Steep pit wall mining

Abstract

An open pit mine and a mining method are disclosed. The mine comprises a mine pit defined by a pit wall 31, with a target area 29 of the pit wall including a plurality of batters 23 separated by berms 51 and a civil engineering support system for the pit wall. The civil engineering support system makes it possible for the pit wall to have a pit wall slope angle that is greater than would have been possible for safe mining without the civil engineering support system.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to above-ground mines, particularly to open pit mines for mining material containing valuable minerals.BACKGROUND OF THE INVENTION

[0002] The invention applies to greenfield and brownfield above-ground mines, particularly open pit mines, for mining material containing valuable minerals, with the following description focusing on brownfield mines.

[0003] One known approach for designing an open pit mine includes forming a pit wall in at least a section of a target area of the mine with a plurality of successive batters separated by successive benches (also referred to as “berms” when portions are left in place for stability and catchment purposes after benches have been mined) as mining progresses into the target area and material is removed from the target area.

[0004] The geology and geomechanics (including rock properties) of a mine, local mine regulations, and mining company practices, have an impact on the maximum permissible slope angle, maximum batter height, maximum batter width, and other parameters of the pit wall design to facilitate safe mining in the target area.

[0005] The safe mining design of pit walls is an important factor that is considered by mining engineers when they develop a base mine plan and then later, optimised, uplift mine plans for a mine.

[0006] These mine plans allocate some areas of a mine as being a mineral reserve (i.e., material of economic value to be mined with high geological classification certainty) and other areas of the mine as being a mineral resource category (i.e., material in the mining area with low geological certainty and of economic interest), with the allocations being informed by technical, operational and economic factors.

[0007] The term “mineral resource” is understood herein to be a concentration or occurrence of material of economic interest in a mine.

[0008] The term “mineral reserve” is understood herein to be the parts of a mineral resource that can be economically mined at a point in time.

[0009] The invention provides an alternative approach to pit wall design and open pit mining that has an impact on (a) determining maximum safe mining slope angles for a given geology and geomechanics, including rock properties, than would have been the case previously, and (b) minimising the environmental impact of mines.

[0010] The above description is not an admission of the common general knowledge in Australia and elsewhere.SUMMARY OF THE INVENTION

[0011] The invention is based on a realisation that an appropriate selection of a civil engineering support system option for supporting a pit wall in a target area of an open pit mine makes it possible to mine with a steeper pit wall than is currently considered possible for safe mining operations.

[0012] More particularly, the invention is based on a realisation that there is much more scope for the use of civil engineering support system options in the mining industry, such as open pit mine design, than was thought to be possible previously, particularly in applications that have significant economic benefit. In particular, the applicant is aware that previous use of civil engineering support systems on a larger scale were not successful because there were large-scale failures that were difficult to control.

[0013] More particularly, the invention is based on a realisation that civil engineering options provide an opportunity to go well beyond standard pit wall design for safe mining operations, while maintaining the same levels of safety.

[0014] The invention makes it possible, for example, to have a pit wall slope angle of ≥55°, typically ≥60°, more typically ≥65°, more typically ≥70° when the target area is a “soft” rock, as defined herein, with an appropriate civil engineering support system, whereas it would have only been possible to have a smaller pit wall slope angle, for example no more than 50°, for safe mining operations in the soft rock without the civil engineering support system.

[0015] In addition, the invention makes it possible, for example, to have a pit wall slope angle of >70°, typically ≥75°, more typically 85-90°, in a “hard” rock, as defined herein, (which may also be described as “competent” rock) with an appropriate civil engineering support system, whereas it would have only been possible to have a comparatively gentler pit wall slope angle, for example no more than 70°, for safe mining operations in the hard rock without the civil engineering support system.

[0016] In summary, the invention provides opportunities for steeper pit walls in soft rock and hard rock scenarios and the economic and environmental advantages that can be realised.

[0017] More particularly, the invention provides opportunities to:

[0018] (a) maximise the amount of high value material that can be mined from a mine having a given overall footprint by mining areas within the footprint that were not previously part of a base mine plan and later uplift mine plans and therefore move mineral resources to ore reserves in a mine, with the potentially significant economic advantages with this change;

[0019] (b) operate mines with smaller overall footprints and therefore minimise associated waste stripping, getting quick access to the mineral of interest, and later mine remediation and associated costs; and

[0020] (c) operate mines with smaller overall footprints and therefore minimise the environmental impact of mines, both in terms of the areas mined and later remediation of mines—increasing sustainability of mining generally.

[0021] In general terms, the invention makes it possible to mine target areas of a mine that were not previously thought to be able to be mined at all, let alone economically.

[0022] The term “target area” is understood herein to include areas of an existing mine and areas within a new mine design.

[0023] It is noted that the word “area” as used herein is understood to describe a volume of material.

[0024] The invention provides an open pit mine including a mine pit defined by a pit wall, with a target area of the pit wall including a plurality of batters separated by berms and a civil engineering support system for the pit wall that makes it possible for the pit wall to have a pit wall slope angle that is greater than would have been possible for safe mining without the civil engineering support system.

[0025] The term “pit wall slope angle” is understood herein to mean an angle that a pit wall makes to a horizontal line when the angle of the pit wall is measured between a lower part and an upper part of a target area of a mine. It can be appreciated that the pit wall slope angle is an average angle between the lower part and the upper part of the target area and there may be different pit wall slope angles for each batter / berm combination in the target area. For example, it may be possible to have a larger angle in one part of the height of a target area than in other parts of the height of the target between the lower and upper parts. It is also noted that the above-mentioned “lower” and “upper” parts of the pit wall are understood to be spaced apart by a distance that is considered to be significant from a geological and geomechanical engineering perspective to a skilled person.

[0026] The term “bench” is understood herein to mean a horizontal shelf or ledge built into a pit wall to break the continuity of an otherwise long sloping pit wall.

[0027] The term “berm” is understood herein to mean a portion of a bench that is left in place for stability and catchment purposes after benches have been mined.

[0028] The term “batter” is understood herein to mean an inclined section of a pit wall that separates successive 10 berms.

[0029] The term “soft” rock is understood herein to mean rock formations that are relatively “weak” and easily deformable with an intact rock uniaxial compressive strength (UCS) between 0.5-25 MPa. 15

[0030] The term “hard” rock, also referred to as “competent” rock, is understood herein to mean rock formations that are characterized by high strength and minimal deformability with an intact rock uniaxial compressive strength greater than 25 MPa.

[0031] The terms “weak” and “hard” are quantified in terms of uniaxial compressive strength in the following Table adapted from a classification proposed by the International Society for Rock Mechanics and Rock Engineering (ISRM).TABLEDescription of rock strength based on a point load index andits equivalent uniaxial compressive strength (“UCS”)GradeDescriptionEquivalent UCS (MPa)R0Extremely weak rock0.25-1  R1Very weak rock1.0-5.0R2Weak rock5.0-25 R3Medium strong rock25-50R4Strong rock 50-100R5Very strong rock100-250R6Extremely strong rock>250

[0032] The target area of the pit wall may be an area that was previously considered to be a mineral resource but is now a mineral reserve as a consequence of the invention.

[0033] The open pit mine may be a greenfield mine.

[0034] The open pit mine may be a brownfield mine.

[0035] The civil engineering support system may be any suitable system having regard to the geological and geomechanical properties, including rock properties, of the pit wall and mining safety factors.

[0036] More particularly, the selection of a suitable the civil engineering support system in any given situation depends on a number of factors, including:

[0037] (a) The geological structure in and around the pit walls.

[0038] (b) Rock strength-soft rock or hard rock.

[0039] (c) Groundwater.

[0040] (d) Behaviour of the civil engineering support system.

[0041] (e) Rock stress levels and the changes in rock stress during the life of the excavation.

[0042] (f) The potential for seismic events.

[0043] The civil engineering support system may include a plurality of soil / rock anchors at spaced intervals along the length of at least a section of at least one batter that place the section under compression to stabilise the section.

[0044] The term “soil / rock anchors” is understood herein to mean threaded steel bars or cable bolts or dowels or other elements made from steel or other suitable materials that are inserted into soil / rock via drilled holes and bonded to the soil / rock mass by cement grout or epoxy resins or other adhesives.

[0045] The soil / rock anchors may be any suitable reinforcement to place the section under compression to stabilise the section.

[0046] Alternatively, or in addition, the civil engineering support system may include a plurality of piles that have been driven downwardly into a section of at least one berm.

[0047] Typically, the piles are steel piles that are hammered vertically downwardly into the berm.

[0048] Typically, the piles are positioned close to an adjacent batter.

[0049] Alternatively, or in addition, the civil engineering support system may include a diaphragm wall (D-wall) formed in a section of at least one berm.

[0050] The civil engineering support system may include an elongate reinforcement member along the length of at least a section of at least one batter to stabilise the section.

[0051] The reinforcement member may be any suitable member.

[0052] By way of example, the reinforcement member may be a beam, such as a waler beam.

[0053] By way of further example, the reinforcement member may be a mesh reinforcement.

[0054] By way of further example, the reinforcement member may be a layer of fibre-reinforced concrete.

[0055] The civil engineering support system may include a layer of shotcrete or other suitable protective material on at least a section of at least one batter.

[0056] The civil engineering support system may include a drainage system for pit wall.

[0057] Different sections of the height of the target area may have different slope angles, determined having regard to the geological and geomechanical properties, including rock properties, mining safety factors, and any other relevant factors in each section.

[0058] For example, it may be appropriate to have smaller or larger slope angles having regard to different geological and geomechanical properties in different sections to mine safely in the sections.

[0059] The pit wall slope angle may be ≥55° when the target area is a soft rock, as defined herein.

[0060] The pit wall slope angle may be 2 60° when the target area is a soft rock.

[0061] The pit wall slope angle may be ≥65° when the target area is a soft rock.

[0062] The pit wall slope angle may be ≥70° when the target area is a soft rock.

[0063] The pit wall slope angle may be 2 75° when the target area is a hard rock, as defined herein.

[0064] The pit wall slope angle may be ≥80° when the target area is a hard rock.

[0065] The pit wall slope angle may be ≥85° when the target area is a hard rock.

[0066] The batter angle may be in a range of 80-90°.

[0067] The batter angle may be in a range of 85-90°.

[0068] The berm width may be in a range of 5-15 m.

[0069] The batter height (measured as a vertical height) may be in a range of 12-60 m, typically less that 50 m, more typically less than 40 m.

[0070] It is not essential that the civil engineering support system support the entire pit wall in the target area.

[0071] It may be the case that the civil engineering support system is installed in only those sections of the pit wall that are found to require support.

[0072] The open pit mine may include a plurality of the above-described target areas.

[0073] By way of example, it may be the case that the invention provides an opportunity for a re-evaluation to be made of areas of the mine that were thought previously not be suitable for mining economically.

[0074] The invention is equally applicable to the design of new open pit mines.

[0075] Specifically, the invention makes it possible to consider the economic opportunities and environmental impact of new mines with a different lens to standard mine design.

[0076] The invention also provides a method of mining material in an open pit mine including mining material from a target area of the mine by progressively forming a pit wall having successive, batters and berms separating the batters as mining progresses and installing a civil engineering support system for the pit wall that makes it possible for the pit wall to have a pit wall slope angle that is greater than would have been possible for safe mining without the civil engineering support system.

[0077] The open pit mine may be a greenfield mine.

[0078] The open pit mine may be a brownfield mine.

[0079] The method may comprise forming a 1st bench and a 1st batter extending upwardly from the 1st bench by mining material from the target area and installing the civil engineering support system to stabilise the 1st batter, forming a 2nd bench and a 2nd batter extending upwardly from the 2nd bench by mining material from the target area and installing the civil engineering support system to stabilise the 2nd batter, with mining including mining material from the 1st bench and leaving a berm separating the 1st and 2nd batters.

[0080] The method may comprise forming successive benches and batters and installing the civil engineering support system by repeating the steps described in the preceding paragraph

[0081] The method may comprise forming the 1st bench in a series of successively deeper stages and installing the civil engineering support system to stabilise each stage of the 1st batter.

[0082] The method may comprise forming the 2nd and each successive bench in a series of successively deeper stages and installing the civil engineering support system to stabilise each stage of each batter.

[0083] The pit wall slope angle may be ≥55°, typically ≥60°, more typically ≥65°, more typically ≥70° when the target area is in soft rock, as defined herein.

[0084] The pit wall slope angle may be >70°, typically ≥75°, more typically ≥80°, typically ≥85°, when the target area is a hard rock, as defined herein.

[0085] Different sections of the height of the target area may have different slope angles, determined having regard to the geological and geomechanical properties, including rock properties, mining safety factors, and any other relevant factors in each section.

[0086] For example, it may be appropriate to have smaller or larger slope angles in different geologies to mine safely in the sections.

[0087] For example, the target section may have an upper section of soft rock and a lower section of harder rock, such as epithermal rock, and the pit wall may have a slope angle of 55° in the soft rock section and a higher slope angle in the harder rock section.

[0088] Each batter may have a batter angle in a range of 70-90°.

[0089] Typically, each batter has a batter angle in a range of 80-90°

[0090] The batter angle may be in a range of 85-90° The berm width may be in the range of 5-15 m.

[0091] The bench width may be up to or greater than 50 m.

[0092] The batter height (measured as a vertical height) may be in a range of 12-60 m, typically less that 50 m, more typically less than 40 m.

[0093] The method may comprise installing a plurality of soil / rock anchors at spaced intervals along the length of at least a section of at least one batter and placing the section under compression to stabilise the section as a part of the civil engineering support system.

[0094] The soil / rock anchors may be any suitable reinforcement to place the section under compression to stabilise the section.

[0095] The method may include driving a plurality of piles downwardly into a section of at least one berm to stabilise the section.

[0096] The method may include installing a diaphragm wall (D-wall) in a section of at least one berm to stabilise the section.

[0097] The method may include installing an elongate reinforcement member along the length of at least a section of at least one batter to stabilise the section.

[0098] The reinforcement member may be any suitable member.

[0099] By way of example, the reinforcement member may be a beam, such as a waler beam.

[0100] By way of example, the reinforcement member may be a mesh reinforcement.

[0101] By way of further example, the reinforcement member may be a layer of fibre-reinforced concrete.

[0102] The method may include forming a layer of shotcrete on at least a section of at least one batter.

[0103] The method may include installing a drainage system for the batter as a part of the civil engineering support system.

[0104] The method steps to form the civil engineering support system in a section of at least one batter may be as follows:

[0105] (a) mining and forming at least a section of a batter having a selected batter angle,

[0106] (b) installing soil / rock anchors in the section of the batter in preparation for steel mesh sheets and waler beams or other suitable elongate reinforcement,

[0107] (c) installing steel mesh sheets,

[0108] (d) installing waler beams or other suitable elongate reinforcement,

[0109] (e) stressing and testing soil / rock anchors, and

[0110] (f) optionally, installing a drainage or a depressurisation system.

[0111] The method may include installing soil / rock anchor instrumentation and additionally performing anchor quality assurance and quality control.

[0112] The selected batter angle may be any suitable angle within the context of forming the pit wall with a steeper pit wall slope than would have been possible for safe mining without the civil engineering support system.

[0113] The method may include forming a plurality of the above-described target areas during the course of mining the mine.

[0114] The method may include forming different sections of the height of the target area with different slope angles, determined having regard to the geological and geomechanical properties, including rock properties, mining safety factors, and any other relevant factors in each section.BRIEF DESCRIPTION OF THE DRAWINGS

[0115] In order that the invention may be more fully explained embodiments of block cave mining methods and mines in accordance with the invention are described with reference to the accompanying drawings, in which:

[0116] FIG. 1 is a diagrammatic perspective view of a typical open pit mine, copied from the following website: (http: / / strategicimages.com.au / images / system_open_pit_mine.jpg);

[0117] FIG. 2 is a diagrammatic cross-section of a standard pit wall having a plurality of berms and batters separating the berms; and

[0118] FIGS. 3-12 are front elevations illustrating one, although not the only, embodiment of a method of forming a steep pit wall having successive, batters and berms separating the batters as mining progresses and a civil engineering support system in a target area of a mine in accordance with the invention and an embodiment of an open pit mine in accordance with the invention.DESCRIPTION OF EMBODIMENT

[0119] The invention extends to greenfield and brownfield mines.

[0120] The following description of an embodiment in relation to the Figures focuses on a brownfield mine that is well-established in a predominantly soft rock and has existing infrastructure.

[0121] As noted above, the invention is based on a realisation that an appropriate selection of a civil engineering support system option for supporting a pit wall in a target area of an open pit mine (greenfield and brownfield mines) makes it possible to mine with a steeper pit wall than is currently considered possible for safe mining operations.

[0122] A typical open pit mine 1 shown diagrammatically in FIG. 1 is a large scale mine that is based on drill and blast technology to fracture ore in a section 3 of the mine so that fractured ore slumps into a mine pit 7 for removal from the mine pit 7, for example by haul trucks 9 loaded by excavators 11 operating in the pit, to a mineral processing plant 15.

[0123] The drill and blast technology is shown in part in FIG. 1 to include drill rigs 13 drilling a plurality of blast holes 17 in a new section of the mine to be mined and an explosives truck 19 filling the holes with explosives.

[0124] As shown in FIGS. 1 and 2, open-pit mines are dug on benches (also referred to as “berms” when portions are left in place for stability and catchment purposes after benches have been mined) 21 which describe vertically spaced apart levels of the mine pit 7.

[0125] Batters 23 separate the benches 21.

[0126] The vertical height of the batters 23 depends on the geological and geomechanical and other properties of a deposit being mined and the size of machinery that is being used in the mine 1 and the local regulatory requirements for a mine and additional mining company mandated safety factors. The slope of the batters 23 is typically as close to 90° as possible. The batter height (measured as a vertical distance) is typically less than 60 m, more typically less than 50 m.

[0127] The width of each bench 21 is determined by the size of equipment being used, generally ≥50 m metres wide.

[0128] Mining can be conducted on more than one bench 21 at a time.

[0129] A haul road 27 is situated at the side of the pit 7, forming a ramp, up which trucks can drive, carrying ore and waste rock, and down which empty trucks can drive to be loaded again with ore and waste rock.

[0130] FIG. 2 is in a link https: / / www.e-education.psu.edu / geog000 / node / 877 prepared by John E. Dutton in the e-Education Institute in PennState College of Earth and Mineral Sciences.

[0131] FIG. 2 is a diagrammatic cross-section of a standard pit wall having a plurality of benches 21 and batters 23 separating the benches 21. The Figure refers to the following features.

[0132] Bench 21 a horizontal surface.

[0133] Batter face angle (α): an average angle an exposed face 25 of a batter 23 makes with the horizontal.

[0134] Batter height (H): A vertical distance between successive benches 21.

[0135] Toe: an interior vertex formed at an intersection of a batter 23 and an exposed face 25.

[0136] Crest: an exterior vertex formed at an intersection of a bench 21 and a batter 23.

[0137] Bench width: a horizontal distance between a toe and a crest measured along an upper surface.

[0138] Bank width: a horizontal projection of a batter 23.

[0139] FIGS. 3-12 are front elevations illustrating installing one embodiment of a method of mining material in an open pit mine (and a resultant open pit mine) including mining material from a target area of the mine by progressively forming a pit wall having successive, batters and berms separating the batters as mining progresses and installing a civil engineering support system for the pit wall that makes it possible for the pit wall to have a pit wall slope angle that is greater than would have been possible for safe mining without the civil engineering support system in accordance with the invention. As noted above, the target area in this embodiment is a soft rock.

[0140] More particularly, FIGS. 3-12 illustrate mining the target area 29 and forming the pit wall 31 with a plurality of batters 23 separated by benches 21 with a pit wall slope angle α (see FIG. 3) of ≥55°, typically ≥60°, more typically ≥65°, supported by a civil engineering support system to facilitate safe mining of the soft rock target area 29.

[0141] In the embodiment shown in FIGS. 3-13, the target area 29 is an area, specifically a volume, of the mine 1 that was not previously part of a base mine plan and later uplift mine plans of the mine 1 and therefore was not previously thought to be able to be mined at all, let alone economically.

[0142] The extent of the material that can be mined as a consequence of the invention is illustrated in FIG. 3.

[0143] In FIG. 3, the amount of material that can be mined as a consequence of the invention is the amount of material between (a) the pit wall 31 that has a steep pit wall slope angle α (see FIG. 3) of ≥55° (in accordance with an embodiment of the invention), and (b) what would have been a pit wall 33 in a typical mine construction, multiplied by the length of the target area (assuming the area shown in FIG. 3 is the same along the whole length of the target area). It can be appreciated that this can be a significant amount of material.

[0144] A consequence of mining the target area 29, and therefore a driver to do this, is to move mineral resources to ore reserves in a mine. This is an important economic outcome.

[0145] One feature of the steep pit wall 31 shown in FIG. 3 is that it is formed with a plurality of narrow berms 51, typically up to 10 m wide, and not with wider benches that are typically greater than 10 m wide.

[0146] Designing the pit wall of the target area 29 to have a steep pit wall slope angle α (see FIG. 3) of ≥55°, typically ≥60°, more typically ≥65° in the soft rock in that area 29 is possible because of the civil engineering support system described below.

[0147] From a practical perspective, it can be the case that batters 23 having a selected steep batter angle α (typically in a range of) 80-90° and a vertical height of 40-60 m, have to be formed in several stages, typically with each stage having heights on 15-20 m, in view of limitations.

[0148] FIGS. 4 and 5 show a 1st stage in the construction of a 1st bench. FIGS. 5 to 10 show subsequent steps to form a 2nd stage of the 1st bench. FIG. 11 shows the pit wall at a much more advanced point in construction, with two completed benches (which at this point are narrow-width berms 51), and a new bench 21 under construction.

[0149] With reference to FIGS. 4 and 5, after mining ore from a 1st section of the target area 29 and forming an initial bench 21 and a section on a 1st batter 23, with the bench 21 typically being 10-15m wide and the batter 23 having a selected steep batter angle α (typically in a range of) 80-90° and a vertical height of 15-20 m, a drill rig 41 drills a plurality of holes 39 for soil / rock anchors that, in this embodiment, are in the form of cable bolts (not shown), for a section of the batter 23.

[0150] A cable bolt supply vehicle 43 (FIG. 5 only) inserts the cable bolts and grouts the cable bolts in position. FIG. 5 shows that the cable bolts are supplied in a coil of a continuous length of cable bolts on the cable bolt supply vehicle 43 and, in use, a required length of a cable bolt for a given hole is unwound from the coil and inserted into the hole and cut at a required length.

[0151] With reference to FIG. 6, after the cable bolts are grouted into position in the section of the 1st batter 23, sheets 45 of steel mesh are positioned against the section of the 1st batter 23, with the cable bolts extending through openings in the mesh sheets 45. The mesh sheets 45 are then secured in position by mine bearing plates and nut assemblies, generally identified by the numeral 49 in FIG. 6.

[0152] With reference to FIG. 7, a final step in installing the civil engineering support system is to apply a layer 47 of shotcrete (or any other suitable protective material) onto the section of the 1st batter 23. This is applied by a shotcrete delivery vehicle 61, supplied by shotcrete trucks 63.

[0153] After the civil engineering support system has been installed in FIG. 7, work commences to form a 2nd stage of the 1st bench. This work involves progressively drill and blasting and removing sections of the material in the target area 29 via standard drill and blast technology. This mining is illustrated in FIGS. 8-10.

[0154] These Figures show a drill rig 13 drilling a plurality of boreholes 17 for explosives in a section of the target area. These holes 17 are subsequently filled with a suitable explosive, such as an emulsion explosive, and then blasted after the explosives have been initiated, thereby forming an area 53 of fractured ore (FIG. 9), which slumps into the mine, as shown in FIG. 10. The slumped ore is then removed via an excavator 11 and haul trucks 9 (only one of which is shown in FIG. 10) from the mine for mineral processing in a mineral processing plant-see FIGS. 1 and 2.

[0155] As drilling and blasting and removal of material continues, the civil engineering support system described above in relation to FIGS. 4 to 7 is installed to stabilise the newly-exposed surfaces of the 1st batter 23.

[0156] This process of forming successive stages of the 1st bench continues until the batter 23 is extended down to a required level of the 1st bench.

[0157] At this point, work commences on forming a 2nd bench. The steps involved in doing this are as described above in multiple stages. The construction work also includes substantially mining the 1st bench, save for leaving a narrow-width berm 51 as shown in FIGS. 3 and 12. Basically, forming the 2nd bench starts with mining material from the 1st bench and leaving the narrow-width berm 51 as shown in FIGS. 3 and 12.

[0158] As noted above, FIG. 11 shows the pit wall at a much more advanced point in construction, with two completed benches (which at this point are narrow-width berms 51), and a new bench 21 under construction. FIG. 11 shows the three batters 23 that are separated by the completed benches with installed civil engineering support systems that stabilise the pit wall. In this Figure, a mobile draw point feeder 55 replaces the above-described excavator 11 to transfer slumped ore to haul trucks 9. This is one of a number of excavator options.

[0159] FIG. 12 is a wider view of the mine 1 after mining of the target area 29 is well-advanced.

[0160] FIG. 12 shows the pit wall at a much more advanced point in construction, with:

[0161] a completed section of a 1st bench 21 (which at this point is a narrow-width berm 51) (see the top left hand side of the Figure) and the batter 23 extending upwardly form the completed bench section,

[0162] a substantially completed section of a 2nd bench below the 1st bench—with the bench 21 still under construction and a completed batter 23 extending upwardly to the 1st bench,

[0163] extensions of these two benches 21 underway (in particular, see the right hand side of the Figure for one of the bench extensions), and

[0164] new benches 21 under construction.

[0165] FIG. 12 shows the batters 23 of the completed benches with installed civil engineering support systems that stabilise the pit wall. FIG. 11 also shows installation of civil engineering support systems to complete bench extensions and new benches

[0166] It can be appreciated from FIG. 12 that the embodiment of a steep pit wall stabilised by the described civil engineering support system provides considerable flexibility in facilitating mining the target area 29.

[0167] In another embodiment (not shown), which is an extension of the embodiment shown in FIGS. 3-12, the following steps are taken to provide additional support in the civil engineering support system for each batter:

[0168] (a) Drilling anchor holes and installing a collar casing subsequent to drilling a full length of the anchor holes and installing liners.

[0169] (b) Installing rock or soil anchor assemblies in the anchor holes and grouting the anchors of the assemblies in the anchor holes.

[0170] (c) Installing waler beams along a section or sections of the length of the batter as additional batter reinforcement.

[0171] (d) Installing rock or soil anchor instrumentation and additionally performing anchor quality assurance and quality control.

[0172] (e) Stressing and testing rock or soil anchors and undertaking post grout injection.

[0173] (f) Optionally, installing a drainage or a depressurisation system.

[0174] As noted above, the selection of a suitable the civil engineering support system in any given situation depends on a number of factors, including:

[0175] (a) The geological structure in and around the pit walls.

[0176] (b) Rock strength-soft rock or hard rock.

[0177] (c) Groundwater.

[0178] (d) Behaviour of the civil engineering support system.

[0179] (e) Rock stress levels and the changes in rock stress during the life of the excavation.

[0180] (f) The potential for seismic events.Design Example

[0181] This section describes design criteria for a civil engineering support system for a batter in a target area of a mine in accordance with an embodiment of the invention.

[0182] The description is intended to be a general description of design criteria.

[0183] It is noted that this is not an exhaustive description of the design criteria for the civil engineering support system of the embodiment.

[0184] It is noted that a skilled person would understand that additional design criteria may be required in some situations and that the selection of design criteria will depend on a range of factors including geological and geomechanical properties and other factors of a target area of a mine.

[0185] It is noted that a skilled person would understand that different design criteria are required for the civil engineering support systems of other embodiments.

[0186] 1.0 Basis of the design

[0187] 1.01 Stability for a design life of 10 years.

[0188] 1.02 Pit wall stability provided by a civil engineering system comprising sheets of steel mesh, a layer of shotcrete over batters, soil / rock anchors (in the form of dowel bars in this embodiment), and waler beams that provide localised face support and erosion control.

[0189] 1.03 Surface water drainage for the batters that ensures surface water drainage to minimise erosion and ensure integrity of soil / rock anchors is not compromised.

[0190] 1.04 To achieve the 10 years design life, the following design criteria are adopted:

[0191] 2 mm sacrificial allowance on bar diameter for dowel bars,

[0192] 40 mm minimum grout cover of dowel bars,

[0193] 70 mm cover from rock to mesh, and

[0194] 40 mm coverage from mesh and tops of dowel bars to outer surface of shotcrete.

[0195] 2.0 Batter preparation

[0196] 2.01 Excavation / face stripping

[0197] a) The surfaces of batters are stripped of all topsoil and vegetative matter and any loose or unstable rock mass.

[0198] b) Over-excavation of batters is limited to a tolerance of −0 mm and +150 mm, where a positive tolerance is over-excavation.

[0199] c) The batters are inspected and mapped to confirm if the exposed conditions are consistent with design criteria.

[0200] 3.0 Dowel bars

[0201] 3.01 Face support dowel holes.

[0202] a) Dowel bar holes are drilled to selected depths in each batter, with at least a minimum hole diameter that provides 40 mm grout cover to the dowel bars (and any included couplers).

[0203] b) After holes are drilled to a desired depth and diameter, the holes are thoroughly cleaned to ensure satisfactory bond between the grout and the rock surface.

[0204] c) The completed drill holes are plugged or otherwise protected to prevent entry of foreign matter prior to grout and dowel bar installation.

[0205] 3.02 Placement of dowel bars in drilled holes

[0206] a) Each dowel bar is fitted with sufficient centralisers to maintain a required grout cover over the grouted length of the dowel bar.

[0207] 3.03 Grout quality and testing

[0208] a) The grout includes a mix of sulphate resisting cement (type d) and water. Additives or admixtures may be used, as required.

[0209] b) Grout mix design including admixtures, specific gravity, water: cement ratio value, bleed, fluidity and characteristic compressive strength of the grout at 7, 14 and 28 days, grout water: cement ratio not exceeding 0.4 by mass and the specific gravity of the cement grout not less than 1.90.

[0210] c) Grout is pumped into each dowel bar hole until fresh grout is forced out of the top of the hole.

[0211] d) The amount of grout pumped into each hole is recorded to assess if the hole is blocked, if there are voids in the hole walls, or if there is any grout loss through the surrounding rock mass.

[0212] 3.04 Records

[0213] a) Records of all work are maintained, with the records including:

[0214] drilling location

[0215] changes in ground type

[0216] ground water levels encountered (if any)

[0217] drilled length

[0218] cased length

[0219] volume of grout pumped

[0220] time and date of start and end of drilling

[0221] time and date of grouting and dowel bar placement

[0222] compliance certification

[0223] 4.0 General

[0224] 4.01 Batter drainage

[0225] a) Batter drainage includes strip drains on a rock surface beneath steel mesh or shotcrete treatment.

[0226] 4.02 Strip drains

[0227] a) Strip drains are 200 mm wide (u.n.o.) with faces and ends wrapped in a geotextile fabric or equivalent to be approved by the engineer. Strip drains are placed centrally between dowel bars.

[0228] b) The face of the strip drains away from the soil / rock surface and receiving sprayed shotcrete are covered by protection (e.g., Fotecon / Coreflute) prior to spraying with shotcrete to prevent clogging of the strip drainage covering fabric and drainage channels.

[0229] 4.03 Spraying procedure

[0230] a) All shotcreting is carried out in accordance with an approved work method statement.

[0231] b) Freshly sprayed shotcrete is protected as far as practicable from rain or running water until the shotcrete surface is sufficiently hardened to prevent damage.

[0232] 4.04 Construction joints

[0233] a) Construction joints are located at mid-distance between adjacent dowel bar rows.

[0234] 4.05 Steel mesh

[0235] a. After dowel bars are installed and grouted, the steel mesh is placed.

[0236] b. Steel mesh is fixed to dowel bar cogs so as to provide a 40 mm shotcrete cover to the mesh and dowel bars from the outer face of the shotcrete and a 70 mm cover from the rock substrate to the mesh.

[0237] c. Shotcrete is applied to ensure 40 mm cover from an outer face of the mesh to a surface of the shotcrete.

[0238] 5.0 Substrate preparation

[0239] a) All surface or exposed ground is trimmed and graded before the application of shotcrete. Natural surfaces must be sufficiently cohesive to prevent erosion when the shotcrete is applied.

[0240] 6.0 Construction joints

[0241] 6.01 General

[0242] a) Construction joints are located at mid-distance between adjacent dowel bar rows.

[0243] 7.0 Dowel bars and other ground anchors

[0244] 7.01 General

[0245] a) Dowel bars are multi-strand anchors.

[0246] b) Dowel bars are designed for a minimum 25 years design life.

[0247] c) Dowel bars include 15.2 mm diameter 7 wire strand, grade 1830 MPa steel, relaxation class 2 and conforming with requirements of AS4672.1 and AS4672.2.

[0248] d) All dowel bars are installed at selected locations and drilled at selected dip and azimuth.

[0249] e) Ground anchors are designed for ultimate bond stress value of 300 KPa and 255 mm diameter boreholes.

[0250] f) Waler beam are designed for 32 MPa strength prior to stressing anchors.

[0251] 7.02 tolerances

[0252] a) Vertical location of dowel bar heads: +50 mm, −50 mm.

[0253] b) Horizontal location of dowel bar heads: +50 mm, −50 mm.

[0254] c) Initial dowel bar hole azimuth at dowel bar entry when setting up the drilling rig must not deviate by more than ±1° from the specified azimuth of the selected dowel bar hole.

[0255] d) Dowel bar deviation from a target alignment must not exceed 1m deviation in 30 m of drill hole.

[0256] e) Hole diameter must be no less than a selected hole diameter.

[0257] 8.0 Toe drains

[0258] a) A toe drain is installed along a length of a batter to convey runoff from the batter.

[0259] Many modifications may be made to the embodiment of the invention described in relation to the Figures and the design example without departing from the spirit and scope of the invention.

[0260] By way of example, the embodiment described in relation to the Figures is one of a number of civil engineering support system options that could be used for building steep pit walls.

[0261] The selection of a preferred option in any given situation will depend on the geological and geomechanical properties and other factors of a target area of a mine and having regard to local regulatory requirements and additional mining company safety requirements.

[0262] By way of example, other embodiments include different combinations of civil engineering support system options in different sections of a target area, as a consequence of different geological and geomechanical and other properties in the sections.

[0263] In addition, whilst the embodiment described in relation to the Figures is focused on a brownfield mine, as noted above, the invention is equally applicable to a greenfield mine. A skilled person will understand that the basic steps described above in the context of a brownfield mine will be equally applicable to a greenfield mine and that the additional steps required for any given greenfield mine will be focussed on assessing the conditions of the greenfield mine and understanding and planning for the opportunities.

[0264] The benefits of the invention are equally if not more applicable to a greenfield mine. The applicant has calculated that, for an example of a greenfield mine, the invention makes it possible to recover 80% of the valuable material, with a 50% smaller footprint, and with 70% less waste material than would be the case if the mine was a conventional open pit mine.

[0265] In addition, whilst the embodiment described in relation to the Figures is focused on a predominantly soft rock target area and the slope angles mentioned in the description are on this basis, the invention is not confined to mining in soft rock.

[0266] Specifically, other embodiments of the invention relate to predominantly hard rock target areas. In these embodiments, the pit wall slope angles are 85-90° with appropriate civil engineering support systems, whereas it would have only been possible to have smaller pit wall slope angles, for example no more than 70°, for safe mining operations without the civil engineering support systems.

Claims

1. An open pit mine including a mine pit defined by a pit wall, with a target area of the pit wall including a plurality of batters separated by berms and a civil engineering support system for the pit wall that makes it possible for the pit wall to have a pit wall slope angle that is greater than would have been possible for safe mining without the civil engineering support system.

2. The open pit mine defined in claim 1 wherein the pit wall slope angle is ≥55°, typically ≥60°, more typically ≥65° when the target area is a soft rock, as defined herein.

3. The open pit mine defined in claim 1 wherein the target area of the pit wall is an area that was previously considered to be a mineral resource but is now a mineral reserve.

4. The open pit mine defined in claim 1 wherein the civil engineering support system includes a plurality of soil / rock anchors at spaced intervals along the length of at least a section of the batter that place the section under compression to stabilise the section.

5. The open pit mine defined in claim 1 wherein the civil engineering support system includes a plurality of piles that have been driven downwardly into a section of at least one berm.

6. The open pit mine defined in claim 1 wherein the civil engineering support system includes a diaphragm wall (D-wall) formed in a section of at least one berm.

7. The open pit mine defined in claim 1 wherein the civil engineering support system includes an elongate reinforcement member along the length of at least a section of at least one batter to stabilise the section.

8. The open pit mine defined in claim 7 wherein the reinforcement member is a beam, such as a waler beam.

9. The open pit mine defined in claim 7 wherein the reinforcement member is a mesh reinforcement.

10. The open pit mine defined in claim 1 wherein the civil engineering support system includes a layer of shotcrete or other suitable protective material on at least a section of the batter.

11. The open pit mine defined in claim 1 wherein the civil engineering support system includes a drainage system for the pit wall.

12. The open pit mine defined in claim 1 wherein each batter has a batter angle in a range of 80-90°.

13. The open pit mine defined in claim 1 wherein the berm width is in a range of 5-15 m.

14. The open pit mine defined in claim 1 wherein the batter height (measured as a vertical height) may be in a range of 12-60 m, typically less that 50 m, more typically less than 40 m.

15. The open pit mine defined in claim 1 wherein the open pit mine includes a plurality of the target areas.

16. The open pit mine defined in claim 1 wherein different sections of the height of the target area have different slope angles, determined having regard to the geological and geomechanical properties, including rock properties, mining safety factors, and any other relevant factors in each section.

17. A method of mining material in an open pit mine comprising mining material from a target area of the mine by progressively forming a pit wall having successive, batters and berms separating the batters as mining progresses, and installing a civil engineering support system for the pit wall that makes it possible for the pit wall to have a pit wall slope angle that is greater than would have been possible for safe mining without the civil engineering support system.

18. The method defined in claim 17 comprising forming a 1st bench and a 1st batter extending upwardly from the 1st bench by mining material from the target area and installing the civil engineering support system to stabilise the 1st batter, and forming a 2nd bench and a 2nd batter extending upwardly from the 2nd bench by mining material from the target area and installing the civil engineering support system to stabilise the 2nd batter, with mining including mining material from the 1st bench and leaving a berm separating the 1st and 2nd batters.

19. The method defined in claim 18 comprising forming successive benches and batters and installing the civil engineering support system.

20. The method defined in claim 18 comprising forming the 1st bench in a series of successively deeper stages and installing the civil engineering support system to stabilise each stage of the 1st batter.21.-30. (canceled)

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