Topic : “ Interactive presentation on BG Method of working - Induced Blasting & precautions against Air Blast ”

By V. Veera Swamy, AGM (ISO)

Bellampalli Region.

Induction Training Programme for

SMMC holders to be promotedas Under Managers

Welcome to

• Coal is the world’s most abundant and safe fossil fuel.• World coal reserves are estimated to last almost 200 years from now.• The importance of coal as a primary source of energy is significant in India.• India has a long history of commercial coal mining covering nearly 220 years from 1774 in the Ranigunj Coalfield.

INTRODUCTION

COAL Demand projections of India XI & XII plan (In Million Tonnes)

Sector

X plan XI Plan XII Plan2006-07 2011-12

CAGR (%) of2016-17

Actual Assessed Projected

Power Utilities 310.00 483.00 9.27% 750.00

Power Captive 31.50 57.06 9.50% 85.00

Cement 25.00 31.90 -- 50.00

Sponge Iron & Others 50.00 90.64 12.41% 135.00

Total Non-coking 417.00 662.60 9.70% 1020.00

Coking - Steel 43.00 68.50 9.76% 105.00

Total 460.00 731.10 9.7% 1125.00

CAGR – Compounded Annual Growth Rate

1991-92

VIII plan(96-97)

IX Plan(2001-02)

X Plan(06-07)

GrowthXI plan

(2011-12 Growth

Actual Actual Actual Antic Abs % Projected Abs %

CIL 204.15 250.62 279.65 360.94 81.29 5.40 520.50 156.70 7.43

SCCL 20.58 28.73 30.81 37.71 6.90 4.01 40.80 3.30 1.70

Others 8.09 9.97 17.33 31.81 23.48 12.45 118.70 87.50 30.63

TOTAL 232.82 289.32 327.79 430.46 111.67 5.70 680.00 247.50 9.47

The Company wise coal production trendMillion Tonnes

• EXPEDITING THE PROJECT APPROVAL PROCESS AND FASTER PROJECT COMMISSIONING

For faster execution of projects after they are approved, MoC grants ‘advance action plan’ for larger projects.

• PRIVATE MINING GoI has issued some of the coal blocks to private

companies for captive mining.• HIGHER IMPORT

To enable higher imports, the GoI lowered the effective import duty on non-coking coal.

Policy decision and initiatives for enhancing coal production in India

• OVERSEAS MINING CIL has formed a subsidiary, Coal Videsh Limited

(CVL) to acquire coal blocks in a number of countries including Indonesia, South Africa and Australia.

• ENHANCING PRODUCITION FROM OPENCAST MINES Opencast mines allow higher mechanisation and can

therefore ensure faster step-up in production.• INCREASING THE EXTENT OF OUTSOURCING IN

VARIOUS MINING OPERATIONS Outsourcing of mining operations can lead to faster

project implementation as the private parties can readily procure machinery.

Policy decision and initiatives

• CREATING AN ENABLING POLICY ENVIRONMENT FOR PRIVATE PARTICIPATION

The magnitude of coal shortage is such that active participation of private players is urgently required to broad base the country’s efforts at increasing coal supply.

Policy decision and initiatives

“ A through review of mining technologies may help in evolving suitable methods for maximizing recovery.”

Strategy of mining in SCCL

• Exploitation of coal seams from u/g mines became a major challenge for Indian Coal Mining Industry.

• Ever increasing demand year by year as coal is the main fossil fuel used by power sector.

• SCCL has initiated several steps like re-organization of existing mines to augment production.

• One example is mechanized open cast mining with techno-economic viability.

• Introduction of mechanization for higher rate of production such as long wall system and intermediate technology etc., liquidation of long standing good quality coal pillars.

• About 50 % of coal reserves in India are in seams with thickness more than 4.5 m which fall under the category of thick seams.

• Exploitation of thick seams by u/g method poses certain difficulties / problems.

• Extraction of thick seams by conventional hand section is neither productive nor viable from conservation point of view.

• Percentage of extraction by hand section in thick seams is as low as 25 – 30 %.

Strategy of mining in SCCL….Contd

• However, some attempts have been made to extract thick seams with sand stowing. Sand stowing for working thick seams cannot be considered as an option because the cost is prohibitive as sand is becoming increasingly scarce commodity along with timber.

• At the same time, coal industry was in search of an economic method for dealing with thick / standing developed pillars.

• SCCL is of the opinion that blasting gallery (BG) method is the appropriate method for the extraction of thick seams up to a thickness of 8 – 11 metres. Mining by BG method produces about 1000 T/day with 85 % of extraction which has been in SCCL.

Strategy of mining in SCCL….Contd

Carbonnage de France (Cdf) suggested Blasting gallery (BG) for extraction of thick

seams in India

• The 1st BG Panel was started in the country at East Katras colliery in Jharia Coal fields (BCCL) in 1987.

• The method was not successful at East Katras colliery where overriding of pillars (strata control) occurred.

• In Chora – 10 Pit colliery in Raniganji (ECCL) in the year 1987, the method was partially successful giving encouraging results.

• However, it was discontinued due to spontaneous heating. • Expected production and percentage of extraction could not

be achieved in both the above mines.• SCCL 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 mtrs. Thickness.

• The method was very successful resulting in 85 % of extraction with high productivity.

• At the same mine, where the thick seam was developed fully in top section and partially in bottom section, BG was introduced.

• Subsequently, SCCL has introduced BG in other mines also, namely :i. GDK-8, where bottom section was developed by bord and pillar method along the floor of the seam.ii. VK-7 Incline, Kothagudem area, where the seam was developed in two sections. During the development of BG panel, the galleries were driven in staggered manner.iii. GDK – 11 A Inc., RG-I Area and later at No. 21 Area, YD Area in the year 2006.

Carbonnage de France (Cdf) suggested Blasting gallery (BG) for extraction of thick

seams in India

PRINCIPLE OF BG METHOD• The basic principle of BG method is to extract thick coal seams

by drilling and blasting of roof and sides of galleries, which are driven 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 0.75 to 1.5 m. by a crawler mounted JUMBO drill.

• Blasting is done using explosive cartridges separated by inert spacers and detonating fuse, so that the explosive spreads all along the length of the hole.

• Load Haul Dumpers( LHDs) with remote control carry out loading of coal enabling the operator to stand under the supported roof and operate the LHD. LHDs 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 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.

ADVANTAGES OF BLASTING GALLERY METHOD

• Full thickness of the seam can be extracted in a single lift.• Higher percentage of extraction i.e. 75 – 85.• Capital investment is nominal when compared to longwall

project. • Easy to train the man power and easy maintenance of the

equipment.• Extraction is carried under fully supported roof i.e. with

remote controlled 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 methods.

ADVANTAGES OF BLASTING GALLERY METHOD …Contd

LIMITATIONS OF THE METHOD

• This method is not suitable for gassy mines and seams with degree-I gassiness are most preferable.

• The method is suitable only for gradient more than 1 in 5 to allow easy movement of tyre mounted LHDs and crawler mounted electro- hydraulic jumbo drills.

• Though the percentage of extraction is around 75-85, still coal left in the goaf is likely to create spontaneous heating.

THE MANNER OF EXTRACTION

• Each pillar shall be split into two equal parts by level split of width not more than 4.2 m. 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 free faces are not provided.

• In order to create free faces in this operation / beginning of extraction in BG Method.

THE MANNER OF EXTRACTION…Contd

• 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 with about 33 shot holes.

Potato BlastingPotato Blasting

• The shot holes are drilled in ring pattern and sloping at an angle of about 300 to 400 from the vertical towards the goaf.

• The spacing between consecutive rings at shot holes shall be 1.5 m.

• The shot holes are drilled in a ring spaced 1.5m. apart by means of JUMBO drill from the level rooms in such a way that they cover half the pillar on rise side and 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 of about 600 to the level.

THE MANNER OF EXTRACTION…Contd

• A curtain of thickness of coal not less than 1.5m shall be left between two adjacent rooms after blasting of rings.

• However, it was observed that this curtain provides protection during remote operation of the LHD in the goaf.

THE MANNER OF EXTRACTION…Contd

Dip

DRILLING• In BG Method, drilling is done by crawler mounted

electro-hydraulic jumbo drill which can drill at any angle in the vertical plane, as the method envisages drilling of holes in Fan Pattern.

• The length of hole depends on its position and seam thickness.

• The jumbo drill can drill upto 30 m. long incline hole with a speed of 1m/minute.

• The drill rods are 1.13 m. long with connecting features (both male female type) with rope thread at the end.

• The drill rods are provided with a central hole to facilitate wet drilling. Water at the rate of 2.5m3 / hr under pressure of 8-10 bars is flushed during drilling to clean the cuttings out of the hole.

• The diameter of drill rod and drill bits are 32mm. and 34 mm respectively. The finished hole diameter is around 43 mm.

• On an average, 30- 34 holes are drilled in ring pattern.• All the holes are drilled in the roof leaving towards the

goaf line at 550 to 600 from horizontal and 450 towards the goaf from the pillar side.

• The holes in the roof are drilled to the seam thickness, whereas the holes in the side are drilled in such a manner that they cover nearly half of the pillar on both dip and rise side from the gallery where jumbo is operating.

• A curtain of about 1.5m. in the middle of each pillar is left after drilling for facilitating safe loading by LHD.. However, it was observed that this curtain fell subsequently due to blasting.

DRILLING

Blasting of Ring holes• 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.• 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 No: 6 electric detonator.

• About 0.5 – 0.6 in length of all holes are stemmed with clay at the end.

• 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.

The whole ring is blasted in one round using instantaneous electric detonators.Generally, 250 – 350 tonnes of coal is produced in one round of ring blast.

Blasting of Ring holes …Contd

PRODUCTION PER RING BLAST

a

b

x

y

z

(X y - a b)z d r

A=width of the gallery=4mB=height of the gallery=2.7m

X = length of half pillar=17.5mY=total working thickness of seam=8.3mZ= distance between successive rings =1.5m

D=sp. Gr. Of the coal=1.5R= percentage of extraction=0.85

Specification of Explosives :

I-Stage

Explosive : Uniring (IEL)

(a) Weight of explosive : 200 g

(b) Diameter of explosive : 32 mm

(c) Length of explosive cartridge : 200 m

Blasting of Ring holes …Contd

II-Stageb) Explosive

Explosive type : Belgex Coal (R), Bharat

Explosives Limited

Weight of explosive : 185 g

Diameter of explosive : 32 mm

Length of explosive cartridge : 200 mm

Density : 1.18 – 1.19 g/cc

VOD : 2826 M/S

Air – gap in unconfined condn : 5 cm pass.

Blasting of Ring holes

Composition of explosive

Nitroglycerine : 12 + 0.5%Nitro-Cellulose : 0.2 + 0.5 %Ammonium Nitrate : 46 + 3.0 %Cellulose (Woodmeal): 1.5 + 0.5 %Salt : 37 + 2.5%Sodium Nitrate : 2 %Others : 6.0 + 0.5 %

Detonating Cord

• Type and manufacture : i) Ring chord (IEL)

ii) G-Chord (IDL)• Weight of ring cord : 25 g/m• Diameter : 6 mm• Weight of PETN in G-cord : 3.6 g/,

Spacers• Length of long spacer : 600 mm• Length of shorter spacer : 250 mm

• Type and manufacturer : Copper coated instant; Premier Explosives Ltd.

• Range : 1• Number : 6

Detonator

POWER RING(IEL) 32 MM DIA,

DETONATING FUSE: POWER-CORD(IEL)

DIA 4 -4.5 MMPETN-8-9 G/M

DETONATORCu COATED INSTANTANEOUS

NO. 6 TYPE

III Stage :

Charging of holesCharging of holes

Drill Hole pattern in Ring blastDrill Hole pattern in Ring blast

II-Stageb) Explosive

Explosive type : Belgex Coal (R), Bharat

Explosives Limited

Weight of explosive : 185 g

Diameter of explosive : 32 mm

Length of explosive cartridge : 200 mm

Density : 1.18 – 1.19 g/cc

VOD : 2826 M/S

Air – gap in unconfined condn : 5 cm pass.

Blasting of Ring holes

Composition of explosive

Nitroglycerine : 12 + 0.5%Nitro-Cellulose : 0.2 + 0.5 %Ammonium Nitrate : 46 + 3.0 %Cellulose (Woodmeal): 1.5 + 0.5 %Salt : 37 + 2.5%Sodium Nitrate : 2 %Others : 6.0 + 0.5 %

Detonating Cord

• Type and manufacture : i) Ring chord (IEL)

ii) G-Chord (IDL)• Weight of ring cord : 25 g/m• Diameter : 6 mm• Weight of PETN in G-cord : 3.6 g/,

Spacers• Length of long spacer : 600 mm• Length of shorter spacer : 250 mm

• Type and manufacturer : Copper coated instant; Premier Explosives Ltd.

• Range : 1• Number : 6

Detonator

• The main junction girders are secured tightly by clamps suspended by steel bolts grouted in the roof.

• The goaf edges and the entries of the central dip / rise galleries of panel immediately out bye of the goaf edges shall be kept supported by row cogs set an interval of 0.25 m.

• All roof bars set on hydraulic props shall be braced suitably.

• Adequate setting load of not less 6 T shall be provided.

Support System in BG Method …Contd

Support System in BG Method• The level split and dip/rise galleries shall be kept

supported by a set of ISMB girders of 150 mm x 150 mm mounted on 40 T hydraulic props at either end.

• The first set of cross girders shall be erected close to the goaf edges, but in no case less than 0.7 m.

• The distance between two such sets along the gallery shall not exceed 1.00 m/1.5 m depending on the roof conditions.

• The roof between the bars shall be suitably lagged by wooden sleepers.

• Entire roof is supported for a distance of 40 m. from the face by 250 mm x 250 mm IBMS steel bars placed on 2 No. of 40 T capacity open circuit hydraulic props.

• The interval between the bars being 1.00 m / 1.5 m.

• All junctions are supported by 6 Nos of 5.5 m long roof bars which are held in position by means of 2 Nos of 5.5 m roof bars at either end set over a cluster of 4 Nos of hydraulic props at each corner.

• In between the roof bars, the roof is further supported by 3 Nos of grouted wooden/bamboo roof bolts.

• As a precaution against the dislodging of hydraulic props accidentally by moving machinery, the hydraulic props are tied together to roof bars by means of flexible steel wires.

Support System in BG Method …Contd

Gallery Support SystemGallery Support System `

• As per the permission condition specified that, ventilation shall be adequate to bring down the concentration of NO2 and CO in post detonation fumes at the face to 5 ppm and 50ppm respecting within 5 minutes .

• In no case, quantity of air at any working place shall be less then 284 m3/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 ways round the clock.

Ventilation

• No persons 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 then 0.5% is detected in the General Body of air, blasting operation shall not be carried out until the danger from inflammable gas is removed .

Ventilation …Contd.

• 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 43 mm diameter is drilled in the roof with 450 inclination towards the horizontal as shown in the Figure 8.1. Depth of hole naturally depends on the seam thickness and it should penetrate the coalface at the roof-top.

Testing of Methane Presence in goaf

• After drilling is completed, PVC pipe with 38 mm outer diameter and 36 mm inner diameter is inserted inside the drilled hole through the length. This PVC pipe should penetrate to the coalface and reach upto the roof of the goaf. A small suction pipe (8 mm outer and 6 mm inner diameter) is then again inserted throughout the length of the pipe.

Methanometer (Micro Guard, MSA) is then connected to the lower end of the suction pipe. After sucking air inside the pipe, reading is recorded from the methanometer.

Testing of Methane Presence in goaf …. Contd.

GALLERY 2.7 M

COAL 5.6M

STONE

PVC PPE

METHNOMETER & SMALL DIA TUBE

TESTING FOR INFLAMMABLE GAS

Goaf

• When the method of extraction is to remove all the coal or as much of coal practicable and to allow the roof to cave in, the operations shall be conducted in such a way as to leave as small an area of uncollapsed roof as possible.

• Where possible suitable means shall be adopted to bring the goaf at regular intervals.

• In blasting gallery method of extraction, induced blasting has become an integral part of mining operation during depillaring of developed coal pillars.

Why induced blasting is necessary ?

• When the method of extraction is to remove all the coal or as much of coal practicable and to allow the roof to cave in, the operations shall be conducted in such a way as to leave as small an area of uncollapsed roof as possible.

• Where possible suitable means shall be adopted to bring the goaf at regular intervals.

• In blasting gallery method of extraction, induced blasting has become an integral part of mining operation during depillaring of developed coal pillars.

Why induced blasting is necessary ?

INDUCED BLASTING IN BG PANELS

• In Blasting Gallery method of winning coal, usually more area of goaf is exposed after extraction of coal.

• If the roof does not cave by its own weight, induced blasting is generally carried out at regular interval when the roof span is about 120 – 190 sq. mtrs.

• As per the DGMS strictures, explosive charge per hole is limited to 1.0 kg only. However, it is found practically difficult to conduct successful induced blasting with such limited charge.

Why induced blasting is necessary ?……Contd

DRILLING

• Jumbo drill is used for drilling of holes during induced blasting in the stone roof.

• Generally, 5-7 holes (depending on the roof span) with 15 to 20 m (generally 16.5m) depth are drilled through the roof of the developed gallery keeping 450 inclination to the horizontal at a distance of 3.5m from the goaf edge.

• The drill rods are 32 mm dia. While the drill bit is of 34 mm dia.

Why induced blasting is necessary ?……Contd

EXPLOSIVE – BRAND AND TYPE

• Powergel – 101 (P1 group, Emulsion explosive of M/s IEL) is used for carrying out induced blasting.

• Super Cord – 10 (M/s AEL, 3.5 g/m core) or G-cord (M/s IDL) being the approved detonating fuse systems used during charging of holes.

• The explosive cartridge used is 32 mm dia., 150 gm weight and 180 mm length.

Why induced blasting is necessary ?……Contd

CHARGING OF HOLES

• Generally, 6m long plastic pipes, 36 mm and 38 mm inner and outer diameters respectively are used for charging of holes.

• Where plastic pipes are not available, charging arrangement is done by cutting the plastic spacers and then making a slot where explosives are inserted and tied together with cellotape as practiced in Chora-10 pit colliery of ECL.

• Approximately, 6.5-8.5 kg of explosive is charged in each hole depending on the site condition and actual hole length.

• Remaining portion of the hole is stemmed with bamboo spacers. • All the holes are fired in one round with miscellaneous detonators.• Before firing five rows of girders are reinforced with extra props.• During blasting all related measurements like gas survey, vibration,

convergence and strata loads are monitored for safe and useful implementation of design and charge loading parameters.

Why induced blasting is necessary ?……Contd

CONCLUSION

• Induced caving by blasting becomes more important especially, in case of winning of coal by BG method when the overhanging of roof in the goaf area is difficult to cave by it’s own weight.

• Though, the whole operation is non-productive work, it ensures safety to the persons and the u/g working environment.

• Strata monitoring through measurements of roof convergence, strata load and ground vibrations during enduced blasting are very essential for succesful implementation of induce blasting.

Why induced blasting is necessary ?……Contd