Charging large diameter vertical boreholes

A method of charging upwardly extending, large diameter boreholes with cylindrical explosive cartridges is provided employing a longitudinally inflating flexible tube as the pushing mechanism. A fluid-impervious flexible tube is turned over or everted at one end and secured. A fluid, preferably air, at about 3 psi is passed into the tube causing the tube to elongate and the everted tube face to travel along the length of a borehole. An explosive cartridge mounted against the tube face is carried to a desired location in the borehole after which the tube is partly deflated and withdrawn from the borehole.

The present invention relates to a method of charging boreholes with 
packages of explosives or tamping material. In particular, the invention 
is concerned with the loading of boreholes with packaged material when the 
boreholes are of relatively large diameter and are drilled vertically into 
the ceiling of an underground chamber. 
Modern mining procedures now permit the excavation of large underground 
chambers in stable ore bodies. These procedures make use of relatively 
large diameter boreholes, up to 15 cm. in diameter or larger, and 
frequently these boreholes are drilled upward vertically into the ceiling 
of the chamber to depths (lengths) of 10 meters or longer. The placing of 
cylindrical packaged explosive charges into these vertical boreholes has 
been accomplished only with difficulty since a typical 15 cm. diameter 
explosive package may weigh up to 36 kilograms or more. In the procedure 
normally employed, a cylindrical explosive package is fitted into the 
mouth of the vertical borehole and manually pushed upward into the 
borehole using a wooden push rod. A locking device adapted to grip the 
borehole wall is located below the explosive package to retain the package 
in the borehole. A subsequent explosive package or packages plus packages 
of tamping material are similarly loaded into the borehole. The operation 
is labour intensive, time consuming, physically demanding, unsafe and 
expensive. 
It has now been found that large diameter cylindrical explosive packages 
and tamping packages may be simply and conveniently elevated and placed 
into vertical boreholes (upholes) employing as the pushing or carrying 
means a longitudinally inflating, resilient, fluid impervious tube. By 
securely everting the end of a resilient tube close to the mouth or 
opening of a borehole and applying fluid pressure within the everted tube, 
the tube is caused to inflate longitudinally and migrate along the 
borehole pushing or carrying before it any appropriately sized cylindrical 
package or cartridge. When the cartridge has reached the desired location 
in the borehole, the tube is retracted to the mouth of the borehole 
leaving the cartridge suspended in the borehole. The method of the 
invention thus comprises the steps of inserting a material-containing 
cylindrical cartridge into the opening of a borehole, the cartridge being 
of a size to permit free passage through the borehole, pushing the 
cartridge along the borehole to a desired location by means of an everted, 
longitudinally, inflating resilient tube and, thereafter, withdrawing the 
resilient tube. A low air pressure is maintained in the system during 
withdrawal to prevent undue wrinkling or creasing of the tubing. 
Various known means may be employed to retain the cylindrical cartridge in 
the borehole after withdrawal of the resilient push tube and include, for 
example, an oversized, resilient or hinged disk or spider adjacent the 
package base which disk or spider grips the internal borehole wall and, 
thus, anchors the package in the borehole. Such a gripping device is 
disclosed in British Pat. No. 800,676.

With reference to the Figures of the drawing where like parts are 
designated by like numbers, there is shown a floor or platform base 1 and 
a ceiling 2 of, for example, an underground ore chamber. Located in 
ceiling 2 is an upward extending vertical borehole 3 of a diameter of, for 
example, 16.5 cm. Inserted into the mouth of borehole 3 is the end of 
loading pipe 4 having a diameter less than that of borehole 3. A 
restraining collar 5 restricts the entry of pipe 4 too deeply into 
borehole 3. Loading pipe 4 comprises a metal or plastic tube having a 
semi-circular cut-out section or area 6 along its length of a dimension 
adequate to receive a large diameter, for example, 15 cm. diameter, 
cylindrical explosive cartridge 7. Loading pipe 4 is connected or coupled 
at junction 8B to cylindrical guide section 8A of air-tight housing unit 
8. Housing unit 8, shown in cross-section, comprises a hollow structure 
within which is mounted a reel or roll 9 of elongated, fluid-impervious, 
flexible tubing material 10 having an inflated diameter slightly less than 
borehole 3. An air- or hydraulic-operated motor 11 which provides powered 
rotation to reel 9 is mounted upon housing 8. Compressed air from a source 
(not shown) enters housing 8 through conduit 12 and valve controls 13. Air 
is exhausted from housing 8 via a pressure relief valve 14 which maintains 
an appropriate back pressure (approx. 2 psi). The assembly of pipe 4 and 
housing 8 is mounted securely between ceiling 2 and floor or platform 1 by 
means of adjustable leg 15. In FIG. 2, a fuse 16 and associated detonator 
or primer 17 is shown connected to cartridge 7. A slotted opening 18 is 
provided in pipe 4 to permit the unobstructed passage through pipe 4 of 
fuse 16 as cartridge 7 is pushed upwardly through pipe 4 into borehole 3. 
Within housing 8, the leading circumferential edge of tubing 10 is everted 
and secured within and around the interior of guide section 8A by means 
of, for example, a securing ring 19. When pressurized air is admitted into 
housing 8 via conduit 12 and valve controls 13, the air presses against 
the everted inside face of the tubing 10 in the direction shown by the 
arrows, causing tubing 10, which is slightly less in diameter than 
borehole 3, to unwind from reel 9 and to inflate and unroll longitudinally 
within and along pipe 4 pushing cartridge 7 before it into borehole 3. 
When the cartridge has reached the closed end (the toe) of borehole 3, air 
flow to housing 8 is cut off and air motor 11 is operated to withdraw the 
everted tubing 10 against a back pressure maintained by pressure relief 
valve 14 from borehole 3. As it is withdrawn, tubing 10 is rewound upon 
reel 9. 
In use in the field, an apparatus as shown in the Figures of the drawing is 
assembled at the blasting site with an appropriate pressurized air 
connection being made from a mine source (not shown) to air conduit 12. 
The leading end of pipe 4 is inserted into a borehole and the apparatus 
secured in alignment with the borehole by means of adjustable leg 15. A 
cylindrical explosive cartridge 7 having a diameter slightly less than 
that of borehole 3 is prepared by connecting thereto the appropriate 
initiation system, for example, fuse 16, cap and primer 17 or electric 
wires, electric cap and primer. The prepared cartridge is placed into pipe 
4 through semi-circular cut-out section 6 and air is gradually admitted 
into housing 8 through valve control 13 to inflate and unroll the everted 
tube 10 longitudinally and so deliver cartridge 7 to a desired position in 
the borehole. Cartridge 7 is adapted by means such as a spider gripper 
(not shown) to remain in the desired position in the borehole. The tubing 
10 is, then, rewound upon reel 9 by means of air motor 11. Air relief 
valve 14 maintains an air pressure of about 2 psi to prevent wrinkling of 
tube 10 as it is rewound. A subsequent explosive cartridge or tamping 
cartridge can, then, be loaded into the borehole by repeating the 
procedure. 
It will be appreciated that the length of tubing 10 required to push 
cartridge 7 to the toe of borehole 3 will be twice the length of the 
borehole since, when extended, tubing 10 is doubled back upon itself. 
The material of construction of housing unit 8 and pipe 4 is, preferably, 
metal but pipe 4 may be usefully made from rigid plastic, such as, for 
example, ABS, PVC or the like. Fluid-impervious tubing 10 must combine the 
properties of flexibility and durability since it is exposed to sharp rock 
projections in the borehole. A material, such as, for example, rubber or 
plastic impregnated fabric having a wall thickness of from about 0.5 mm. 
to 2 mm. has been found suitable. When damaged or punctured, tubing 10 is 
easily replaced and additional lengths may be stored upon reel 9. 
EXAMPLE 
To test the utility of the method of the invention, a simulated vertical 
borehole was provided consisting of a 12.7 cm. internal diameter section 
of plastic pipe 3.66 meters in length. An apparatus as depicted in the 
Figures of the drawing was fitted with a length of 6 mil polyethylene 
tubing 8.9 cm. in diameter as the `pusher` tube. A twenty pound dummy 
explosive cartridge weighing 9 kg. was lifted the full height of the 
simulated borehole upon the application of 3 psi air pressure. 
As described, the present invention provides a convenient and safe means 
for elevating heavy explosive and tamping cartridges into upwardly 
extending boreholes. While particularly adapted for the charging of 
upholes, the method may also be employed in charging horizontal boreholes.