Title of Invention

"A METHOD FOR IN-HOLE DELAY SOLID BLASTING"

Abstract

A method for in-hole delay solid blasting, characterized by distributing or splitting explosive charge loaded in an individual blast hole in drivage of mine, roadways & tunnels having two or more sections separated by decking, each of the said sections being blasted using at least one delay detonator in each section and the said detonator having different delay timing with top section(s) being blasted prior to the bottom section(s) enabling the bottom section(s) to be blasted with lesser confinement leading to better blast efficiency. (Fig-1)

Full Text

The present invention relates to a method for in-hole delay solid blasting. The present invention particularly relates to application of multiple electric, electronic or non-electric delay detonators in a hole during solid blasting in underground mine roadways or tunnels to improve the blasting efficiency. The main use of the method of the present invention is to blast a shot hole in underground solid blasting in stages using more than one delay detonator in a single shot hole. This should enable the shot holes to blast with reduced confinement and pull maximum efficiency in a blasting round. Background of the Invention Blasting for developments in tunnels and mine roadways, hereinafter may be called as drivage, is characteristically different from surface blasting due to initial lack of free face or void parallel to the drivage axis. This type of blasting is known as solid basting. In absence of initial free face, the rock is more confined in the drivages and requires more effort to break rock mass than in surface blasting. To minimise the confinement, a free face or void is created parallel to the drivage axis. Accordingly, a number of holes are blasted initially to create a void parallel to tunnel axis, which is called cut. The blast holes used in the drivages are generally of smaller sizes, varying from 25 to 64 mm, than those used in surface blasting where the sizes may vary from 75 to 310 mm. The holes in the drivages are horizontal or nearly horizontal and those in the surface blasting are drilled vertically. The charge concentration in the cut creation holes in the drivages, may be called as cut holes, remain very high to counteract the initial confinement. Each cut hole is blasted with a delay detonator, hereinafter may be referred as DD. The DD used here are of electric, electronic or non-electric type. The delay period in the DD increases with the number assigned to it. As for example, number 3 DD has more delay period than number 2 DD. The DD are generally available from 0 to 6 numbers for drivages in coal mines and 0-10 for drivages in metal mines or tunnels. The delay period is generally designed as 25 millisecond for short delays and 300 or 500 ms for long delays. The cut holes are blasted with DD of first 2-3 delay numbers. Once the cut is created and the confinement is reduced, the rest of the holes in the drivage are blasted towards the cut with lesser charge concentration. The rest of the holes also are blasted with a delay sequence so that the holes nearest to the cut are blasted before those away from the cut. It is evident that DD is used to provide a sequence of blasting so that the holes are blasted in stages. The holes blasted initially brings down the confinement for the holes to be blasted next. The blasting efficiency in the drivages essentially depends on the proper development of the cut. The face advance in a blast round generally equals to the depth of the developed cut. Hence, the cut needs to be developed to its full depth to maximise the advancement. The cut holes when are angled to the drivage axis the cut is called convergent cut. If the cut holes are parallel to drivage axis, the cut is called parallel cut. It is evident that the use of DD and its sequencing are of utmost importance in the solid blasting, specially in the cut hole blasting to reduce confinement from a hole or a set of holes to another hole or another set of holes so that the overall blasting efficiency is maximised. However, application of DD inside an individual shot hole, may be cut hole or other hole in the round, to blast the shot hole in stages has not yet been suggested. But it appears that the confinement could be further reduced in any individual hole, if the hole could be blasted in stages using more than one DD. This should be effective in further improving the solid blasting efficiency. In case of surface blasting the bench face acts as the free face and hence the confinement encountered is much less. The blast holes, which are generally of larger and longer in comparison to those used in drivages. Similar to solid blasting, the holes in surface blasting are generally blasted with a delay sequence using DD, either electric, electronic or non-electric type. The sequence is so maintained that the holes nearest to the free face are blasted first to enlarge the free face and then the holes nearest to the enlarged free face are blasted individually or in a set. The sequence goes on till the last hole is blasted. Here also, the sequence of delay is so arranged that the holes to be blasted are encountered with minimum confinement. However, in many cases in surface blasting the explosive charge in a blast hole is distributed in two to three sections providing some inert material like air, drill dust or chips in between each section of explosive column. When all the different sections are blasted simultaneously, the purpose of distribution is to provide longer explosive column height. But, if different sections in a hole are blasted at different timing providing different DD in each section, then the picture is a bit different. In such case, blasting of a section helps to reduce confinement for the next section to be blasted. The sequence of delay can be so arranged that the blasting of different sections in a hole can either start from top to downward or from bottom to upward. Generally, the arrangement from bottom to top is preferred to restrict the throw of fragmented material and reduce underbreak. This type of blasting with delay in different sections of a hole is called in-hole delay blasting. The technique provides better utilisation of explosive energy in the terms of fragmentation, vibration, explosive consumption and throw. The only disadvantages of the technique is the added cost of multiple delay arrangement. Efforts are being made how to reduce this additional cost. Hence, it is evident from the aforesaid discussion that though the in-hole delay provides additional advantages and its use in surface blasting is common, it has not yet been tried in underground blasting. Of course, the In-hole delay technique or specifications used In surface blasting may need modifications to apply In the solid blasting to suit the condition. References In literature In this context may be made to: 1. Du Pont, 1977. Blasters' Handbook, E. I. du Pont de Nemours & CO. (Inc.), Wilmington, Delaware, pp. 526-541. 2. Hagan, T. N., 1980. Understanding the bum Cut - A key to greater advance rates. Trans. Inst. Mining and Metall., London, Vol. 89, pp. A30-A36. 3. Holmberg, R., 1982. Charge calculations for tunnelling. Underground Mining Methods Handbook, Society of Mining Engineers, American Inst, of Mining, Metall. and Pet. Eng., New York, pp.1580-1589. 4. Konya, C. J., Rock Blasting and Overbreak Control, National Highway Institute, US Dept. of Transportation, 400 p. 5. Lopez Jimeno, C, Lopez Jimeno, E., Carcedo, F. J. A. and De Ramiro, Y. V., 1995. Drilling and Blasting of Rocks, Balkema A. A., Rotterdam, 391 p. 6. Olofsson, S., O., 1988. Applied Explosives Technology for Construction and Mining, Applex, Aria, Sweden, 303 p. 7. Pokrovsky, N. M., 1980. Driving Horizontal Workings and Tunnels, Mir Publishers, Moscow, pp. 38-41. 8. Pradhan, G. K., Explosives and Blasting Techniques, MINTECH Publications, Bhubaneswar, 388 p. 9. Singh, S. P., 1995. Mechanism of cut blasting. Trans. Inst. Mining and Metall., Section A, Mining Industry, Vol. 104, Sept-Dec, The Inst, of Mining and Metall., U.K.,pp.A134-A138 The present invention details a method of applying in-hole delay in individual shot holes in solid blasting so that the overall solid blasting efficiency can be maximised. To minimise the additional cost for multiple delay, the use of in-hole delay in the present invention is limited to the holes in the cut only, which are the primarily responsible for the blast efficiency. References have been collected through patent search on the use of delay detonation in surface and underground mine blasting and are detailed in the following paragraphs. Reference may be made to US Patent no. 6460462, wherein a method of blasting has been described for underground and surface mines with detonators proposed with respective delay interval according to the firing pattern and the mineralogical/geological environment and the resulting seismic vibration. Further reference may be made to CA 2339167, wherein a method of and apparatus for blasting arrangement by atleast one detonator in each of many blast holes which are connected to a sequential blasting machine, which imparts pre-defined time delay to each detonator stored in the memory has been described. Another reference may be made to GB 2373521 wherein the delay blasting arrangement for the assembly of holes in surface blasting is described so as to create a free face for other assembly of holes to be blasted in next delay. The mechanism is useful for control of size and blasting nuisance and to improve the blasting efficiency. Yet another reference may be made to GB 651552, which describes a short delay electric blasting cap. Still another reference may be made to WO 02057707 which describes a method of delay blasting arrangement between and within individual blast hole alongwith suitable design of blast parameters for controlling the blasted rock mass profile or for control ore dilution in surface blasting. Reference may also be made to patent no. RU 2203419, wherein application of delay detonators is proposed for creating a pre-blast crack to hinder the propagation of shock waves to the adjacent rock mass or structure. Further reference may be made to patent no. CA 2265629, wherein method for calculation of vibration and sound for subsequent for delay blasting is suggested based on the already available data analysis of each delay timing. Yet another reference may be made to patent no. US 2003029344, wherein an electronic delay detonator assembly with programmable delay arrangement at site has been described. The programmed time delay in the assembly can be double checked through wireless communication link between the electronic delay and programming unit. Further reference may be made to patent no. RU 2164658, wherein duplicate use of short delay detonator has been suggested in deep hole blasting to minimise the chance of blast failure. Yet further reference may be made to patent no. RU 2161770, wherein detonating device is suggested without primary explosive. Still yet further reference may be made to patent no. US 2001025583, wherein centre-cut blasting method for tunnel excavation utilising large unloaded blast holes using delay detonation is suggested. Still yet another reference may be made to patent no.GB 416349, 389309, 383650, 374912, 588613, 566063, 728598, 708422, wherein improvements related to delay blasting device or method are suggested. Still yet further reference may be made to patent no. US 4060033, wherein non-electric delay detonation for surface mines is suggested. Yet further reference may be made to patent no. US 3987732, wherein non-electric double delay borehole downline unit is suggested for surface blasting. Still yet another reference may be made to patent no. US 4165691, wherein non-electrically initiated delay booster assembly for multi-deck blasting using detonating cord has been suggested wherein single or separate delay can be incorporated in each deck. Yet further reference may be made to patent no. JP 11030500, wherein delay blasting method to minimise the chance of overlap is suggested. Still yet fiirther reference may be made to patent no.IN 171586, wherein improved delay device for use in delay blasting has been made. Yet still another reference may be made to patent no. IN 152674, wherein delay blasting cap for underground and surface blasting operation has been suggested. Still yet another reference may be made to patent no. US 5388521, wherein method of reducing ground vibration for delay blasting is suggested. Still yet further reference may be made to patent no. SU 711792, wherein method of multirow short delay blasting is suggested. Still another reference may be made to patent no. CN 22172124, wherein two direction delay blasting cartridge is suggested. Still yet further reference may be made to patent no. CA 1155338, wherein non-electric delay blasting is method is proposed. Still further reference may be made to patent no. JP 60176000, wherein method and device for triggering electronic short delay blasting detonator while forming time difference is proposed. The drawbacks in the referred work are that in spite of various developments in the blasting practices in-hole delay has not been considered for improvement in solid blasting, though the technique is widely used in surface blasting to derive various benefits. The main object of the present invention is to provide a method for in-hole delay solid blasting. Another object of the present invention is to improve the blast efficiency in solid blasting used for development of underground mine roadways and tunnels. Another object of the present invention is to blast each hole in solid blasting used underground mine roadways or tunnels is to be splitted in two or more sections separating each section by stemming material like mud capsules. The splitting of the charge may be done in such a manner that the section of the hole to be blasted earlier should contain equal to or more charge than section to be blasted subsequently as the confinement is more in the section to be blasted earlier. Yet another objective of the present invention is to blast each section of a blast hole in solid blasting at different timings with electric, electronic or non-electric DD. The time of delay between each section may be 25-500 milli-second or more depending on the strata. Smaller delay is recommended for weaker strata and larger delay is proposed for stronger strata. Still another objective of the present invention is to blast a hole in solid blasting in two or more sections with a time delay in each section to minimise the confinement for the deeper section of the blast hole so that the blast efficiency is improved.Still yet another objective of the present invention is to blast the bottom section/s of the blast hole with greater delay timing than that provided in the top section/s so that the section near the tunnel face is blasted prior to the section away from the tunnel face. This will provide release of confinement for the bottom section/s to be blasted and the blast efficiency will be improved. Still further objective of the present invention is to essentially blast the cut holes in different sections with different time delay in solid blasting underground mine roadways or tunnels. The blast performance of the cut holes in mine roadways and tunnels influence the tunnel blast performance the maximum. Hence, this method in the present invention is the most suitable for cut hole blasting. However, the method may be used for improving the efficiency the other holes considering the overall benefit which includes the improvement in blast efficiency and the additional cost towards the use of multiple delay detonators in all the holes. Still yet further objective of the present invention is to blast the cut holes in different sections in solid blasting using electric, electronic or non-electric delay detonators. SUMMARY OF THE INVENTION The invention provides a method of for in-hole delay solid blasting for underground mine, roadways and tunnels, wherein an individual blast hole in solid blasting is loaded with explosive distributed in two or more sections separated by capsules of inert material like air, water, mud and stone chips, each section being blasted with delay detonator having different delay timing with top section/s being blasted prior to the bottom section/s enabling the bottom section/s to be blasted with lesser confinement leading to better blast efficiency. The present method improves the blast efficiency, reduces blast vibration and is economical Accordingly, the present invention provides a method for in-hole delay solid blasting, characterized by distributing or splitting explosive charge loaded in an individual blast hole in drivage of mine, roadways & tunnels having two or more sections separated by decking, each of the said sections being blasted using at least one delay detonator in each section and the said detonator having different delay timing with top section(s) being blasted prior to the bottom section(s) enabling the bottom section(s) to be blasted with lesser confinement leading to better blast efficiency. In an embodiment of the present invention the blast holes are of conventional type and their diameter are in the range of 32-50 mm. In another embodiment of the present invention the explosive charge in a hole is splitted in two or more sections. In yet another embodiment of the present invention the splitting of the charge is done in such a manner that the section of the hole to be blasted earlier contains equal to or more charge, by one or more explosive cartridges, than the section to be blasted subsequently. In yet another embodiment ofthe present invention the explosive charge in each section comprises of either cap-sensitive or a combination of cap-sensitive and non-cap sensitive explosives. In yet another embodiment of the present invention the cap sensitive explosives may be selected from slurry, gelatinous or emulsion types and the proportion of cap-sensitive explosive in a mixture of cap-sensitive and non-cap-sensitive explosive if used is in the range of25-30 per cent. In yet another embodiment of the present invention the decking is comprised of inert material like sand and clay mixture, stone chips, water or air and said decking may have length of at least 10-12 times the blast hole diameter. In yet another embodiment of the present invention the decking length is in the range 0.4-1 m depending on the blast hole diameter, rock type and explosive type. In yet another embodiment of the present invention the delay time between two sections of explosive may be in the range of25-500 ms. In yet another embodiment of the present invention the top or upper section of the charge is to be blasted prior to the deeper or bottom section. In yet another embodiment of the present invention the detonations of the explosives may be done with electric, electronic or non-electric delay detonators. In yet another embodiment of the present invention smaller delay time may be used for soft strata and that of larger delay may be used for strong strata. In yet another embodiment of the present invention the stemming and delay detonators either electric or electronic leads are of conventional type. Detailed Description In the present invention there is provided a method for in-hole delay solid blasting, wherein an individual blast hole in solid blasting is loaded with explosive distributed in two or more sections separated by capsules of inert material like air, water, mud and stone chips, each section being blasted with DD having different delay timing with top section/s being blasted prior to the bottom section/s enabling the bottom section/s to be blasted with lesser confinement leading to better blast efficiency. Such a method is not known in the hitherto disclosed prior art and hence, the method of the present invention of blasting a shot hole in underground mines and tunnels in different sections providing separate delay timing for each section is novel. In the drawing accompanying this specification, figure 1 represents a schematic of an embodiment of the device of the present invention of a method for in-hole delay solid blasting. The various parts which in combination constitute the device of the present invention are: 1. Underground mine or tunnel face 2. Blast hole 3. Section of explosive charge 4. Decking 5. Delay detonator (I) 6. Delay detonator (II) 7. Detonator lead 8. Stemming The present invented method comprises two delay detonators (5 & 6) inserted in two sections of an explosive charge (3), the said delay detonator (I) being blasted ahead of delay detonator (II), in a blast hole (2) drilled on an underground mine or a tunnel face (1). The blast holes diameter may vary from 32 to 50 mm depending on the site requirements. The holes would be in horizontal or near to horizontal direction and drilled on the tunnel face. The hole length may suit to the site requirements. The explosive charge, normally cap sensitive in nature, are blasted by electric, electronic or non-electric delay detonators. The non-cap sensitive explosives like ANFO are provided with primer cap-sensitive explosives in a proportion of generally 25-30 per cent of the total charge. The cap sensitive explosives may be slurry, gelatinous or emulsion type. Generally all the small diameter explosives, except ANFO, used in underground mines or tunnels are cap sensitive. The delay detonators are fixed with the primer charges in case of non-cap sensitive explosives. The delay timing in delay detonator (II) is more than that in delay detonator (I). The time difference between the two delay detonators may range from 25-500 millisecond. More time is required for harder formation than for softer formation. The total required explosive charge has been distributed or splitted in two sections. The distribution may depend upon the site condition. Generally, the explosive charge with delay detonator (I) i,e, the charge to be blasted first shares greater portion as the confinement initially remains maximum. These two sections are separated from each other my decking (4). The decking material consists of inert material like sand and clay mixture as is generally used for stemming during blasting in underground mines and tunnels. The decking material may also be of stone chips, air or water poured in plastic capsules. Sometimes, air gap is provided between various sections of explosives which are separated by inserting bamboo or wooden sticks in between two sections. This type of decking by air gap is known as air decking. The length of decking may vary depending upon the charge quantity and hole depth but should not be less than 12 times the hole diameter to avoid sympathetic detonation by which different sections of explosive may be simultaneously blasted without any delay and not fulfilling the purpose of in-hole delay. The leads (7) of the two delay detonators, through which the required electric current or shock is sent to blast the detonators are brought out of the blast hole. All the detonator lead wires of delay detonator (I) from different blast holes are connected in series out side the blast hole. Similarly all the lead wires of delay detonators (II) fi-om different holes are brought out of the blast holes and connected in series. The two ends of the series connection of the lead wires of delay detonators (I) are connected in series with two ends of the lead wires of delay detonators (II). The two open ends of the joint connections are connected in series with the lead wires of other blast holes. However, the connections may also be made in parallel in all the cases. But parallel connection is not a fool-proof connection in respect of misfires. It may be noted here that the total explosive charge may be splitted in more than two sections, each section to be separated from the other by decking and blasted with different delay period. The splitting of the charge may be done in such a manner that the section of the hole to be blasted earlier should contain equal to or more charge than the section to be blasted subsequently as the confinement is more in the section to be blasted earlier. The number of sections in which the total charge to be splitted should depend on the total explosive quantity, depth of hole, rock type and other site conditions. The present invention of a method for in-hole delay solid blasting for underground mine roadways and tunnels was tested in the drivages of two coal mines. The in-hole delay method was applied only in the cut holes with an aim to minimise the additional cost towards extra electric, electronic or non-electric delay detonator consumption and to develop the cut, which is the most important part in overall blast efficiency. The total charge in every cut hole was splitted in two sections and the top section was provided with milli-second short delay no 0 and the bottom section was provided with milli-second short delay no. 1, thus providing a time gap of 25 milli-second between blasting of the two sections of charge. A technical comparison on the blast performances with and without in-hole delay are provided in Table 1. Table -1 Comparison of blast performances with and without in-hole delay in the drivages in coal mine using convergent cut (TABLE REMOVED) * different size of drivage in the same mine It can be noted from Table 1 that the savings in detonators/t (%) is less in mine no. 2 compared to mine no. 1 because of less increase in advance per round. Thus use of more number of detonators per hole (i.e more number of splitting the charge) or double detonators in all the holes would bring down the savings in detonators/t of coal produced. Hence, the in-hole delay should be judiciously used so that the method becomes economically viable in all respect of blast results. From the review of hitherto known prior art survey it is seen that there is no technique developed in India and abroad on a method for in-hole delay solid blasting for underground mine roadways and tunnels. Though in-hole delay devices and methods have been invented and applied in surface blasting to improve the blast efficiency but no effort has yet been made to apply such a technique for underground solid blasting. The solid blasting is always carried out without any delay inside the blast hole, though delay is provided from one hole or one set of holes to another hole or another set of holes. Providing in-hole delay in the shape of delay inside the hole leading to blasting of hole in stages should be more useful in case of solid blasting than in surface blasting due presence of larger confinement in solid blasting. The application of such technique, hitherto unknown, has been found to improve the blast efficiency considerably in two coal mines. Therefore, the present invention is unique and an innovative application of already existing facilities for different condition to improve the overall eficiency. Advantages The main advantages of the present invention over existing commercial solid blasting methods are: 1. This method improves the blast efficiency and economy. It should include a greater yield using smaller quantity of explosives. 2. The blast vibration should be reduced as the charges to be blasted is splitted and blasted under different delay timing. The reduction in vibration should reduce strata control problems. We claim: l.A method for in-hole delay solid blasting, characterized by distributing or splitting explosive charge(3) loaded in an individual blast hole(2) in drivage of mine, roadways and tunnels having two or more sections separated by decking(4), each of the said sections being blasted using at least one delay detonator(5,6) in each section and the said detonator having different delay timing with top section(s) being blasted prior to the bottom section(s) enabling the bottom section(s) to be blasted with lesser confinement leading to better blast efficiency. 2 A method as claimed in claim 1, wherein the blast holes are of conventional type and their diameter are in the range of 32-50 mm. 3. A method as claimed in claims 1 and 2, wherein the explosive charge in a hole is splitted in two or more sections. 4. A method as claimed in claims 1-3, wherein the splitting of the charge is done in so that the section of the hole to be blasted earlier contains equal to or more charge by one or more explosive cartridges, then the section to be blasted subsequently . 5. A method as claimed in claims 1- 4, wherein the explosive charge in each section comprises of either cap-sensitive or a combination of cap-sensitive and non-cap sensitive explosives. 6. A method as claimed in claim 5, wherein the cap sensitive explosives selected from slurry, gelatinous or emulsion types and the proportion of cap-sensitive explosive in a mixture of cap-sensitive and non-cap-sensitive explosive used is in the range of 25-30 per cent. 7. A method as claimed in claims 1 to 6, wherein the decking comprises of inert material like sand and clay mixture, stone chips, water or air and the said decking having length of at least 10-12 times the blast hole diameter. 8. A method as claimed in claims 1 and 7, wherein the decking length is in the range 0.4-1 m depending on the blast hole diameter, rock type and explosive type. 9. A method as claimed in claims 1 to 8 wherein the delay time between two sections of explosive is in the range of 25-500 ms. 10. A method as claimed in claims 1 to 9, wherein the top or upper section of the charge is to be blasted prior to the deeper/bottom section. 11. A method as claimed in claims 1 to 10, wherein the detonations of the explosives done with electric, electronic or non-electric delay detonators. 12. A method as claimed in claims 1 and 11, wherein smaller delay time used for soft strata and that of larger delay used for strong strata. 13. A method as claimed in claims 1 to 12, wherein the stemming and delay detonators either electric or electronic leads are of conventional type. 14. A method as claimed in claims 1-13, wherein the leads of the delay detonators from different sections of an individual blast hole are connected in series or parallel with the lead wires from those of other holes as is done conventionally.

Documents:

417-del-2004-Abstract-(23-11-2010).pdf

417-del-2004-abstract.pdf

417-del-2004-Claims-(23-11-2010).pdf

417-DEL-2004-Claims-(24-02-2012).pdf

417-del-2004-claims.pdf

417-DEL-2004-Correspondence Others-(24-02-2012).pdf

417-del-2004-Correspondence-Others-(23-11-2010).pdf

417-del-2004-correspondence-others.pdf

417-del-2004-correspondence-po.pdf

417-del-2004-Description (Complete)-(23-11-2010).pdf

417-del-2004-description (complete).pdf

417-del-2004-Drawings-(23-11-2010).pdf

417-del-2004-drawings.pdf

417-DEL-2004-Form-1-(24-02-2012).pdf

417-del-2004-form-1.pdf

417-del-2004-form-18.pdf

417-DEL-2004-Form-2-(24-02-2012).pdf

417-del-2004-form-2.pdf

417-del-2004-Form-3-(23-11-2010).pdf

417-del-2004-form-3.pdf

417-del-2004-form-5.pdf