Blasting Gallery Method
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The document discusses the blasting gallery method of underground coal mining, which is effective for extracting thick seams of coal (8-11 meters). It outlines the principle, advantages such as increased extraction rates (75-85%) and safety, as well as limitations including unsuitability for gassy mines. Key operational details include drilling techniques, support systems, ventilation requirements, and methane testing procedures prior to blasting.
Blasting Gallery Method
- 1. Department of Mining Engineering BIT Sindri,Dhanbad Topic:-Blasting Gallery Method Mining Engineering Presentation regarding Underground Coal Mining – BIT Sindri Prateek Verma
- 2. Contents Introduction Principle Advantage Limitation Manner extraction Support system Ventilation Testing of U/G Methane
- 3. Introduction 1. Blasting gallery method is the appropriate method for the extraction of thick seam. 2. The thick seam thickness will be up to 8-11 metres. 3. The 1st BG panel was started in the country at East katras colliery in Jharia coal field (BCCL) in 1987. The method was not successful at east Katras where overriding of pillar (Strata control ) occurred . 4. In chora – 10 pit couiary in Raniganj (ECCL) in the year 1987 the method was 5. Partiary successful giving encouraging result . 6. SSCL introduced BG method in collaboration with carbonnage de France at GDK -10 incline in the year 1989 for extraction of a coal seam with 11 matra,thickness. 7. The method was very successful resulting in 85% of extraction with high productivity.
- 5. Principle The basic principle of BG method is to be extract thick coal seams by drilling and blasting of roof and sides of gallery, which are driven at the bottom at the bottom of the seam at regular intervals. Ring holes are drilled in the rooms left between the two adjacent galleries in the roof and sides at regular intervals varying between 0.75m to 1.5m by a crawler mounted JUMBO drill. Blasting is done using explosive cartridge separated by inert spacers and detonating fuse , so that the explosive spreads all along the length of the holes. Load Haul Dumpers (LHD) with remote control carry out loading of coal enabling the operator to stand under the supported roof and operate the LHD carry the coal from the face and discharge into the armoured chain conveyor, which feeds to the belt conveyor network for transport to the surface . The development galleries are driven at the bottom floor of the seam. It is important that the correct size of rise/dip and rooms are maintained to avoid roof control problems during the retreating of the panel.
- 7. Blasting of Ring Holes
- 8. Advantages The thickness of seam can extracted in single slice. Higher percentage of extraction i.e 75-85%. Capital investment is nominal when compare to longwall project. Easy to train the man power and maintance of the equipment. Extraction is carried under fully supported roof i.e with remote control LHDS. Safety of the workmen can be fully ensured. This method can be also be adopted in virgin/developed seams. Most of the equipment and spares are indigenously available. Loss of production is minimum while shifting the equipment. This method is highly flexible as several units are in operation in a district. Even if one of the units is under break down production from the district will continue to come. The time required for preparation of panel in relation to the total life of the panel is less than other mechanised method.
- 9. Limitations This method is not suitable for gassy mines and seams with degree-1 gassiness are most preferable. The method is suitable only for gradient more than 1in5 to allow easy movement of tyre mounted LHDS and crawler mounted electro hydraullic jumbo drills. Through the percentage of extraction is around 75-85 , still coal left in the goaf is likely to undergo spontaneous heating.
- 10. Manner of Extraction Each pillar shall be split into two equal parts by level split of width not more than 4.2m and height not more than 3m along bottom section. The splitting of pillars shall be restricted to one pillar from the pillar under extraction. The long hole blasting shall not be practiced at any place where two faces are not provided. Before practicing long holes blasting (ring holes) the operation of drilling and blasting are carried out in stages to a height of full thickness to expose roof with increasing angle and length of short holes in bye of the galleries i.e called “potato blasting”. The full thickness of the seam is extracted by blasting a ring of shot holes B with about 33 shot holes. The shot holes are drilled in ring pattern and stopping at an angle of about 300 to 400 from the vertical towards the goaf. The spacing between consecutive rings at shot holes shall be 1.5m . The shot holes are drilled in a ring spaces 1.5m apart by means of JUMBO drill from the level rooms in such a way that they cover half the pillar on the dip side. Extraction in level galleries shall be from in bye to out bye forming a diagonal line at an angle about 600 to the level. A certain thickness of coal not less than 1.5m shall be left between two adjacent rooms after blasting of rings. After drilling is completed , shot holes are charged with the explosive approved by DGMS. The total number of shot holes in a ring are 33. About 0.5-0.6 in length of all holes are stemmed with clay at the end. The cartridges of explosives are distributed over the whole length of shot holes by spacers tied together by a detonating fuse called “RING CORD” Which are initiated by Number 6 electric detonator. On completion of charging and stemming of all holes,the circuit is connected in series before blasting the last installed roof support at the goaf line is removed and next support line is reinforced with extra support.
- 11. Support System I. All roof bars set on hydraullic props shall be breced suitably. II. Adequate setting load of not less 6T shall be provided. III. The distance between two sets along the gallery shall not exceed 1.00m/1.5m depending on the roof conditions. IV. The roof between the bars shall be suitably lagged by wooden sleepers. V. As a precaution against the dislodging of hydraullic props accidentally by moving machinery the hydraullic prop are tied together to roof bars by means of flexible steel wires.
- 12. Ventilation Ventilation shall be adequate to bring down the concentration of NO2 and CO in post detonating fumes at the face to 5ppm and 50ppm respecting within 5 minutes. In no case quantity of air at any working place shall be less than 284 m^3 /minute. No shot shall be charged or fired ,if 0.1%or more inflammable gas is found . During the extraction the tele monitoring system shall be maintained at the surface for monitoring of carbon monoxide and inflammable gases at the faces and in return air way round the clock. No person shall be allowed to remain on the return side of the false when blasting is done till the concentration of oxides of Nitrogen and Carbon monoxide in the return airway comes down to the limits specified . Before and during blasting if inflammable gas is found more than 0.5% is detected in the general body of air, blasting operation shall not be carried out untill the danger from inflammable gas is removed .
- 13. Testing of methane presence in goaf Testing of methane (CH4) presence in the goaf area is essential before conducting any blasting operation. No blast should be conducted if CH4 is present at the face. In order to determine the presence of methane in the goaf a hole of 43mm diameter is drilled in the roof with 450 inclination towards the horizontal. Depth of hole naturally depends on the seam thickness and it should penetrate the coal face at the roof-top. Methanometer is then connected to the lower end of the suction pipe. After sucking air inside the pipe,the pipe reading is recorded from the methanometer.
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