MXPA00000893A - Method for filling voids with aggregate material - Google Patents

Abstract

A method for filling a void using an aggregate material, such as mine tailings, the fill material being pumped from a site which is located remote from the void. A fluid, aerated material is formed by mixing the particulate solid material with finished foam. The aerated material may also include cement or another binder for applications requiring structural strength. The bubble structure which results from incorporating the foam constituent in the fill material renders this much more fluid and pumpable, thereby allowing the use of much higher solids-to-water ratios than would otherwise be possible while still being able to pump the material over significant distances. This reduces the possibly of fluidic collapse of the material in the void, and produces other advantages as well.

Description

METHOD FOR FILLING CAVIDADAES WITH AGGREGATED MATERIAL Field of the Invention This invention relates generally to methods for filling cavities with particulate material or aggregate material such as crushed rock or gravel and, more particularly, refers to an improved method for filling cavities located below and above the ground using debris and similar aggregate materials produced by mining and operations Background of the Invention This is a continuation application in part of the Patent Application Serial Number 09 / 015,374, entitled "Underground Cavity Backup Filling", filed on January 29, 1998, which is based on the Application for Provisional Patent Serial Number 60 / 036,174, entitled "Underground Cavity Backup Filling", filed on January 29, 1997. A number of mining, excavation and construction operations require the deposition of large amounts of aggregate material in some form of cavity or hollow. For example, the operations of the mining industry usually involve the removal of rock or mineral-bearing earth from a geological formation, thereby creating one or more gaps in the formation. The excavated rock is typically crushed and processed to extract the minerals, leaving the residue of crushed rock as waste. If left above the unconfined land, the massive amounts of waste produced by a routine mining operation present a space, as well as serious environmental problems. However, the waste is commonly returned to the mine to backfill the cavities that have been formed in the underground formation, while in other operations these are deposited in a pit or containment area that is above the ground.

For example, it is common to extract ore from the subsoil by forming a vertical rising well or a helical tunnel and then extracting the ore by horizontally extending tunnels at different levels. The large volumes of ore are then removed through the horizontal tunnels by blasting a succession of estopes or subterranean holes in an upward direction from the far end of each tunnel and back towards the central axis. With the purpose that the safe extraction of the mineral takes place it is necessary to practice the backfill of each underground hole or estope formed as part of the blasting and of the process of evacuation of the ore, in order to support the "roof" above of the estope and in this way allow it to be flown immediately and without danger of damage by collapsing an adjacent volume of ore. Backup backfill is typically carried out by mixing an appropriate solid material that is made up of particles, usually mining waste, with cement and water, and then hauling, trucking or pumping the filler mixture to the cavity location . The drainage of excess water from the fill mixture must be pumped from the mine and the filler mixture must be allowed to set to form a solid fill in the stope. The cost of backfill is important and can be as much as % of the total cost of the mining operation. The cost of the backfill backfill is directly related to the cost of the content of the cement in the backfill mix, but a significant cost is also involved in the transportation of the material into the cavity. The most convenient way to transport the material to the cavity is by pumping through pipes, but this requires a high water content in the backfill mix. This is particularly the case with most of the mining waste, due in part to the high cavity content resulting from the comparatively uniform aggregate size of the crushed rock. A conflicting requirement is that, in order to avoid slippage of sludge to the subsoil (that is, the fluidic collapse of part of the backfill material), the recommended percentage of solids in the backfill is above 74%. It is often difficult to pump such a mixture (in this proportion of solids) for significant distances, but any increase in water content to improve pumping properties increases the risk of mud slides and increases the volume and cost of the cement required in the mix so that it sets and reaches the specified resistances, which are typically of the order of 1 Mpa. The amount of cement varies according to the backfill material and the water content, but is usually around 6% in order that the filler reaches the required strength. In some types of mining operations, the waste is not used for the backfill of the mine as described above, but instead is deposited on the ground in a large pit or similar containment area. The process is essentially similar to that described above, except that in the absence of a requirement for structural strength, the cement or other binder component can be removed. The large amounts of water that are required to pump the material continue to present serious problems, notwithstanding that the disposal is above the ground. For example, dykes, retaining walls or similar structures must often be provided to prevent mud slides and spills. Moreover, water often becomes highly contaminated from contact with the waste (either by naturally occurring minerals or by chemical products used in the extraction process of the minerals), with the result that the use of large volumes of water to place the waste leads to a serious problem of containment and water treatment itself. It is therefore desirable to be able to provide an aggregate filler material that is easy to pump and, therefore, economical to place, without requiring the high water content that increases the risk of mud slides or that requires a high cement content, which in turn increases the cost of the operation. Said filler material is desirable for use in a wide variety of mining situations, such as, for example, stuffing of estopes, filling of used mines to eliminate dangerous threats from subsidence in subsequent mining operations to open sky, and other similar situations. Moreover, said filler material is desirable for use in a wide range of other mining and non-mining operations, both external and underground.

OBJECTIVES OF THE INVENTION The present invention therefore provides a method for filling cavities with aggregate material, in mining operations and in other operations, said method comprising the steps of forming a fluid filling material by mixing solid particulate material with a fluid foam material in an amount sufficient to form an aerated and pumpable slurry, pouring the aerated slurry into the cavity, and allowing the slurry to set there. The particulate solid material may comprise mining waste. The fluid foam material may comprise a mixture of a binder and foam. The binder can be a hydraulic cement. The foam can be formed from water and foaming agents. Preferably the step of spilling the aerated slurry into the cavity includes pumping the slurry from the mixing point into the cavity. The spill stage of the aerated slurry within the cavity may further comprise the step of applying a defoaming agent to the slurry in order to collapse the foam therein when the slurry is in the cavity.

The step of applying the defoaming agent to the aerated slurry can comprise the step of mixing the defoaming agent with the slurry as the slurry is injected into the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic elevational and cross-sectional view illustrating the backfill of an exemplary mine stope, in accordance with the present invention; and Figure 2 is a perspective view, somewhat diagrammatically, of a nozzle assembly for mixing a defoaming agent with the aerated slurry as the slurry is injected into a cavity.

Detailed Description of the Preferred Modality In spite of any other forms that may fall within its scope, a preferred form of the invention will now be described by way of example only with reference to the accompanying drawings, which show a mining operation typical in which the present invention can be used. The cavities in the illustrated example are underground, but in other instances the cavity may be a containment area disposed above the ground. As used in this description and in the appended claims, the term "cavity" includes all shapes of voids, pits, openings and the like, whether they are above or below the ground, and whether they are man-made or are a natural formation Moreover, while the example described below is directed to the disposal of waste which is essentially a "waste product" of the operation of the mining industry, it will be understood that the present invention is also applicable to pumping and laying of aggregates that have been provided for the express purpose of providing landfill in a selected area or in the construction of a designed structure. In a typical mining operation in which the present invention can be employed, and as can be seen in Figure 1, a vertical access, which can be for example an ascender or a spiral tunnel 10, is excavated within the ground 12 from the surface 14. At the required depth, at various intervals, horizontal tunnels 16 extend outwardly from the shaft 10 towards their remote ends 18. To extract minerals from a body of ore an area 20 is drilled above the surface of the body. end of tunnel 18 and explosives are placed and detonated to collapse the ore material within area 20 so that it falls into tunnel 16 and can be removed by well-known mining techniques. In order to continue with the mining operation by the following blasting and collapse of the adjacent area 22, it is necessary first to fill the empty gap 24 that was formed by the collapse and removal of the material from the area 20 (the cavity 24 is commonly referred to as a "estope" in the particular form of the mining operation shown in Figure 1). This can be conveniently accomplished by piercing a small access hole 26 from the surface 14 within the upper portions of the stope 24., and blocking the tunnel at point 28 (where it penetrates the estope) in an appropriate way. The backfill material is then prepared in accordance with the present invention by mixing an appropriate particulate material (typically, the mining debris resulting from processing the ore removed from the mine) with aerated slurry in a mixing apparatus. In many embodiments, the slurry will include a predetermined amount of binder, such as portland cement. The aerated slurry is formed in an appropriate manner by mixing the binder with the finished foam, which is typically formed from suitable foaming agents.; in those modalities where no binder is used, the aggregate can be mixed with the finished foam itself. As shown schematically in Figure 1, the apparatus preferably includes components for supplying the binder, such as a cement slurry 32, debris or other particulate material 34, and foam 36, and for feeding these into a mixer. 38. The binder component can be any suitable material for bonding the aggregate immediately to laying, including portland cements and other hydraulic cements, slag cements, fly ash type C and other fly ash, as well as binders. not suitable hydraulic. The waste or other solid material, in turn, can be crushed if necessary to provide the particulate constituent; due to the presence of the foam component, however, the category of the aggregate or other particulate material is usually not critical. The foam component, in turn, may be provided by any suitable foam material or foaming / foaming agent, such as the various aqueous and non-aqueous foam materials and chemical foaming agents that are known to those skilled in the relevant art. . Aqueous foam materials, which are generally preferred for their economy, consistency and ease of use, are typically formed by mixing a liquid foam concentrate material (suitable examples of foam concentrate material include the "Mearl Geocell Foam Liquid", available in Mearl Corporation, Roselle Park, NJ, in conjunction with similar products available from Elastizell Corporation, Ann Arbor, Ml, and other suppliers) with water to form a foam solution, and subsequently mixing the foam solution to form a finished foam having a stable bubble structure (suitable foam generators of this type can be obtained from The Mearl Corporation and Pacific International Grout Company, Bellingham, WA). Also available in the Pacific International Grout Company is an apparatus suitable for the generation of large quantities of foam material for mixing the slurry, and which is described in US Pat. serial number 5,803,596, which is incorporated herein by reference. In some embodiments it may be desirable to configure the feeding mechanisms in order to make it possible for the operator to control the relative amounts and proportions of the constituents as they are being fed into the mixing apparatus; for example, the relative proportions of cement slurry and foam solution can be controlled using variable speed metering pumps, and waste particles can be fed from a hopper using a controllable speed conveyor or a rotary metering valve. It will be understood, however, that any suitable feeding and mixing mechanisms can be used in the practice of the present invention, and that the choice of mechanisms will depend to a high degree on the importance of the way in which the constituents of Fillings are supplied. For example, Figure 1 shows a mixer 38 as a horizontal paddle mixer, which can provide certain advantages where the cement is already in the form of a slurry and the foam constituent is added as a finished aqueous foam. In other embodiments, however, the mixing of water and cement powder can be carried out in the mixer itself, and the foam component can be supplied as a chemical foaming agent in liquid or dry form which is combined with water and either on or before entering the mixer. Accordingly, a vertical tub mixer or other form of mixer may be preferred in some embodiments.

Similarly, Figure 1 shows the system as incorporating a large positive displacement, progressive cavity and screw type pump, of the kind that is available under the registered trademark Moyno ™ at Robbins & Meyers, Dayton, OH, which has several advantages (including efficiency, precise control of pumping speed, and prevention of damage to bubble structure in aerated fill material), but again it will be understood that any type of Pump can be used for this paper. The resulting fluid filler material contains a large amount of entrapped air by virtue of the foam component. As can be seen in Figure 1, it is flowed from the mixer 38 into the cavity 24, for example, using the pump 40 and the pipe 42. It has been found that by using an aerated grout (as opposed to a conventional water aggregate slurry), the structure of the bubble in the filling material makes it much more fluid and more susceptible to being pumped than it is with a conventional mixture of water and solid particulate material and, therefore, , it is relatively easy to pump across large distances using the pump 40 and the pipe 42, even when the percentage of solids in the filling material is kept above the minimum required to avoid the risk of sludge in the stope 24 Moreover, where cement is used in the mixture, the comparatively lower water content in the aerated slurry makes it possible to use much less cement compared to the non-foamed materials; for example, to achieve comparable strength, now approximately 4.5 to 5% cement is required, compared to at least 6% that is required when foam is not used. The additional expense of the foam, both in the mixing process and in the foaming agents, is more than compensated by the decrease in the quantities of cement (by reducing the water content), improvements in the properties of pumping, increase in volume global and increase in the percentage of solids in the mixture. While the examples described above note the advantages of the present invention when the filler material contains cement, it will be understood that in some applications the filler material of the present invention may contain little if not any cement or other binder. For example, if there is no requirement that the filler have any significant structural strength, the fluid filler material may be essentially composed of aggregate (eg, crushed rock) and finished foam alone. Hence, depending on the application and the specifications for a particular task, the cement or other binder component may be zero or may be high enough to react with the water component and provide the backfill with maximum available strength when set . The amount of foam required, that is, the ratio of foam to solids, will vary somewhat depending on the size and roughness of the particulate material (eg, crushed waste), the shape of the particles, the stability of the foam material which is being used, the distance over which the material is being pumped, and other factors to be determined by the particular task. From a practical point of view, however, the amount of water that is added to the filling by the foam component will always be much less than the amount of water that would be required to return the particulate material capable of pumping without the foam; for example, in test applications it has been found that the amount of water contained in the foam required to make the shredded waste pumpable is about 1 to 18 compared to water without foam. The aerated grout can be poured directly into the cavity and allowed to set without further treatment, as shown in Figure 1. In many applications, however, it is desirable to collapse the bubble structure of the material once it has penetrated the cavity and that the quality of pumping is no longer required. For example, in the case of a backfill operation there is usually a large volume of waste to be disposed of and only a limited amount of hollow space inside the mine to house them. Even in the upstream arrangement of soil, a reduced final volume generally considers a smaller and more economical containment area. In order to collapse the bubble structure of the filling material, a suitable defoaming agent can be added to the fluid material at the injection point, as it is discharged into the cavity. For example, Figure 2 shows a nozzle assembly 50 by means of which a defoaming agent is added to the filling material immediately before it enters the cavity. As can be appreciated, the nozzle assembly 50 is mounted to the discharge end of the conduit 42 in order to receive the flow of the aerated slurry therefrom, as indicated by the arrow 52. The defoaming agent is fed into the nozzle assembly at liquid form, via a secondary conduit 54, in the direction indicated by arrow 56. For efficiency purposes, the defoaming agent can be fed to the nozzle assembly at a dosed rate corresponding to the flow velocity of the aerated fill; an example of a suitable apparatus for providing an additive to a discharge nozzle at said dosed rate is described in US Pat. No. 5,803,685, which is incorporated herein by reference. The defoaming agent is mixed with the filling material in a static mixer 58 which is mounted in the downstream assembly of the secondary conduit 54, and the mixed material is discharged therefrom into the cavity through an outlet pipe 60, in the direction indicated by arrow 62. The defoaming agent, having been mixed with the filling material, collapses the bubble structure very quickly once the material has been deposited, without interfering with the pumping capacity of the upstream filler material of the nozzle assembly. It will be understood, however, that the relationship of the components shown in Figure 2 is only illustrative of an exemplary embodiment. For example, the static mixer may or may not be present in all modes, and the line for the addition of the defoaming agent may be attached above the main conduit 42 so that mixing simply takes place within the conduit itself. In addition, the defoaming agent line can simply be discharged into the mass along the end of the main conduit, or it can be applied to the filler material after it has been deposited in the cavity, using a line or a separate container. While the amount of defoaming agent required will vary depending on the actual composition and operating conditions, in general only a very small amount is needed to completely collapse the bubble structure. While any suitable defoaming agent that effectively collapses the bubble structure can be employed, silicone oils and other silicone-based defoaming agents are generally preferred because of their good initial action, rapid knockdown, and effectiveness within wide pH ranges.; An example of an oil-silicone based defoaming agent is "ANTIFOAM-A", available from Dow-Corning. Other suitable defoaming agents, some of which are limited in their effectiveness at certain pH ranges, include fatty amide based products (eg, "NOPCO 198", available from Diamond Shamrock), fatty acid based products (e.g. " NOPCO KR ", available from Diamond Shamrock), and fatty ester based products and hydrocarbon paraffins (suitable examples of which are also available in Diamond Shamrock). Because the defoaming agent removes the bubble structure during or shortly after the placement of the filler material, the operator may nevertheless add much foam as required to ensure the pumping capacity of the material, without concern about the increase in volume end at the reception end. The relatively small amount of water that is released when the bubbles collapse can serve to hydrate the cement or other aqueous binder when it is present in the mixture. The result is a dense fill in the cavity having very little volume larger than the volume of the debris or other particulate material that was initially incorporated in the fill. Furthermore, there is little or no excess water that must be disposed of, treated, or handled in any other way at the job site. It should be recognized that various alternative modifications and / or additions may be introduced within the constructions and arrays of parts described above without departing from the spirit or scope of the present invention as defined by the appended claims.

Claims (16)

1. Novelty of the Invention 1. A method for filling a cavity using solid particulate material, said method comprising the steps of: forming an aerated and fluid filling material by mixing: solid particulate material; and foam material in an amount sufficient to make it possible for said filler material to flow over a predetermined distance from a site remotely located to said cavity; and spilling said aerated and fluid filling material into said cavity. The method of claim 1, wherein the step of forming said aerated and fluid fill material comprises the step of: mixing a binder material with said particulate material and foam materials in a predetermined amount. The method of claim 2, wherein the step of mixing a binder material with said particulate material and foam materials comprises: mixing a hydraulic cement material with said particulate material and the foam materials. The method of claim 1, wherein the step of forming said filling material further comprises the step of: mixing a foaming agent with water to form said foam material. The method of claim 1, wherein the step of forming said filler material further comprises the step of: mixing a solution of aqueous foam and air to form said foam material. The method of claim 1, wherein the step of forming said filler material further comprises the step of: forming said particulate solid material from mining debris. The method of claim 1, wherein the step of forming said filler material further comprises the step of: forming said filler material at said site which is located away from said cavity. The method of claim 1, wherein the step of spilling said packing material into said cavity comprises: pumping said aerated packing material into said cavity. The method of claim 1, further comprising the step of: collapsing said foam material in said filling material when the filling material is in said cavity. The method of claim 9, wherein the step of collapsing said foam material comprises: mixing a defoaming agent with said aerated filler material as said filler material is spilled into said cavity. The method of claim 10, wherein said defoaming agent is a defoaming agent of silicone oil base. The method of claim 3, further comprising the step of: collapsing said foam material in said filler material when said filler material is in said cavity. The method of claim 12, wherein the step of collapsing said foam material comprises: mixing a defoaming agent with said aerated filler material as said filler material is spilled into said cavity. The method of claim 1, wherein said cavity is an underground cavity. 15. The method of claim 14, wherein said subterranean cavity is a mine stope. 16. The method of claim 15, wherein said cavity is a containment area located above the ground.