Note: Descriptions are shown in the official language in which they were submitted.
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1 The present invention relates to -the production
of blast chambers in formations to receive exPlosives for
fragmenting the formations. Such blast chambers are used in
blowing o-ff the bench in strip or open pi-t mining, coal gasi-
fica-tion, and leach mining.
Heretofore, blast chambers have been produced in forma-
tions through use of a one~pass method, in which a lower pilot
bit is secured, directly or indirectly to an expanding
cutter type of bit, known as a hole opener or underreamer.
This combination is secured to a string of drill pipe. An
upper pilot hole is produced by the pilot bit to a desired
depth in the formation which will be the location of the
upper end of the proposed blast chamber. During the production
of the pilot hole ~o the depth just referred to, the expandable
cutters of the hole opener remain retracted or in inoperative
condition. The hole opener cutters are then expanded, while
the pilot bit and hole opener are rotated, to commence enlarge-
ment of the pilot hole and formation of the blast chamber, the
combination being progressively lowered, with the pilot bit
continuing to drill the pilot hole, and -the hole opener there-
above the enlarged blast chamber, until the pilot bit reaches
the desired final depth of the pilot hole. The result is the
production of an upper pilot hole extending downwardly from the
ground surface, an enlarged blast chamber extending downwardly
from the upper pilot hole, and a lower pilot hole extending
downwardly from the blast chamber.
There are many disadvantages to the one-pass method.
Since the pilot bit and hole opener are in the hole at the same
time, they are both subject to the drilling weight required for
penetration of the pilot bit cutters in-to the forrnatlon, which
1 urges the arms and cutters against the formation while -the upper
pilot hole is being produced and also exposes them to the cuttings
carried upwardly by the drilling fluid, thereby subjectiny their
outer portions to wear. The wear on the cutters and arms, while
the upper pilot hole is being drilled, and before chambering is
to be performed, shortens the effective life of the chambering
tool or hole opener.
Another disadvantage to the simultaneous presence of
the pilot bit and hole opener in the hole, stems from the require--
ment for conducting drilling fluid through the drill pipe and
hole opener to the pilot bit, which necessitates the p:resence ~.
of a fluid conductor in the hole opener, which limits the axial
length of hole opener cutters that can be used, to insure their
ability to be fully retracted within the confines of the hole :
opener body. The necessity for transmitting torque and drilling
weight through the hole opener to the pilot bit requires
sufficient steel structure in the hole opener between the
retracted cutters, which allows space for small diameter cutters
only in the hole opener tool. As a result, the cutters
of small axial and radial size severely limit the diameterto which the hole produced bv the pilot bit can be enlarged.
In actual practice, such limit is a blast chamber or enlarged
hole of about one and one-hal.f times the diameter of the
pilot hole.
Since a large increase in diameter of the pilot hole
cannot be effected to produce the blast chamber, the latter
must be made longer to receive the required large quan-tity
of explosives. In addition, the pilot hole portion below
the chamber will also be packed with explosives. As a
result, the blasting force occurs along extended portions of
0
1 the bench, as well as below the lower end of the bench,
where a large portion of the blasting ef.Eect is reduced or
is inef.Eec-tive. Desirahlv, the chamber shou].d be :~ormed to
-the bott:om of the enlarged hole only and should not include
any pilot hole portion depending therefrom~
Because of the relatively small diameter of each
blasting chamber, more chambered holes in spaced relation to
each other and more rows of holes must be drilled to effectively
blast the bench, which is time consuming and costly.
The present invention involves a two-pass method of
producing blast chambers. First, a pilot hole of a pre-selected
diameter is produced to total depth by a suitable drill bit.
This bit is then removed from the hole. Secondly, a hole
opener or underreamer having initially retracted cutters is
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secured to a drill string and lowered in the pilot hole to a
location corresponding to the upper end of the chamber to be
produced. The cutters are expanded while the hole opener is
rotated to cut out the pilot hole and form the upper end of the
enlarged chamber. With the cutters expanded, and the hole ~ -
opener rotating, drilling weight is imposed on the tool and the
tool progressively lowered to drill the enlarged chamber down
to the bottom of the pilot hole, the chamber bottom coincid:ing
with the bottom of the pilot hole.
The hole opener cutters, when in retracted position
can be placed closely adjacent to each other and can, therefore,
be of maximum axial extent, enabling the cutters to be expanded
laterally to drill a chamber of much larger diameter t:han can
be produced with the above described one-pass method. Addition=
ally, since there is no pilot bit below the hole opener, the body
of the latter need not embody any structure for feeding fluid to
1 the pilot bit, which enables the cutters and the cutter bear:ings
to be made of L~er diameters and, therefore, havlng a mllch
longer drilling life. Since chambers can be formed having
considerably larger diameters, they can be spaced further apart
and made of shorter length, re~uiring fewer chambered holes per
unit of ground area.
The hole opener cutters and cutter supporting arms
are subjected to much less wear than occurs in the single-pass
method, since the hole opener or underreamer is in the hole
only when the chamber is being formed, and not during the
drilling of the smaller diameter pilot bore.
The hole opener cutters produce a blast chamber
having a Elat bottom; that is, the bottom of the enlarged portion
of the bore and the bottom of the pilot hole lie in the same
plane/ avoiding the production of an unneeded and undesired
pilot hole below the chamber. ~s a result, the explosives
need not fill a pilot hole below the chamber, which is not
required and costly to produce. The explosives in such lower
pilot hole are also largely ineffectual.
This invention possesses many other advantages and
has other purposes which may be made more clearly apparent from :
a consideration of a method embodying the invention. This
method is shown and described in the present speciEication in
connection with the drawings accompanving and constituting a
part thereof. Such drawings and method will now be described
in detail, for the purpose of illustrating the general principles
of the invention; but it is to be understood that such detailed
description is not to be taken in a limiting sense.
Referring to the drawings:
FIGURE 1 is a diagrammatic view of a blast hole
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1 which has been produced through use of the above~described one-
pass method;
FIG. 2 i9 a diagrammatic view of the blast hole or
chamber produced with the two-pass method wh:ich constitutes
the present invention;
FIG. 3 is a longitudinal section and side elevational
view of a hole opener or underreamer with its cutters ln
retracted position and located to commence enlarging the diameter
of a previously drilled pilot hole to produce the blast
chamber disclosed in Fig. 2;
FIG. 4 is a view similar to Fig. 3, illustrating the
cutters having been expanded and the blast chamber enlarged to
the bottom of the previously drilled pilot hole; and
FIG. 5 is a diagrammatic view of a plurality of blast
chambers produced in the formation, each corresponding to Fig. 2
and used for blasting a bench in surface mining.
Fig. 1 illustrates a pilot hole 10 and blast chamber 11
produced with the one-pass method, in which a pilot bit (not
shown) is secured, directly or through an intervening member, to
the lower end of an underreamer or hole opener (not shown) having
expandable cutters. The pilot bit and hole opener can be of
known constructions and are, therefore, not illustrated. The
upper portion lOa of the pilot hole is drilled by the pilot bit
with the usual hole opener body, cutter arms and cutters subject
to the action of the drilling fluid which causes their wear,
expansion of the arms and cutters occurring after the hole opener
cutters reach a location 12 at which the pilot hole is to be
enlarged in diameter to form the blast chamber 11. At that
time, the cutter arms and cutters are expanded outwardly to
enlarge the top portion o~ the pilot hole to a particular
1 diameter, whereupon continued rotation oE the hole opener
and pilot bit will produce the pilot hole in advance o~ the
hole opener, and permit the cutters of the latter to enlarge
the pilot hole to a particular diameter. The drilling
continues until the cutters have enlarged the pilot hole
down to a desired location or bottom 13. However, -the pilot
bit will also form a lower portion lOb of the pilot hole
below the bottom 13 of an enlarged hole or blast chamber 11.
The disadvantages of using the combination pilot
bit and hole opener in performing the one-pass method of
producing the blast chamber have been noted above. In
practice, it is possible to enlarge the pilot hole diameter
about 50%, because of the relatively small size of the
cutters that can be used in the expansible hole opener or
underreamer tool.
By virtue of the present invention, a two~pass
method is practiced in which the pilot hole 10 is first drilled
from the surface 14 of the ground down to the desired bottom
location 13 of the proposed blast chamber, as shown in broken
lines in Fig. 2. The pilot bit and the drill pipe string
secured thereto are then removed from the hole and a hole
opener or underreamer 15, shown in Figs. 3, 4, attached to
the string of drill pipe 22. The hole opener cutters 16,
which can be of the roller type, form the terminal portion
of the hole opener tool. Thexe are no obstructions in the
tool to the full retraction of the cutters within the confines
of the hole opener body 17. Each cutter can have an axial
extent e~ualling the axial extent of the cu-tters used on the
pilot bit, so that the cutters can be expanded outwardly
until the inner cutter portions 18 of each cutter are located
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1 at the wall 19 of the pilot hole, and wi-th the ou-ter reamer
portion 70 o:E each cutter located at the wall 71 oE the
enlarged hole or blast chamber 11. This ahi].it~ to expand
the cutters outwardly to a greater extent -thcln -the cutters
of a hole opener run in the pilot hole with a pilot bit
depending therefrom enables the blast chamber to be produced
with a diameter twice the diameter of the pi].ot hole 10.
In fact, it is possible to increase the diameter of the
blast chamber more than twice the diameter of the pilot hole
through using different lengths of cutters :L6 in the hole
opener, in which one of the cutters can have its inner
portion extend across the axis of the hole opener tool when
the cut-ters are in retracted position. Such an arranqement
is illustrated and described in United States Patent No.
2,941,785.
The rotation of the hole opener 15 will continue,
and its downward feeding with its cutters 16 expanded continued,
until the bottom 13 of the pilot hole is reached by the
cutters, resulting in the production of a comparativel~ flat
bottom across the entire enlarged blast chamber 11, with no
lower pilot hole being EormedO
The hole opener can then be removed from the blast
chamber 11 and upper pilot hole portion 10, with its cutters
having first been placed in retracted position, in a known
manner.
A hole opener apparatus for producing the blast
chamber disclosed in Fig. 2 is illustrated in Figs. 3 and
4 in a partially diagrammatic fashion. This tool is essentially
the same as disclosed in U.S. Patent No. 2,9~1,785, except
that its cutters 16 form the lowermost portion of the tool,
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1 to permit the cutters -to be disposed closely adjacent one
another when in retracted positi.on. In fact, as notecl
above, one of the cutters can be provided extending radially
inwardly across the axis of the tool, in accordance with the
teachings of the above patent.
The hole opener 15 includes a mandrel 20 having a
threaded pin 21 for threadedly securing it to the lower end
of the string of drill pipe 22, which will extend to the top
of the pilot hole previously drilled, and which is rotated
by suitable and well known mechanism tnot shown) at the top
of the hole to effect the enlargement of the borehole. This
mandrel is piloted within the main body 17 of the tool,
which has a plurality of cutter supporting arms 23 disposed
in body slots 24 and pivotably mounted on hinge pins 25 bridging
the slots and suitably secured to the body of the tool. The
lower end of each supporting arm carries an appropriate
conical type of roller cutter 16, which can extend under the
lower end of the body 17 of the tool when the supporting
arms and cutters are in their fully retracted position,
as disclosed in Fig. 3. The mandrel has a non-circular
portion 26 which can be slidably moved longitudinally along
a companion non-circular socket 27 in the body of the tool
above the body slots, to transmit the rotation of the ma.ndrel 20
to the body 17 and from the body through the cutter supporting
arms 23 to the cutters 16.
The upper portion of the body constitutes a cylinder 28
slidably longitudinally with respect to a piston 29 integral
with the mandrel, there being a cylinder space 30 between
the piston and an upper cylinder head 31 into which fluid,
such as compressed air, is directed through one or a plurality
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1 of mandrel ports 32 communicating with the central passage 33
through the mandrel, for the purpose of elevat.ing the cylinder
and body 17 upwardly along the mandrel 20, in order to
secure outward expansion of the supporting members 23 and
cutters 16. A suitable seal 34 is provided on the piston
for slidably and sealingly engaging the wall of the cylinder.
A like seal 3~a is mounted in the cylinder head 31 which is
slidably and sealingly engageable with the periphery of the
mandrel above its ports 32.
The lower portion 20a of the mandrel is slidable
within a suitable bxidge portion 17a of the body, this lower
portion having suitable side ports 35 communicating with the
central passage 33 of the mandrel, but which are initially
closed when the cutters are in retracted position by the
bridge portion 17a of the body ~Fig. 3). When the cutters
are to be expanded, compressed air is forced down the drill
string 22 and mandrel passage 33, which passes through the
ports 32 into the cylinder space 30~ urging the body 17, sup- .
porting arms 23 and cutters 16 in an upward direction along the
mandrel~ Expander surfaces 36 in the upper portions of the
arms will slide along a mandrel expander 37, which will move
the supporting arms 23 about their pivot pins 25 outwardly
of the body, the outer portions of the cutters 16 engaging
the wall of the pilot hole and enlarging it while the rotary
drill string 22 and the tool 15 connected thereto are being
rotated. ~s the cutters 16 continue to enlarge the pilot
hole 10, the body 17 of the tool shifts upwardly along the
mandrel 20 to a fuller extent, until lock surfaces 38 on the
supporting arms are disposed along companion lock surfaces 39
on the mandrel expander. At this time shoulders ~0 on each
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1 suppor-ting arm will engage companion body shoulders 41 on
opposite sides of the slot to limit the exte:nt of expansion
of the arms and of the cutters rotatably car.ried therehy,
the co-engaging holding surfaces 38, 39 preventing any
inward retraction oE the supporting arms and cutters.
With the cutters locked in their outwardly expanded
position, a downwardly facing shoulder 50 on the mandrel
will engage a companion upwardly facing shoulder 51 on the
body 17, enabling drilling weight to be imposed from -the
drill string 22 through the mandrel 20 -to the body 17, and
from the body through the hinge pins 25 and the co-engaging
stop surfaces 40, 41 to the supporting arms 23 and cutters 16.
With the cutters fully expanded, the mandrel will have been
relatively shifted downwardly below the bridge portion 17a
of the body, enabling the compressed air to discharge through
the side ports 35 toward the cutters 16 to clean and cool them
and force the cuttings upwardly around the tool 15 and through
the annulus 52 around the drill pipe string 22 to the top of
the borehole. The cutting action will proceed in a downward
direction until the bottom 13 of the blast chamber 11 is
reached, the hole having been enlarged to a much grea-ter
extent than with the one-pass method, as disclosed in Fig. 2.
The hole opener can now be withdrawn from the
borehole. The pressure in the too]. is relieved and the
drill pipe string 22 elevated, which will elevate the mandrel 20
within the body 17, until a shoulder 53 of the mandrel
engages a companion inwardly directed lug 54 on the upper
portion of each arm 23, swinging the supporting members or arms
and cutters 16 in an inward direction fully within the
confines of the body 17 of the tool. The tool can now be
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1 elevated through the upper por-tion oE -the pllo-t ho]e 10 to the
top of the ground.
In known manner, the explosive is placed in the
blast chamber 11 and de-tonated to fracture the Eormation.
In the case of blasting a bench 80 in a surEace mining
operation (Fig. 5), a known procedure is followed of drilling
several rows of blast hole chambers, packing them with
explosives, and simultaneously detonating the explosives in
all holes to blast the bench and effect its fragmentation.
The advantages of the two-pass me-thod have been
pointed out above, including the concentration of a larger
volume of explosive in each chamber 11 located at -the optimum
position with respect to the lower end of the bench. Because
of the greater charge that can be put in each blast chamber, they
can be spaced further apart for each row of blast chambers,
and the rows themselves can be spaced further from one
another. In addition, each chamber can be of less length, reducing
the time for producing the blast chamber. As a result, large
economies in drilling equipment and time result.
Wear on the hole opener 16 cutters and their supporting
arms 23 is also considerably reduced, inasmuch as the hole -
opener is not disposed in the pilot hole 10 during drilling
of the latter. When the lower portion of the previously
produced pilot hole is to be enlarged to form the blast
chamber 11, the hole opener or underreamer 15 is lowered
through the upper portion of the pilot hole without any
pressure being present in the string of drill pipe and the
too] itself. As a result, there are no forces present
tending to expand the supporting arms 23 and cutters 16
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1 outwardly. It is only when the upper location 90 of the blast
chamber to be produced has been reached that Eluid pressure is
imposed in the tool for the purpose of urging its cutters
and the supporting arms outwardly to cut into the formation
and commence the production of the enlarged blast chamber.
As previously pointed out, a pilot hole below the chamber is
not produced. Such chamber in the one-pass rnethod results
in a pilot hole lOb of extended length below the blast
chamber, particularly in the event that a stabilizer is
mounted between the underreamer and the pilot bit. Not only
is the drilling of the lower pilot hole costly, but the
explosives placed in such lower pilot hole is substantially
ineffective in disintegrating the formation.
The two-pass method of producing blast chambers
has other specific uses than in strip or open pit mining.
Pilot holes and associated chambers can be drilled in underground
coal seams, mineral deposits. Explosives can be placed in each
chamber to fragment or fracture the surrounding formation. In
the case of a coal strata, an appropriate medium can be pumped
into the enlarged chamber and fractured formation to gasify the
coal. With respect to mineral deposits, a leaching agent is
pumped into the framented formation to release the minerals.
