Field of the Invention

The present invention relates to mining, and more specifically blocking off mining exploration drill holes. The invention has particular application for blocking off underground diamond drill exploration holes, however the product may also be applied to surface drill holes.

Background to the Invention

Once underground access is commenced through a portal or shaft for a new mine, diamond drill crews begin drilling from the first available underground location to allow geologists to better define the ore body so that the design of the mine can be optimised. Therefore exploration drilling usually occurs in advance of the mine development, and typically the exploration drill holes range from horizontal to downward dipping to delineate the ore body beneath and to the side of the main access.

When these exploration drill holes are abandoned, they leave an open hole between the main access and the ore body location which will at some stage be advanced upon. At a later date when the mine does advance across the path of the exploration drill hole, there is a danger that when firing of explosives occurs gases and other debris will rifle back up through the open hole connecting the two locations. This presents a serious safety hazard to any occupants of the mine. There are three ways a Mine Manager may deal with this situation:

(i) Ensure the mine is fully evacuated prior to firing. This is not practical in most larger mines where multiple firings occur during the allotted firing time.

(ii) Ensure all intersections are planned and anticipated. This is difficult due to variation between a hole's expected location and its actual location. These exploration holes may be hundreds of metres long and while they are logged the accuracy of the logging is not necessarily dependable to the extent of knowing exactly when the hole will be advanced upon.

(iii) Ensure all potential exploration drill holes are blocked off to prevent the danger of rifling. Prior art methods for plugging exploration drill holes (or in fact any mining holes) include various mechanical devices and/or grouting.

US 3,756,316 (Van Ruth) describes a mechanical bore hole plug which can be passed through a drill stem to plug a bore hole. A variety of these kinds of plugs are available as can be seen at http://www.vanruth.com.au/default.htm. These plugs are not suitable to block an exploration drill hole on their own to prevent rifling. Specifically, they are designed for static forces whereas an explosive intersection of a diamond drill hole results in substantial dynamic forces. There is a substantial risk that the plug will blow out and become a projectile, particularly since it is only anchored in the very collar of the hole where there is often broken ground.

Various other kinds of "packer" are available which are similar to the Van Ruth plug in that they are mechanical devices for plugging a drill hole. They are also referred to as Margo plugs in Canada. A packer may be made with a longer stem which would place its rubber anchor further in the hole so that it is less affected by the broken ground at the collar. Even so, the same criticisms apply as to the Van Ruth plug above; it is dangerous to use a packer to protect from rifling when subject to dynamic forces.

Both types of mechanical devices are designed to transmit grout, and only when the hole has been grouted through these plugs and the grout has cured will it be safe from rifling or venting. However, there is considerable expense involved in doing this, including the cost of the mechanical plug itself, the installation of the mechanical plug by knowledgeable staff, and then the grouting through the mechanical plug by an experienced grout crew using a conventional grout machine. Grouting the full length of exploration drill holes is not practical, where holes may be up to 200m or more in length, and those that are angled upward beyond 30m or so are technically impossible to grout full length. An alternative therefore is to grout the collar of the hole which will effectively prevent rifling. "Grout" is a term that is used to refer to cementitious slurries used in mining which may cure to a strength similar to that of concrete (harder, but typically more brittle). A basic grout may be as simple as a mixture of Portland cement and water. Grout is mostly used for ground support in mining which involves anchoring a tendon into a hole that has been drilled in the surrounding rock for stabilisation of the strata above and around mine excavations. For this purpose grouts tend to have additives included in addition to Portland cement, such as plasticisers to increase fluidity and reduce the hydration requirement for curing, accelerators or retarders to reduce or delay curing time, and additives to improve bond strength particularly with reinforcing steel, i.e. ground support elements.

Occasionally, grout is also used to simply fill voids or prevent high pressure water inflow.

Traditionally grouting is carried out using a grout pump with one of two water/cement ratios (WC ratio). Greater than 0.35 WC ratio gives a runny slurry which needs a grouting technique using a breather tube to bleed the air out. Less than 0.35 WC ratio gives a thick grout mix being the consistency of toothpaste in which case the operator slowly withdraws the pump delivery tube as the grout enters the hole. Generally, the grout with the lower WC ratio will be the stronger one.

Pumping grout requires continuity of operations. Delays of more than an hour or so results in the grout mix beginning to set in the pump and will stop the pump from running. Continuity of grouting requires enough work for a grouting crew to continue grouting. However, grouting of exploration drill holes provides only piecemeal work and is inefficient for an experienced crew unless the crew has other work in that area to carry on with. The alternative is for grouting to be carried out inefficiently by non-grouting proficient diamond drill crews on an ad hoc basis when required, which means that the drill is standing idle while they do this.

The present invention was developed with a view to providing a plug and method of plugging a mining drill hole that is less susceptible to the disadvantages of the prior art noted above.

References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.

Summary of the Invention

According to one aspect of the present invention there is provided a grout plug for plugging a drill hole in a mine, the plug comprising: an elongate sleeve of porous material adapted to be received in a drill hole; a volume of dry grout material in particulate form contained in the sleeve wherein, in use, when the plug is exposed to water it mixes with the grout material to form a slurry which can seep through the porous sleeve when the plug is tamped into the drill hole to block the drill hole when the grout material cures.

Preferably the porous sleeve is made from a water-absorbent material wherein, in use, the porous sleeve helps maintain a moist environment in the hole during curing by wicking moisture to the grout to assist with curing the grout. Preferably the porous sleeve is made from a lightweight, biodegradable mesh material. Preferably the porous sleeve is made from hessian or jute. Preferably the plug further comprises a liner of water-soluble material, the liner being provided within the porous sleeve for containing the grout material within the porous sleeve in its dry form and wherein, in use, when the plug is exposed to water the liner dissolves.

Preferably the liner is in the form of an inner sleeve made from a thin film of plastics material which is separate from the porous sleeve. Preferably the sleeve is designed with a curved leading edge for installation to assist in guiding the grout plug into a hole of only marginally larger diameter. Preferably the grout plug is cylindrical or sausage shaped, and is preferably 600mm in length. The grout plug may be of varying outer diameters, but preferably the grout plug has an outer diameter of about 46mm, 58mm, 74mm or 94mm.

According to another aspect of the present invention there is provided a grout plug for plugging a drill hole in a mine, the plug comprising: an elongate sleeve of porous material adapted to be received in a drill hole; a volume of dry grout material in particulate form; and a liner of water-soluble material, the liner being provided within the porous sleeve for containing the grout material within the porous sleeve in its dry form and wherein, in use, when the plug is exposed to water the liner dissolves and the water mixes with the grout material to form a slurry which can seep through the porous sleeve when the plug is tamped into the drill hole to block the drill hole when the grout material cures.

Typically the porous sleeve is made from a water-absorbent material wherein, in use, the porous sleeve helps maintain a moist environment in the hole during curing by wicking moisture to the grout to assist with curing the grout. Preferably the porous sleeve is made from a lightweight, biodegradable mesh material. Advantageously the porous sleeve is made from hessian or jute, which is a low cost, environmentally sustainable material.

Typically the liner is in the form of an inner sleeve received within the porous sleeve. Preferably the liner is in the form of an inner sleeve made from a thin film of plastics material which is separate from the porous sleeve. Alternatively the liner is formed integral to the porous sleeve. Preferably the liner is made from polyvinyl alcohol (PVA) which is a water soluble plastic that dissolves within seconds when immersed in water. Typically the grout material is ordinary Portland cement. However, depending on the application various additives may be added to the grout material or cement as required, such as plasticisers, retarders, accelerators, clays, and aggregates. The grout material may be comprised chiefly of bentonite clay or other clay, as required. Preferably the grout plug is cylindrical or sausage shaped, and preferably is 600mm in length.

According to a further aspect of the present invention, there is provided a clay plug for plugging a drill hole, the clay plug comprising: an elongate sleeve of porous material adapted to be received in a drill hole; a volume of dry clay material; a liner of water-soluble material, the liner being provided within the porous sleeve for containing the clay material within the porous sleeve in its dry form; and a substantially solid central core of low permeability, the central core running substantially the length of the plug.

This embodiment has particular application for sealing water flow from a drill hole. Preferably the central core comprises wood, metal, steel or cured grout. In this embodiment, preferably the clay material is bentonite or other suitable clay material. The clay is typically in particulate form, or other suitable form. According to another aspect of the present invention, there is provided a plug system for plugging a drill hole, the plug system comprising one or more grout plugs of the present invention, in combination with one or more clay plugs according to the invention.

According to a still further aspect of the present invention there is provided a method of plugging a drill hole in a mine, the method comprising: filling an elongate sleeve of porous material, adapted to be received in a drill hole, with a volume of dry grout material in particulate form to form a grout Plug; providing one or more of the grout plugs to a mine site ready for use in the event that a drill hole needs to be blocked; immersing one or more of the grout plugs in water for a prescribed time until the water mixes with the grout material to form a slurry; inserting the one or more wetted grout plugs in the drill hole and tamping each grout plug into the drill hole so that some of the grout material squeezes out through the porous sleeve; and allowing the grout material to cure so that the one or more grout plugs block the drill hole.

Preferably the method further comprises the step of maintaining a moist environment in the drill hole during curing by employing a water-absorbent material to make the porous sleeve wherein, in use, the porous sleeve assists with curing the grout by wicking moisture to the grout.

Preferably the method further comprises the step of providing a liner of water-soluble material, the liner being provided within the porous sleeve for containing the grout material within the porous sleeve in its dry form and wherein, in use, when the plug is immersed in water it is allowed to soak for the prescribed time until the liner completely dissolves.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. Likewise the word "preferably" or variations such as "preferred", will be understood to imply that a stated integer or group of integers is desirable but not essential to the working of the invention.

Brief Description of the Drawings

The nature of the invention will be better understood from the following detailed description of several specific embodiments of grout plug and method of plugging a mining drill hole, given by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates a preferred embodiment of a grout plug in accordance with the present invention;

Figure 2 is a cut-away section view of the grout plug of Figure 1 ;

Figure 3 illustrates a first step in the process of constructing the grout plug of Figure 1 ;

Figure 4 illustrates a second step in the process of constructing the θ

grout plug of Figure 1 ;

Figure 5 illustrates how the grout plug in accordance with the present invention can be used to prevent rifling and venting in underground exploration drill holes;

Figures 6 and 7 illustrate a preferred method of installing the grout plugs in accordance with the present invention in a drill hole; and

Figure 8 illustrates a second preferred embodiment of a clay plug in accordance with the present invention.

Detailed Description of Preferred Embodiments

A preferred embodiment of grout plug 10 in accordance with the invention, as illustrated in Figures 1 and 2, comprises an elongate sleeve 12 of porous material adapted to be received in a drill hole (see Figure 5). The porous sleeve 12 contains a volume of dry grout material 14 in particulate form. When the plug 10 is exposed to water it mixes with the grout material 14 to form a slurry which can squeeze through the porous sleeve when the plug is tamped into the drill hole. In this way the grout plug 10 can be used to block the drill hole once the grout material 14 cures. Preferably the grout plug 10 further comprises a liner 16 of water-soluble material. The liner 16 is provided within the porous sleeve 12 for containing the grout material 14 within the porous sleeve 12 in its dry form. In use, when the plug 10 is exposed to water, the liner 16 dissolves and the water mixes with the grout material 14 to form a slurry. The slurry can seep through the porous sleeve when the plug 10 is tamped into the drill hole to block the drill hole when the grout material cures.

Typically the porous sleeve 12 is made from a water-absorbent material wherein, in use, the porous sleeve 12 helps maintain a moist environment in the hole during curing by wicking moisture to the grout material 14 to assist with curing the grout. Preferably the porous sleeve 12 is made from a lightweight, biodegradable mesh material. Advantageously the porous sleeve 12 is made from hessian or jute, which is a low cost, environmentally sustainable material. In the described embodiment 18oz hessian is employed to make the porous sleeve 12.

Typically the liner 16 is in the form of an inner sleeve received within the porous sleeve 12. Preferably the liner 16 is made from a thin film of plastics material which is separate from the porous sleeve 12. Alternatively the liner 16 is formed integral to the porous sleeve 12. Preferably the liner 16 is made from polyvinyl alcohol (PVA) which is a water soluble polymer that dissolves within seconds when immersed in water.

Typically the grout material 14 is ordinary Portland cement. However depending on the application various additives may be required such as plasticisers, retarders or accelerators, and aggregates.

A currently preferred process of manufacturing the grout plugs 10 will now be described with reference to Figures 1 to 4. A rectangular, elongate sheet of hessian or jute material 14 is cut and folded in half length ways as shown in Figure 3. Then the open side and one end of the sheet 14 is stitched together along the stitch line 18 as shown in Figure 4. The resulting sleeve 12 is turned inside out to conceal the hem. The sleeve 12 is designed with a curved leading edge 26 for installation to assist in guiding the grout plug 10 into a hole of only marginally larger diameter. The plug 10 still needs to be capable of installation even where the hole may have surface irregularities through deviation or broken ground.

Preferably the PVA liner 16 is formed in a similar way, either by stitching or heat welding along the open side and one end to form an inner sleeve. The PVA liner 16 is not turned inside out. Assembly is simple and involves inserting the PVA liner 16 into the hessian or jute sleeve 12 and filling it with the dry grout powder 14 (and the central core if the configuration requires, as discussed below for the second embodiment 40) . The grout plugs preferably have a bulk density after filling with grout of 1.5 - 2.5g/cc, more preferably about 1.9g/cc. This is driven by the need for the grout plug to retain its shape for installation, and to maintain a low watencement ratio on immersion. Both sleeves 12 and 16 are then wire tied or cable tied at the open tail end, resulting in the completed grout plug 10 as shown in Figures 1 and 2.

The completed grout plug 10 is cylindrical or sausage shaped and typically is manufactured in lengths of 600mm, with an outer diameter of about 46mm (allowing a tolerance of about 2mm within a drill hole with 48mm inside diameter, and allowing for bit wear and irregularities within the hole). On tamping, the grout material extrudes through the hessian sleeve 12 to engage more fully with the hole and make up the hole diameter. The outer diameter of the porous sleeve 12 may be selected to suit the nominal drill hole size. Colour-coded hessian may be used to clearly identify different diameter plugs for ease of use for the various standard diameter drill holes.

The grout plugs 10 will nominally be 2mm smaller in diameter than the new bit size for each of the standard sizes shown below, to allow for bit wear.

The PVA liner 16 may not be in the form of a separate inner sleeve 16 as in the illustrated embodiment. The liner 16 could be formed integral to the porous sleeve 2, as a layer on the inside or outside of the sleeve 12 which blocks the pores in the porous hessian material. The liner helps to prevent the grout powder, typically Portland cement, from leaking through the pores of the porous sleeve 12. However the liner 16 could be dispensed with altogether if a degree of leakage of the dry grout material during transport and storage can be tolerated. Alternatively the grout material may be selected to be of a particle size that cannot easily escape through the pores of the porous sleeve 12 in its dry form.

A preferred method of plugging a mining drill hole using the grout plugs 10 according to the invention will now be described with reference to Figure 5. The method preferably comprises filling an elongate sleeve 12 of porous material, adapted to be received in a drill hole, with a volume of dry grout material 14 in particulate form to form a grout plug 10 as described above. One or more of the grout plugs 10 are then provided to a mine site ready for use in the event that a drill hole needs to be blocked. Rigidity is provided by using a hessian or jute skin, and leakage of a small amount of grout through this skin during handling is inconsequential in comparison to the advantage gained through maintaining simplicity of use and low cost.

When a drill hole 20 is required to be blocked, one or more of the grout plugs 10 is carried down to the diamond drill location 22 (see Figure 5). Each grout plug 10 is immersed in water for a prescribed time until the water mixes with the grout material 14 to form a slurry. Soaking the grout plug 10 until the cessation of production of bubbles, generally around 2 - 3 minutes, dissolves the PVA liner 16 and automatically wets the grout to a WC ratio of 0.35, which develops a strong, low shrink grout. This avoids the requirement for mixing.

PVA is commonly used in the concreting industry and has a documented effect of increasing the strength and decreasing the porosity of the cured product. However for the purpose of this application, the diluted PVA content of the water in which the grout plugs soaks is unlikely to provide any advantage. More importantly it will not be detrimental to the integrity of the cured grout. One or more wetted grout plugs 10 is then inserted in the drill hole 20 and each grout plug is tamped into the drill hole so that some of the grout material extrudes or squeezes out through the weave of the porous hessian sleeve 12, as shown in Figures 6 and 7. Tamping is typically done using a rigid plastic tube 24, and is similar to the process used for tamping explosives into a drill hole. Tamping it into the drill hole 20 avoids the requirement for pumping, and the time to set up and strip down a grout pump. The grout quality does not suffer, and in fact the self wetting aspect of the grout plug removes the human error involved in achieving a certain WC ratio. The grout material is then allowed to cure so that the one or more of the grout plugs block the drill hole. Typically up to five of the 600mm grout plugs 10 may be tamped into the collar of the drill hole 22 to form a 3m plug.

Thus it can be seen that the method of the invention further comprises the step of maintaining a moist environment in the drill hole during curing by employing a water-absorbent material to make the porous sleeve 12. The porous sleeve 12 assists with curing the grout by wicking moisture to the grout. The method may include the further step of providing a liner 16 of water-soluble material as noted above. The drill hole 20 is effectively sealed off with a 3m grout plug, being five such sausages tamped into place one behind the other, for the purpose of preventing rifling. Mines would be free to use more or less sausages as the circumstances dictate. Curing time is achieved with an initial set at 24 hours, early strength at 7 days and full strength at 28 days. A 7 day cure is sufficient to prevent rifling, although earlier set times may be achieved by using alternate cements.

The hessian or jute sleeve 12 is economical, environmentally sustainable, and allows some storage of moisture and the wicking of moisture to the grout material 14 to assist with curing the grout. The curing of grout is essentially the same as curing concrete. It is assisted by continued hydration, resulting in a stronger end result than if it cures in a dry environment. The grout plugs 10 are intended to block exploration drill holes to prevent rifling or venting from blasts at any location along the hole if that hole is intersected at a later date. The grout plugs 10 are designed to quickly, efficiently and economically make a mine drill hole safe for these circumstances. Additives would generally not be required for this purpose since they will increase the cost and complexity of the product where the basic product satisfies the purpose at the lowest cost. The grout plugs 10 according to the first embodiment are not intended to completely seal off the hole 20 from the flow of groundwater or gases but may in some instances be able to do this.

A second embodiment of a clay plug 40 of the invention as illustrated in Figure 8 resembles the first embodiment in many ways and will not be described in detail. The clay plug 40 comprises an elongate sleeve 42 of porous material containing a volume of clay material 44 which in this instance is bentonite clay (although other clays may also be suitable). The clay plug 40 further includes a liner 46 of water-soluble material, and a substantially solid central core 48 running substantially the length of the plug. The central core 48 is preferably of low permeability and typically made from a substance such as wood, metal, steel or cured grout. The central core 48 forms a substrate against which the clay material may cure or seal. This will prevent the clay material from remaining dry at the core of the plug, and will provide surface pressure for the sealing property of the clay.

The clay plug 40 has particular application for sealing water flow from a drill hole. The advantage of using bentonite clay as the "grouting" material in this embodiment is that bentonite clay slowly expands and seals when in contact with water. To be effective in sealing against flowing water, the bentonite 44 needs to be in a relatively thin annulus (as can be seen in Figure 8), for example about 10mm to 15mm thickness. Therefore to seal a bore hole of 48 to 96mm diameter a low permeability core needs to be included inside the plug. By way of explanation for a 74mm plug, if the bentonite is 10mm thick inside, the central core needs to be 54mm (74mm less two "thicknesses" of 10mm each for the bentonite). The problem with the bentonite is it will seal itself from the water, remaining dry if it is thicker than about 15mm. In this instance it will not provide sealing pressure against the hole because the dry bentonite inside does not expand, and in fact it will compress eliminating the sealing pressure from the wet bentonite in contact with the hole.

It should be noted that in the second embodiment, due to the presence of natural water in the drill hole, it is not necessary for the clay plug 40 to be immersed in water prior to insertion into the hole (although it is still permissible to do this as it will not be detrimental to the end result).

It should also be noted that in the case of the second embodiment, tamping is not required as the bentonite exudes through the weave of the sleeve 42 under its own expansion. A still further aspect of the invention relates to a plug system for plugging a drill hole, such as in a mine. The plug system (not shown in the drawings) comprises a combination of one or more grout plugs 10 with one or more clay plugs 40. Typically the system has application for sealing water flow from a drill hole. For example, a clay plug 40 with bentonite is firstly placed in a drill hole followed by one or more grout plugs 10 behind the clay plug. The grout plug(s) then cure behind the bentonite plug forming a secure seal.

Whilst the invention has been described with particular application to prevent rifling back through exploration drill holes, it is anticipated that the invention may also have application in the following additional markets: 1. grouting surface exploration drill holes to prevent native fauna from falling down these drill holes in addition to protection from rifling in mining areas, 2. grouting both open pit and underground blast holes to prevent the escape of explosives where those holes break through into existing workings, 3. grouting the collars of open pit blast holes where a blast will "sleep" at least overnight, preventing rifling of the stemming material,

4. grouting the collars of Vertical Crater Retreat (VCR) type blasting to improve the impact of explosives on the development, and

5. assisting in sealing off drill holes to prevent water flow.

Now that preferred embodiments of the plug and a method of plugging a mine drill hole have been described in detail, it will be apparent that the described embodiments provide a number of advantages over the prior art, including the following:

(i) Since the plugs are completely prepared off site, where labour is more economical than on site or underground, they can be manufactured at low cost and provide an extremely economical alternate to mixing and pumping the grout on site.

(ii) A supply of the grout plugs can easily be kept in storage at the mine site ready for use when required for blocking a drill hole.

(iii) The hessian or jute sleeve is environmentally sustainable and its porosity assists with retaining and wicking moisture during curing.

(iv) Tamping the plug extrudes some of the grout material through the porous sleeve which helps to retain the plug in the drill holewhen the grout cures. (v) Soaking the grout plug for the prescribed time dissolves the PVA liner and automatically wets the grout to a WC ratio of 0.35, which develops a strong, low shrink grout. This also avoids the requirement for mixing.

(vi) Use of the liner in the grout plug helps to prevent grout powder (such as Portland cement) from leaking through the pores of the porous sleeve.

(vii) In at least one embodiment of the invention, the plug assists in sealing off drill holes to prevent water flow.

It will be readily apparent to persons skilled in the relevant arts that various modifications and improvements may be made to the foregoing embodiments, in addition to those already described, without departing from the basic inventive concepts of the present invention. For example, whilst hessian or jute has been described as the preferred material for making the porous sleeve, the porous sleeve may be made from any suitable material. Therefore, it will be appreciated that the scope of the invention is not limited to the specific embodiments described.