|Title of Invention||
"A NOVEL METHOD FOR UNDERGROUND EXTRACTION OF COAL FROM CONTIGUOUS SEAMS / SECTIONS"
|Abstract||This invention relates to a novel method for underground extraction of coal from contiguous seams/sections.|
|Full Text||This invention relates to a novel method for underground extraction of coal from contiguous seams/sections. This invention particularly relates to a method for extraction of coal from contiguous seams/sections by using underpinning where parting is weak and/or bottom seam/section is thick.
According to the Indian Coal Mines Regulation, 1957, if two seams/sections are situated within 9m to each other then these are called contiguous seams/sections. Extraction of contiguous seams/sections is a major problem. This problem is further enhanced when parting is weak, laminated and fragile. The problem becomes more complex if bottom seam/section is thick. In India, a seam/section is considered thick if thickness is 4.8m or more. The novel methoo of tha present invention can be used for extraction of coal from contiguous seams/sections v/Jiere bottom seam/section is thick besides strengthening weak, laminated and (.-agile parting. This method also helps to keep thin roof coal band of bottom seam/section effectively intact with the parting if required for further strengthening of the parting or other purpose. The novel method also helps to maintain coal quality during extraction of contiguous seams/sections.
In a contigucus seam/section working, the stability of parting, which is by definition will be 9m or less in thickness, is very important and working of these seams/sections warrants special attention since it serves the dual role of being the floor of the upper seam and the roof of the lower seam workings. In India, there are a number of cases of mishaps or strata control problems; in coal mines due to failure of parting between contiguous seam/section workings. To the best of our knowledge and belief no suitable technology is available for extraction of coal from contiguous seams/sections by strengthening the parting in between where the parting is weak, laminated and fragile. Generally tho parting is supported by conventional supports such as vertical pro;:: i.e., hydraulic, friction or pit props and chocks set below parting. These conventional supports are not efficient and effectiva enough in case of high roof as they loose their strength with increase in height. Moreover these conventional supports are passive in nature and offered resistance only after allowing a certain limit of roof movement. In some cases roof bolting is used for supporting/reinforcing immediate roof only and the method is not suitable for supporting/reinforcinq the parting of thickness 3m or more for contiguous seams/sections.
A number of researchers have worked with the problems of contiguous or multiple seams. But all these works are limited to study of interaction between two close seams, loading characteristics, failure mechanics, pillar load transfer, subsidence, prediction of stability status and influence of upper seam goaf. Till date no work has been reported for artificial improvement in strength of weak and banded parting. Most of She reported work concentrated on visualization of the problems of contiguous/multi-seam mining without suggesting any technical solution of artificial improvement in the parting strength.
Reference may be made to the research work of Haycocks, C., Wu, W. and Zhou, Y (1986) - "Integrated design for stability in multiple-seam mining", Proceedings of the Bureau of Mines Technology Transfer Seminar, Pittsburgh, PA, November 19, 1C 3197, United S'aies Department of Interior, Bureau of Mines, pp. 44-55, wherein research into ground .-.ontrol problems resulting from mining in a multiple-seam environment has been carried out. Findings demonstrate situations under which the worst ground control conditions can be expected to occur for a specific geological environment, depth innerburden spacing and mining geometry. Emphasis has been placed on the effect of upper pillar load transfer on the lower seam in terms of pillar and floor stability and roof control. The researchers have identified interaction mechanisms and also proposed methods for evaluating upper seam stability. The drawback is that nothing has betn suggested in the paper for strength improvement of a weak parting. They have suggested norms for prediction of interaction effects and their magnitude but not suggested anything about how to deal with the conditions of weak and banded parting and possibility of parting strength improvement by artificial means. For a better stability of parting the suggested methods in this paper are limited to control the configuration, shape and size of the excavation?.
Another reference may be made to the research work of Chekan, G. J , Matetic, R. J an d Galek, J. A. (1986) - "Multiple-seam mining problems in Eastern United States", Proceedings of the Bureau of Mines Technology Transfer, Seminar, Pittsburgh, PA, Nov. 19, 1C 9137, United States Department of Interior, Bureau of Mines, pp. 27-43 wherein the researchers presented case studies to demonstrate the interaction mechanisms and their influence on mine ground stability during multiple seam mining. The purpose was to develop a better understanding of
subsidence and pillar load transfer along with its effects on workings. The drawback is lint nothing like artificial improvement in strength of weak and banded parting between contiguous seams/sections has been suggested.
Still another reference may be made to the research work of Hsiung, S. M. and Peng, S. S. (1987) -"Design Guidelines for multiple seam mining", Part I and II, Coal Mining, Sept., pp. 42-46 wherein the authors have described the effects of multiple seam mining for better identification and understanding of the influencing parameters for design purposes. The drawbacks are that nothing has been studied or suggested for improvement of stability of weak, fragile and banded parting between the contiguous seams/sections where optimal extraction of coal is a difficult task due to premature failure of the parting.
Yet another reference may be made to the Ph.D. thesis of Chiranjib Bandopadhyay entitled "an analysis for stability of parting between contiguous pillar workings", submitted to Indian School of Mines, Dhanbad in the year 1987 containing 154 pages wherein detailed study has been made to identify major factors contributing parting stability of contiguous seams/sec!i r,. ,n his thesis, six parameters viz. depth cover, extraction ratio, parting thickness, eccentricity between top and bottom pillars, ratio of modulus of coal and parting and parting rock competence have been studied through numerical modelling with reference to some failure and stable case studies from field. Based on the influence of these parameters design norms for contiguous seams/sections workings have been framed. The drawbacks are that the thesis deals with analysis of the stability problem only and nothing has been studied or suggested for stabilizing weak, fragile and banded parting between the contiguous seams/sections. However, a large number of seams have already been developed according to regulation 104 of Indian Coal Mines Regulation, 1957, making contiguous seams/sections. The developed contiguous seams/sectpns with weak and laminated parting needs further study with an object to reinforcing the parting to avoid premature parting failure. The technique should also be able to take care of production, productivity and safety during further extraction of coal from thick bottom seam/section.
Yet another reference may be made to the research work of Sheorey, P. R., Barai, 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 lor depillaring of contiguous sections (double-section) of a 12.6m thick coal seam under massiv, and uncaveable sandstones. This paper presented a method to arrest the violent failure of massive roof during depillaring. Authors of this paper have designed a method for depillaring of contiguous seam sections where strata is massive and not easily caveable but the drawback is that this paper does not discuss the stability of parting.
Yet another reference may be made to the research work of Sinha, A. K., Mazumder, T. K. and Mahajan, V. (1996) -"An introspection to design guidelines for multi-seam mining with thin parting- an Indian case study", Rock Mechanics, Aubertin & Mitri (editors), Balkema, Rotterdam, pp. 455-463 wherein the paper outlines the details of two case studies while mining in ascending order (lower seam mined first with stowing) and the findings of the investigation point out the fact that mining of multiple seams/sections could be accomplished with minimum interaction effects, provided certain guidelines are followed. The drawback is that, except the conventional roof bolting nothing has been suggested for improvement of entire parting strength for working vith a weak and banded parting. Generally, stowing facility is not available at all mines and involves extensive time and cost. Furthermore, working of thick/contiguous seams/sections are generally not recommended In ascending order from strata control point of view. And also the effectiveness of stowing remains under doubt for a nearly flat seam.
For strengthening banded, weak and fragile parting some type of active support/reinforcement is necessary for efficient extraction of coal from contiguous seams/sections. The technology for strengthening the parting should be able to arrest all chances of bed separation of the banded parting and should make the banded parting like a composite beam. Further complication arises when bottom seam/section is thick. Recovery of coal from this thick seam/section is restricted to 30 percent or less only by conventional mining methods resulting in loss of valuable coal. Where conventional support systems such as timber props and chocks are used to support the parting as well as to support the roof coal of thick bottom seam/section during drivage and depillaring. These conventional systems of support often
becomes ineffective and unstable for high mine roof and also a hindrance for mechanisation because of the swinging limitation of loader boom. Using these supports, it is not possible to maintain the stability of required thin band of roof coal of variable thickness of the bottom seam/section during depillaring. In absence of a proper reinforcing system, sometimes weak and laminated non-coal parting breaks (due to bed separation) during extraction of bottom soam resulting coal quality dilution. So there is a definite need to develop a method for extraction of coal from contiguous seams/sections where parting is weak and banded and/or bottom seam/section is thick.
The main object of the present invention is to provide a novel method for extraction of coal from contiguous seams/sections which obviates the drawbacks as detailed above.
Another object of the present invention is to use underpinning for strengthening the parting between contiguous seams/sections and makes the banded parting like a composite beam.
Figure 1 of the drawings accompanying this specification represents the schematic sectional view of an embodiment of the installation of a single underpinning support used in the novel method of the present invention for extraction of coal from contiguous seams/sections, where lower seam/section is thick and roof coal band of variable thickness is left during drivage/development of bottom seam/section.
In figure 1 of the drawings:
(A) is the developed gallery of the top seam/section
(B) is the developed gallery of the bottom seam/section
(1) is the vertical hole
(2) is the reinforcing element
(3) is the grouting mixture
(4) is bottom seam/section roof coal to be extracted
(5) & (6) depicts coal to be extracted
(7) is coal/non-coal parting between top and bottom seams/sections
Figure 2 of the drawings accompanying this specification shows the sectional plan view of an embodiment of the top seam/section. In figure 2 of the drawings: (A) is the developed gallery of the top seam/section
(C) is the split gallery of the top seam/section
(D) is the slice gallery of the top seam/section
(E) is the underpinning
Accordingly, the present invention provides a novel method for extraction of coal from contiguous seams/sections which comprises:
a) making a plurality of vertical holes (1) by known means from the floor of tha
developed galleries of the top seam/section (A) up to or above the corresponds ,y roof
of the developed galleries of the bottom seam/section (B), inserting a reinforcing
element having length equal to that of the vertical hole length (2) in each of the said
vertical holes (1), grouting by known methods of the said inserted reinforcing element
(2) using grouting mixture (3) to obtain a plurality of underpinnings, allowing the
underpinnings to set to a load bearing capacity of at least 6 tons;
b) extracting coal by known methods in the top and bottom seams/sections (5 & 6) by
making a superimposed split gallery (C), having height same a;s that of respective
developed galleries (A & B), repeating step (a) to obtain a plurality of underpinning!, in
the said split gallery;
c) extracting coal by known methods in the top and bottom seams/sections (5 & 6) by
making a superimposed slice gallery (D), having height same as that of respective
developad galleries (A & B), repeating step (a) to obtain a plurality of underpinn'ros .n
the said slice gallery;
d) extracting bottom seam/section roof coal (4) above the slice gallery and part of
adjoining other galleries starting from one end by known blasting techniques below
underpinning supported roof in single round blasting or in stages in retreating mode;
e) repeating steps (c) and (d) till complete extraction of the pillar formed by the developed galleries.
In an embodiment of the present invention the vertical holes may extend up to or above the estimated roof position of the bottom seam/section undeveloped galleries.
In another embodiment of the present invention the reinforcing element used may be flexible or rigid such as wire ropes/cables, iron/steel rods, bamboos or any other reinforcing element with a load bearing capacity not less than 6 tons.
In still another embodiment of the present invention the grouting mixture used may be such as cement slurry with or without quick setting agents or any other grouting mixture capable of providing requisite anchorage strength.
In yet another embodiment of the present invention the superimposed gallery in the bottom seam/section may be equal or narrower than the gallery in the top seam/section.
The development districts of top and bottom seams/sections which are divided in panels of adequate size are depillared by conventional method of splitting and slicing by underpinning of the parting in between two seams/sections including the roof coal band of lower seam/sec ton, if any. Underpinning strengthens the parting and makes the parting like a composite beam if the parting is laminated/banded. Underpinning also acts as high roof support to the lower thick seam/section.
The method of underpinning is as follows:
Plurality of vertical holes are drilled from the floor of the galleries of the top seam/section up to or above the corresponding roof of the galleries of the bottom seam/section. A reinforcing element, having length equal to that of the vertical hole length, like wire rope/cable or steel/iron rods or bamboos or any other reinforcing element with a load bearing capacity not less than 6 tons is inserted in each of the said vertical holes. Grouting of the said element is done by pouting grout mixture like cement slurry with or without quick setting agents or any other grouting mixture capable of providing requisite anchorage strength of 6 to 18 tons. The grouting mixture is poured from top seam/section under gravitational flow. In case of full thickness development of lower seam/section i.e., non-existence of roof coal of lower seam/section then underpinning will is one
in the parting only. A tapered plug is required to be fitted in the lower most portion of the hole before grouting if the hole is done from bottom seam/section or required thin band is not possible to be maintained when hole is done from top section and it becomes through to bottom seam/section. The process is adopted repeatedly to obtain a plurality of underpinnings, a'bwing the underpinnings to set to a load bearing capacity of at least 6 tons. Where bottom seam/section galleries are yet to be developed/made, the vertical holes may extend up to or above the estimated roof position of the bottom seam/section. The reinforcing element used may be flexible or rigid such as wire ropes/cables, iron/steel rods, bamboos or any other reinforcing element with a load bearing capacity not less than 6 tons. The superimposed gallery in the bottom seam/section may be equal or narrower than the gallery in the top seam/section.
The depillaring method is based on the principal of supporting the parting and lower seam/section roof coal by way of reinforcing the parting and anchoring the roof coal band of bottom seam section below the parting as a substitute to conventional supports - vertical props and chocks set below parting. The pin using up to 9m long pieces of reinforcing elements, grouting retained anchorage at least 6 tons during rope pull test even after blasting of the coal below parting.
The contiguous seams/sections which are developed on pillars leaving paruig, is supported by underpinning. The splits and slices are also supported by underpinning during depillaring and the roof coal of bottom section is extracted on retreat by blasting to the required height/thickness under underpinning supports in single round blasting or in stages. 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 Side Discharge Loader (SDL)/Load Haul Dumper (LHD) fitted with protected canopy or by remote SDL/LHD 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 SDL/LHD. But entire roof coal may be blasted down by single round of blasting if coal is evacuated by remote SDL/tHD. The parting (coal or non-coal) which is left along the roof remained underpinned.
For underpinning of parting by wire ropes/cables, 19-25mm diameter wire ropes'rablas up to 9m in length are grouted in 43mm diameter hole in the parting. The distance between) the two underpinning bolts varies from 0.5 to 3m or as per the requirements depending on the quality of the parting and/or support density required for holding bottom seam/section roof coal band. The top section coal is taken by conventional method of mining. The roof coal of bottom seam/section is subsequently blasted in stages using coal as platform under reinforced parting or by single round of blasting. The observed holding capacity of the underpinning varied between 6 to 18 tons sufficient to justify its use as independent support for strengthening the parting for extraction of bottom seam/section coal. The use of SDL or LHD with hanging type of support improves the coal loading efficiency and overall production and productivity.
If roof bolt is used as immediate roof support during drivage/development or during making of split and slice galleries in bottom seam/section then, underpinning may be done at these places from top seam/section floor up to the upper end of the roof bolt.
The steps involved in the novel method of the present invention for extract!:.in of contiguous seams/sections developed on pillars by way of reinforcing the parting and anchoring to the lower seam/sec'.ion coal are summarised as follows:
a) Underpinning (method of underpinning is already described) of parting is done in advance
of depillaring operation to all the developed galleries in the panel or at least up to two
pillars in advance from the face from where depillaring is to commence. At least two
pillars of underpinning in advance is to be maintained to the developed galleries through
out the panel.
b) Extraction of coal by drilling and blasting in the top and bottom seams/sections by making
a superimposed split gallery, having height same as that of respective developed galleries
and subsequent underpinning of parting in between the said split gallery. Drivage of single
split is done for dividing a pillar in two halves, both in top and bottom seams/sections, and
systematic support of the parting including coal band below parting in the slices! by
c) Extraction of coal by drilling and blasting in the top and bottom seams/sections by making
a superimposed slice gallery, having height same as that of the respective developed
galleries and width 4-5m, leaving 2-3m thick coal rib against the goaf and subsequent
underpinning to the said slice gallery.
d) Extraction of roof coal band above the slice gallery of bottom seam/section and part of
adjoining other galleries up to required height, starting from one end by drilling and
blasting techniques below the underpinning supported roof in stages or single round of
blasting in retreating mode and drawing coal by special canopy mounted SDL or LHrj or
remote SDL/LHD and loading in tubs or conveyor.
e) Repeating steps (3) and (4) till complete extraction of the pillar formed by the developed
galleries and split galleries.
f) Top seam/section coal is extracted simultaneously or zero to two pillars in advance tfan
bottom seam/section coal by conventional blasting and loading in tubs or conveyors.
g) Reduce the ribs judiciously both in top and bottom seams/sections on retreat to facilitate
settlement of goaf.
h) Pillar extraction is In a fashion to form diagonal line, minimum of stooks or ribs withiii
Support of the developed and split galleries and slices is done as per systematic support rule (that is, by combination with additional conventional and/or other type of supports if imposed)
with main emphasis on underpinning for parting stability and/or facilitating extraction of lofver
seam/section and also safety of the lower seam/section working.
The novelty of the present invention is that it can be used for extraction of coal frpm
contiguous seams/sections where parting is weak, laminated and fragile by strengthening |he
ii parting. The support system used for strengthening the parting is also used for extraction of
bottom seam/section coal of desired height. The inventive steps resides in the underpinning |iat is, the grouted reinforcing element which acts as the support system for strengthening the paring and makes laminated parting and/or coal below parting like a composite beam. This enables extraction of coal from lower seam/section by single round blasting or blasting in stages on retreating mode.
The following example is given by way of illustration and therefore should ;,ct be construed to limit the scope of the present invention.
Chirimiri underground coal mine of M/s South Eastern Coalfields Limited (SECL), a subsidiary of Coal India Limited (GIL) has zero seam of about 12 - 13m thickness underneath Bartunga hill. Though, the seam is named as a single seam (namely zero seam) but incidentally, the quality of the seam is not uniform from top to bottom, there is a non-coal/very poor quality coal parting in between divided the seam virtually into two seams. These virtual two seams are called as top and bottom sections (of the single zero seam). The thickness of top and bottom sections varies from 3-3.5m and 5-6m respectively. The thickness of non-coal/poor quality coal in betwaen varies from 3-3.5m. The top and bottom sections are developed into superimposed pillars of 2£rn x 22m (centre to centre) with 4.5m wide galleries. The top section is developed up to 2.5 to ,2.9m in height leaving 0.6 to 1 m coal in the roof as the immediate shale/mudstone/carbonaceous roof is very weak and bottom section is developed along floor up to 3m height leaving 2-3m coal in the roof. Both the sections are developed using roof bolts of 1.5m length as immediate roof support. The parting in between top and bottom section excluding 3m coal in the bottom section roof is weak and banded/laminated. The Bartunga hill which is 650 to 690m above sea level has staep escarpment with estimated reserve of nearly 10.4 Million tons spread over 1.5 sq. km hill cep area. The future of the mine depended upon the exploitation of 5-6m thick bottom section and also coal from top section. The geo-mining conditions of the deposit demands a suitable mining method for optimal extraction of coal with productivity, safety and economy. Therefore, this mine has been chosen as a site for the field trial. Extraction of pillars of about 6m thick bottom section was planned with the following objectives:
a) Depillaring of both the section as final operation.
b) Strengthening the weak and banded/laminated parting to sustain burden load upto t\ limit
during caving of top section for safety.
c) Design of suitable support system to facilitate the extraction of about 5-6m thick bottom section.
To make like a composite beam of the weak and laminated parting for strengthening purpose and also to facilitate extraction of bottom section roof coal, underpinning was done at the developed galleries starting from the dip side of the panel. For the purpose, vertical holes were drilled at the interval of 1.2 m in between two holes and across two holes of diameter varying 38-45mm up to the upper end of -bottom section roof bolt. Old haulage ropes of diameter 19-25mm were inserted inside each hole according to the length of the holes. The holes were grouted by pouring cement-slurry mixture with quick setting agent. This was done at least up to two pillars in advance before starting depillaring. The same rate of advancement of underpinnings for the developed galleries were maintained with the advancement of the face also. The anchorage average strength of each underpinning was observed to be at least 10 tons. It was also decided that 1m roof coal will be left with parting for further strengthening of parting during extraction of bottom section roof coal.
Split gallery of width 4.5m and height same as that of the respective developed gallery is made both at top and bottom section by attacking dip most corner pillar by dividing the pillsvr, into two halves and underpinning is done for the freshly exposed parting in similar way as dore for development galleries. Then slice gallery is also made with 5m width at top section and 4.5 width at the bottom section leaving a rib of 2 and 2.5m at top and bottom section respectively starting from the dip most position having height same as that of respective development gallery height and underpinning is adopted in similar fashion to strengthen the parting in between the slices of top and bottom sections. Then 2m roof coal of bottom section is extracted by blasting into two to three stages leaving 1 m coal with parting starting from dip most corner of the developed and s||ce gallery. Similarly adjoining slices are made one after another and underpinned them and heightened them during retreat of the face maintaining diagonal line of extraction. This proces^ of extraction and underpinning continued for extracting all pillars from the panel. Extracted coal is loaded on conveyors with the help of special canopy mounted SDLs.
The extraction of 12-13m thick zero seam developed in top and bottom sections with weak, fragile and banded parting was tried in conjunction with underpinning of the parting as a major support system and bolting of the roof underneath Bartunga hill at Chirimiri colliery of SEfcL. Cumulative convergence and convergence rates observed in top section were more as compared to their representative values in bottom section. This indicates that parting was made sufficiently stable by underpinning. Similarly, stress and load measuremonts in top section show that th^se values were more here than their representative value in bottom section. Two bore Ho'e extensometers were installed in the parting showed no bed separation even after splitting and slicing of adjacent pillars. All these strata behaviour observations strongly established the fact that underpinning of parting was very effective. The local and main falls have been regular in the panel without excessive convergence, stress build up or loading. Generally after 3 - 4 local falls in top section, fall of parting took place. It was also noticed that strata above top section came down as main fall but the fall did not propagated through the parting. The parting between the two s The main advantages of the present invention are:
a) Depillaring of contiguous seams/sections even when lower seam/section is thick.
b) Holding capacity of the weak, fragile and laminated parting increases substantially.
c) Underpinning acts as an active support contrary to the use of pit, hydraulic or friction
props and chocks which act as passive supports.
d) Underpinning also provides advance support to the lower thick seam/section and, during
depillaring, required height of lower seam/section working can be maintained.
e) Development of underpinning support has enabled replacement of wooden support, thus
conservation of wood and the ecology.
f) Reinforcement of parting through underpinning makes it like a composite beam rosjiiing
increase in strength.
g) Any necessary thickness of roof coal band of bottom seam/section can be maintained
using this hanging type of support during extraction of coal from bottom seam/section.
h) Maintenance of required blasting height through underpinning also stops or minimize quality dilution as caving of non-coal parting is difficult and so chances of mixing it with bottom seam coal is remote.
i) The strengthened parting by underpinning absorbs the caving impact of top seam/section up to a reasonable limit to provide adequate safety for the workings of the bottom seam/section.
j) The pins can be inserted and installed without any tube contrary to tho requirement of the breather tuba for the upward hole grouting.
k) The gout mix can be poured directly and no injection pump is required for the purpose.
I) The grouting is very efficient and full column under the influence of the gravitation.
m) Old haulage ropes can be used for underpinning which makes this technique cost-effective.
1. A novel method for extraction of coal from contiguous seams/sections which comprises:;
a) making a plurality of vertical holes (1) by known means from the floor of the developed
galleries of the top seam/section (A) up to or above the corresponding roof of the
developed galleries of the bottom seam/section (B), inserting a reinforcing element having
length equal to that of the vertical hole length (2) in each of the said vertical holes (1),
grouting by known methods of the said inserted reinforcing elements (2) using grouting
mixture (3) to obtain a plurality of underpinnings, allowing the underpinnings to set to a
load bearing capacity of at least 6 tons;
b) extracting coal by known methods in the top and bottom seams/sections (5 & 6) by
making a superimposed split gallery (C), having height same as that of resp'.'cbe
developed galleries (A & B), repeating step (a) to obtain a plurality of underpinnings in the
said split gallery; c) extracting coal by known methods in the top and bottom seams/sections (5 & 6)| by
making a superimposed slice gallery (D), having height same as that of respective
developed galleries (A & B), repeating step (a) to obtain a plurality of underpinnings in the
said slice gallery;
d) extracting bottom seam/section roof coal (4) starting from one end by known blasting
techniques below underpinning supported roof in single round blasting or in stages in
e) repeating steps (c) and (d) till complete extraction of pillar formed by the developed
2. A novel method as claimed in claim 1, wherein the vertical holes is extended up to or abjcve
the estimated rcof position of the bottom seam/section undeveloped galleries.
3. A novel method as claimed in claim 1-2, wherein the reinforcing element used is flexible or
rigid such as w're ropes/cables, iron/steel rods, bamboos or any other reinforcing element
with a load bearing capacity not less than 6 tons.
4. A novel method as claimed in claim 1-3, wherein the grouting mixture used is such as
cement slurry with or without quick setting agents or any other grouting mixture.
5. A novel method as claimed in claim 1-4, wherein the superimposed gallery in the bottom
seam/section is equal or narrower than the gallery in the top seam/section.
6. A novel method for extraction of coal from contiguous seams/sections, substantially as
herein described with reference to the drawings accompanying this specification and
|Indian Patent Application Number||1120/DEL/2000|
|PG Journal Number||36/2008|
|Date of Filing||08-Dec-2000|
|Name of Patentee||COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110 001, INDIA.|
|PCT International Classification Number||E21C 29/16|
|PCT International Application Number||N/A|
|PCT International Filing date|