Title of Invention

"A METHOD FOR SOLID BLASTING IN UNDERGROUND COAL MINES"

Abstract The present invention provides a method for solid blasting in underground coal mines using spacer-aided-initiation technique relates to solid blasting in development faces of underground coal mines for improving pull, blast economics, fragmentation and reducing ground vibration, noise and generation of fines or boulders. In contrast to the existing method of solid blasting wherein continuous column of P5 type of explosive cartridges are loaded to the bottom of the hole, in the present invention spacer-aided-initiation (SAI) technique is used for providing air decking between the explosive cartridges with the help of spacers in solid blasting in underground coal mines. Length of spacers (i.e. air decking length) are decided based on the results of laboratory and field studies for air gap sensitivity of different P5 permitted explosives so that air decked cartridges get initiated by sympathetic detonation using single detonator in a hole. Trial blasts in different SCCL underground coalmines have shown promising results with increase in pull, yield and fragmentation and reduction in socket formation, ground vibration and noise.
Full Text The present invention relates to a method for solid blasting in underground coal mines. This invention particularly relates to a method for solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique for improving pull per blast. The present invention more particularly relates to solid blasting in development faces of underground coal mines for increasing pull, blast economics and decreasing side effects, such as noise, generation of fines or boulders by distributing the energy of the explosive over greater length with intermittent air gaps, such as air decking using spacers.
Most of coal production from underground coal mines in India is through drilling and blasting. Bord and pillar method is the predominant underground coal mining system in India, contributing over 90% of the total underground coal production. Winning of coal from bord and pillar method in underground coal mines using explosives in India is done by either (i) cut face blasting using P3/P1 explosives with instantaneous detonators or (ii) solid blasting i.e. blasting off-the-solid (BOS)) using P5 explosives and delay detonators. Major portion of the production from underground coal mines using explosive and blasting comes from the development faces by solid blasting using P5 explosives.
In India, blasting off-the-solid (BOS) was started with the development of P5 type of permitted explosive and non-incendive delay electric detonators in 1969. Since then it has become the predominant method of blasting in development faces of underground coal mines. Now, coal cutting machines for creating cut faces are rarely used in any mines of India. However, a maximum charge weight per hole of 1000g in degree I and 565g in higher degree gassy coal mines has been stipulated by Director General of Mines Safety (DGMS). In the presently practiced method of solid blasting in development faces of underground coal mines, continuous column of explosive cartridges of P5 types primed with permitted delay detonators are pushed to the bottom of the shot-holes. Then the holes are stemmed to its full length using inert (clay + sand) material.
So far there has not been any change or innovation in application techniques of P5 explosives in solid blasting. Due to concentration of the charge at the bottom of the hole only, it is not very effective in providing the expected pull, yield and powder factor. At the same time it generates high vibration and non-uniform fragments with more fines and boulders. Due to less pull, sockets are also left which are not only waste of drilling but also undesirable from safety point of view. There have been incidences when misfired cartridges left in sockets have caused accidents.
Moreover, P5 explosive, being the weakest of all permitted explosives, alongwith limitation on maximum charge weight per hole, blasting off-the-solid (BOS) has always suffered from low productivity. An average pull of 0.8 to 1.0m and yield of 10 to 16 tonne per blast in BOS have never been considered satisfactory for optimum utilization of men and machines at faces. Efforts to mechanize bord and pillar workings by introducing intermediate technology i.e with SDLs (Side Discharge Loaders) and LHDs (Load Haul Dumpers) as loading machines, could not achieve expected production targets due to poor availability of coal at the faces.
Thus, conventional method of solid blasting in underground coal mines in India suffers from low pull and yield per blast leading to underutilization of men and machine at face which is the main reason for low production and productivity of Indian underground coal mines. The researchers and mine managements have realized that there is a definite need to take a close look to ensure a minimum pull of 1.5m per blast to ensure coal for handling machines. Unless this is achieved low productivity of underground coal mines will continue to plague Indian coal mining industry.
Reference may be made to Melnikov and Marchenko (1971), Chiapetta et. al (1987), Bussey and Brog (1988), Rowlands (1989), Meed et. al. (1993), Moxon et. al. (1993), Jhanjhwar et. al. (1998), wherein decking have been applied in a variety of applications like pre-splitting, controlling ground vibrations and fly rocks, reducing fines and improving blast economics. Numerical and physical modeling by Fourney et. al. (1981) and Liu and Katsabanis (1996) have also supported this theory.
The drawbacks of these studies are that by all these researchers, experiments and full scale blasts have been done either in opencast mines or in tunneling. In their trials they have used separate initiation for each of the decks or a device useful for transmission of detonation from one deck to other (e.g. detonating cord) which are unsafe and are not approved in underground coal mines.
Reference may also be made to U.S. Patent No. 6,330,860 of December, 2001, titled: Method of blasting using air tubes charged in a blast hole, wherein a method of blasting using air decking for reducing ground vibration and noise and improvement in blast economics has been described. In this method an air deck is provided by inflatable cylindrical flexible air tubes which have an air injection port and is made of synthetic materials which can be inflated by using an air injection of air compressor for use in pre-splitting and production blasts. The decking is provided at the bottom, top and between the cartridges. Each hole is provided with multiple explosives and detonators or with explosive cartridges which can get sympathetically detonated.
In another U.S. Patent No. 6,454,359 of October, 2002, titled: Method for blasting tunnels using an air bladder, wherein is described a method for blasting in tunnels in which cut holes are drilled deeper than the other holes and air bladders are situated in the extruded portion of the cut holes to form free surfaces. Each of the holes are loaded with one or more explosives and detonators and each hole have one or more air bladders. Explosive are sympathetically detonated to reduce the consumption of detonators. As per the disclosure, this method is suitable for tunnel blasting and can reduce ground vibration, noise, explosive consumption.
The drawbacks of the methods described in above mentioned US patent nos. 6,330,860 and 6,454,359, are that these methods can not be applied in underground coal mines as there is unavailability of compressed air at the blasting face and in underground coal mines permitted explosives are used which usually have different air gap sensitivity characteristics. The type of air bladder or inflatable tubes as described by them are not
suitable for use in underground coal mines because of possibility of insertion of coal dust, coal chips or any other materials between the cartridges in air deck thus hindering the propagation of detonation from one deck to other. Another drawback is use of multiple initiation points within same holes using separate detonators which may also not be safe for use in underground coal mines. In underground coal mines there is risk of gas / coal dust explosion due to deflagration of explosives. The quality of the air decking device also has important role on the toxic fume generated during the blasting when the method is applied in development faces of underground coal mines.
From the hitherto known prior art as detailed above it is seen that there is a definite need to provide a method for solid blasting in underground coal mines, which obviates the drawbacks.
The main object of the present invention is to provide a method for solid blasting in underground coal mines, which obviates the drawbacks of the hitherto known prior art as described above.
Another object of the present invention is to provide a method for solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique for increasing pull per blast.
Yet another object of the present invention is to provide a method for solid blasting in underground coal mines, for increasing coal availability at the face through increased yield per blast at the face for optimum utilization of men and machines resulting in improving production and productivity of underground coal mines.
Still another object of the present invention is to provide a method for solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique, for increasing powder factor and detonator factor. Thus improving the blast economics by effective utilization of explosive energy by distributing it over longer length using spacers.
Still yet another object of the present invention is to provide a method for solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique, for improving fragmentation and reducing production of more fines or boulders.
A further object of the present invention is to provide a method for solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique, for reducing side effects like ground vibration and noise.
The present invention relates to effective utilization of explosive energy for improving blast results in solid blasting of coal by application of spacer-aided-initiation (SAI) technique in which P5 explosive cartridges are air decked using spacers in the shot holes. Air decking of the cartridges distributes the explosive energy over longer length of the shotholes. Air decks in the shotholes act as energy accumulators which first stores and later releases the energy in the form of additional stress waves thus prolonging the detonation process for improved fragmentation. Air decks help in minimizing that part of explosive energy which is consumed in crushing and pulverizing the area immediately adjacent to the borehole wall. In contrast to air-decked boreholes, continuous column explosives generate a large amplitude impulse into the medium that succeed in creating many fractures, but decays very quickly and stress field around the charge decays to a quasi-static state. In decked boreholes, by reducing the initial pressure of the detonation products and increasing the duration of their action on the rock, energy in crushing around the borehole wall would be reduced while increasing the amount of the amount of the energy transmitted into the surrounding medium.
In the present invention there is provided a method using spacer-aided-initiation technique for solid blasting in underground coal mines, which relates to solid blasting in development faces of underground coal mines for improving pull, blast economics, fragmentation and reducing ground vibration, noise and generation of fines or boulders. In contrast to the existing method of solid blasting wherein continuous column of P5 type of explosive cartridges are loaded to the bottom of the hole, in the present invention spacer-aided-initiation (SAI) technique is used for providing air decking between the
explosive cartridges with the help of spacers in solid blasting in underground coal mines. Length of spacers (i.e. air decking length) are decided based on the results of laboratory and field studies for air gap sensitivity of different P5 permitted explosives so that air decked cartridges get initiated by sympathetic detonation using single detonator in a hole.
The present invention provides important improvements over commonly practiced blasting method, in which explosive cartridges are kept in contact with each other, by using air decks for enhancing the efficiency of the permitted explosives without compromising on the safety. The present invention is suitable for underground coal mine and in this method different decks of P5 explosives given with help of spacers will be initiated sympathetically with single priming at one end of the shothole without using any detonating cord for transmission of detonation from one deck to other.
In the present invention of a method for solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique, spacers of predetermined length, wherein the length is determined by the air gap sensitivity of different P5 permitted explosives, are used between the cartridges for providing the air decking. Spacers having provision for fixing P5 permitted explosive cartridges at both ends are used.
Figures 1-A & 1-B of the drawing accompanying this specification shows the diagram of the spacer used between the cartridges for providing the air decking. Figure 1-A shows the longitudinal view and figure 1-B shows the cross-sectional view of the spacer. The spacer is a hollow cylindrical lightweight synthetic material, such as PVC pipe of thickness in the range of 0.5 to 0.8 mm. The spacers have provision for fixing the cartridges at both ends (1). Both ends (1) have internal diameter of 32+0.5 mm for tight fitting of the P5 permitted explosive commercial cartridges of 32mm diameter. The length of the ends (1) is about 4 to 5cm. The middle portion (2) of the spacer has inner diameter of 26±1.0 mm and its length may vary from 5 to 50cm depending on the requirements determined by the air gap sensitivity of different P5 permitted explosives. Effective air gap between two cartridges is equal to the length of narrow middle portion
(2) of the spacer. Tight coupling of the cartridges with the spacer eliminates chances of any insertion of coal dust, chips or any other foreign material, which can reduce the sympathetic detonability of the explosives cartridges.
The explosives meant for use in underground coal mines are made weaker by mixing cooling agents to pass the statutory requirements of incendivity tests for their categorization into permitted groups. P5 explosives being weakest of all permitted explosives possess least air gap sensitivity of all permitted explosives and because of their use with delay detonators may undergo deflagration reaction, which is a grave hazard in underground coal mines. However, based on laboratory experimentations by us, it has been found that some Indian permitted explosives may pass air gap several times higher than the minimum requirement of 2 cm.
Based on results of studies by us, of air gap sensitivity (AGS) and velocity of detonation (VOD) of different P5 explosives under varying confinement in the laboratory and in coal bed confinement in opencast mines, it was observed by us that a slurry P5 explosive composition has been found suitable for use with air decking upto 12 cm between two explosive cartridges. Its deflagration behaviour has also been studied and it exhibited non-deflagrating nature even under severe laboratory experimental conditions. Effect of use of spacers on toxic fume generated during blasting were also studied and its maximum weight was found which will not make the explosive to cross the limit of permissible ranges and approved mine safety regulations for CO and NOx.
Accordingly the present invention provides a method for solid blasting in underground coal mines, which comprises drilling a plurality of shot holes in a development face in an underground coal mine and charging each of the said shot holes with air-decked explosive cartridges, characterized in that the said explosive cartridges being air-decked using spacers between the explosive cartridges and also at the top and bottom of the explosive cartridges inside the said shot holes.
In an embodiment of the present invention, the explosive cartridges are P5 permitted explosive commercial cartridges and are non-deflagrating.
In another embodiment of the present invention, the spacer having provision for fixing P5 permitted explosive cartridges at both ends of the said spacer is a hollow cylindrical lightweight synthetic material, such as PVC pipe of thickness in the range of 0.5 to 0.8 mm and of length in the range of 5 to 50 cm depending on the requirements determined by the air gap sensitivity of different P5 permitted explosives.
In still another embodiment of the present invention, the spacers having provision for fixing P5 permitted explosive commercial cartridges of 32mm diameter at both ends having length in the range of 4 to 5cm and internal diameter of 32 ± 0.5 mm.
In yet another embodiment of the present invention, the inner diameter of the.middle portion of the spacer is 26 ± 1.0 mm.
In a further embodiment of the present invention, the length of the spacers in between cartridges is in the range of 5 to 20 cm, depending on the air gap sensitivity values of explosive composition.
In a still further embodiment of the present invention, the length of the spacers at the top and bottom of an explosive charge in a shot hole is in the range of 10 to 50 cm.
In another embodiment of the present invention, only one detonator is used in each shot hole and lead-wires of the detonators of all the shot holes are connected in series and fired in one round using suitable exploder.
In the present invention, cartridges inside a shot hole are air decked in contrast to conventional method wherein all cartridges are in contact. The air gap provided by spacers are predetermined keeping in mind the results of studies of air gap sensitivity of the explosive under different confinements so that the cartridges can be sympathetically
detonated without misfires. The explosive cartridges are of P5 type and are non-deflagrating. The effect of spacer on the toxic fume generation by decked explosives have been studied and it is within the permissible ranges. The spacers are having provision for fixing the cartridges at both ends so that chances of any insertion of coal dust, chips or any other foreign materials can be eliminated which are known to reduce the sympathetic definability of the explosives cartridges. Use of spacers for air decking increases the specific area, over which explosive power is exerted, provides additional free faces and explosives are situated more near to the working face. Additionally use of spacers of this type as described above helps in channelising the shock wave and post detonation product for improving air gap sensitivity for sympathetic detonation of the decked cartridges and thus aids in detonation of the decked cartridges.
The novelty of the method of the present invention for solid blasting in development faces of underground coal mines, resides particularly in increasing pull, blast economics and decreasing side effects, such as noise, generation of fines or boulders by distributing the energy of the explosive over greater length with intermittent air gaps, such as air decking using spacers. In the present invention the method of solid blasting in underground coal mines using spacer-aided-initiation (SAI) technique improves the performance and reduces side effects.
The non-obvious inventive step which particularly enables the novelty resides in explosive cartridges being air-decked using spacers between the explosive cartridges and also at the top and bottom of the explosive cartridges both at the top and bottom of each of the said shot holes. The air decking in solid blasting in development faces of underground coal mines without use of detonating cord or multiple initiation in same shot hole provides the novelty of the method of the present invention.
In the present invention each of the shot holes are loaded with predetermined quantity of approved type of P5 explosives keeping in mind inverse initiation pattern of blasting and holes are stemmed upto its full length after explosive cartridges have been loaded. Different holes are blasted at predetermined millisecond time intervals using delay

detonators. Lead-wires of the detonators of all the holes are connected in series and fired in one round using suitable exploder.
The essential steps in the present inventions are:
a. Selection of suitable P5 explosive and length of air decking based on
scientific data generated under simulated conditions for air gap sensitivity
and continuity of detonation under varying confinements.
b. Selection of quality and length of spacer for providing air-decking between
the cartridges based on its post detonation fume quality.
c. Drilling of shot holes in development faces of underground coal mines as
per pre-designed pattern.
d. Loading of shot holes with selected P5 explosive with air decking using
spacers with single priming and without use of any detonating cord.
e. Firing of shot holes after connecting them in series
The following example(s) are given by way of illustration of the working of the invention in actual practice and therefore should not be construed to limit the scope of the present invention.
Few experimental trials in different mines were carried out to prove the efficacy and safety aspects of the present invention in the solid blasting of development faces of underground coal mines. During the experimentations all the safety rules including the stipulation of maximum charge weight per hole were observed.
Example 1
A number of shot holes were drilled according to a designed pattern and the shot holes were charged with spaced cartridges of commercial P5 explosive in development faces in underground coal mines in which 10 cm PVC spacers between the cartridges were used to provide air decking for distribution of explosive energy over greater length. Only one detonator per shot hole was used and decked cartridges detonated sympathetically without any use of detonating cord or any other device for transmission of detonation from one to other decks. The lead-wires of the detonators of all the shot holes were connected in series and fired in one round using an exploder.
The comparison of the presently known prior art method of blasting off-the-solid (BOS) and the method for solid blasting in underground coal mines of the present invention using spacer-aided-initiation (SAI in BOS) has been given below:

(Table Removed)
From the experimental results given above, inference may be drawn that under different geo-mining conditions the optimization of different blast design parameters, such as hole length, hole directions, delay sequence, length of stemming, air decking length, quantity of explosive charge in each hole, will result in further improved blast performance.
The advantages of the present invention are :
1. Improvement in the pull per blast (i.e. advancement per blast).
2. Improvement in the yield of coal per blast, thus increasing the coal availability at the face for better utilization of men and machine at face and thus improving the production & productivity of the mine.
3. Improvement in the powder factor thus improving the blast economics.
4. Improvement of fragmentation and reduction in production of boulders or fines.
5. Reduction in blast vibration and noise generated by the blast.
6. There is no increase in cycle time.
7. Socket formation can be reduced / eliminated.



We claim:
1. A method for solid blasting in underground coal mines, which comprises drilling a plurality of shot holes in a development face in an underground coal mine and charging each of the said shot holes with air-decked explosive cartridges(l), characterized in that the said explosive cartridges being air-decked using spacers(2) between the said explosive cartridges(l) and also at the top and bottom of the said explosive cartridges(l) inside the said shot holes.
2. A method as claimed in claim 1, wherein the explosive cartridges are P5 permitted explosive commercial cartridges and are non-deflagrating.
3. A method as claimed in claim 1-2, wherein the spacer having provision for fixing P5 permitted explosive cartridges at both ends of the said spacer is a hollow cylindrical lightweight synthetic material, such as PVC pipe of thickness in the range of 0.5 to 0.8 mm and of length in the range of 5 to 50 cm depending on the requirements determined by the air gap sensitivity of different P5 permitted explosives.

4. A method as claimed in claim 1-3, wherein the spacers having provision for fixing P5 permitted explosive commercial cartridges of 32 mm diameter at both ends having length in the range of 4 to 5cm and internal diameter of 32 ± 0.5 mm.
5. A method as claimed in claim 1-4, wherein the inner diameter of the middle portion of the spacer is 26 ± 1.0 mm.
6. A method as claimed in claim 1-5, wherein the length of the spacers in between cartridges is in the range of 5 to 20 cm, depending on the air gap sensitivity values of explosive composition.
7. A method as claimed in claim 1-6, wherein the length of the spacers at the top and bottom of an explosive charge in a shot hole is in the range of 10 to 50 cm.
8. A method as claimed in claim 1-7, wherein only one detonator is used in each shot hole and lead-wires of the detonators of all the shot holes are connected in series and fired in one round using suitable exploder.

Documents:

1538-del-2005-Abstract-(19-08-2014).pdf

1538-del-2005-abstract.pdf

1538-DEL-2005-Claims-(22-03-2012).pdf

1538-del-2005-claims.pdf

1538-del-2005-Correspondence Others-(19-08-2014).pdf

1538-DEL-2005-Correspondence Others-(22-03-2012).pdf

1538-del-2005-correspondence-others.pdf

1538-del-2005-description (complete).pdf

1538-del-2005-drawings.pdf

1538-del-2005-form-1.pdf

1538-del-2005-form-18.pdf

1538-del-2005-form-2.pdf

1538-DEL-2005-Form-3-(22-03-2012).pdf

1538-del-2005-form-3.pdf

1538-del-2005-Form-5-(19-08-2014).pdf

1538-del-2005-form-5.pdf


Patent Number 263217
Indian Patent Application Number 1538/DEL/2005
PG Journal Number 42/2014
Publication Date 17-Oct-2014
Grant Date 14-Oct-2014
Date of Filing 14-Jun-2005
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address ANUSANDHAN BHAWAN, RAFI MARG, NEW DELHI-110001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 1.ROY SANJAY KUMAR;2.Singh Rajeev Ranjan;3.Verma Harsh Kumar;4.Paul Ranjit Kumar CENTRAL MINING RESEARCH INSTITUTE BARWA ROAD, DHANBAD, JHARKHAND-826001 INDIA
PCT International Classification Number E21C 37/14
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA