Field of the invention

[001 ] This invention relates generally to particulate material retaining bags for wall construction and erosion control and in particular to such bags for use in mining backfill systems.

Background to the invention

[002] In most mining applications, mined ore is transported to processing plants where it is crushed and processed to extract the valuable minerals. In conventional practice, the processed ore waste, typically finely crushed particulate waste material mixed with water, is transported hydraulically to tailings dams that eventually become mine dumps. It is conventional to transport the processed ore hydraulically back to the point of mining where it is used to refill the mined out areas, hence the name "backfill". In the process, the backfill - hydraulically transported granular or particulate material— is pumped into holding areas and allowed to dewater by the provision of drainage facilities that allow the hydraulic transportation fluid to drain from the placed backfill.

[003] Various means are used to ensure that the backfill remains in place as it is pumped. In general, backfill installation processes are directed to the creation of walls or bulkheads that dam up the pumped- in backfill, the walls or bulkheads being porous†o allow dewafering of the pumped-in backfill. Once dewafered, the placed backfill is intended to provide hanging wall support to the mined-out underground areas.

[004] In typical installations in tabular stopes, a fabric-lined trough is created by draping a fluid-permeable fabric, typically woven polypropylene fabric, between two lines of permanent supports. The fabric is suspended in an open trough that creates a dam into which backfill may be pumped. The task of draping and supporting the fabric with ties is physically demanding work and if workmen are required to work inside the trough during this operation, they are un-sighted and to some extent unaware of what is happening around them, which can be dangerous. In addition, considering the typical size of the fabric-lined trough— on average 10m in circumference and 30m long— and the fact that these backfill dams are often constructed on steeply angled dips, it will be appreciated that the large internal volume of the trough equates to a large hydraulic head of wet backfill in the fabric trough during and immediately after pumping. If the trough fabric ruptures for any reason, the potential exists for catastrophic flows of large quantities of wet particulate material (essentially mudslides) which could potentially overwhelm workmen and equipment. The volume-to-surface- area ratio of the conventional backfill trough is relatively large, this means that backfill dewatering is slow, resulting in slumping of the backfill as it dewaters fully over time. Such slumping gives rise to progressive loss of hanging wall contact.

[005] It is an object of this invention to address these concerns. Summary of the invention

[006] According †o this invention, a particulate material retaining bag assembly for wall construction and erosion control comprises: a plurality of tubular bags juxtaposed lengthwise and extending parallel to one another; the bag assembly including at least one filling inlet for feeding a fluid fill material constituted by a particulate material entrained within a transporting hydraulic fluid into the bags; the bags being formed of a material suitable for retaining a particulate material therein and permitting the transporting fluid to pass therethrough; and the bags being secured to one another at least along upper and lower securement zones extending along the juxtaposed sides of the bags.

[007] For purposes of this specification, the term "fluid fill material" will be used to refer to any hydraulically transported granular or particulate material, in fluid form— the particulate material mixed in with the transporting hydraulic fluid. The term "transporting fluid" and its equivalent "carrier fluid" will be taken to refer to the transporting hydraulic fluid in which the particulate material is transported. It will be appreciated that the term "fluid fill material" is not restricted to hydraulically transported backfill material and the terms "carrier fluid" and "transporting fluid" are not restricted to water.

[008] The securement zones are preferably positioned such that the bags are constrained to assume a substantially rectangular cross- sectional shape after filling with the fluid fill material in use, the securement zones being positioned to define bag walls that extend vertically between the upper and lower securement zones and the upper and lower bag surfaces that extend horizontally between the upper and lower securement zones.

[009] The terms "upper", "lower", "vertical" and "horizontal" are not intended to refer to absolute orientation of the bag surfaces and walls or absolute positioning of the securement zones. These terms are used figuratively with reference to the bag assemblies in use and in relation to notional horizontal and vertical working planes that assume a horizontal working surface. In the event that a working surface other than horizontal is used, the orientation implied by these terms must be adjusted accordingly.

[0010] The bags may be secured directly to one another.

[0011] Alternatively, the bag assembly may be constituted by at least two bags separated from one another and secured to one another by means of upper and lower strips of material interposed lengthwise between the separated bags and secured, along their length, along upper and lower securement zones extending along the juxtaposed sides of the bags, the ends of the upper and lower material strips being secured to one another to define a closed bag, the side walls of which are defined by the sidewalls of the bags separated by the material strips.

[0012] To facilitate filling of the bags, one or more fluid flow apertures may be formed in the sidewalls extending between the bags, the fluid flow apertures being configured to permit fluid fill material to flow from one bag to another during filling of the bags. [0013] Whether such fluid flow apertures are provided or not, in one embodiment of the invention, each bag is provided with a filling inlet for feeding a fluid fill material into the bag.

[0014] The alternative is to have a bag assembly in which the entire assembly has a single filling inlet for feeding a fluid fill material into a first bag, the other bags being configured to receive fluid fill material through the fluid flow apertures between the bags.

[0015] The invention includes a method of placing backfill in an underground mine comprising the steps of: in a preparatory step, preparing a bag assembly by juxtaposing a plurality of tubular bags lengthwise and parallel to one another, the bags being configured for filling with backfill constituted by a particulate mine backfill material entrained within a transporting hydraulic fluid, the bags being made from a fluid-pervious fabric suitable for retaining the particulate material within the bag and permitting the transporting fluid to pass therethrough, and securing the bags to one another at least along upper and lower securement zones extending along the juxtaposed sides of the bags; the backfill placing method comprising the steps of locating the bag assembly on a support surface where backfill is to be placed in use; and filling the bag assembly with backfill.

[001 6] In practice, the backfill placing method will include the steps of preparing a number of bag assemblies, sequentially locating one or more additional bag assemblies in the stacked layers on the bag assembly located on the support surface and sequentially filling the additional bag assembly or assemblies with backfill.

[0017] Since the backfill so placed is required to provide active support to the hanging wall, the method conveniently includes the steps of locating bag assemblies in stacked layers on one another, sequentially filling the bag assemblies with backfill, locating a final bag assembly between an uppermost bag assembly and the hanging wall and filling the final bag assembly with backfill to a predetermined pressure to provide immediate active support to the hanging wall.

[0018] The bag assemblies used in the backfill placing method may be any one or more of the alternative embodiments of the invention described above.

Brief Description of the drawings

[0019] The invention will be further described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic isometric view of a bag assembly according to the invention;

Figure 2 is a diagrammatic cross-section through an assembled structure consisting of a plurality of bag assemblies according to one embodiment of the invention stacked in layers on top of one another between vertical supports;

Figure 2A is a detail on the area A of Figure 2; Figure 3 is a diagrammatic cross-section through an assembled structure consisting of a plurality of bag assemblies according to a second embodiment of the invention stacked in layers on top of one another between vertical supports;

Figure 3A is a detail on the area A of Figure 3;

Figure 4 is a diagrammatic cross-section through an assembled structure consisting of a plurality of bag assemblies according to a third embodiment of the invention stacked in layers on top of one another between vertical supports;

Figure 4A is a detail on the area A of Figure 4;

Figure 5 is a diagrammatic cross-section through an un-filled bag assembly according to the second embodiment of the invention (Figure 2);

Figure 5A is a detail on the area A of Figure 5;

Figure 6 is a diagrammatic cross-section through an un-filled bag assembly according to the third embodiment of the invention (Figure 3); and

Figure 6A is a detail on the area A of Figure 6.

Description of embodiments of the invention

[0020] The particulate material bag assemblies of this invention are similar in some respects to the composite fabric bags described and claimed in PCT patent applications nos. PCT/ZA2008/000085 (WO 2009/039536) and PCT/ZA2012/000003 (WO 2012/1 12995), which are incorporated herein by reference.

[0021 ] There are substantive differences, however, between these composite bags and the bag assemblies of this invention.

[0022] Similarly to the bag assemblies described in the PCT applications, the particulate material retaining bag assemblies of this invention comprise a number of fluid pervious fabric bags secured to one another along their length, with the bag assemblies being intended to be laid lengthwise on a working surface, such as a footwall in an underground mine. The bag assemblies of the invention include one or more filling inlets by means of which a fluid fill material (typically a particulate material such as mine backfill transported in a fluid such as water) is conveyed (normally by pumping) into the bag assembly. The bags are folded and gusseted before filling so that, after filling, the pumped-up bag assembly presents, in cross-section, a substantially block-shaped form with rounded sides and a relatively flat upper surface.

[0023] The term "support" normally refers to substantially vertical support between two substantially horizontal surfaces, normally a support surface and a supported surface such as a footwall and hanging wall in an underground mine respectively. The bag assemblies of this invention lend themselves to the construction of structures in which a first bag assembly is laid down on a support surface and additional bag assemblies are then layered or stacked on the first bag assembly in layers. The term "stacking" normally implies substantially vertical stacked structures, but this is not necessarily essential. Any suitable stacking angle is envisaged, including bank-type support where the bag assemblies of the invention are stacked on top of one another at an angle deviating from the vertical to provide support to a sloping earth bank for instance.

[0024] The drawings illustrate embodiments of the invention in which the bag assemblies are configured for use in mining backfill systems and the bag assemblies can conveniently be referred to as backfill bags.

[0025] Referring to Figure 1 , the bag assembly or backfill bag 10 comprises three tubular bags 12 juxtaposed lengthwise and extending parallel to one another. The backfill bag 10 includes at least one filling inlet for feeding backfill into the bags 12. In the embodiment illustrated in Figure 1 , each backfill blade 12 is provided with a valved backfill inlet 14.

[0026] The bags 12 are made from a fluid-pervious fabric, preferably woven polypropylene, the weave density of which is selected to retain the particulate backfill material and to permit the transporting fluid to weep through the fabric. This allows the backfill to dewater naturally.

[0027] The bags 12 are secured to one another along upper and lower securement zones extending along the juxtaposed sides of the bags. The fabric bags 12 are simply stitched together along the securement zones, which are not really visible in Figure 1 , but which can be seen in Figure 2, where the bags are shown stitched together along stitching zones 16 located at the top 16.1 and bottom 16.2 of the sidewalls 18 of the bags 12.

[0028] As can be seen from Figure 2, the positioning of the securement zones 16 constrains the bags 12 to assume a substantially rectangular cross-sectional shape after filling with backfill. In this regard, the securement zones 16 are positioned to define bag walls that extend vertically between the upper 16.1 and lower 16.2 securement zones 16. In the horizontal direction, the upper 16.1 and lower 16.2 securement zones 16 constrain the bag upper 20 and lower 22 surfaces to extend horizontally between the upper 1 6.1 and lower 16.2 securement zones 16 respectively.

[0029] In Figures 1 and 2, the bags 12 are secured directly to one another.

[0030] Alternative embodiments of the invention, using alternative bag securement arrangements, are illustrated in Figures 3 and 4.

[0031 ] These drawings illustrates backfill bag assemblies 1 10, 210 constituted by two bags 1 12, 212 that are located apart from one another and then secured to one another by means of upper and lower strips of woven polypropylene fabric 24 interposed lengthwise between the separated bags 1 12, 212. The fabric strips 24 are secured along their length, along upper 1 16.1 , 216.1 and lower 1 16.2, 216.2 securement zones 1 16, 216 extending along the juxtaposed sides 1 18, 218 of the bags 1 12, 212.

[0032] The fabric strips 24 define a bag-like cavity 28 extending between the bags 1 12, 212 on either side thereof. The upper and lower fabric strips 24 define upper 24.1 and lower 24.2 bag cavity surfaces.

[0033] To complete the bag cavity 28, the ends of the upper 24.1 and lower 24.2 fabric strips 24 are secured to one another to define a closed bag around the bag cavity 28. The side walls of the bag cavity 28 are defined by the side walls 1 18, 218 of the bags 1 12, 212.

[0034] Like the bag 10 illustrated with reference to Figure 1 , the bags 1 12, 212 and the bag cavity 28 are each provided with a filling inlet (not shown).

[0035] To facilitate filling of the bags, one or more fluid flow apertures may be formed in the sidewalls extending between the bags.

[0036] This embodiment of the invention is illustrated in Figure 4, which illustrates the formation of fluid flow apertures 30 in the side walls 218 of the bags 212. The apertures 30 are dimensioned to permit free backfill fluid flow between the bags 212 and the bag cavity 28 during filling of the backfill bag assemblies 210.

[0037] The use of fluid flow apertures 30 makes it possible to do away with separate filling inlets for all the bags 212 and in these backfill bag assemblies 212, eight is merely necessary to provide a single filling inlet (not shown), preferably on one end of the central bag 28. As backfill is pumped into the backfill bag 210, the backfill flows into the central bag 28 and, as the bag 210, inflowing backfill flows through the fluid flow apertures 30 into the side bags 212, thereby filling up the entire backfill bag 210.

[0038] The structure of the backfill bag assembly 10 of Figures 1 and two can be seen from Figure 5, which illustrates the backfill bag 10 prior to filling. The backfill bag 10 comprises three interconnected bags 12 stitched together along upper stitching zones 16.1 and lower stitching zones 16.2. The bags 12 are folded in lengthwise with longitudinally extending folds 34 that allow the bags to fold relatively flat. This facilitates storage, transport and installation.

[0039] The structure of the backfill bag assembly 1 10 of Figure 2 can be seen from Figure 6, which illustrates the backfill bag 1 10 prior to filling. The backfill bag 1 10 comprises two bags 1 12 that are located apart from one another. The bags 1 12 are secured to one another by means of upper and lower strips of woven polypropylene fabric 24. The fabric strips 24 are stitched to the bags 1 12 along upper stitching zones 1 16.1 and lower stitching zones 1 16.2 to define a bag cavity 28 located between the bags 1 12, the sides of which are folded in lengthwise with longitudinally extending folds 134 that allow the bags to fold flat.

[0040] In practice, the backfill bags 10, 1 10, 210 of the invention take the place of the backfill dams or troughs used in conventional practice. The bags 10, 1 10, 210 are pumped between vertical supports placed according to existing mining practice, but being initially flat to not require extensive manhandling.

[0041 ] The bags 10, 1 10, 210 are placed in layers, one on top of the other, within two rows of vertical supports 32 (as illustrated in Figures in 2 to 4). Backfill is then pumped into the bags 10, 1 10, 210. It has been found that better dewatering is achieved if each layer is pumped separately, but it is not essential. As indicated above, the bags 10, 1 10, 210 are made from a fluid-pervious fabric (woven polypropylene or a geotextile) which allows the hydraulic transport water in the backfill to weep through the fabric, leaving the dewatered particulate material under pressure within the bags 10, 1 10, 210.

[0042] Any tubular bag, if it has only one compartment, will tend to fill out to a cylindrical sausage-like shape, which is undesirable. The location of the stitching 16, 1 16, 216 securing the individual bags 12, 1 12, 212 together constrains the overall shape of the filled bag 10, 1 10, 210 to that of a substantially planar mattress rather than a cylinder, thereby constraining a lower bag layer to provide a stable base for the next layer of bags 10, 1 10, 210. [0043] The number of bag layers will depend upon the height of stope to be filled. Ties may be stitched to the bags 10, 1 10, 210 to assist with stability on steep dips.

[0044] The bags 10, 1 10, 210 may be filled either one bag 12, 1 12, 212, 28 at a time, but it has been found that by filling at least two bags 12, 1 12, 212, 28 simultaneously, the bags 12, 1 12, 212, 28 tend to butt up against each other, preventing rolling and providing important lateral stability during pumping.

[0045] The bags 10, 1 10, 210 of the invention have the benefit of reducing the overall volume of backfill required to be placed compared to conventional backfill placement methods whilst nevertheless providing a structure that can be pumped with backfill using conventional vertical support unit protocols.

[0046] The reduced size of the bags 10, 1 10, 210 has the effect of reducing the volume-to-surface area ratio compared to conventional backfill placement thereby improving dewatering and allowing more stable backfilling operations.

[0047] This is facilitated by the layered stacking of the bags 10, 1 10, 210 which has the effect of the mass of a layer above compressing the layer below. As a result, any slump occurring during filling is immediately apparent and can be counteracted during filling. In addition, due to the enclosed nature of the bags 10, 1 10, 210, backfill can be pumped tighter to the hanging wall with internal backfill pressure being maintained by the bags 10, 1 10, 210 it to ensure that contact with the hanging wall and therefore active support are maintained.

[0048] The safety benefits of the bags 10, 1 10, 210 are to be found in the reduction of the overall volume of backfill material and the fact that hydraulic head is confined to single bags 12, 1 12, 212, 28. In the event of a rupture, therefore, the resultant outflow is unlikely to be catastrophic.