GB2177389A - Filling and solidifying grout slurry in coal pit - Google Patents

Abstract

A method of filling and solidifying a grout slurry in an underground coal pit includes preparing the grout slurry containing 30 to 70 wt% of fine washery tailing and/or fly ash, 1 to 15 wt% of cement and the balance of water; the grout slurry is fed and filled through a pipe line to an underground site and allowed to solidify in situ at the filled position.

Description

SPECIFICATION Method of filling and solidifying grout slurry in coal pit The present invention relates to a method of feeding a grout slurry into an underground coal pit to allow the same to solidify in situ, and more particularly it relates to such a method wherein a grout slurry containing an industrial waste material, such as fine washery tailing or sludge and/or fly ash is fed through a pipe line.

Roadways of a coal mine must be hardened by filling with a grout slurry or solidifier in order for ensuring safe maintenance thereof or for sealing a certain roadway air-tightly so that the sealed roadway is isolated from the atmosphere for the prevention of spontaneous combustion.

Another purpose for such grouting resides in that an artitificial roof of multi-slicing faces must be hardened or consolidated to improve operation efficiency and to provide safeguard for workers.

In the conventional method for satisfying the aforementioned requirements, crushed rock or crushed waste materials are brought in the roadways and filled and then solidified using machines or by manual labour. However, cumbersome and time-consumting operations are necessitated for bringing machinery and filler materials to a place at which solidification of the filler should be effected. A further disadvantage of the conventional method is that it is difficult or even impossible to fill the solidifier sufficiently firm, leading to unsatisfactory strength against rock pressure or for air-tight sealing.

On the other hand, a large amount of fine washery tailing or sludge is discharged from mines and a large amount of fly ash is discharged from thermal-power stations. These materials had, hitherto, been disposed as industrial waste materials without being applied for any useful application, and disposal thereof often caused environmental pollution problems since such waste materials could hardly be treated not to cause pollution problems at the place onto which they were stacked.

The present invention provides a method of filling and solidifying a grout slurry in an underground coal pit including the steps of preparing the grout slurry containing 30 to 70 wt% of fine washery tailing and/or fly ash, 1 to 15 wt% of cement and the balance of water,feeding and filling said grout slurry through a pipe line to an underground site, and allowing the grout slurry to solidify in situ at the filled position.

DRA WINGS: Figure 1 is a graph showing the change in reduction rate by dehydration in terms of change in pulp concentration and variation of the used pulps.

Figure 2 is a graph showing the change in solidified strength in terms of change in pulp concentration and variation of the used pulps.

Figure 3 is a schematic view, in longitudinal section, of a roadway filled and sealed air-tightly by the practice of the invention.

Figure 4 is a schematic plan view showing multi-slicing faces at which goaf side stowing and solidification filling for artificial roof are effected.

Figure 5 is a sectional view taken along line A-A of Fig. 4.

Figure 6 is a sectional view taken along line B-B of Fig. 4.

In the first step of the invention, prepared is a grout slurry containing 30 to 70 wt%, of fine washery tailing and/or fly ash, 1 to 15 wt%, preferably 2 to 10 wt%, of a cement and the balance of water. The fine washery tailing may be obtained as sludge discharged from coaldressing facility of a coal mine. Since the fine washery tailing is generally low in concentration as it is discharged from an ordinary coal-dressing facility, it is desirous to concentrate the same before use. The fly ash is formed as fine ash particles entrained in flue gases, and may be collected from a flue gas discharged, for example, from a coal combustion boiler using a precipitator. The fine washery tailing and the fly ash may be used singly or in combination.If the content of fine washery tailing and/or fly ash is less than 30 wt%, the reduction rate (i.e. the percentage height of the grout slurry which has been reduced by dehydration after the lapse of predetermined time period relative to the initial height of the deposited slurry at the filling time when a unit volume thereof is filled) becomes too high with the increase in volume of drained water and attendant postponement of solidification. On the contrary, a grout slurry containing more than 70 wt% of washery tailing and/or fly ash is detrimental, since such a composition has poor fluidity and thus cannot be fed through a pipe line.

It is desireous that 20 to 75 wt%, preferably 30 to 65 wt% of the fine washery tailing and/or fly ash has a particle size of less than 325 meshes, and any of particles of the fine washery tailing and/or fly ash has not a particle size of 30 meshes or larger. If the content of the fine washery tailing and/or fly ash particles having a particle size of less than 325 meshes is decreased below 20 wt%, dregs may possibly be deposited in the feed pipe line. It is undesirable to increase the content of fine washery tailing and/or fly ash particles having a particle size of less than 325 meshes to more that 75 wt%, because reduction rate by dehydration may increase and solidified strength may decrease.The fine washery tailing and/or fly ash may preferably not contain particles having a particle size of larger than 30 meshes, since such particles tend to settle in the feed pipe line to blockade the pipe. It is also desirous that the fine washery tailing has a calorific value of not more than 1500 kcal/kg, preferably not more than 1000 kcal/kg. If the unit calorific value of the used fine washery tailing exceeds 1500 kcal/kg, there arises a risk that the filled grout slurry is combusted when a fire takes place in the roadway.

The cement which may be used according to the present invention may be Portland cements, mixed cements, expansive cements or rapid hardening cements or mixtures thereof. The Portland cement may be normal Portland cement, high early strength Portland cement, moderate heat Portland cement or white Portland cement or mixtures thereof. The mixed cement may be silica cement, fly ash cement or blast furnance cement or mixtures thereof. The expansive cement may contain as a main expansive agent a combination of calcium sulfoaluminate, lime and calcium sulfate, a combination of calcium aluminate and calcium sulfate, high sulfate slag, lime or MgO or mixtures thereof. The rapid hardening cement may contain 12CaO 7AI203 and/or 11Ca O7Al2O3CaX2 (X being a halogen), or calcium sulfate.

If the content of cement is less than 1 wt%, the grout slurry is not solidified to develop negligibly low reinforcing strength. On the contrary, if the content of cement is more than 15 wt%, the fluidity of the grout slurry is lowered so as not to be fed through the feed pipe line.

In the present invention, the fine washery tailing and/or fly ash and the cement are mixed with water using a mixer or agitator to prepare a grout slurry having the composition as described hereinabove. The fine washery tailing may be concentrated preliminarily to have an adjusted water content so that the content of the fine washery tailings in the grout slurry is controlled to be in the range of 30 to 70 wt%. In such a case, a grout slurry containing 30 to 70 wt% of fine washery tailing and 1 to 15 wt% of cement can be prepared only by adding a calculated amount of cement to the thus concentrated fine washery tailing. The grout slurry may be added with an additive, such as granulated slag, calcium sulfate or lime or mixtures thereof, in an amount of not to affect the fluidity of the grout slurry significantly.

In the next step of the present invention, the grout slurry prepared in the first step is fed through a pipe line to a place in an underground coal pit at which it is placed. The grout slurry of the invention can be fed by gravitational force between pit mouth and underground site without the need of using a pump, except in a case where the grout slurry is fed from the outside of the underground pit through a passage having sever undulations. Although the length of the pipe line might be so long as up to 3 to 7 killometers when the grout slurry is fed from the outside, the pipe line is not blockaded by the use of the grout slurry of the invention.

The grout slurry fed to the desired place is then solidified. According to the method of the invention, the grout slurry may be deposited directly at the desired place and allowed to solidify without any support, or may be filled in a space or room surrounded by dehydrating walls made of a water-permeable material, such as polypropylene cloth, supported by props, plates or piles.

The grout slurry of the invention may be applied, for example, for stowing in a sealing zone between a goaf and a driftway, for filling to air-tightly seal a certain portion of a roadway, for solidifying or reinforcing an artificial roof of lower multi-slicing faces, and for filling in the backsides of supporting frames installed in roadways. However, the method of the invention may be applied for many other applications, and it is not intended to limit the applications thereof only to those as described illustratively in the preceding passage.

When the method of the invention is applied for stowing in the sealing zone between a goaf and a driftway, the grout slurry is prepared in a plant placed outside of the underground pit, fed through a pipe to a desired position in the goaf, and filled in a cavity surrounded by a box-like casing formed by props, piles, plates and dehydrating polypropylene cloth walls. When used for filling to seal a certain portion of a roadway, a preset zone of the roadway is closed by fore-and aft-dehydrating walls (a single wall may suffice to close a zone when a portion of an inclined roadway is to be sealed) and the grout slurry is filled in the zone.A grout slurry composition having a relatively low strength after solidification thereof is used if the zone is sealed temporarily, whereas a grout slurry composition having a relatively high strength after solidification thereof is used if the zone is sealed permanently or the rock pressure is high even if the zone is sealed temporarily.

The method of the invention may be applied for filling at a side of sandbag stack to isolate the inside of the solidified partition from the outside atmosphere rapidly and effectively in an emergency state, for instance a spontaneous combustion or a fire in a roadway, where an urgent air-tight sealing is required. When the grout slurry of the invention is injected and filled in a zone where a spontaneous combustion takes place, the grout slurry acts as a cooling agent and then solidifies to interrupt the air flow. In such an emergency state, crushed rock particles were injected, according to the conventional method. Only inferior extinguishing effect was obtained by the injection of crushed rock particles, since they are not solidified and dispersed over the excessively wide bottom area.The present invention provides an effective counter measure when such an emergency accident occurs.

When the method of the invention is applied for solidifying or reinforcing an artificial roof of lower multi-slicing faces by filling the grout slurry of the invention to provide a layer to cover the entire ceiling face formed by the upper multi-slicing operation, the artificial roof and the voids in the collapsed sludges above the artificial roof are filled with the grout slurry which is solidified under the pressure from the upper region to form a strong roof with the lapse of time as if it is formed of a prepact concrete. With the provision of such a stong ceiling, the subsequent mining operation for forming the lower faces can be carried out at high operation efficiency without the fear of collapse of ceiling. The thickness of the solidified layer is not particularly limited, and preferably ranges from 10 cm to 50 cm.The reinforcing effect of the solidified layer is unsatisfactory if the thickness thereof is less than 10 cm, whereas the reinforcing effect is not enhanced higher so much even if the solidified layer is thicker than 50 cm with redundant increase in cost. However, installation of expensive artificial roof may be dispensed with to realize extreme reduction in operation cost, when a grout slurry of the invention enriched in solidifier ingredients is used to build a highly strong filler layer having a thickness of 50 cm to 1 meter.

In filling operation, a filling pipe having a multiplicity of manifolds extending towards the goaf is laid parallel to the plane of coal bed, and the grout slurry is filled successively as the coal seam is cut continuously. A water spraying pipe may be used as the filling pipe by changing over a valve provided for this purpose. When a moderately inclined coal bed slanting at an angle of 20 to 30 is sliced, a combination bundle of short and long filling pipes, for example disposed alternately, is inserted from the upper driftway into the goaf so that the grout slurry discharged from the filling pipes is allowed to flow down by gravity.

An artificial roof made of a steel strip, steel sheet pile or metal net is installed along the ceiling for the lower multi-slicing operation, according to the conventional technology. However, such an artificial roof used in the conventional technology tends to be damaged, resulting in breakdown or downward bending, during the lower multi-slicing operation due to the fact that the collapsed sludges falling on the roof are not solidified.

The known methods of filling the backsides of the supporting frames in the roadway, as a measure to prevent air leakage from cracks of roof wall, according to the conventional technology, includes a clay filling method wherein a clay is filled in the backsides of plates extending between the adjacent supporting frames by manual labour, and a spraying method wherein an organic foaming agent is sprayed onto the roof and wall of the roadway. However, the clay filling method is a time-and labour-consuming process. On the other hand, the spraying method has disadvantages that the apparatus and foaming material used therein are expensive, and that the strength of the resultant foam is too low to be peeled off by the pressure of leaking air when it is applied in a return air roadway.The method of the invention provides an improved method for the prevention of air leakage superior to the aforementioned conventional methods, wherein the backsides of supporting frames can be filled with the grout slurry of the invention to form a durable backing rapidly. More particularly, according to the present invention, the grout slurry may be filled rapidly through pipes at the backsides of dehydrating walls disposed between the supporting frames. The grout slurry thus filled is solidified to develop strength to contribute to maintenance of the driftway. The filled slurry solidifies to form integral mass. The strength of the solidified mass is increased considerably within 3 to 7 days after the filling, and the strength is then increased progressively to reach a high level.

The method according to the present invention has the following advantages.

(1) The dehydration of filled grout slurry proceeds rapidly with minimum reduction rate due to dehydration.

(2) The filled grout slurry develops a strength within a relatively short time after the filling operation to ensure air-tight solidification strength after the lapse of short time period.

(3) The grout slurry is not shrinked after solidification, is not poisonous to human being in itself, and does not provide any risk of spontaneous combustion or flammability.

(4) The grout slurry has little tendency of separation, sedimentation or blockade of feed pipe while it is fed through a pipe.

(5) The aimed filling operation can be easily carried out without the need of precise adjustment operations, such as particle size control, mixing operation control or concentration control.

EXAMPLES: Example 1 A fine washery tailing discharged from the working site of Minami-oyubari Mine of Mitsubishi Mining & Cement Co., Ltd. and a fly ash discharged from Takashima Thermal-Power Station were subjected to tests to determine particle size distribution thereof. The results are shown in Table 1.

Table 1 Mesh Fine Washery Tailing (wt%) Fly Ash (wt%) - 30 * 30 - 60** 60 - 100 18.1 2.0 100 - 200 6.9 15.8 200 - 325 14.7 21.7 325 - 60.3 60.5 Total 100.0 100.0 * determined according to Japanese Industrial Standard Z8801 ** Other mesh sizes based on the Tyler mesh Standard The fine washer tailing was subjected to industrial The fine washery tailing was subjected to industrial analyses. The results are shown in Table 2.

Table 2 Inherent Volatile Ash Fixed Calorific Value Moisure Matter Carbon (kcal/kg) 1.9 11.9 82.1 4.1 500 The fine washery tailing, the fly ash, and a normal Portland cement were mixed with water, while varying the pulp concentration (pulp concentration being the total content of the cement and the fine washery tailing or fly ash) as plotted on the abscissa in Figs. 1 and 2, and the reduction rate and the solidified strengths after ageing for 24 hours of respective samples were measured. The results are shown by the polygonal graphs in the Figures.The reduction rate is the percentage of the height of grout slurry after the lapse of 24 hours from the time of filling the grout in a 1.5 mX1.5 mX1.5 m cavity surrounded by dehyrating walls made of polypropylene cloth relative to the initial height of the grout slurry immediately after the filling operation.

The solidified strength was measured in accordance with the Japanese Industrial Standard M-0302 Method. In Figs. 1 and 2, the plots A show the results of the samples wherein the pulp concentrations were 50 wt% (Content of Cement: 2.2 wt%, Content of Fly Ash: 47.8 wt%), the polygonal lines B show the results of the samples wherein the contents of cement were 3 wt% and the balance of fine washery tailing, the polygonal lines C show the results of samples wherein the contents of cement were 5 wt% and the balance of fine washery tailing, and the polygonal lines D show the results of the samples wherein the contents of cement were 7 wt% and the balance of fine washery tailing.

Example 2 A horizontal roadway 1 was sealed ait-tightly as shown in Fig. 3. A zone of the roadway 1 was partitioned by two dehyrating walls 4 and 5, each being constructed of polypropylene cloth 2 and cross beams 3 and props (not shown). A portion of the ceiling in the zone, within which a grout slurry of the invention was filled, was cut away as denoted by reference numeral 7, and a feed pipe 6 was laid so that the discharge port thereof opened near the top the cut-away portion to preclude the discharge port from being blocked. An inspection pipe 8 was laid to have its end opened at the level lower than the discharge port of the feed pipe 6 by about 10 cm. The inspection pipe 8 served as means for purging air therethrough and also served to inform that the zone had been fully filled with the grout slurry when the slurry returned back through the pipe 8.

A grout slurry was prepared outside of the pit by mixing 50 wt% of the fine washery tailing as described in Example 1 and 3 wt% of a normal Portland cement with 47 wt96 of water using a mixer, and the thus prepared slurry was fed through a pipe line by gravitational force into the feed pipe 6. The slurry was fed until it is returned back through the inspection pipe 8.

Additional filling of the slurry was repeated two times, the first additional filling operation was carried out after 24 hours and the second additional filling operation being carried out after 48 hours from the initial filling operation, in order to fill the rooms formed by sinking due to dehydration of the filled slurry. It was confirmed that the zone had been sealed tightly so that leakage of air under a differential pressure of 60 m m by water column was not found at all after the lapse of 10 days. The pipe line was not blocked even slightly.

Example 3 In a multi-slicing operation for mining from a coal seam extending at an inclination angle of 25 from the horizontal plane as shown in Figs. 4 to 6, goaf side stowing operations were conducted, in accordance with the method of the present invention, in an upper driftway 10 and a lower driftway 11.

In the Figures, reference numeral 12 is used for denoting upper multi-slicing forces, 1 2a for a goaf formed by the upper slicing operation, 13 for lower multi-slicing faces, 14 for an artificial roof, 14a for a solidified filler layer, 15a and 15b for goaf side stowing zones, 16 for steel props, 17 for link bays, 18 for a self-advancing support, 19 for a drum cutter, 20 for a conveyor, 21 for crib chocks, 22 for a feed pipe, 23 for filling hoses, 24 for gas detection pipes, 25 for feed pipes for feeding a slurry over the artificial roof, 26 for wooden props, 27 for wooden plates, 28 for polypropylene cloths, 29 for sheet piles, 30 for dehydrating walls, and 31 for a floor.A grout slurry was prepared outside of the pit by mixing 50 wt% of the fine washery tailing as described in Example 1 and 5 wt% of a normal Portland cement with water, and fed through the feed pipe 22 and the filling hoses 23 into a box-like cavity 30 adjacent to the upper driftway 10 and surrounded by dehydrating walls constructed of the wooden props 26, the wooden plates 27, the polypropylene cloths 28 and the sheet piles 29. An additional filling for filling the room formed by sinking of the slurry was carried out on the next day of the initial filling operation day. The room formed by sinking was fully filled by a single additional filling operation, and no further filling was needed. The operations were repeated successively to fill the adjacent sections as the mining proceeded, whereby goaf side stowing zones 1 5a and 15b were formed.The dehydrating walls 30 and the feed pipe 22 for the formation of goaf side stowing zone 15b in the lower driftway 11 are omitted in the Figure in the interest of clarity. As a result of filling the grout slurry, the driftway provided with the goaf side stowing zones was maintained in a satisfactory condition. The quantity of water oozed through the dehyrating walls 30 was too small to affect the bottom of the driftway. The pipe line was not blocked even slightly.

Example 4 In the same multi-slicing faces as described in Example 3, a slurry was flowed from the upper driftway 10 of the upper slicing goaf 12a through the feed pipe 22, the gas detection pipes 24 and the feed pipes 25 for feeding the slurry over the artificial roof 14, whereby the slurry was fed on the artificial roof 14.The gas detection pipes 24 having the ends opened beyond the inside of the goaf side stowing zone 15a, were used both for detecting gases and for feeding the slurry,whereas the feed pipes 25 for feeding a slurry over the artificial roof 14 were strainer pipes, each having side walls provided with a number of small pores and each having the fore end extending to the substantial center of the slicing width, the feed pipes 25 being laid along the floor 31 during the coal mining operation of the upper slicing so that they were burried under the slag masses fallen from the ceiling. The pipes 24 and the pipes 25 were disposed alternately at equal intervals of 10 meters and both having diameters of 50 m m.

A grout slurry having a composition composed of 50 wt% of the fly ash described in Example 1, 3 wtQ of a normal Portland cement and the balance of water. The slurry was filled for three times to form a covering layer having an average thickness of 30 cm over the artificial roof 14.

The filling operations were repeated successively as the operation of cutting the upper multislicing faces 12 was proceeded. When the lower slicing faces were cut to excavate coal from the coal seam beneath the zone filled with the aforementioned slurry after about one month from the filling time, the upper ceiling of the lower slicing faces was filled substantially uniformly in its entirety to form a continuous solidified filler layer with the thickness somewhat varying within the range of from 20 cm at the minimum to 40 cm at the maximum. A dense solidified layer 1 4a had been filled in-between the artificial roof material and the sludges falling thereon to leave no empty cavities or channels and solidified in situ for form a concrete-like stusture. The ceiling had thus been improved remarkably to exclude troubles due to collapse thereof to increase the coal output. The pipe line was not blocked even slightly.

Claims (14)

1. A method of filling and solidifying a grout slurry in an underground coal pit including the steps of preparing the grout slurry containing 30 to 70 wt% of fine washery tailing and/or fly ash, 1 to 15 wt% of cement and the balance of water, feeding and filling said grout slurry through a pipe line to an underground site, and allowing said grout to solidify in situ at the filled position.

2. A method according to claim 1, wherein 20 to 75 wt% of said fine washery tailing and/or fly ash has a particle size of less than 325 meshes, and wherein any of particles of said fine washery- tailing and/or fly ash has not a particle size of 30 meshes or larger.

3. A method according to claim 1 or 2, wherein the calorific value of said washery tailing is not more than 1500 kcal/kg.

4. A method according to any of claims 1 to 3, wherein said fine washery tailing is concentrated preliminarily to have an adjusted water content so that the content of said fine washery tailing in said grout slurry is controlled to be in the range of 30 to 47 wt%.

5. A method according to claim 1, wherein said cement is Portland cements, mixed cements, expansive cements or rapid hardening cements or mixtures thereof.

6. A method according to claim 5, wherein said Portland cement is normal Portland cement, high early strength Portland cement, super high early strength Portland cement, moderate heat Portland cement or white Portland cement or mixtures thereof.

7. A method according to claim 5, wherein said mixed cement is silica cement, fly ash cement or blast furnance cement or mixtures thereof.

8. A method according to claim 5, wherein said expansive cement contains as a main expansive agent a combination of calcium sulfoaluminate, lime and calcium sulfate, a combination of calcium aluminate and calcium sulfate, high sulfate slag, lime or MGO or mixtures thereof.

9. A method according to claim 5, wherein said rapid hardening cement contains 12CaO 7- Al2O3 and/or 1 1CaO'7Al2O3CaX2 (X being a halogen) or calcium sulfate.

10. A method according to claim 1, wherein said grout slurry further includes an additive.

11. A method according to claim 10, wherein said additive is granulated slag, calcium sulfate or lime or mixtures thereof.

12. A method according to any of claims 1 to 11, wherein said grout slurry is allowed to solidify in a space or room surrounded by dehydrating walls.

13. A method according to claim 1, substantially as described in the Examples herein.

14. A method according to claim 1, as herein described with reference to Figs. 3 to 6 of the drawings.