Protection of blast holes

Abstract

A method of protecting predilled, uncharged bore holes for use in an underground mine engaged in stope mining; the method comprising the steps of filling the uncharged bore holes with a liquid and sealing the entry of the liquid-filled blast holes prior to detonating adjacent blast holes. The liquid to be used will depend on the material being mined. In impervious material, the liquid is water. In porous material, the liquid may be viscous or have sealing properties such as a drilling mud or bentonite mud. Various plugs for sealing the bore holes are also described and claimed.

The claims defining the invention are as follows:  
     
         1 . A method of protecting a predrilled, uncharged blast hole comprising the steps of substantially filling the blast hole with a liquid before adjacent blasting is conducted and sealing the entry of the blast hole.  
     
     
         2 . A method of protecting a predrilled, uncharged blast hole as claimed at  claim 1  wherein the entry of the blast hole is sealed by inserting a plug into the entry of the blast hole and positioning the plug adjacent to the entry of the blast hole.  
     
     
         3 . A method of protecting a predrilled, uncharged blast hole as claimed at  claim 2  wherein liquid is delivered into the blast hole after the plug is inserted.  
     
     
         4 . A method of protecting a predrilled, uncharged blast hole as claimed at  claim 2  or  claim 3  wherein the entry of the blast hole is lined before it is sealed by the plug.  
     
     
         5 . A plug adapted to seal a blast hole against leakage of liquid comprising sealing means adapted to provide sealing engagement between the bore of the blast hole and the plug, and retaining means adapted to positionally retain the plug within the blast hole.  
     
     
         6 . A plug as claimed at  claim 5  wherein the sealing engagement is releasable.  
     
     
         7 . A plug as claimed at  claim 6  wherein the sealing means is adapted to provide sealing engagement between the bore of the blast hole and the plug by expansion of the sealing means.  
     
     
         8 . A plug as claimed at any one of  claims 5  to  7  wherein the sealing means is responsive to pressure to provide sealing engagement.  
     
     
         9 . A plug as claimed at any one of  claims 5  to  8  wherein the sealing means comprises a seal seated in a groove.  
     
     
         10 . A plug as claimed at any one of  claims 5  to  9  wherein the sealing means comprises a seal having a ‘U’ shaped cross-section.  
     
     
         11 . A plug as claimed at any one of  claims 5  to  9  wherein the sealing means comprises a seal having a circular cross-section.  
     
     
         12 . A plug as claimed at any one of  claims 5  to  11  wherein the retaining means is adapted to retain the plug within the blast hole by releasable engagement of the retaining means with the bore of the blast hole.  
     
     
         13 . A plug as claimed at any one of  claims 5  to  12  wherein the engagement of the retaining means with the bore of the blast hole is effected by expansion of the retaining means.  
     
     
         14 . A plug as claimed at any one of  claims 5  to  13  wherein the retaining means, when in use, is adapted to provide additional retaining force to the bore of the blast hole when additional force is applied to the plug from within that portion of the blast hole enclosed by the plug.  
     
     
         15 . A plug as claimed at any one of  claims 5  to  14  wherein the plug is associated with a supply duct adapted to allow the passage of liquid past the plug.  
     
     
         16 . A plug as claimed at any one of  claims 5  to  15  wherein the supply duct is provided through the plug.  
     
     
         17 . A plug as claimed at  claim 16  wherein the plug is further provided with pressure-communication means adapted to communicate pressure from the supply duct to the sealing means.  
     
     
         18 . A plug as claimed at either of claims  16  or  17  wherein the supply duct is provided with a pressurising nozzle adapted to restrict the flow of liquid through the nozzle and thereby ensure pressure is provided within the supply duct during filling of the blast hole with liquid.  
     
     
         19 . A plug as claimed at any one of  claims 5  to  18  wherein the plug is associated with a breather duct adapted to allow the passage of air past the plug.  
     
     
         20 . A plug as claimed at  claim 19  wherein the breather duct is provided through the plug.  
     
     
         21 . A plug as claimed at either of claims  19  or  20  wherein the plug further comprises a bleed hole adapted to provide re-sealable communication between the breather duct and an external surface of the plug.  
     
     
         22 . A plug as claimed at any one of  claims 22  to  24  wherein a tube is associated with the plug, the tube extending from the plug substantially to the inner end of the blast hole.  
     
     
         23 . A plug as claimed at  claim 25  wherein the tube engages the breather duct.  
     
     
         24 . A plug as claimed at  claim 25  wherein the tube engages the supply duct.  
     
     
         25 . A plug as claimed at any one of  claims 5  to  24  wherein the plug comprises a plug body and the retaining means, the retaining means comprising an annular member received around the plug body, the annular member having a plurality of axially spanning engagement ribs surrounding the periphery of the annular member means.  
     
     
         26 . A plug as claimed at  claim 25  wherein the annular member comprises a plurality of part-annular segments.  
     
     
         27 . A plug as claimed either of claims  25  or  26  wherein the retaining means is provided with an inner surface which is tapered.  
     
     
         28 . A plug as claimed at any one of  claims 25  to  27  wherein the external surface of the main body is tapered.  
     
     
         29 . A plug as claimed at  claim 28  wherein the tapered surface of the main body is adapted to cooperate with the tapered surface of the retaining means to provide expansion of the retaining means.  
     
     
         30 . A plug as claimed at any one of  claims 5  to  29  wherein the plug is re-usable.  
     
     
         31 . A plug as claimed at any one of  claims 5  to  29  wherein the plug is disposable.  
     
     
         32 . A method of protecting a predrilled, uncharged blast hole substantially as herein described.  
     
     
         33 . A plug adapted to seal a blast hole against leakage of liquid substantially as herein described.  
     
     
         34 . A plug adapted to seal a blast hole against leakage of liquid substantially as herein described with reference to the accompanying drawings.