Title of Invention

A NOVEL METHOD OF MINING FOR UNDERGROUND EXTRACTION OF COAL FROM A CRITICALLY THICK COAL SEAM STANDING ON PILLARS AND THE DEVELOPMENT MADE ALONG THE ROOF HORIZON

Abstract A novel method of mining for underground extraction of coal from a critically thick coal seam standing on pillars and the development made along the roof horizon. In India, a coal seam is called thick if its thickness is 4.8m or more. Again, if two seams/sections are situated within 9m to each other then these are called contiguous seams/sections. According to the Indian Coal Mines Regulation, 1957, superimposed development is must for contiguous sections. On the other hand, minimum 3m thickness of the parting between the working of two contiguous sections is also a statutory requirement. Critically thick seams are less than 9m in thickness and they do not provide the required minimum 3m thickness of parting between the two contiguous sections to be developed for optimal exploitation of the seam. The novel method of the present invention can be used for extraction of a critically thick coal seam developed along the roof horizon. Multi-section working with stowing option of this method helps to maintain coal quality of a banded critically thick coal seam while the caving option of this method provides way to extract complete thickness of the seam in one lift.
Full Text This invention relates to a novel method of mining for underground extraction of coal from a critically thick coal seam standing on pillars and the development made along the roof horizon.
In India, a coal seam is called thick if its thickness is 4.8m or more. Again, if two seams/sections are situated within 9m to each other then these are called contiguous seams/sections. According to the Indian Coal Mines Regulation, 1957, superimposed development is must for contiguous sections. On the other hand, minimum 3m thickness of the parting between the workings of two contiguous sections is also a statutory requirement. Critically thick seams are less than 9m in thickness and they do not provide the required minimum 3m thickness of parting between the two contiguous sections to be developed for optimal exploitation of the seam. The novel method of the present invention can be used for extraction of a critically thick coal seam developed along the roof horizon. Multi-section working with stowing option of this method helps to maintain coal quality of a banded critically thick coal seam while the caving option of this method provides way to extract complete thickness of the seam in one lift.
In fact, high exploitational losses and dilution of safety norms during underground mining of a thick seam globally is an area of concern. However a number of attempts have been made to solve different problems of thick seam mining. A more complex situation arises if a critically thick coal seam is developed along the roof horizon. One simple option is to depillar developed top section first and then bottom section can be developed and depillared after settlement of the top section goaf. However, there is no standard time and process to ensure the settlement of the top section goaf. Stress concentration over the stooks, left inside the goaf of the top section, poses serious threat

to the safety of the thin and incompetent parting (less than 3m) during bottom section working. Accumulation of gas and heating of coal left inside the top section goaf are further cause of concern during bottom section working. To the best of our knowledge and belief no suitable technology is available for extraction of coal from critically thick coal seam developed along roof horizon. A number of research works have been reported to tackle different problems of underground mining of thick seams. But all these works are limited to study of safe and optimal underground extraction of virgin thick coal seams, developed seams (thick enough to provide 3m thick parting between two sections during multi-section working) and critically thick coal seams developed along floor.
Reference may be made to the research work of Hams, A.H. (1979) - "A new design for thick seam mining in Australia". Journal of Mines, Metals & Fuels, Thick seam mining number, pp. 267-271, where investigations were conducted on physical models to visualise ground control problems during application of Wongawilli system of mining (multi-section mining in descending order) for mechanised extraction of a thick seam. Findings demonstrate that the success of the method depends on determining the correct fender width, maintaining this width during its formation and fully extracting it on retreat. The method is not oversensitive to geological variations and emphasis has been placed on application of mobile machines. The drawbacks are: that the influence of stress concentration over the residual fenders/stooks, left inside the goaf of the top section, over a thin parting (less than 3m) has not been studied. A critically thick seam, developed along roof horizon, cannot adopt this system of mining as the thin parting may not be able to tackle strata control problem along with the threat of gas and heating of coal left inside the top section goaf.

Another reference may be made to the research work of Singh, T. N. (1988) -"Soutirage - a dream mining method of thick coal seams", Transactions of Mining, Geological and Metallurgical Institute of India, vol. 85, No. 1, pp. 88-110, where the scope of a mechanised longwall sub-level caving (Soutirage) method has been presented. High-level success of this method for underground winning of entire thickness of a thick coal seam in one lift in France has attracted the author. The drawbacks are: this is an approach suitable for virgin the patch of a thick coal seam. Further, the field trial of this method could not fulfil the techno-economic expectations in India, mainly due to massiveness of the coal mass. The performance of this method is presented by Singh. R.. Kushwaha, A. and Singh, T. N. (1993)-"Geotechnical evaluation of a mechanised Longwall - Soutirage face" Minetech, vol. 14, No. 4 & 6, pp. 42-45 which shows a number of limitations of this method for Indian geo-mining conditions.
Still another reference may be made to the research work of Verma, B. P., Prasad, S. and Dhar, B. B. (1992) - "Blasting gallery method and its support design - a critical analysis", Proceedings of International Symposium on Thick Seam Mining (Editors: T. N. Singh and B. B. Dhar), pp 471-492, CMRI, Dhanbad, India, where a French mining method called "Blasting gallery" was tried in couple of Indian coalmines to extract the full height of a thick and developed coal seam in one lift. The drawbacks are: the thick seam should be developed along floor for application of the "Blasting gallery" method. Although this method provided an opportunity and technology to win the roof coal band during depillaring of a thick and developed coal seam, a number of practical problems like high roof support, long hole blasting technology etc. were faced during these field trials under Indian geo-mining conditions.

Yet another reference may be made to the research work of Sheorey, P. R., Barat, D., Mukherjee, K. P., Prasad, R.K., Das, M. N., Banerjee, G. and Das, K. K. (1995) -"Application of yield pillar technique for successful depillaring under stiff strata". Int. J. Rock Mech. Min. Sci. & Geomech. Abstr., vol. 32,No. 7, pp. 699-708 wherein they have presented a case study for depillaring of contiguous sections (double-section) of a 12.6m thick coal seam under massive and uncaveable sandstones. This paper presents a method to arrest the violent failure of massive roof during depillaring. The drawback is that this method fails to address the problem of a critical thick coal seam developed along the roof horizon.
Yet another reference may be made to the research work of Singh, R., Mandal, P. K., Singh, A. K. and Singh, T. N., (2001)-"Cable bolting based semi-mechanised depillaring of a thick coal seam", Int. J. Rock Mech. & Min. Sci., vol. 38, No. 2, pp. 245-257, where, based on simple rock mechanics principles, the idea of using grouted steel rope under tension to support an overlying coal band, as well as, a high roof and to improve safe span of the overhanging beam/cantilever near the goaf edge of semi-mechanised depillaring of a developed thick coal seam (standing on pillars) provided excellent results during the field trial and discarded haulage ropes were well utilised. Reinforcement of the immediate coal roof band and the overlying roof well in advance of the actual depillaring operation are going to play an important role in extraction of thick and developed coal seams in India. Perhaps the most challenging job during implementation of the "Blasting gallery" method was to provide an effective support to the high roof after winning of the roof coal. Taking advantage of the massiveness of the coal seam and overlying roof strata, CMRI has almost solved this problem here simply by

introducing cable bolting as a support system for the high roof as well as for the roof coal bed over the existing galleries. The drawback is that: this method of mining is not suitable for a critically thick coal seam, developed along the floor.
For safe and optimal extraction of a critically thick seam, developed along roof horizon, the first task is to make development in the floor coal as the extraction of top section first will virtually lock the floor coal due to its poor thickness. Here, contiguity condition will force to opt superimposed development of bottom section but the requirement of 3m thick parting will not allow this development. The development along floor will provide a chance to win entire thickness of the seam in one lift by caving or multi-section workings with hydraulic sand stowing in ascending order. Once the development is made along the floor, suitable rock mass reinforcement system may be adopted for controlled caving of the roof coal band. Considering these facts, there is a definite need to develop a new method of development and manner of depillaring for a critically thick coal seam, developed along the roof horizon.
The main object of the present invention is to provide a novel method of mining for underground extraction of coal from a critically thick coal seam standing on pillars and the development made along the roof horizon, which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a novel method for the extraction of the complete thickness of the seam in single lift.
Yet another object of the present invention is to provide a novel method which obviates strata control problems due to critical thickness and top section development of the seam.

Still another object of the present invention is to provide a novel method which provides opportunity to improve the quality of coal if a stone band is present in the middle of the seam.
A further object of the present invention is to provide a novel method which obviates gas, heating and stress concentration problems.
Indian Coal Mines Regulation, 1957 forces to opt superimposed development for contiguous sections. While, on the other hand, minimum 3m thickness of the parting between the workings of two contiguous sections is must as per the same regulation. Critically thick seams, developed along the roof horizon, do not satisfy these conditions, so apparently the extraction in single lift is not possible. No effective method is hitherto known for safe, optimal and economical underground extraction of the critically thick coal seam. The novelty of the present invention is that it can be used for extraction of a critically thick coal seam developed along the roof horizon. The non-obvious inventive steps in the present invention are: multi-section working in ascending order with sand stowing option which helps to maintain coal quality of a banded critically thick coal seam and the caving option provides way for extraction of complete thickness of the seam in one lift.
Figure 1 of the drawings accompanying this specification represents the schematic sectional view of an embodiment of the cross development of bottom section used in the novel method of the present invention for underground extraction of coal from a critically thick coal seam standing on pillars and the development made along the roof horizon.
In figure 1 of the drawings:

(A) is the developed galleries of the top section
(B) is the crossly developed galleries of the bottom section
(C) is the roof rock mass
(D) is the floor
(E) is the critically thick coal seam to be extracted
(F) is the stone band in the coal seam
(G) is the underpinning to support and guide bottom section working
(H) is the cable bolt to support high roof and roof coal band
Figure 2 of the drawings accompanying this specification shows the plan view of an embodiment of the top and bottom section developments and manner of pillar extraction.
In figure 2 of the drawings:
(A) is the developed galleries of the top section
(B) is the crossly developed galleries of the bottom section
(G) is the underpinning of floor all along the top section development
(1) is the slice gallery of the bottom section
(2) is the rib of the bottom section
(3) is the manner of pillar extraction
Figure 3 of the drawings accompanying this specification shows the schematic sectional view of an embodiment of the application of mixed support system (Goal-post, Underpinning and Cable bolting) for single lift extraction of the critically thick coal.
In figure 3 of the drawings:
(A) is the developed galleries of the top section

(B) is the crossly developed galleries of the bottom section
(G) is the underpinning of floor all along the top section development
(H) are the cable bolts to support high roof and roof coal band
(i) is the main roof over the seam
(ii) is the immediate roof over the seam
(iii) is the hole for roof coal blasting
(iv) is the roof coal bad to be supported by cable-bolts
(v) is the goal post support for bottom section working below top section
roadways, (vi) is the Side Discharge Loader (SDL)/Load Haul Dumper (LHD) for coal
evacuation from the face (vii) is the blasted roof coal at face (viii) is the Caved roof rock-mass Accordingly, the present invention provides a novel method of mining for underground extraction of coal from a critically thick coal seam standing on pillars and the development made along the roof horizon, which comprises:
a) underpinning (G) complete floor of top section development (A) by conventional methods, cross development of bottom section along floor (B) with cable bolt support (H) of roof coal band and goal-post support (v) below top section roadways, level galleries of bottom section (B) with at least 3.5m deviation and rise galleries with maximum eccentricity;

b) extracting bottom section pillar (3) by making conventional slices (1) and ribs (2), under mixed supports such as cable bolting (H), underpinning (G) and goal-post (v), having height same as that of respective developed galleries of bottom section (B);
c) extracting roof coal (iv) by blasting during retreat with immediate roof being
supported by cable bolts;
d) evacuating blasted coal (vii) by conventional SDL/LHD (vi) under reinforced
immediate roof (ii).
In an embodiment of the present invention support placement in bottom section development (B) is guided by underpinning (G).
In another embodiment of the present invention the height of bottom section roadways are kept minimum possible.
In a further embodiment of the present invention the extraction of a seam having a band as parting between two sections is effected in two sections, in ascending order with hydraulic sand stowing.
In yet another embodiment of the present invention the frequency of the underpinning is determined by the conventional rock mass rating (RMR) of the parting and capable of providing load-bearing capacity of at least 8 tons.
In still another embodiment of the present invention the length of underpinning is kept up to or below the corresponding roof of the galleries of the bottom section.
In another embodiment of the present invention staggered galleries development is provided in the bottom section so as to form roadways junctions below solid roof coal mass.

In a further embodiment of the present invention the width of the bottom section galleries are equal to or narrower than top section galleries.
In yet another embodiment of the present invention the bottom section development is done in conjunction with cable bolting support for the overlying coal band.
In still another embodiment of the present invention there is provided goal-post support in the bottom section development below top section galleries.
In another embodiment of the present invention the SDL/LHD used is non-remote or remote.
In a further embodiment of the present invention the blasting sequence for evacuation by non-remote SDL/LHD is restricted in a cyclic manner such as blasting a web in the range of 1.5m to 2.0 m in each cycle.
In yet another embodiment of the present invention the blasting sequence for evacuation by remote SDL/LHD is effected in a single round for the entire roof coal.
The novel method of mining for underground extraction of coal from a critically thick coal seam standing on pillars and the development made along the roof horizon is as follows:
Underpinning of floor of the galleries of the top section is to guide and support bottom section development. The frequency of the underpinning was determined by well-established norms of RMR (rock mass rating) of the parting. The process adopted for underpinnings was evaluated to provide a load bearing capacity of at least 8 tons. The length of underpinning was kept up to or below the corresponding expected roof of the galleries of the bottom section.

The staggered galleries development in bottom section is to overcome the problem of thin parting between the two sections. The width of the bottom section galleries may be equal or narrower than the gallery in the top section. Bottom section development is to be done in conjunction with cable bolting support for the overlying coal band. However, taking help of the underpinning, bottom section development below top section galleries are to adopt goal-post support. Cross development of bottom section with staggered galleries is to provide minimum interaction between the two workings as the roadways junctions of the bottom section is to be formed below solid roof coal mass.
The depillaring of bottom section method is based on the principal of supporting the parting and roof coal by full column grouted cable bolts. Anchoring the roof coal band of bottom section as a substitute to conventional supports - vertical props and chocks provides space for unhindered movement of the machines used for coal transportation from face. The splits and slices of the bottom section are also supported by the mixed support system during depillaring. The roof coal is extracted on retreat by blasting. The reinforcement of roof coal mass provides an opportunity for controlled winning (in single round blasting or in stages) of roof coal mass during retreat. In case of blasting in stages generally blasted coal is used as a platform for reaching to the height. Fallen coal is loaded on conveyors/tubs by LHD/SDL fitted with protected canopy or by remote LHD/SDL and loading in tubs or conveyor. The blasting sequence is restricted in a cyclic manner, blasting 1.5 to 2m web in each cycle so that the operator need not to enter under the blasted roof in case of non-remote LHD/SDL. But entire roof coal may be blasted down by single round of blasting if coal is evacuated by remote LHD/SDL.

The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.
EXAMPLE 1
The existing geo-mining conditions of GDK-6B incline, RG-I area of M/s Singareni Collieries Company Limited (SCCL) is a critically thick coal seam standing on pillars and the development made along the roof horizon. Here, No. 1 seam of about 6.1 m thickness, under caveable roof strata, has been developed on pillar along roof horizon with roadways of 4.2m width and 2.1m height. This seam, developed along the roof horizon, is not thick enough to provide a 3m thick parting for the lower horizon development of the seam. Here the extraction of lower portion of the seam experienced an extremely complex situation as the statutory requirement cannot be met. It is to be noted here that superimposed development of contiguous sections of a seam is a statutory requirement. Even for this superimposed working of the contiguous sections, the parting thickness between the two sections should not be less than 3m in thickness. Conventionally, the developed top section can be depillared first and then bottom section can be depillared after settlement of the top section goaf. Here stress concentration over the stooks, left inside the goaf of the top section, may create problems for the safety of the thin parting during bottom section working. Accumulation of gas and heating of coal left in side the top section goaf are the cause of concern during bottom section working. Further, no standard procedure or time is available to ensure the settlement of the top section goaf.
Computer simulation of geo-mining conditions of this coal mining site was carried out and subjected to the steps of the novel method of mining of the present invention.

As per the results of numerical modelling, maximum eccentricity provides the best stability for staggered development. But, keeping final splitting and slicing into consideration, the method of the present invention of development and manner of depillaring seams was found to be most suitable for the condition simulated in the model. Here the split galleries of bottom section during final extraction will have the maximum possible eccentricity as that of the level development galleries. Adopting conventional splitting and slicing of normal height along floor, the roof coal can be won during retreat. The roof and floor of the top section working has to be bolted before bottom section development. The simulation also suggested goalpost support systems for the roadways/slices of bottom section below the top section galleries. Rest of the roadways/slices of the bottom section is to be supported by cable bolts, which will work as high roof support to win the roof coal during retreat.
The main advantages of the present invention are:
1. The complete thickness of a critically thick seam is extracted in single lift.
2. No strata control problems due to critical thickness and top section development of the seam.
3. Multi-sectional (in ascending order with sand stowing) working option of the seam provides opportunity to improve the quality of the coal if a stone band is present in the middle of the seam.
4. Gas, heating and stress concentration problems of multi-sectional working (in descending order with caving) do not exist in this method.

Documents:

120-DEL-2002-Abstract-(27-02-2008).pdf

120-DEL-2002-Claims-(27-02-2008).pdf

120-DEL-2002-Correspondence-Others-(27-02-2008).pdf

120-DEL-2002-Description (Complete)-(27-02-2008).pdf

120-DEL-2002-Form-1-(27-02-2008).pdf

120-DEL-2002-Form-3-(27-02-2008).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 215649
Indian Patent Application Number 120/DEL/2002
PG Journal Number 11/2008
Publication Date 14-Mar-2008
Grant Date 28-Feb-2008
Date of Filing 15-Feb-2002
Name of Patentee COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001, INDIA
Inventors:
# Inventor's Name Inventor's Address
1 RAJENDRA SINGH CENTRAL MINING RESEARCH INSTITUTE, BARWA ROAD, DHANBAD, JHARKHAND-826001
2 PRABHAT KUMAR MANDAL CENTRAL MINING RESEARCH INSTITUTE, BARWA ROAD, DHANBAD, JHARKHAND-826001
3 ARUN KUMAR SINGH CENTRAL MINING RESEARCH INSTITUTE, BARWA ROAD, DHANBAD, JHARKHAND-826001
PCT International Classification Number E21D 23/03
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA