It is known to require the use of plugs within boreholes, Typically, boreholes are drilled through ore bodies to a particular depth. It is frequently desirable to locate explosives within a borehole at a shallower depth than that of the hole. In these circumstances a plug is placed into the hole at the required depth, with the explosives being placed on top of the plug. The plug engages with a side wall of the borehole in order to maintain position.

A known type of borehole plug consists of an inflatable bag having a gas source contained therein. The gas source may consist of a compressed gas or propellant canister, or a set of chemicals which release gas when combined, These plugs are typically arranged so as to require the source to be activated to release the gas into the bag immediately before the plug is placed into a borehole, The plug is then lowered to the required depth whilst the gas is being released, and the bag inflated. When the bag is fully inflated it engages with the side walls of the borehole by means of an interference fit.

A common problem experienced with such plugs is that in some situations the bag can inflate too quickly, and lodge within the borehole at a position above the desired location. In other situations the converse problem may occur, that the bag must be held at its desired level by means of a string or rope for a long period before it is sufficiently inflated to engage the side walls of the borehole.

Further problems have been experienced during the transportation and storage of bags containing compressed gas or propellant canisters, for instance due to overheating and splitting of the canisters in hot conditions.

SUMMARY OF THE INVENTION The present invention attempts to overcome at least in part, some of the aforementioned disadvantages of previous borehole plugs.

In accordance with one aspect of the present invention there is provided a borehole plug comprising an inflatable bag having a valve, the valve allowing the passage of gas into the bag but preventing the passage of gas out of the bag, the valve being connected to a gas supply by a supply means, wherein the supply means is arranged to be disconnected from the valve by a user remote from the bag.

In accordance with second aspect of the present invention, there is provided a method for plugging boreholes, the method comprising the steps of lowering an inflatable borehole plug to a desired location within the hole, supplying gas to inflate the borehole plug from an external gas supply source through a valve, and removing the connection between the valve and the gas supply source when the borehole plug has been inflated to a desired pressure.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a borehole having a blast plug in accordance with the present invention in an un-inflated state; Figure 2 is a schematic view of the blast hole of Figure 1 showing the blast plug in an inflated state; Figure 3 is a plan view of the borehole plug of Figure 2; Figure 4 is a cross sectional view of a first embodiment of valve of the borehole plug of Figure 2 shown connected to a nozzle; Figure 4a is a perspective view of the nozzle of Figure 4; Figure 5 is a cross sectional view of a second embodiment of valve of the borehole plug of Figure 2 shown connected to a nozzle; Figure 5a is a perspective v of the nozzle of Figure 5; Figure 6a is a plan view of the borehole plug of Figure 1 shown connected to a gas supply means; Figure 6b is a plan view of the borehole plug of Figure 6a after inflation; and Figure 7 is a schematic view of a gas supply means in accordance with an alternative embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring to the Figures. there is shown an ore body 10 into which a borehole 12 has been drilled. An inflatable borehole plug 14 is shown within the borehole 12 in an un- inflated state in Figure 1, and an inflated state in Figure 2.

The borehole plug 14 is shown in greater detail in Figure 3. The borehole plug 14 is typically comprised of two bags constructed from a high strength, hermetic plastic material. A third bag constructed of abrasion resistant material such as woven polypropylene may encase the borehole plug 14.

The bags comprising the borehole plug 14 are preferably heat sealed.

The borehole plug 14 includes a valve 16. The valve 16 extends outwardly of the borehole plug 14 through an aperture 18 within the borehole plug 14. The valve 16 is preferably welded about the aperture 18 by a technique such as ultrasonic welding or heat seal to create a hermetic seal against the bags with the aid of energy directors located at suitable positions on the valve 16.

A first embodiment of the valve 16 is shown in more detail in Figure 4. The valve 16 comprises of a hollow stem 20 having a circumferential or annular rib 22 protruding externally about the stem 20 at a location approximately half way along the stem 20.

The valve 16 further comprises an external circumferential groove 24 located adjacent to the outer end of the stem 20. A resilient sealing ring 26 is located within the groove 24.

A second embodiment of the valve 16 is shown in Figure 5. In this embodiment the circumferential groove 24 and associated sealing ring 26 are located approximately halfway along the stem 20. The sealing ring 26 thus fulfils the function of the rib 22 in the first embodiment. Both embodiments of the valve 16 include an inner core (not shown), which is arranged to allow the passage of gas into the borehole plug 14 but prevent the passage of gas out of the borehole plug 14. Preferably the inner core consists of a Schrader valve.

Each embodiment of the valve 16 is designed to mate with a nozzle 30. The nozzle 30 has a substantially cylindrical first portion 32 having an internal bore approximately equal in diameter to the external diameter of the stem 22, and a tapered second portion 34. The internal bore of the second portion 34 increases away from the first portion 32.

A circumferential groove 36 forms an internal shoulder between the first portion 32 and the second portion 34, In use, the rib 22, or sealing ring 26, of the valve 16 respectively locates within the groove 36.

When the first embodiment of the valve 16 is used, the sealing ring 26 seals against the first portion 32 of the nozzle 30. When the second embodiment is used, the sealing ring 26 seals against the internal shoulder formed by the groove 36.

It will be appreciated that the arrangement of the valve 16 internally of the nozzle 30 allows the passage of air through the entire core of the valve 16.

The nozzle 30 is mounted at the end of a gas supply line 38. The gas supply line 38 is preferably formed of a composite reinforced Teflon hose material. The nozzle 30 and gas supply line 38 comprise a gas supply means for the borehole plug 14 In a preferred embodiment as shown in Figure 1, an end remote to the nozzle 30 of the gas supply line 38 is connected to a regulating device 40. The regulating device 40 is connected to a supply of compressed gas. The regulating device 40 includes a pressure detection means.

In use, the nozzle 30 is mounted to the valve 16 of an un-inflated borehole plug 14.

The borehole plug 14 is then lowered into the borehole 12 to the required depth, being held in position by the gas supply line 38. The un-inflated borehole plug 14 may be maintained in a constricted position by the application of tape 15 as shown in Figure 6a, to allow easy location within the borehole 12.

When the borehole plug 14 has been located at the required position, filling of the bag is commenced. In the simplest form of the invention, an operator operates the regulating device 40 to allow compressed gas to pass into the gas supply line 38 and thence to the borehole plug 14 In this embodiment the pressure detection means is connected to a signal or visual display which informs the operator of the pressure in the gas supply line 38 and thus the borehole plug 14. When the desired pressure is reached the operator ceases the supply of air to the gas supply line.

In another embodiment of the invention the regulating device 40 may be operated by remote means, such as by UHF transmission, In this embodiment the regulating device 40 is arranged to supply compressed gas at a relatively high pressure, and hence at a high flow rate, to the gas supply line 38 for a predetermined time period. At the conclusion of this time period the pressure detection means determines whether the borehole plug has been inflated to a desired pressure. If more inflation is required the pressure detection means electronically regulates the further supply of gas to the gas supply line 38 at a lower pressure, to provide greater control, until the desired pressure is reached.

The regulating device is designed to emit a signal to an operator when the filling operation is complete.

In a third embodiment of the invention, as shown in Figure 7, the supply of compressed gas is provided in a tank 42. The tank 42 is provided with a particular volume of gas at a predetermined pressure. The pressure and volume of gas in the tank 42 is arranged such that connection of the gas supply line 38 to the tank 42 results in the required quantity of compressed gas being supplied to the borehole plug 14.

When the borehole plug 14 has been inflated by any of the means described herein above, the borehole plug 14 will form an interference fit against the sides of the borehole 12. This situation is shown in Figure 2. The application of a pulling force to the gas supply line 38 will cause the nozzle 30 to disengage from the valve 16. The gas supply line 38 can thus be removed from the borehole 12 whilst the inflated borehole plug 14 remains in the required position.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.