EP0034520B1 - Mining excavating process using the bord and pillar method - Google Patents

Description

The present invention relates to a method of operating a mine by chambers and pillars in which the chambers are filled with fill.

In mine sites, the ore is extracted according to this known process. We excavate chambers which are supported by several pillars of ore left in place. These pillars support all of the pressure from the terrain overlying the abandoned chambers. The pillars, thus compressed, undergo long-term swelling which could cause them to rupture.

In addition, to improve the efficiency of ore mining it is desirable to reduce the section of the pillars.

There is already known (US Pat. No. 3,817,039) a method of backfilling underground chambers in operation according to the chamber and pillar method consisting in injecting a material in the form of particles, such as fly ash, sand, crushed slag or the like, suspension in a liquid.

Finally, patent FR-1 452 419 describes a backfill product based on fly ash which, under the effect of hydration and pressure, makes it possible to obtain a self-supporting backfill mass. However, this “self-supporting” effect is only obtained after several weeks and during this entire period the risk of collapse remains.

Works in "Reinforced Earth" have been described in particular in patents FR 1 393 988 (US 3 421 326), US 3 981 038, FR 2 315 572, US 4 125 970, all in the name of the Applicant, and the teaching is partly applicable to the subject of the present invention.

The object of the invention is to propose new methods of implementing the backfilling process known in the application to the exploitation of a mine by chambers and pillars. In fact, in this particular case, it is desirable to make pillars of section as small as possible and to reinforce them by backfilling having, as soon as it is put in place, sufficient strength.

The invention therefore relates to a method of operating a mine by chambers and pillars in which the chambers are filled with fill, characterized in that, around a group of pliers, we build from the ground of the chamber an enclosure of closed outline, for example rectangular, the walls of which are obtained by horizontal juxtaposition and superposition of U-shaped profiles whose concavity is turned inward, and whose wings form reinforcements and / or support, reinforcements form of relatively flexible bands and is carried out inside the enclosure a backfilling with a material whose solid particles form an initially pulverulent material which becomes subsequently coherent.

If the particles of the backfill have pozzolanic or hydraulic characteristics, they can be drawn from volcanic ash, such as pozzolans, or from volcanic tuffs or trass. Most often, particles with pozzolanic or hydraulic characteristics will come from industrial by-products, such as fly ash, produced by thermal power plants for the production of electricity, and blast furnace slag, which normally takes the form of aggregates. .

As for the additives having the function of an adhesive, they can be used in the form of a solution, suspension, emulsion, etc.

The method according to the invention makes it possible to execute structures which, in their final state, are more rigid than structures in reinforced earth, which in principle have a certain flexibility.

Another advantage of the proposed process is that it makes possible the recovery of products available near the site where the structure is to be built and which, sometimes, as in the case of fly ash, are bulky, even polluting.

In addition, in the case where solid particles, such as ash or cohesion-generating additives do not contain aggressive elements, the cohesion of the solid mass due to the setting phenomenon can lead to savings in terms of the reinforcements, in the sense that the latter, like the reinforcements used for reinforced concrete, can be made of a material which is not particularly resistant to corrosion and is consequently less expensive than that of the reinforcements normally incorporated in reinforced earth works.

The resistant enclosure which surrounds the pillars over a significant height, without necessarily reaching the roof of the chamber, thus achieves around the pillars a hooping which partially restores the state of embrace that the digging of the chambers had made disappear. As a result, the tendency to swell under compression load, which could occur in the central area of the pillars, is completely suppressed.

• la Figure 1 est une vue en coupe verticale de piliers d'une mine, consolidés au moyen d'un remblai contenu dans une enceinte ;
• la Figure 2 est une vue en coupe suivant la ligne 2-2 de la Fig. 1.

The invention will be explained in a purely indicative manner during the description which follows, of an example of implementation of the method according to the invention, with reference to the appended drawing, in which:

• Figure 1 is a vertical sectional view of pillars of a mine, consolidated by means of an embankment contained in an enclosure;
• Figure 2 is a sectional view along line 2-2 of FIG. 1.

Figs. 1 and 2 represent a part of a coal mine site from which the ore was extracted by the chamber and pillar process. The pillars aligned 1 to 3, delimiting two chambers 4,6 of supposed constant height, support all the pressure of the ground 7 overlying the abandoned site.

To remove the risk that the pillars as well tablets undergo long-term swelling which could cause them to rupture, and also to improve the yield of exploitation, by a reduction in the section of the pillars, the latter are surrounded by a rectangular enclosure 8 which is filled to a level located clearly above the middle of the pillars, without however reaching the roof 9 of the chambers, of a material 11. spilled by hydraulic backfilling.

The four walls 12 to 15 of the enclosure 8 are constituted by superimposition of a certain number of seats of metal profiles 18, 18a of U-shaped section, arranged approximately contiguously in each seat and the lower wing 19 a a free edge shaped as a hook 20, so as to come into engagement with the smooth edge of the upper wing 21 of one or more underlying profiles.

The reference 25 designates elbow-shaped fittings at a right angle provided in each seat at the four corners of the enclosure 8 to connect to each other the profiles of two adjacent perpendicular walls.

The profiles 18, of which the end walls 12, 14, one of the edge walls 13 and the end portions of the other edge wall 15 are formed, are profiles with broad wings, while the profiles 18a constituting , over the greater part of its length between the end parts, the edge wall 15, are profiles whose wings are relatively narrow. The sections 18a are however completed by reinforcements 22 constituted by metal bands, relatively flexible, which are each bolted, at one of their ends, through two wings 19, 21, in mutual contact, of superimposed sections, and which are coated in the backfilled solid 11, their other end being free of any attachment. This provision is quite usual in reinforced earth constructions, as is apparent from the patents FR 1 393 988 and US 3 421 326.

In these same patents is also stated the possibility of assigning to the wings of U-shaped profiles the reinforcement function of a structure in reinforced earth, as is the case of the profiles 18 with wide wings of the present application.

The material 11 poured by hydraulic backfilling inside the enclosure 8 delimited by the walls 12 to 15 is a mixture essentially comprising water and powdery ash. The solid ash particles which, as the backfilling progresses upwards, come into frictional contact with the wings of the profiles 18, 18a and with the reinforcements 22, giving cohesion to the solid mass formed in the enclosure which, in accordance with the teaching of the cited patents, has the characteristics of a reinforced earth construction, stable and resistant.

The choice of ash as a constituent of backfill is justified on the one hand, by the fact that so-called fly ash is generally available near coal mines, as by-products of thermal power plants, on the other hand, by the property of these ashes mixed with water to set after a relatively long time, so that in the long term the backfilled massif, which initially formed reinforced earth, turns into a kind of concrete very thin, like reinforced concrete, by the presence of the wings of the sections 18, 18a and the reinforcements 22.

Consequently, whatever the age of the massif enclosed in enclosure 8, the pillars 1 to 3 which are trapped there over a significant height benefit from a hooping or embracing effect allowing them to resist indefinitely pressures that the overlying terrains 7 exert on them.

Although the joint use of wide-flange profiles 18 and flexible strips 22 attached to the profiles 18a has been described, to constitute the reinforcements of a volume of reinforced earth, it goes without saying that an enclosure such as 8 could be constructed with walls made exclusively by means of sections 18 with wide wings, or else with walls made exclusively of sections 18a with short wings to which armatures 22 in the form of a strip are fixed.

By making the edge walls 13, 15 exclusively by means of profiles 18 with wide wings, these profiles would define in combination with the solid particles filling their cavities a thick wall of reinforced earth whose stability would be sufficient to withstand the thrust exerted by the unreinforced material contained between the two walls 13, 15.

In the example described, the walls 12 to 15 of the enclosure and the backfill material 11 remain at a level lower than that of the roof 9. It is however possible to carry out a hydraulic backfill which reaches the level of the roof, and , if necessary, also raising all or part of the walls to the roof level.

Claims (8)

1. A method for working a mine by the bord-and-pillar method in which chambers adjacent the pillars are filled with a fill, characterised in that it comprises constructing, around a group of pillars (1, 2, 3), on a foot wall of a chamber, an enclosure (8) having a closed contour, for example a rectangular contour, whose Walls are obtained by horizontal juxtaposition and superimposition of U-section elements (18, 18a) whose concavity faces inwardly and whose flanges form reinforcements and/or support reinforcements in the form of relatively flexible bands (22), and producing inside the enclosure a fill with a material (11) whose solid particles form an initially pulverulent material which subsequently becomes coherent.

2. A method according to claim 1, characterised in that the fill material (11) comprises solid particles having pozzolanic or hydraulic properties.

3. A method according to claim 2, characterised in that the solid particles having pozzolanic or hydraulic properties are based on ash or slag.

4. A method according to claim 2, characterised in that the solid particles having pozzolanic or hydraulic properties are of volcanic origin, for example formed by pozzolana or trass.

5. A method according to one of the claims 1 to 4, characterised in that a product of addition, such as lime, cement or calcium chloride, which is capable of setting, is incorporated in the fill material (11).

6. A method according to one of the claims 1 to 4, characterised in that the product of addition comprises a substance which, after having been employed, changes physically or chemically, and acquires the properties of an adhesive or of a plastic or rigid binder.

7. A method according to one of the claims 5 and 6, characterised in that the product of addition is employed in the form of a solution, suspension, emulsion, etc.

8. A method according to one of the claims 1 to 7, characterised in that the material (11) is placed in position by a hydraulic filling.

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