Title of Invention

AN IMPROVED CAVING LONGWALL METHOD FOR WINNING OF COAL FROM THICK SEAM IN SINGLE LIFT UNDER MASSIVE AND HARD ROOF CONDITIONS IN UNDERGROUND MINES

Abstract The present invention is an improved method over the conventional longwall for extraction of coal from thick seam in single lift and with lower support resistance under massive and hard strata within the active caving zone overlying the coal seam. This method requires driving an additional central injection gallery in the centre of the panel, drilling a plurality of inclined boreholes towards the goaf from central injection gallery and injecting water at a high pressure through injection assembly grouted in the boreholes in the overlying rock beds over the goaf. This method provides an effective means for injecting water for softening and fracturing the strong rock beds over the goaf in middle zone of the face. This reduces stress concentration in the working area and eliminates the problems of working in conventional longwall faces in thick seams and under massive and hard rock beds.
Full Text This invention relates to an improved caving Longwall method for winning of coal from thick coal seam in underground mines. This invention particularly relates to an improved caving Longwall method for winning of coal from thick coal seams in single lift extraction under massive and hard strata such as 'difficult to cave' rock within the active caving zone overlying the coal seam.
Longwall is a worldwide popular method of underground mining and has a very high potential of production and productivity with increased safety to workmen.
The conventional longwall method is shown in Fig. 1 of the drawings accompanying this specification. A longwall panel (1) is usually of width 90-150m, length 800-1500m and height of extraction 1.8-4.5m. The conventional longwall method essentially consists of driving two long galleries (2,3) which forms the gate roads and these are joined by a longwall face (4). The longwall method requires a coal cutting machine- shearer (5) for cutting and loading of coal, armoured flexible conveyor (6) for transporting the coal from the longwall face (4), a set of self advancing hydraulic operated powered supports (7) with canopy to support the roof in the working area, bridge stage loader (8), series of belt conveyors (9) for transporting the coal to the surface and other accessories which comes with a longwall package. The next longwall panel (1) is isolated by a chain pillar (10) and a gallery (11), which forms one of the gate roads of the next longwall panel. As the longwall face (4) advances (shown by arrow in Fig.l) from the start of the panel at the barrier pillar (12) the overlying roof rock strata formed by different layers of rock beds (16) (shown in vertical cross section over the Longwall panel in fig. 3) is allowed to fall (caving of overlying roof) behind the powered supports (7), which forms the goaf (13).
Hard and massive rock beds (16) are frequently encountered in Indian coal measure rocks within the active caving zone overlying working coal seams. References may be made to Sarkar S.K. & Singh B. ' Longwall Mining in India', Scientific Mining Publishers, Dhanbad, Nov. 1985, pp 237 and Sarkar, S.K.: "Mechanised Longwall Mining - The Indian Experiences", Oxford & IBH Publication, 1998, pp 240. The caving property of the rock bed (16) depends upon its "cavability Index" calculated by an empirical equation with the parameters such as thickness, uni-axial compressive

US Patent No. 4119346 "Longwall mining system" describes the conventional longwall system of mining with conventional coal cutting, support & transportation means.
Another US Patent No. 4324509 "Mechanised longwall mining system of mining" describes the method utilising self advancing hydraulic supports connected to the conventional conveyor with hydraulic cylinders and other mechanised hydraulic controls.
Another US Patent No. 4382633, "Longwall mining system", describes the bi-directional shearer with plurality of picks, plurality of vanes disposed over the cutting drum surface for cutting and loading the mineral on Armoured Flexible Conveyor.
Another US Patent No. 4030752 " Longwall mining of thick underground mineral seams" describes a method of sublevel caving for thick seam mining by longwall.
Yet another US Patent No. 4065929 "Mine roof support & method in longwall mining of thick mineral" describe the method of longwall mining of thick mineral seams where in the thick seam is allowed to cave behind the powered support in the goaf side and transported by another armoured flexible conveyor placed at the back of the supports.
Yet another US Patent No. 4883323, "Longwall mining machine for the mining of thick mineral seams", describes the cutting machine with a drum supported by a jib and an arm extension, which facilitates mining of thick mineral seams.
Still another US Patent No. 4265487 "High pressure water jet mining machine" describes a machine with plurality of nozzles as a replacement of shearer for cutting coal for longwall mining
Still another US Patent No. 5425601 "Longwall mining roof control system" describes a system for supporting the roof of the recovery room to withstand the abutment pressure generated as the longwall face approaches the termination line.

The problems associated with hard and massive rock beds are:
a. Delayed caving of the rock bed(16),
b. Greater length of cantilever rock bed (16) behind the powered supports(7),
c. Increased concentration of vertical stress (called abutment stress) ahead of the longwall face (4),
d. Spalling of coal at the longwall face(4),
e. Cavity formation and fractured roof over the supports(7),
f. Large area roof falls in the goaf (13),
g. Periodic increased load on supports (7) or weighting, due to the load thrown before the breakage
of the cantilever strong rock bed (16).
All these lead to difficult working conditions at the face (4) and frequent damage to support (7) components during the periods of severe weighting. Under these conditions, the working area at the face (4) also becomes excessively unsafe. The estimation of support capacity required at a longwall face for effective strata control increases with increase in height of extraction and higher cavability index of the rock bed (16). For extraction of thick seams and under "difficult to cave" roof, the requirement of support capacity for effective strata control becomes either very high or practically not feasible. At Khottadih colliery of Eastern Coalfields Ltd., the seam thickness was 6m but the height of extraction had to be limited to 4.5m only. RVII-A coal seam in Jhanjra 1&2 Incline of Eastern Coalfields Ltd., is 3.8 to 4.2m thick but the thickness of extraction by conventional longwall is limited to 2.2 to 2.4m to reduce strata problems and improve safety at the working area.
Longwall mining in India suffered a major setback in the last decade with the collapse/failures of the two prime longwall faces at Churcha Colliery of South Eastern Coalfields Ltd. in May 1990 and at Khottadih Colliery of Eastern Coalfields Ltd., in April 1997. The powered supports (7) collapsed and the longwall faces had to be abandoned. The overlying roof was found to be massive and difficult to cave and the support resistances were found inadequate to cope up with the caving of coal roof in these coalmines.
To improve the caving characteristics of the overlying roof rock beds (16) the usual method is to drill
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longwall face (4) supported by powered support (7) is a very inconvenient and unsafe operation. The strong rock beds (16) lying above could not be blasted and the problem remained.
The other method to improve the caving characteristics of the overlying roof rock beds (16) is by softening the overlying roof by injecting water through long inclined boreholes drilled from the gate roads (2,3) towards the face (4). This method requires long boreholes to be drilled at a very low inclination, with long length of the borehole to be sealed which is difficult and sealing is not effective. The low inclination of the borehole and ineffective sealing causes flow of water to short circuit toward the gate road and trickle from the roof of the gate roads (2,3). The water never reaches the middle zone of the face (4) where the softening is most essential. The injection method is suitable for softening and fracturing the roof rock beds (16) ahead of the face (4) prior to mining and this method is ineffective for injecting water for softening and fracturing the roof rock beds (16) over the goaf (13). Injecting water prior to mining causes the roof rock beds (16) to get saturated and weakened. Numerous cracks are formed at the working area causing cavity formation and roof falls at the longwall face (4) and the workers are exposed to unsafe and unstable roof in the working area.
The main objective of the present invention is to provide an improved caving longwall method for winning of coal from thick seam in underground mines in a single lift extraction under hard and massive roof strata, which obviates the above noted drawbacks.
Another object of the present invention is to improve the stability of the immediate roof in the working area of the longwall face by eliminating strata problems encountered at the longwall face during extraction of thick seams and under 'difficult to cave' roof conditions.
Yet another object of the present invention is to provide an economic method to increase the recovery of coal from thick coal seam reserves by increasing the height of extraction by longwall method in single lift and lower support resistance.
Still another object of the present invention is to reduce the occurrence of cavity formation, spalling

Another object of the present invention is to increase safety of workmen and productivity of coal from underground mines under 'difficult to cave' roof conditions.
A further objective of the present invention is to provide effective softening and fracturing of the roof rock beds(16) over the goaf and controlled caving as and when required.
The present invention is an improved method over the conventional longwall for extraction of coal from thick seam in single lift and with lower support resistance under massive and hard strata within the active caving zone overlying the coal seam. This method requires driving an additional central injection gallery in the centre of the panel, drilling a plurality of inclined boreholes towards the goaf from central injection gallery and injecting water at a high pressure through injection assembly grouted in the boreholes in the overlying rock beds over the goaf. This method provides an effective means for injecting water for softening and fracturing the strong rock beds over the goaf in middle zone of the face. This reduces stress concentration in the working area and eliminates the problems of working in conventional longwall faces in thick seams and under massive and hard rock beds.
The novelty of the present invention is that it is an improved method over the conventional longwall method for extraction of coal from thick seams in single lift and with lower support resistance under massive and hard strata within the active caving zone overlying the coal seam. This method provides an effective means for injecting water for softening and fracturing the strong rock beds over the goaf in middle zone of the face. This reduces stress concentration in the working area and eliminates the problems of working in conventional longwall faces in thick seams and under difficult-to-cave rock beds.
The inventive steps resides in driving an additional central injection gallery in the centre of the panel, drilling a plurality of inclined boreholes towards the goaf from central injection gallery and injecting water at a high pressure through injection assembly grouted in the boreholes in the overlying rock beds over the goaf.

Fig. 1 of drawings shows the conventional layout of the caving longwall panel (1) worked with powered supports (7) by caving method. The conventional caving longwall method essentially comprises:
(i) Driving two long galleries, which forms the gate roads (2,3).
(ii) Joining the gate roads (2,3) by a longwall face (4).
(iii) A coal cutting machine - shearer (5) for cutting and loading of coal, an armoured flexible conveyor (6) for transporting the coal from the longwall face (4), a set of self advancing hydraulic operated powered supports (7) with canopy to support the roof in the working area, bridge stage loader (8), series of belt conveyors (9) for transporting the coal to the surface and other accessories which comes with a longwall package.
(iv) Isolating the longwall panel (1) from the next longwall panel by a chain pillar (10) and a gallery (11), which forms one of the gate roads of the next longwall panel.
(v) Advancing the longwall face (4) from the start of the panel at the barrier pillar (12) and the
overlying roof rocks formed by different layers of rock stratum (rock beds) (16) is allowed to fall (caving of overlying roof) behind the powered supports (7) which forms the goaf (13).
Figures 2, 3, 4, 5 & 6 of the drawings accompanying this specification shows the improved caving longwall method of the present invention for winning of coal from thick coal seams in single lift with water injection under high pressure.
This improved method of the present invention as shown in figure 2, consists of an additionally driven central injection gallery (14) in centre of the panel in the top section of thick coal seam and within the coal seam in thin seams. Further, a plurality of inclined boreholes (15) are drilled towards the goaf (13) in the overlying strata (16) from the central injection gallery (14) and repeating drilling of similar boreholes (15) along the central injection gallery (14) at a regular interval.
Figure 3 of the drawings shows vertical cross-section parallel to the longwall face (4) with the coal seam and the different rock beds (16) till the surface at the section A-A in the Figure 2. The gate roads (2,3), the additional central injection gallery (14) and the vertical projection of the inclined bore i- -i- /i c\ ~i — „ ii,^ nsmi\s*r, ora olon elir»iji7ri in thp. Figure 3

Figure 4 of the drawings shows the vertical cross-section perpendicular to the longwall face (4) along the section B-B in Figure 2 along the central injection gallery (14). Further, figure 4 shows the injection pipe (17) in the borehole (15), connected to a high pressure flexible hose (18) and a power pack pump (19) capable of developing high flow rate of water at high pressure. These will help in injecting water in the overlying strata (16) behind the powered support (7) over the goaf (13).
Figure 5 of the drawings shows the injection assembly grouted by quick setting cement (22) in a borehole (15). The injection assembly comprises of a injection pipe (17) with a flange (20) and a plurality of asbestos washers (21) and an injector (23). The injection pipe (17) essentially consists of plurality of high-pressure steel pipes threaded together with a flange (20) and internal threaded portion on one end and an adapter for connecting a high-pressure hosepipe on the other end. The injector (23) shown in figure - 6 of the drawings essentially consists of a high-pressure manganese steel pipe closed at one end and externally threaded on the other end. A flange (24) is welded to the injector (23) above the externally threaded portion. The injector (23) is specially designed with a plurality of radial injection holes (25) for injecting water at a high pressure facilitating development of cracks and fractures in the intact rock. Figure 6 shows the assembly of the injector (23) to the injection pipe (17).
The injector (23) is screwed to the injection pipe (17) with a plurality of asbestos washer (21) in between the flanges (20,24). The total assembly is installed inside the borehole (15) and grouted by quick setting cement (22) throughout the length till the asbestos washer (21). The outer end of the injection assembly protruding from the borehole (15) is connected to power pack pump (19) by a high-pressure flexible hose (18). As the longwall face advances and approaches the mouth of the borehole (15) and the injector (23) is positioned behind the powered support (7), water at a very high pressure is injected in the borehole (15) through the injection radial holes on the injector (23). This widens the existing joints and further develops cracks and fractures in the intact rock. The water flows through the rock mass and decreases its strength. This improves the caving characteristics of the hard and massive roof rock beds (16). The cantilever portion of the hard and massive rock beds (16) breaks and caves in the goaf (13). The stability of the immediate roof in the working area

same height of extraction. The workers at the longwall face are not exposed to unsafe and unstable roof in the working area. With the maximum available support capacity world wide, this method will be feasible for working thick seam in single lift.
The length of the boreholes (15) to be drilled will be of shorter length and of higher inclination compared to the boreholes drilled from the gate roads (2,3). As the sealing column is smaller, sealing can be effectively done by injecting quick setting cement (22). The softening and fracturing process of the overlying rock beds (16) take place in the middle zone of the face and behind the powered support (7) over the goaf (13).
Accordingly, the present invention provides an improved caving longwall method for winning of coal from thick seam in single lift under massive and hard roof conditions in underground mines which comprises; providing conventional layout of caving longwall panel and conventional longwall coal cutting and transportation means, characterised in that:
(i) cutting an additional central injection gallery (14) in centre of the panel in the top section of
thick coal seams and within the coal seam in thin seams;
(ii) drilling a plurality of inclined boreholes (15) towards the goaf (13) in the overlying strata (16)
from the roof/fhe central injection gallery (14) and repeating drilling of similar boreholes (15)
along the central injection gallery (14) at a regular interval; (iii) providing a plurality of injection assembly capable of injecting water inside each borehole
(15); (iv) grouting the said injection assembly inside the said borehole (15) by means such as quick
setting cement (22);
(v) connecting the outer end of the injection assembly protruding from the borehole (15) to power
pack pump (19) by a high-pressure flexible hose (18);
(vi) injecting water at a very high pressure in the plurality of boreholes (15) through the injector,
positioned behind powered supports (7), as the longwall face advances and approaches the
mouth of the borehole (15) ; (vii) repeating steps (iv) (v) and (vi) for all the boreholes (15) in the central injection gallery (14)

In an embodiment of the present invention the layout is such as that of conventional longwall panel with two gate roads (2,3) connected by longwall face (4), isolated by chain pillar (10) on both sides and barrier pillar (12) and essentially provided with a central injection gallery (14) having a plurality of goaf (13) directed inclined boreholes (15) on the injection gallery roof.
In another embodiment of the present invention the conventional longwall means used are equipment such as a coal cutting machine-shearer (5), armoured flexible conveyor (6), a set of self advancing hydraulic operated powered supports (7), bridge stage loader (8), series of belt conveyors (9) and conventional accessories.
In another embodiment of the present invention, the injection assembly consists of an injector (23) made of high-pressure manganese steel pipe closed at one end and externally threaded on the other end, the said injector (23), having a plurality of radial injection holes (25) and a flange (24) welded to it above the externally threaded portion, the said injector (23) being screwed to the injection pipe (17) with a plurality of asbestos washers (21) in between the flange (24) of the injector (23) and flange (20) welded to the injection pipe (17).
The novelty of the present invention is that it is an improved method over the conventional longwall
method for extraction of coal from thick seams in single lift and with lower support resistance under
massive and hard strata within the active caving zone overlying the coal seam. This method provides
an effective means for injecting water for softening and fracturing the strong rock beds over the goaf
in middle zone of the face. This reduces stress concentration in the working area and eliminates the
problems of working in conventional longwall faces in thick seams and under difficult-to-cave rock
beds.
The inventive steps resides in driving an additional central injection gallery in the centre of the panel,
drilling a plurality of inclined boreholes towards the goaf from central injection gallery and injecting
water at a high pressure through injection assembly grouted in the boreholes in the overlying rock
beds over the goaf.
The following examples are given by way of illustration of the present invention and should not be
construed to limit the scope of the present invention:
Water immersion test was conducted at Geo-mechanics laboratory of Central Mining Research

strength on absorption was calculated for each rock sample. The reduction of compressive strength varied between 15% to 79% depending on rock petrographic constituents and framework grain size. The present invention utilises this softening technique by injecting water at high pressure to make the overlying rock beds saturated with water. This will reduce the compressive strength of the hard and massive rock beds making it easy to cave.
Experiment was conducted at Churcha Colliery, South Eastern Coalfields Ltd. of Coal India Ltd., where the coal seam is overlain by massive and hard rock. Eleven number of incline boreholes were drilled of diameter 54mm, length varying between 45m to 70m at an inclination of 25 to 30 degree from horizontal in the rock beds overlying the coal seam. The water was injected in the holes with a high-pressure pump through the injection assembly grouted upto a length of 6m in each hole. The initial injection pressure varying between 1400 to 2400 psi, gradually reduced to a stabilizing pressure ranging betweenl30 to 600 psi. The total amount of water injected in each hole varied between 12000 to 34000 litres. It was observed that water flows through the joints and discontinuities and destroys the integrity and also creates new cracks and breaks the rock. The strata control problem such as spalling of coal, overriding of coal pillars, large area roof falls were reduced significantly at the experimental site. The reduced stress concentration and better roof control was achieved in the panel.
The following advantages are gained by the improved caving longwall method of the present invention for thick seam in single lift under hard and massive roof strata:
1. Improves the stability of the immediate roof in the working area.
2. Reduces the occurrence of cavity formation, spalling of coal from face and load on supports.
3. Increased safety of workmen at longwall face.
4. Provides an economic method for maximum recovery of coal from the reserves in thick seams.
5. Makes longwall a feasible method for thick seam and under hard and massive roof strata.
6. Effective for softening and fracturing the roof rock beds over the goaf and controlled caving as and when reciuired.

Documents:

212-DEL-2002-Abstract-11-04-2008.pdf

212-del-2002-claims-11-04-2008.pdf

212-DEL-2002-Correspondence-Others-11-04-2008.pdf

212-DEL-2002-Form-1-11-04-2008.pdf

212-DEL-2002-Form-2-11-04-2008.pdf

212-DEL-2002-Form-3-11-04-2008.pdf

abstract.pdf

claims.pdf

correspondence-others.pdf

correspondence-po.pdf

description complete.pdf

drawings.pdf

form-1.pdf

form-18.pdf

form-2.pdf

form-3.pdf


Patent Number 219305
Indian Patent Application Number 212/DEL/2002
PG Journal Number 25/2008
Publication Date 20-Jun-2008
Grant Date 28-Apr-2008
Date of Filing 11-Mar-2002
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address
Inventors:
# Inventor's Name Inventor's Address
1 SHRI ANIL KUMAR RAY
2 SHRI RAJESHWAR PRASAD
3 SHRI GAURI SHANKAR PRASAD SINGH
4 DR. KESHAR PRASAD YADAVA
5 SHRI GAUTAM BANERJEE
PCT International Classification Number E21C 41/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA