Patent Publication Number: US-10774644-B2

Title: System and method for forming a cavity in a backfilled stope

Description:
FIELD OF THE INVENTION 
     The present invention is a system and a method for draining a backfill mixture including granular material and water that is positioned in an excavated stope. 
     BACKGROUND OF THE INVENTION 
     Mined-out portions of stopes are often backfilled with tailings (often referred to as “backfill”), pumped into the stope from a mill. As is well known in the art, the tailings typically include substantial amounts of water. Draining the backfill is a difficult task that may take a long time. The undrained water can exert significant pressure on structures at the stope entrances (fill fences). The known practices tend to rely on relatively slow drainage, which results in substantial water pressure exerted against fill fences over extended periods of time. 
     For instance, a first “panel”, or portion, of the ore may be removed, and the opening left by its removal may be backfilled. Typically, once the backfill has been drained sufficiently and “cured”, a second “panel” of the ore is removed. Subsequent panels may also be removed, sequentially. 
     As is well known in the art, as an initial step in excavating the first panel, a raise (i.e., an elongate generally vertical opening) is formed at an outer end of the first panel, to provide a blasting void in which the broken ore caused by blasting the first panel is receivable. The raise may be formed by incremental drilling and blasting, or by a raise bore, or by any other conventional means. Driving a raise by conventional means is an extremely expensive and time-consuming process. 
     A blasting void is an opening into which some of the broken ore is partially directed by the blast. The blasting void is needed due to the rapid increase in volume of the blasted ground of the second panel, upon ignition of the blast. 
     In conventional mining, one of the first steps in mining the second panel would be to create a blasting void for the second panel. Typically, this is done by creating a substantially vertical void in the solid rock of the second panel (at one side or end of the second panel), by conventional means. 
     As is well-known in the art, the step of forming the blasting void for each panel is relatively expensive and time-consuming. Once the blasting void for the second panel is created, the second panel may be drilled using conventional drills, to produce a blasting pattern in the second panel designed to blast toward the blasting void. Subsequently, the second panel is blasted, and the broken ore therefrom is removed by conventional mucking methods. 
     After the broken ore of the second panel has been excavated, the opening created by the removal of the second panel is backfilled. Typically, the process is repeated with respect to a third and possibly further subsequent panels until the stope has been fully excavated. 
     SUMMARY OF THE INVENTION 
     For the foregoing reasons, there is a need for a drainage system and method for a backfilled stope that overcomes or mitigates one or more of the deficiencies of the prior art. Such deficiencies are not necessarily included in those described above. 
     In its broad aspect, the invention provides a system for forming a cavity in a backfill mixture comprising granular material and water positioned in an at least partially excavated stope. The system includes a base located on a floor that partially defines the at least partially excavated stope, and a drainage tube assembly in an extended condition thereof. The drainage tube assembly extends between a lower end secured to the base and an upper end positioned above an upper surface of the backfill mixture. The extended drainage tube assembly includes a tube portion thereof with a permeable material and defining the cavity therein into which the water from the backfill mixture is drainable, through the permeable material. The system also includes a drainage pipe, for permitting the water that has drained into the cavity of the extended drainage tube assembly to exit the stope. 
     Once the backfill has been sufficiently drained and is sufficiently firm to support further mining, the cavity created by the system may be used as a blasting void, for a panel to be subsequently blasted. 
     In another aspect, the invention provides a method of forming a cavity in a backfill mixture positioned in an at least partially excavated scope. The backfill mixture includes a granular material and water. The method includes providing a base on a floor partially defining the at least partially excavated stope, and providing a drainage tube assembly in a retracted condition thereof. The drainage tube assembly includes a tube portion having a permeable material, the drainage tube assembly extending between lower and upper ends thereof. The lower end is secured to the base. The upper end is attached to a connecting element that is suspended from a roof partially defining the at least partially excavated stope. With the connecting element, the upper end is raised to a predetermined position above the floor in which the drainage tube assembly is in an extended condition to locate a top end of the tube portion in a preselected location above the floor, the tube portion defining the cavity therein when the drainage tube assembly is in the extended condition. A drainage pipe in fluid communication with the cavity is provided, to enable the water that drains into the cavity to exit the stope via the drainage pipe. The at least partially excavated stope is backfilled with the backfill mixture to the extent that an upper surface of the backfill mixture positioned in the stope is below the top end of the tube portion. The water is permitted to flow into the cavity via the permeable material and to exit the stope via the drainage pipe. 
     The invention also includes using the cavity as a blasting void for a panel to be subsequently blasted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood with reference to the attached drawings, in which: 
         FIG. 1  is a cross-section of a partially excavated stope, with an embodiment of a drainage tube assembly of the invention positioned therein proximal to a drift, in a retracted condition; 
         FIG. 2  is a cross-section of the partially excavated stope of  FIG. 1  in which the drainage tube assembly of  FIG. 1  is located substantially vertically aligned with a pulley secured in a back partially defining the partially excavated stope, the drainage tube assembly being located on a base; 
         FIG. 3  is a cross-section of the partially excavated stope of  FIGS. 1 and 2  in which the drainage tube assembly of  FIG. 2  has been pulled upwardly a first vertical distance by a winch, via a connecting element drawn through the pulley, and in which a drainage pipe is connected with the drainage tube assembly; 
         FIG. 4  is a cross-section of the partially excavated stope of  FIGS. 1-3  in which the drainage tube assembly of  FIG. 3  has been pulled upwardly a further second vertical distance by the winch, via the connecting element drawn through the pulley; 
         FIG. 5  is a cross-section of the partially excavated stope of  FIGS. 1-4  in which the drainage tube assembly of  FIG. 4  has been pulled upwardly to its fully extended condition by the winch, via the connecting element drawn through the pulley; 
         FIG. 6  is a cross-section of the partially excavated stope of  FIGS. 1-5  in which a backfill mixture has been positioned in the partially excavated stope around the drainage tube assembly of  FIG. 5 ; 
         FIG. 7  is a portion of  FIG. 6 , drawn at a larger scale; 
         FIG. 8  is another portion of  FIG. 6 ; and 
         FIG. 9  is a top view of the drainage tube assembly of  FIG. 6 , drawn at a smaller scale. 
     
    
    
     DETAILED DESCRIPTION 
     In the attached drawings, reference numerals designate corresponding elements throughout. Reference is made to  FIGS. 1-9  to describe an embodiment of a system in accordance with the invention indicated generally by the numeral  20  ( FIGS. 5, 9 ). As will be described, the system  20  is for forming a cavity  21  in a backfill mixture  22  ( FIGS. 6-9 ) comprising granular material and water positioned in an at least partially excavated stope  24  ( FIGS. 1-5 ). In one embodiment, the system  20  preferably includes a base  26  ( FIGS. 3-7, 9 ) located on a floor  28  ( FIGS. 1-8 ) that partially defines the at least partially excavated stope  24  and a drainage tube assembly  30  in an extended condition thereof ( FIGS. 5, 6 ). Preferably, and as can be seen in  FIGS. 5 and 6 , the drainage tube assembly  30  extends between a lower end  32  secured to the base  26  and an upper end  34  positioned above an upper surface  36  of the backfill mixture  22 . It is also preferred that the extended drainage tube assembly  30  includes a tube portion  38  thereof ( FIGS. 5, 9 ) comprising a permeable material  39  ( FIG. 9 ) and defining the cavity  21  ( FIGS. 5-7, 9 ) therein into which the water from the backfill mixture  22  is drainable, through the permeable material  39 . The system  20  preferably also includes a drainage pipe  68 , for permitting the water that has drained into the cavity  21  of the tube portion  38  to exit the stope  24 . 
     Those skilled in the art would appreciate that the at least partially excavated stope  24  may be of any size, and as illustrated in  FIGS. 1-5 , includes an opening “X” partially defined by somewhat irregularly-shaped walls. As can be seen, for instance, in  FIG. 1 , the opening “X” in the partially excavated stope  24  is substantially defined by the floor  28 , first and second side walls  42 ,  44 , and a back, or roof,  46 . Access to the stope  24  is provided by an upper drift “UD” and a lower drift “LD”. 
     Those skilled in the art would appreciate that, in the partially-excavated stope illustrated in  FIGS. 1-9 , a first panel has been excavated, resulting in the opening “X”. As is well-known in the art, the mining of the first panel may have commenced with the excavation of a raise (not shown) located at a side or an end of the first panel, using any suitable conventional method. It would also be understood by those skilled in the art that the raise would be needed to provide a blast void into which the broken ore of the first panel may be received, i.e., when the first panel is blasted, in production blasts. 
     In  FIGS. 1-6 , a second panel to be excavated in the stope is identified by reference numeral  47 . It will be understood that the cavity  21  provided by the system and method of the invention may be used as a blast void in respect of the second panel  47 . 
     Accordingly, in one embodiment of the method of the invention, after the cavity is formed, and when the backfill is sufficiently drained and cured to support the surrounding ground, a blast pattern “BP” is drilled in the second panel  47  to receive explosives ( FIG. 6 ). The blast pattern “BP” is located proximal to the cavity, so that at least a portion of the broken ore pieces resulting from blasting the blast pattern is receivable in the cavity. 
     Those skilled in the art would appreciate that the system and method of the invention have significant advantages over conventional systems and methods. In particular, utilizing the cavity  21  formed by the drainage tube assembly as a blasting void for a subsequent panel results in a major cost reduction, and also permits faster mining of the subsequent panel. The system and method of the invention enable the operator, in connection with mining the second and subsequent panels, to avoid the significant costs and delays that accompany conventional raise mining methods. 
     As can be seen, e.g., in  FIG. 6 , in order for the cavity  21  to be used as a blast void for the subsequent panel, the drainage tube assembly  30  preferably is located proximal to the subsequent panel. It is believed that those skilled in the art would be able to determine an appropriate distance for the purpose between the subsequent panel and the drainage tube assembly. For example, as can be seen in  FIG. 6 , the drainage tube assembly  30  is positioned proximal to the face  44  of the second panel  47 . 
     In  FIG. 6 , blastholes “BH” for a production blast of the second panel  47  are illustrated. The blastholes “BH” are drilled in the blast pattern “BP”. Those skilled in the art would appreciate that the production blast preferably is designed to utilize the cavity  21  as the blasting void therefor, as described above. 
     The backfill mixture  22  may include any suitable granular material, and the water. Those skilled in the art would appreciate that the granular material may, for example, include tailings resulting from the mineral processing of the ore from the mine. It will be understood that the tailings granular material is generally relatively fine. Those skilled in the art would also appreciate that the backfill mixture may include cement and/or other materials intended to provide a backfill positioned in the stope (and once much of the water has drained away, and after time for curing) that will be cohesive to an extent, and therefore provide enhanced support to the walls and pillars defining the stope  24 . 
     The permeable material  39  of the tube portion  38  preferably is any suitable material. For example, it is believed that a geotextile material would be suitable. For instance, a material with a tensile strength of approximately 600×700 lbs. (approximately 2,670×3,115 N), with an apparent opening size of 40 U.S. Std. Sieve (approximately 0.425 mm), and permittivity of 0.26/second allowing a water flow rate of approximately 20 U.S. gpm/ft 2  (approximately 815 lpm/m 2 ) is believed to be a suitable material. Those skilled in the art would be aware of other suitable permeable materials. It will be understood that, in  FIG. 9 , the thickness of the permeable material  39  has been exaggerated for clarity of illustration. As illustrated, for example, in  FIGS. 5 and 7 , the tube portion  38  preferably also includes a frame  48  which, in one embodiment, includes a number of rings  50  to which the permeable material  39  is secured. The rings  50  are made of any suitable strong material, e.g., steel. The rings  50  preferably are secured to the permeable material  39 , so that the rings  50  support the permeable material  39  after installation. Because of the support provided by the rings  50 , the permeable material  39  resists the backfill mixture  22  that presses against the permeable material  39  after the backfill mixture  22  has been positioned in the stope  24 . 
     When the drainage tube assembly  30  is in its retracted condition, the rings  50  are positioned proximal to each other, and may be piled so that they are substantially aligned ( FIGS. 1-3 ). In  FIG. 4 , it can be seen that the tube portion  38  preferably extends smoothly as the upper end  34  of the drainage tube assembly  30  is pulled upwardly, with the rings  50  proximal to the upper end  34  being located in position spaced apart from each other sequentially, under the influence of gravity. The upper end  34  is pulled upwardly until the drainage tube assembly  30  is in its fully extended condition. As can be seen in  FIGS. 5-7 , once the drainage tube assembly  30  is in the extended condition thereof, the rings  50  preferably are vertically spaced apart from each other by a distance “D” respectively ( FIG. 7 ). It is preferred that the rings  50  are connected with each other, in series, by one or more central connectors  52  ( FIGS. 4-6 ) that preferably are included in the frame  48 . 
     The connectors  52  may be made of any suitable material. Preferably, the connectors  52  are long pieces of wire, connected to the rings  50  respectively. In one embodiment, the frame  48  preferably includes three connectors  52 , spaced angularly equidistant from each other so that they are attached to the rings respectively at approximately 120° from each other. When the drainage tube assembly  30  is in its extended condition, the connectors  52  preferably each extend from the topmost ring to the bottom-most ring, and each of the connectors  52  is also substantially straight. Those skilled in the art would appreciate that the connectors  52  serve to strengthen the frame  48 , supporting the rings  50  so that permeable material  39  is supported by the frame against the backfill mixture  22  pressing against it. 
     Those skilled in the art would appreciate that, when the drainage tube assembly  30  is in its extended condition, the tube portion  38  may have any suitable dimensions. In addition, the frame  48  and its elements may have any suitable dimensions and configurations. For instance, the rings  50  may each have an inner diameter of approximately 60 inches (152.4 cm) and the cavity  21  therefore may have a minimum inner diameter of approximately 60 inches (152.4 cm) also. It is believed that the rings  50  should preferable be secured to the permeable material  39  so that “D” is approximately 24 inches (approximately 60.96 cm). As noted above, the rings  50  preferably are also connected to each other respectively by the one or more connectors  52 . 
     In one embodiment, the drainage tube assembly  30  preferably also includes one or more suspension elements  54  secured to the frame  48 , to attach the frame  48  (and ultimately, the rings  50 , and the permeable material  39 ) with a connecting element  56  ( FIGS. 3-5 ). As will also be described, the connecting element  56  preferably is used to raise the drainage tube assembly  30  from its retracted condition ( FIG. 2 ) to its extended condition ( FIG. 5 ). It is also preferred that the connecting element  56  remains in position after the drainage tube assembly  30  has been moved to its extended condition, to maintain the drainage tube assembly  30  in its extended condition. 
     An embodiment of a method of the invention includes providing the base  26  on the floor  28 , and providing the drainage tube assembly  30  in the retracted condition thereof ( FIG. 1 ). Those skilled in the art would appreciate that the base  26  may be made of any suitable materials, e.g., concrete. The lower end  32  of the drainage tube assembly  30  preferably is secured to the base  26 . The lower end  32  may be secured to the base  26  in any suitable manner, using any suitable devices (not shown). Also, it will be understood that the base  26  is also secured to the floor  28  in any suitable manner. Those skilled in the art would be aware of suitable means for securing the base  26  to the floor  28 , and also of suitable means for securing the lower end  32  to the base  26 . 
     As can be seen in  FIG. 1 , the upper end  34  of the drainage tube assembly  30  preferably is attached to the connecting element  56 . It is also preferred that the connecting element  56  is suspended from the back or roof  46  that partially defines the excavated stope  24 . Those skilled in the art would appreciate that the connecting element  56  and the upper end  34  may be attached using any suitable means therefor. As can be seen in  FIGS. 1-5 , in one embodiment, a pulley  58  preferably is secured to the back  46 , and a winch  60  is securely mounted in the upper drift “UD”. Those skilled in the art would be aware of a suitable connecting element  56 , a suitable pulley  58 , and a suitable winch  60 . 
     In one embodiment, and as can be seen in  FIG. 3 , the connecting element  56  extends between a first end  62  thereof that is attached to the upper end  34  of the drainage tube assembly  30 , and a second end  64  thereof that is secured to the winch  60 . It will be understood that the connecting element  56  preferably is passed through the pulley  58 . It will also be understood that the drainage tube assembly  30  is shown in its retracted condition in  FIGS. 1 and 2 . 
     It will be understood that, when the connecting element  56  is attached to the drainage tube assembly  30 , the drainage tube assembly  30  is located in a safe location ( FIG. 1 ). Those skilled in the art would appreciate that the retracted drainage tube assembly  30  may be moved from its location in a “safe” area, as illustrated in  FIG. 1 , to its location as illustrated in  FIG. 2  using any suitable means. For example, the retracted drainage tube assembly  30  may be moved into the location illustrated in  FIG. 2  by a remotely-controlled vehicle that is suitably equipped (not shown). As shown in  FIG. 2 , the retracted drainage tube assembly  30  preferably is located substantially vertically below the pulley  58 . 
     As can be seen in  FIGS. 1-5 , with the connecting element  56  attached to it, the upper end  34  is raised substantially vertically to a predetermined position preferably located a distance “P” ( FIGS. 5, 6 ) above the floor  28  ( FIG. 5 ). In  FIGS. 5 and 6 , it can be seen that when the upper end  34  is at the predetermined position “P”, the drainage tube assembly  30  is in the extended condition thereof. When the drainage tube assembly  30  is in its extended condition, a top end  66  of the tube portion  38  preferably is located in a preselected position preferably located a distance “Q” above the floor  28 . As can be seen in  FIGS. 5, 6, and 9 , it is preferred that the tube portion  38  defines the cavity  21  therein when the drainage tube assembly  30  is in the extended condition thereof. 
     It is also preferred that a drainage pipe  68  is included in the system  20 . As will be described, the drainage pipe  68  preferably is in fluid communication with the cavity  21  ( FIGS. 5-9 ), to enable the water that drains into the cavity  21  to exit the stope  24  via the drainage pipe  68 . 
     Those skilled in the art would appreciated that, once the drainage tube assembly  30  is in the extended condition and the drainage pipe  68  is in position as illustrated in  FIG. 5 , the excavated stope  24  preferably is at least partially filled with the backfill mixture  22 . It is preferred that the stope  24  is filled with the backfill mixture  22  to the extent that the upper surface  36  of the backfill mixture  22  that is positioned in the stope  24  is proximal to, but below, the top end  66  of the tube portion  38  ( FIG. 6 ). The water in the backfill mixture  22  is permitted to flow into the cavity  21  under the influence of gravity via the permeable material  39 , and to exit the stope  24  via the drainage pipe  68 . 
     In use, the system  20  preferably additionally includes a fill fence  70  positioned at an entrance to the stope  24  in the lower drift “LD”. Those skilled in the art would appreciate that the fill fence  70  preferably is formed to retain the granular material in the stope, and also to permit a portion of the water in the backfill mixture  22  to drain therethrough. As can be seen in  FIGS. 5-8 , the drainage pipe  68  preferably defines a slope that is downward from an inner end  72  of the drainage pipe  68  to an outer end  74  of the drainage pipe  68 , to ensure that the water will drain from the inner end  72  to the outer end  74 . It is also preferred that the inner end  72  is located inside the cavity  21 , and on or only a small distance above the base  26 , so that the drainage pipe  68  is in fluid communication with the cavity  21 . 
     The outer end  74  of the drainage pipe  68  preferably is located outward from the fill fence  70 , as illustrated in  FIGS. 5-9 , to ensure that the drainage pipe  68  empties the water into the lower drift “LD”, outside the stope  24 . Those skilled in the art would appreciate that the lower drift “LD” preferably grades downward from the stope entrance (i.e., downward from the fill fence  70 ), and water exiting the drainage pipe  68  at its outer end  74  therefore will not flow back into the stope. It will be understood that the water drained from the backfill mixture  22  as described above, and exiting the outer end  74  of the drainage pipe  68 , ultimately flows to the general mine drainage system (not shown), and is subsequently pumped to the surface for treatment and release. 
     The flow of the water from the backfill mixture  22  into the cavity  21  is schematically represented by arrows “A” and “B” in  FIGS. 6 and 7 , and by arrows “E”, “F”, and “G” in  FIG. 9 . It will be understood that, at least shortly after the backfill mixture  22  has been emplaced in the excavated stope  24 , the water from the backfill mixture  22  through the geotextile material  39  and may flow into the cavity  21  at substantially any and all points along the tube portion  38 . The geotextile material  39  preferably screens much of the granular material, so that the water flows into the cavity  21  but the granular material generally does not. Because of this screening function, it is believed that the cavity  21  will remain empty except for the water, and will not be filled (or partially filled) with the granular material, for some time. 
     As schematically represented by arrow “C” in  FIG. 7 , the water that flows into the cavity  21  falls downwardly therein, under the influence of gravity. The water pools in the bottom part of the cavity  21 , and flows through the drainage pipe  68  to the lower drift “LD”, as schematically represented by arrows “H”, “J”, and “K” in  FIG. 9 . Arrows “J” and “K” are also shown in  FIG. 8 , for clarity of illustration. 
     It will be appreciated by those skilled in the art that the invention can take many forms, and that such forms are within the scope of the invention as claimed. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.