employed in blasting, i.e.,
diameters of about 0.5-15 inches and depths of up to about 100
feet, and avoiding telescoping components, which, while feasible,
are not preferred since their dependable repeated functioning in a
possibly dusty atmosphere may be difficult to achieve, the module
usually will be elongate, i.e., long in proportion to its width.
The overall configuration of the module, i.e., the shape of the
body formed when one or more surfaces are generated about the
periphery of its components, is immaterial to its operation, and
can be generally cylindrical or prismoidal, with any convenient
cross-section, e.g., circular, oval, or polygonal, as is the case
when the basic components are substantially parallel to one
another; or frustoconical or wedge-shaped, as may occur when the
axes of the basic components are convergent. Since, as has been
mentioned previously, it is preferred that the proper positioning
of the basic components during their operation depend on a
sequential coinciding, rather than on a convergence, of their axes,
and since convergence is unnecessary when the axes are adapted to
coincide sequentially, as well as less efficient with respect to
space utilization, substantially parallel positioning of the basic
components, and therfore a generally cylindrical module, are
preferred. In this preferred embodiment, it will be understood that
the cross-sectional area of the cylinder along the cylindrical axis
may vary, e.g., decrease from one end to the other, because of the
presence of certain constructional elements, or a slight
obliqueness e.g., up to about 10.degree., of the basic component
positions with respect to the cylindrical axis.
The support means for the three working components can be a unitary
element, e.g., a rod, bar, pipe, or slab, or a skeletal framework
of elements, of rigid construction, preferably made of metal, e.g.,
steel. If an external housing member, such as a cylinder or box, is
employed to protect the components against impact, the housing
member can serve as a support means with each of the three
components mounted in the housing wall. Alternatively, the housing
member can serve as a support along with an internal support. For
example, when the energy-projecting means is a laser, it may be
desirable to mount the laser in the wall of the housing member, and
the explosives delivery tube and drilling means on a common
internal support means. Any convenient means of mounting the
components onto the support can be employed, provided that the
drilling means and explosives delivery tube are capable of
unobstructed axial motion with respect to the support so that they
can both sequentially extend beyond all other components of the
module at the operating end, the drill bit being capable of
extending beyond the other components for a distance at least equal
to the depth of the drill hole required, and the delivery tube for
only the short distance, at the minimum, required to insert its
discharge end into the drilled hole, although preferably it will be
capable of extending farther into the hole.
In order that the module perform in a predetermined manner, i.e.,
that the achieved conditions such as the location and angle of the
drilled hole, explosive loading and density, and trajectory of the
projected energy, are in accordance with the preselected
conditions, it is necessary that the relative positions of the
basic components be maintained during operation of the module, that
is, that the components be supported while in extended as well as
retracted positions. For this reason, it is preferred that any
axially movable basic component which is insufficiently rigid to
maintain its required position during operation be held in position
by the support for a major portion of the component's length, and
more preferably for essentially its full length, when in the
retracted position, and that the distance between the end of the
support at the operating end of the module and the mass to be
worked when the component is extended beyond the support end, be
insufficient to cause the component to move out of its
predetermined axial position. Added assurance of good positioning
of the extensible components is achieved by providing guide means
on the support near its end through which the components travel as
they move axially beyond the support end. Also, the distance
between the end of the support and the face can be decreased
without having to move the entire module closer to the face by
having the support independently axially movable with respect to a
module mounting member to which it is affixed. A protruding peg
capable of anchoring itself in a rock formation, e.g., by a
piercing (a stinger) or suction action, can be provided at the end
of the support means, if desired.
The specific distances to which the axially movable components can
be extended are not critical to the function of the module and
depend on the depth of drill hole(s) required and how close to the
face the module is operated. From a given operating position of the
module, the explosives delivery tube need not extend as far as the
drill bit, and both tube and drilling means will extend farther
than the support when the latter moves with respect to a mounting
member.
The module is adapted to be mounted on an external supporting arm,
preferably via the support means in the module. While the module's
support means may be designed to permit it to be joined directly to
an external supporting arm, it usually will be more practical to
affix a separate mounting member to the module's support, this
mounting member later to be joined with a mounting member on the
external supporting arm. A convenient construction is one in which
the module's mounting member affords the re-positioning capability
required of the basic components to cause them to sequentially
coincide. For example, the mounting member may incorporate a pivot,
permitting the support means communicating therewith to rotate.
Alternatively, the re-positioning also may be accomplished by a
lateral sliding of the support means. Pivoting and/or sliding of
the support means and the locking of the support means in position
is accomplished by energizing of an indexing mechanism
communicating with the mounting member or support means. The
indexing mechanism can be, for example, an hydraulically actuated
mechanism, providing either linear motion, as does an hydraulic
cylinder, or rotary motion, as does a rotary actuator. Preferably,
the indexing mechanism communicates directly with the mounting
member for the module, e.g., a groove-containing member through
which the support means slides in an axial direction. With respect
to pivoting motion, a preferred procedure is to have the drilling
means on the desired axis in the rest (vertical) position, with the
explosives delivery tube and energy-projecting means mounted on the
same side, or opposite sides, of the drilling means and rotate the
support in one direction to position the tube on the axis desired,
and farther in the same direction, or in the opposite direction, to
position the energy-projecting path thereon.
All of the structural components of the module, as well as the
motion-imparting mechanisms therein, must be shielded against the
effects of air blast and possible missile impact resulting from the
detonation of the explosive charges in the drill holes. Such
shielding may be provided, for example, by a transverse metal plate
(i.e., a plate mounted with its large surfaces substantially normal
to the module axis) between the module(s) and the mass being
worked, with the module(s) operating through apertures in the
plate. Such shielding for the module(s) affords less
maneuverability of the module, however, and is not readily
adaptable for use with masses of all sizes. Therefore, it is
preferred that the module components be surrounded by a shock- and
impact-resistant shielding means, i.e., a housing member,
permitting the module to be operated in direct confrontation with
the mass with no additional shielding necessary between module and
mass. The housing member is made of a sufficiently tough material,
e.g., a metal such as certain steels, and is sufficiently thick
that it will not rupture or plasticially deform to any great degree
as a result of the shock pressures and missile (rock) impacts to
which it is exposed. For a given metal, the minimum necessary
thickness of the housing will be determined in any given case by
the size of the blast (i.e., amount of explosive detonated), size
and velocity of rock fragments produced, how close to the blast the
module operates, etc. For operation under moderate conditions,
e.g., blasts of less than about 4 pounds of explosive, rocks up to
about 12 inches in size and moving at velocities up to about 40
feet per second, and distances of at least about 2 feet between the
module and face, a housing which has a shell at least about 0.5
inch thick may be employed. Like the configuration of the module,
the configuration of the housing member is immaterial, but usually
it will be generally cylindrical or prismoidal, as described
previously for the module configuration.
Usually the module will be mounted in the housing member wall by
affixing to the housing wall a mounting member which is in
engagement with the support means of the module. Affixing the
support means directly to the housing wall is not preferred since
re-positioning of the components would, in such a design, require
movement of the housing as well.
The housing member, like the module itself, is elongate, and, since
it is required to shield all of the module components, at least
during the blast, the operating end of the housing member is
adapted to be closed. The non-operating end can be open, but
usually will be permanently closed. The operating end is adapted to
be opened and closed, for example, as is shown in FIGS. 1 through
5, wherein a shock- and impact-resistant swingable closure member,
e.g., one or more doors, erected on the housing cylinder at the
operating end of the module, is adapted to occupy an open or closed
position with respect to the end of the housing cylinder in
response to a force imparted by a motion-imparting means, e.g., an
hydraulic cylinder, communicating with the closure member from a
location within the housing member. The closure member has an
aperture or porthole therein which, when the closure member is
closed, falls on an axis which is coincident with the axis on which
the three working components of the module preferably sequentially
coincide. The closure member is moved to the open position when the
drilling means, loader, or support means is to be moved axially to
an extended position; and to the closed position when all axially
extendable members are in the retracted position and the energy is
to be emitted from the energy-projecting member. The porthole
allows unimpeded travel of the energy from the energy-projecting
member to the explosive charge in the drill hole. A conical or
wedge-shaped closure configuration is preferred as a means of
providing added protection against rock impacts.
The effect of shock and impact on the module can also be moderated
by use of energy-absorbing means together with the housing, e.g.,
by the use of springs in the system for mounting the module on a
supporting arm. A particularly useful energy-absorbing device is an
inflated pneumatic member, i.e., an elastic member holding fluid
under pressure. Such a member, resembling an automobile tire in its
function, for example, when engaging the end of the housing
cylinder, e.g., as shown in FIGS. 1 through 4, serves to cushion
the front of the module from the impact of shock waves and flyrock.
Several such members can be employed side-by-side around the
housing when additional, and lateral, cushioning is desired.
In the process of this invention, greater efficiency is achieved,
e.g., in terms of weight of material excavated per unit time, by
performing multiple drill-load-blast sequences concurrently. With
the module of this invention, multiple-sequence cycles are achieved
by employing a number of modules equal to the selected number of
sequences to be performed concurrently. Multiple modules each
comprising a single drilling means, single explosives delivery
means, and single energy-projecting means, suitably supported and
housed, can be employed. However, when efficient utilization of
space and weight is of prime consideration, it is preferred to
employ a composite module which incorporates two or more
single-component modules or module units suitably clustered within
a common housing member. The geometric arrangement or cluster
pattern of the basic module units within the composite module, and
the specific number of units, can vary as required. For example,
for working concurrently in essentially straight-line or block
drill-hole patterns, a linear or block cluster of units can be
employed, the overall configuration of the module in such cases
being essentially that of a parallelipiped. For working in a curved
pattern, the cluster may be in the form of an arc of a circle. In
the composite module, each unit can be complete within itself,
i.e., have its own drilling means, explosives delivery means, and
energy-projecting means; or a common component, e.g., an explosives
delivery means, can be shared by more than one unit.
Any type of drilling means can be used in the module, e.g., a
percussion drill or hammer, a rotary drill, or one employing both
percussion and rotary action. An electrical disintegration drill,
providing heat and rotation, also can be used. For hard rock,
rotary percussion drills are preferred. For convenience, i.e., in
order to make use of ready-made components, where available, and in
order not to multiply the number of constructional elements
unnecessarily, in a preferred module the drilling means and support
member constitute a rotary percussion drill and feed, respectively,
both constructed of metal, e.g., steel. The drill rotation can be
imparted through a pneumatically or hydraulically operated motor
mounted in the feed channel, and axial thrust for extension and
drilling can be applied through a heavy-weight chain feed driven by
a pneumatic or hydraulic motor. The explosives delivery tube and
energy-projecting means are mounted on support means, e.g., the
drill feed channel, in a manner such that axial motion of the drill
and the delivery tube is unimpeded.
The explosives delivery tube has an explosives feed end which
communicates with an explosives feed system located outside the
confines of the module. The explosives feed system is comprised of
an explosives supply unit, e.g., a magazine containing cartridged
explosive or bulk solid explosive, or a storage and mixing tank for
slurry explosive ingredients; and a feed unit associated therewith
capable of delivering the explosive therefrom, e.g., a pneumatic
loader for solid explosives, or a pump for slurry explosives. The
tube from the module can be attached to the loading tube of a
pneumatic loader or to the delivery hose of a slurry pump; or, if
long enough, it can replace the loading tube or delivery hose
entirely and be attached directly to the explosive-delivery
mechanism or pump in the explosives feed system. For loading
cartridged explosive, e.g., dynamites, a preferred feed unit is a
pneumatic cartridge loader such as is described in U.S. Pat. No.
3,040,615 and in The Modern Technique of Rock Blasting, N.
Langefors and B. Kihlstrom, Stockholm, Almqvist & Wiksell,
1967, pp. 91-101. The delivery tube, both the portion thereof which
is in the module and that which is outside the module, should be
somewhat flexible and can be made, for example, of metal or
plastic. With the pneumatic cartridge loader, a semiautomatic
breech piece can be used to feed cartridges continuously.
The axial motion of the tube with respect to the support can be
accomplished in any one of various ways. One way is to have a
flexible tube, e.g., a plastic tube, lead into a rigid tube, e.g.,
a metal tube, which is slidably mounted on the support, e.g., in a
guiding track, in the desired position with its free end at the
operating end of the module and its other end in communication with
a pneumatic positioning cylinder. In another method, i.e., that
shown in FIG. 3, the tube may be moved by means of a device, i.e.,
the so-called "robot loader," which is also described by N.
Langefors and B. Kihlstrom, op cit. The robot loader acts in
conjunction with a pneumatic cartridge loader. The robot loader,
mounted on the support means, e.g., the drill feed channel,
consists of a pneumatic cylinder which reciprocates a tubular
piston-rod. The delivery tube is inserted axially through the
piston rod. To the piston-rod is connected a pneumatic grip
arrangement, a "hand" which holds the tube by friction so that it
undergoes reciprocating motion. As the tubular piston-rod
reciprocates, the pneumatic "hand" grips on forward movement and
releases on backward movement, thus imparting an incremental
forward motion to the delivery tube. For retracting the tube after
the drill hole has been loaded, the reverse "hand" action takes
place. Preferably, the delivery tube is passed down to the bottom
of the drill hole and moved out slowly with repeated light
countermovements so as to pack the ejected cartridges to high
density.
In a preferred module, the energy-projecting means is a gun. The
term "gun" denotes an assembly which includes a metal tube or
barrel having one open end (the muzzle end) and the other end (the
after end) adapted to form a chamber into which projectiles are
introduced and gas under pressure is admitted or generated rearward
of the projectiles upon command. The term is meant to include
devices in which projectiles are propelled by gas admitted into the
chamber at high pressure, as well as those in which the propellant
gas is produced in the chamber by the burning of a propellent
composition. When required, as in the latter case, the after end of
the barrel is closed off by a breechblock or plug, seated in a
housing which can be opened, for loading ammunition into the
chamber (forward of the plug), and closed, for igniting the
propellent charge, by a breech mechanism upon command. The type of
gun employed is not critical provided it is capable of propelling
projectile material of sufficient mass at sufficiently high
velocity to subject the explosive in the drill hole to high enough
pressure over a sufficient area and time that the explosive is
caused to detonate. The impact energy required is more readily
attained with solid projectiles, and particularly unitary solids,
i.e., bullets as contrasted with shot, and for this reason bullets
are the preferred projectiles. Also, while the projectile can be
propelled by a stream of gas admitted into the chamber at high
pressure, as in an air gun, there is less restriction on the
attainable impact velocity when the projectile is propelled by the
burning of a propellant composition in the chamber. Consequently,
guns which operate on the propellant burning principle are
preferred. Thus, in the preferred embodiment the gun consists of a
metal barrel having its after end closed off by a breechblock or
plug which can be opened, for loading an ammunition round into a
chamber forward of the plug, and closed, for igniting the
propellant charge in the round, by a breech mechanism operating
upon command from outside the module. Empty cartridge cases can be
continuously ejected from the module, or collected in a container
provided for the purpose in the module, the container being adapted
to be emptied periodically. The ammunition primer can be a
percussion primer, electric primer, or a combination primer.
Electric firing of the primer may be preferred in certain cases
when greater precision with respect to time intervals between
detonations is required.
The magazine for the ammunition can be located inside or outside
the confines of the module. An external magazine is preferred
because of space restrictions in the module and also because
storage of ammunition at a location removed from the operating area
is desirable from a safety viewpoint. Therefore with external
storage, a loading or delivery tube for ammunition leads from an
external ammunition feed system to the chamber of the gun. The feed
system can be, for example, a pneumatic loader such as has been
described for loading cartridged explosive into a drill hole.
While the gun may be constructed completely according to custom
design, in most cases it will be possible to adapt a commercially
available gun, e.g., a bolt-action rifle, semi-automatic rifle, or
pistol, for use in the module. Rifling of the bore, while
desirable, is not strictly required owing to the relatively small
distances over which the projectile will travel when the module is
in operation. Remote firing of the gun can be accomplished by
applying electrical current to a solenoid which actuates a
conventional mechanical firing linkage, i.e., trigger action to
cause motion of the firing pin to ignite the ignition mixture by
percussion; or by applying current to an insulated firing pin in
contact with a bridge wire or an electrically-conductive ignition
mixture in an electric primer, the electrical circuit being
completed through the cartridge case and ground, and the ignition
mixture being ignited by ohmic heating of the bridge wire or
conductive mix.
When a laser is used as the energy-projecting means, a housing
member is required to prevent the entrance of light-absorbing
material, such as rock dust, into the path of the laser beam. The
"laser" includes a laser rod (e.g., ruby), a total reflector at one
end, and a partial reflector at the other end of the rod; one or
more flash lamps to pump the laser rod; a high-voltage electrical
power source to excite the flash lamp(s); a Q-switch or Q-spoiler
in the path of the beam between the front end of the rod and the
partial reflector; and a focussing lens. To afford maximum
protection to the laser during the blast, it is preferred that the
laser be in an offset position with respect to the beam path. For
example, the laser can be mounted in the wall of the housing and
the beam reflected onto the desired path by suitably positioned
reflectors. In such a case, if positioning of the functioning
components onto a common axis is employed, the reflectors can be
positioned on a support means and moved thereon to project the beam
on the required path.
The module also contains, or is in communication with, suitable
motion-imparting mechanisms, e.g., hydraulic or pneumatic devices,
which perform such movements as axially moving the drilling means,
explosives delivery tube, and support means (e.g., drill feed
channel); drilling; delivering explosives to the drill hole; in a
preferred embodiment, delivering ammunition rounds to the gun
chamber and firing the gun; re-positioning the basic components
(i.e., indexing) and opening and closing the housing door at the
operating end. Such mechanisms are well-known to those skilled in
the art and their basic mode of operation therefore will not be
described herein. All power supply lines, e.g., hydraulic lines,
for such devices are shielded in the same way as are the module
components, preferably by surrounding them in a suitable housing
member. When the module includes a housing member, the power supply
lines pass into the module through the housing wall via the
mounting member, or via one or more special apertures provided
therefor.
As stated previously, the module of the invention, when positioned
near a surface of material to be worked, e.g., a rock face, and
suitably energized, can in rapid sequence drill a hole in the rock,
load explosive into the hole, and initiate the explosive by the
rapid release of energy therein, e.g., projectile impact. Inasmuch
as the operation of the module produces an explosion each time the
energy enters the explosive, the module must be mechanically
mounted on a supporting arm or base and its functioning controlled
from a suitably shielded location. While any mounting and control
scheme can be employed, e.g., impact- and shock-resistant jack leg
or jack bar mounting with power controls separated from the mass
being worked by a barricade substantially parallel to the mass, the
fullest benefit of the module is derived when it is incorporated
into a machine adapted to support, maneuver, and operate one or
more of the modules in a substantially continuous manner. For this
reason, the module(s) usually will be mounted on a vehicle, such as
a truck, and manipulated by personnel from a location inside the
vehicle, the vehicle and personnel being suitably protected from
the effects of the relatively small blasts.
For a clearer understanding of the process and module of this
invention, reference is now made to the drawing, which illustrates
the structure and mode of operation of typical modules, and a
typical cyclic pattern in which the process can be carried out.
In FIGS. 1 through 4 a module is in position before rock face 1 on
a longitudinal axis which is substantially normal to face 1 and
parallel to face 2. Each basic working component of the module is
shown in three different radial positions, the drilling means being
in the vertial plane of view in FIGS. 1 and 2, the explosives
delivery tube in FIG. 3, and the energy-projecting means in FIG. 4.
When a working component is in this vertical plane, the
longitudinal axis of the component substantially coincides with the
axis of the drill hole (indicated by a dotted line into the rock in
FIG. 1).
Referring to FIGS. 1, 1A, and 2, elongated support means 3, e.g., a
drill feed channel, has drilling means mounted thereon, shown as a
rotary percussion drill, having an elongated tubular member 4,
e.g., a drill steel, and bit 5. The drilling means is movable
axially on support means 3, e.g., through a chain feed or screw
feed driven by a motor 6, for example an air motor. The
motor-driven chain feed or screw feed applies feed pressure or
thrust for drilling. Drill action (reciprocation and rotation) is
provided by a motor 7, e.g., a pneumatically operated motor.
Support means 3 communicates with a mechanism 9, e.g., an hydraulic
cylinder, which is adapted to move support means 3 back and forth
independently in an axial direction in an axial groove in slide
member 37 (3 shown extended in FIG. 2). Groove-containing slide
member 37, attached pivot member 8, having an axis of rotation
parallel to the axis of elongated member 4, and flange 12 together
constitute the mounting member for the module. An indexing means
31, in this case an hydraulic cylinder (shown in FIG. 1A),
communicates with slide member 37 and housing 13, e.g., a metal
cylinder. A pointed metal peg or stinger 10 extends axially from
the end of support means 3 which faces face 1, and hook-like guide
elements 11 extend from support means 3 at the same end, normal to
the longitudinal axis, in a manner such that elongated member 4
passes through guide elements 11. Flange 12 attached to pivot
member 8 fits through an aperture in the wall of housing 13, flange
12 being adapted to engage a mounting member 14 of a suitable
supporting arm for the module. At the operating end of the module,
i.e., where drill bit 5 is located, an inflated pneumatic member
15, e.g., a rubber tire, engages the end of housing 13. At this
same end, a closure member 16, e.g., a door, is adapted to open or
close by actuation of a motor 17, e.g., an hydraulic motor, mounted
inside the housing and communicating with closure member 16. The
latter has an aperture or porthole 18 therein, so positioned that
when the closure member is closed the axis on which the working
components sequentially coincide (elongated member 4 axis in FIG.
1) passes through aperture 18.
In FIG. 3, 19 is an explosives delivery tube, somewhat flexible,
e.g., made of plastic, and mounted on support means 3 substantially
parallel to elongated member 4, and at the same radial distance as
the elongated member from the pivot member 8. One end of tube 19
leads to a conventional explosives feed system, e.g., a pneumatic
cartridge loader, as described previously, located outside the
confines of the module. The other, free end of the tube is the
discharge end and is located at the operating end of the module.
Tube 19 passes through the aperture in the wall of housing 13. 20
is a feed mechanism adapted to move tube 19 axially, e.g., a robot
loader such as has been described above. Ring-like guide elements
21 extend from support member 3 at the operating end normal to the
longitudinal axis, in a manner such that tube 19 passes through the
guide elements.
In FIG. 4, 22, 23, and 30 are the barrel, chamber and breech
housing, respectively, of a rifle, and 24 is a flexible ammunition
delivery tube which leads into the gun chamber 23 and communicates
with an ammunition feed system, e.g., a pneumatic loader as
previously described, located outside the confines of the module,
tube 24 passing through the aperture in the wall of housing 13. The
rifle is fixedly mounted on support means 3 substantially parallel
to elongated member 4 and at the same radial distance as the
elongated member and explosives delivery tube from pivot member 8.
The gun muzzle is at the operating end of the module.
Prior to a drill-load-blast sequence, the module is positioned as
shown in FIGS. 1 and 1A, elongated member 4 being coaxial with the
axis of the drill hole desired, and in a vertical line with pivot
member 8. Motor 17 has been energized to allow closure member 16 to
open. In the first step of the sequence (FIGS. 2 and 2A),
energizing of mechanism 9 moves support means 3 on slide member 37
axially in the direction of face 1 until stinger 10 firmly engages
face 1, helping to stabilize the module when the components are
extended. With the support means in this position, the elongated
member 4 is moved axially in the direction of face 1 by energizing
of motor 6, the drill bit then boring a hole 25 of the desired
depth in the rock by the thrust and rotating action imparted to it
by the chain or screw feed and motor 7.
After the hole has been drilled, the chain or screw feed acts to
retract the drilling means back into the housing 13, and hydraulic
cylinder 31 moves slide member 37 so that support means 3 mounted
thereon rotates in a counter-clockwise direction by the action of
pivot member 8 so as to position explosives delivery tube 19
coaxially with hole 25 and on a vertical line with pivot member 8
(FIGS. 3 and 3A). Tube 19 moves axially and into drill hole 25 by
the action of feed mechanism 20. While the delivery tube is in this
position, cartridges of condensed high explosive 26 are fed through
tube 19 and ejected therefrom into hole 25, e.g., by means of a
pneumatic cartridge loader.
After the hole has been loaded with explosive, feed mechanism 20
acts to retract tube 19 back into the housing 13, and hydraulic
cylinder 31 again is operated, this time moving slide member 37 and
support means 3 mounted thereon, in a clockwise direction so that
rifle barrel 22 is coaxial with hole 25 and on a vertical line with
pivot member 8 (FIGS. 4 and 4A). Closure member 16 is closed by
energizing motor 17, aperture 18, which is larger in diameter than
the bullet 27 employed, being coaxial with hole 25. The rifle is
fired, e.g., by applying current to the firing pin of the
ammunition primer, propelling bullet 27 at high velocity from the
rifle muzzle, through aperture 18 and the space between the module
and hole 25 and into explosive 26 in the hole 25, along the
trajectory indicated by the dotted line. The impact causes the
explosive to detonate, and the rock to break and move in a manner
as typified in FIG. 4.
FIG. 5 shows a portion of a module similar to that shown in FIGS.
1-4, with the exception that in this embodiment a laser is the
energy-projecting means, and the design of closure member 16 is
modified. The module is shown with components operating in the
intiation step of the sequence. In FIG. 5, a laser assembly 32,
i.e., rod, lamps, Q-switching device, partial and total reflectors,
and focussing lens, is mounted on the wall of housing 13. Laser
assembly 32 is connected to a power supply located outside the
confines of the module. The laser assembly is located off the drill
hole axis. The laser beam 33, after passage through the focussing
lens in laser assembly 32, is reflected from parallel reflectors 34
and 35 which direct the beam onto a path coaxial with the drill
hole 25. Explosive 26 in the drill hole has a transparent end-cap
36, e.g., a cartridge end, made, for example, of plastic. The
module is in a position relative to face 1 such that the focal
point of beam 33 is on the surface of explosive 26. Reflectors 34
and 35 are mounted on support member 3 in a manner such that
operation of indexing means 31 causes the reflectors to adopt a
position such that the path of the beam 33 is coaxial with hole 25.
Closure member 16 is wedge-shaped, and has upper and lower portions
which are adapted to open and close. Energizing of the power supply
to laser assembly 32 causes emission of a beam 33 of
electromagnetic radiation, which travels through the atmosphere to
hole 25, passes through transparent end-cap 36, and focusses on the
surface of charge 26, causing the charge to detonate.
Typical ways in which the present process and module can be
operated to work a geological mass are described in the following
examples.
Example 1
as illustrated in FIG. 6, a face 1, substantially flat and
vertical, has been opened up in a geological formation such as hard
rock, and the face is being advanced, e.g., to drive a tunnel, by
the process of this invention. The face is substantially square and
is 8 feet high and 8 feet wide. Each round (all of the sequences or
holes needed to advance the entire face) consists of 30 holes
arranged in parallel columns and rows spaced, for the most part,
equidistant from each other. That is, the drill-load-blast sequence
of the present process is carried out at 30 locations. The process
is being effected in 5 successive groups of sequences, or five
drill-load-blast cycles per tunnelling round, with six sequences,
or holes, per cycle. Six modules are employed. In each cycle, six
holes are drilled substantially simultaneously and then loaded
substantially simultaneously, and then six bullets are propelled,
one into each loaded hole, within milliseconds of each other so as
to detonate the six charges, the cycle being ended when the
continuity of the series of detonations is interrupted for the time
interval required to drill a new series of holes (the beginning of
the next cycle).
In the situation shown in FIG. 6, the first three cycles (three
center rows, designated Cycles 1, 2, and 3) have been concluded,
and the fourth cycle, 4, is in progress at the blast step of the
sequence. The blasting which has been completed has produced rock
fragments which have separated from the mass forming horizontal
faces 2a and 2b substantially the depth of the drill holes and in
planes substantially those of the original holes of Cycles 2 and 3.
Rock 28 has accumulated on the floor of the tunnel, exposing a
portion 29 of the new vertical face being made.
In the opening cycle, Cycle 1 (center row of six holes), the six
holes are fired in a pattern which differs from the firing patterns
employed in the remaining cycles. In Cycle 1 the two center holes
are fired first, the two holes adjacent to the center holes next,
and the two outermost holes last, each pair of holes substantially
simultaneously, with about 2-millisecond intervals between pairs.
The two center holes lie on convergent axes, each about 10.degree.
to the normal (to the face), and the remaining holes diverge to the
sides about 15.degree. from the normal. In the remaining cycles,
the axis of holes at the facial periphery diverge, while the
remainder are substantially normal to the face (oblique holes at
the top, bottom, and sides are necessitated by the restricted
maneuverability of the modules at the periphery). The six holes in
each of these cycles are fired singly in direct linear
sequence.
The holes are 1.25 inch in diameter and 1.5 feet long. Each hole is
filled, and contains approximately one-half pound of cartridged
GELEX 2, a semi-gelatin dynamite. (See Examples 2-6). The drills on
the modules are rotary percussion drills, and the loaders are
pneumatic cartridge loaders in which the dynamite cartridges are
pushed forward through loading tubes and ejected into the drill
holes, while the cartridge paper is slit and the explosive is
packed to high density. The guns are rifles employing commercial
0.22-caliber ammunition rounds, and they are fired on an axis with
the holes from a distance of 10 feet, providing an impact velocity
of 3,000 feet per second. Each cycle is completed in about 2.5
minutes, the total dead time within the cycle being about 45
seconds. In FIG. 6, the six holes in Cycle 4 have been drilled and
loaded with explosive 26. The bullets 27 are shown just before
impact. Impact of the bullets with the charges (at about 2
millisecond intervals) causes detonation and rock breakage with the
formation of new face 29 to the level of the holes in Cycle 4.
The procedure described for Cycle 4 is repeated for Cycle 5 after
clearing any pieces of rock obstructing the drill hole positions
(at the locations marked with +) to expose the complete new
face.
After the round of five cycles has been concluded (five 2.5 minute
cycles with about 60-second intervals between cycles) and the rock
fragments have been removed from the area, an entirely new face
about 1.5 feet behind the original face is exposed.
The following examples serve to illustrate the performance of the
process of this invention using a high-velocity bullet as the
propagative energy for initiating the explosive, the process being
illustrated with different combinations of conditions, i.e.,
explosive composition, drill hole conditions, and bullet impact
velocity, mass, and trajectory. The impact velocities exemplified
should not be interpreted as being limit velocities for the systems
shown, and in any event the operating limits could be changed as
conditions such as have been described were changed, e.g.,
confinement, contact area, or explosive density. Unless specified
otherwise, in each example in the first step of the sequences a
1.75-inch-diameter 12-inch-long hole is drilled in a rock mass. The
hole then is loaded with condensed high explosive, and the
explosive is initiated by firing a bullet from a rifle, which is
aligned coaxially with the hole except where specified otherwise.
The rifle is triggered remotely. The distance between the rifle
muzzle and the hole is about 10 feet. The impact velocity given is
the velocity of the bullet obtained with the ammunition used and
measured 15 feet from the muzzle. Except where noted otherwise, the
bullets used are soft-point (unjacketed tip) bullets. Where
material other than explosive is present in the drill hole, the
bullet passes through the other material, impacting the explosive
last. In each example, the drill-load-blast sequence is followed by
a second sequence at a different location from the first, and
effected under the same conditions as the first. In every case, the
explosive charge detonates, fracturing the rock.
Example Secondary Explosive Ammunition (Bullet Wt.) Drill Hole
Condition Impact Velocity (ft/sec) No.
__________________________________________________________________________
2.sup.(d) "Gelex" 2.sup.(a) .22-caliber (3.54 g.) Explosive only
3600 3 "Gelex" 2 .22-caliber (3.54 g.) Explosive only 2800 4
"Gelex" 2 .30-caliber (9.57 g.) Explosive only 2800 5 "Gelex" 2
.22-caliber (3.54 g.) Explosive only 1500 6 "Gelex" 2 .22-caliber
(3.54 g.) Explosive in paper cartridge 2800 (fully jacketed)
(3/8-in.-thick end), covered by 4 in. of water 7 "Hi-Cap".sup.(b)
.22-caliber (3.54 g.) Explosive only 3600 8 "Hi-Cap" .22-caliber
(3.54 g.) Explosive only 2800 9 "Hi-Cap" .30-caliber (9.57 g.)
Explosive only 2800 10 "Hi-Cap" .22-caliber (3.54 g.) Explosive
covered by 4 paper 2000 cartridge ends (1.5 in. total thickness) 11
"Hi-Cap" .22-caliber (3.54 g.) Explosive plus 12-in. air 2000mn 12
"Hi-Cap" .22-caliber (3.54 g.) Explosive only 2000 (15.degree. off
drill hole axis) 13 "Hi-Cap" .22-caliber (3.54 g.) Explosive only
2800 (10.degree. off drill hole axis) 14 Water-Gel
Explosive.sup.(c) .22-caliber (3.54 g.) Explosive only 3600 15
Water-Gel Explosive .22-caliber (3.54 g.) Explosive only 2800 16
Water-Gel Explosive .30-caliber (9.57 g.) Explosive only 2800
__________________________________________________________________________
.sup.(a) Semi-gelatin dynamite (63% ammonium nitrate, 20%
nitroglycerin) .sup.(b) Ammonia dynamite (51% ammonium nitrate, 8%
nitroglycerin) .sup.(c) 32% Ammonium nitrate, 15% sodium nitrate,
45% of an 86% aq. soln of monomethylamine nitrate, 3%
ferrophosphorus, 3% fine flake Al powder, and 4% H.sub.2 O.
.sup.(d) 1-in.-diam., 8-in.-long hole
Example 17
the present process is employed to accomplish secondary blasting,
i.e., to break up large rocks produced from a previous blasting
operation. A single module of the type shown in FIG. 5 is employed,
the module being mounted on, and operated from, a vehicle, which
moves along the surface among the rocks as required to perform a
required succession of drill-load-blast sequences. The drill and
loader, and the hole and charge size, are the same as in Example 1,
except that in this case the bottom (outside end) of the outermost
cartridge consists of a 0.5-inch thick disk of transparent plastic,
e.g., polystyrene. The energy-projecting device in the module is a
laser head, model LHM6, manufactured by Raytheon Company, the laser
head comprising a ruby rod 6 5/8 inches long and 5/8 inch in
diameter, two FX-47A-6.5 flash lamps, a front mirror which is 65%
reflective at 6,950A, and a 99.9% reflective rear mirror.
Q-switching is achieved by placing a cell filled with a passive
liquid Q-switch solution in the path of the beam between the front
end of the rod and the 65% mirror. A focussing lens (focal length
45 inches) is positioned forward of the 65% mirror. The laser head,
Q-switch solution, and lens are mounted to the wall of the housing.
Two total reflectors (right-angle glass prisms) are positioned
forward of the lens in a manner such that the axis of the focussed
beam is shifted from that of the laser rod to an axis parallel
thereto, but separated therefrom by 6 inches. The reflecting prisms
are mounted on the drill feed channel. During operation, the module
is positioned so that the laser beam is aligned coaxially with the
drill hole, and the distance between the charge in the drill hole
and the prism nearest to it is 36 inches. After the hole has been
drilled and loaded, the laser is activated by application of a
high-current pulse to the laser head from a remote power supply
unit (Raytheon Model LPS4, with LPS4A control chassis and LPS4B
capacitor banks) having a 2,200 microfarad capacitance. The
capacitors are charged to 3,000 volts giving an energy input of
10,000 joules to the laser cavity. The laser output is focussed
onto the charge surface, causing initiation thereof with 0.1000
joule/sq mm incident energy (monitored by means of a Lear Siegler
Laser Energy Monitor M1-2). Detonation of the charge causes the
rock to fracture.
* * * * *