UNDERGROUND MINE MECHANISATION PROSPECTS
AND CONSTRAINTS
By G K Jha, Chairman & managing Director, South Eastern Coalfields Limited

Coal is the most abundant fuel resource in India and it meets over 60% of total commercial energy requirement of the country. Since nationalization of the Coal Industry, it has shown a phenomenal growth and so far has met the requirement of the country. But this growth is only on account of open cast mining. Stagnation in U/G production continues to be a concern and worry for quite a number of reasons:
 

• UG mines produce better quality of coal, demand for which is rising.
• Profit generation by O/C mines is being eaten away by the large number of loss making U/G mines.
• Reserve of open castable deposit is fast depleting.

Over and above, economic liberalization and consequent reduction of import duty on coal has thrown a new challenge to the Indian coal industry to remain competitive with imported coal. To meet this challenge, India can no longer rely on open cast mining alone but now has to improve production and productivity of its U/G mines to make them efficient and economically viable.   

Reasons of stagnation of U/G production may be

• Inadequate investment in U/G mining because of easily available option of open cast mining and therefore technology up gradation in U/G mines so far has been very marginal.

A large chunk of U/G production still comes from conventional Bord and Pillar mining using drilling, blasting, manual loading on to tubs, supporting by timbers, transportation of tubes by series of rope haulages. In eighties, steps were taken to mechanise various operations by introducing intermediate technology comprising of use of Side discharge loader/Load Hauler Dumper, roof Bolting as support system and transportation of Coal by Chain Conveyers. This intermediate technology could not only reduce/eliminate human drudgery of basket loading but also it could arrest the declining trend of U/G production, productivity and improved safety and economics also.

But this plagued with many weakness such as:
 

• Productivity is unable to match with ever increasing wages cost.
• Sub-operations being inter-linked i.e., cyclic in nature, it is not conducive to very high production.
• Moreover, continuance of use of explosive as means of coal getting remains a source of danger.
• Large number of work persons is required to be engaged at working faces.
• Roof bolting by use of hand held electric drilling is very cumbersome and slow. 
• Recovery of coal, i.e., percentage of extraction is not very high.

However it can be concluded that intermediate technology has served its purpose and in order to achieve very high production and productivity safely and with high percentage recovery of coal from U/G mines it has become imperative to adopt modern technology which eliminates blasting, ensures immediate support of the working face and envisages non-cyclic operation.
The most promising amongst the technologies are Powered support Longwall, Bord and Pillar mining with Continuous miner–shuttle car combination, Short wall Method for extraction of developed Pillar etc. Powered support Longwall Technology contribute nearly 50% of the global production of coal from Underground mines and is thus most prevalent in leading coal producing countries all over the world. In India also this technology was introduced in eighties.
Powered Support Longwall faces in India barring few exceptions have not been able to give desired level of production due to long selection of equipment, for want of adequate geo-technical information, in adequate knowledge about assessment of support requirement, inadequate infrastructural capacity like transport, ventilation, power supply, non availability of spares etc. But the experiences gained the operation of the faces are very valuable and should not be allow to go waste. Every country faced such failures in the initial stage.
So, SECL went ahead to introduce this technology in 3 U/G mines namely Balarampur, New-Kumda and Rajendra. Performance of these 3 Long Wall faces is quite encouraging, each face producing more than 2000 T/OMS on average is as high as 3.0. Singareni Collieries are operating six Powered support Longwall faces with fare degree of success. There is no doubt about immense possibilities of this technology of applied in Suitable locales after through geo-technical investigations.

Strata control problem in Indian Longwall faces are mostly because of difficult caving characteristics of the overlying strata. Possibilities of including caving by blasting the goaf should be seriously explored. At shallow depth, problem of caving could be solved in SECL PSLW projects by goaf blasting drilled from surface. This should be considered as major break through. Also in Bord and Pillar mining with massive stand stone roof induced caving of the roof has been successfully carried out by long hole blasting in the goaf from underground itself. Similarly for Powered Support Longwall faces as greater depth, long hole goaf blasting from underground can also be tried. If this is successful, major battle is own. One such proposal has already been mooted for hard roof management at Churcha UG mine awaiting green signal from DGMS.

The most widely practiced method of mining in India is Bord and Pillar mining. B&P method of mining can also be fully mechanized by using Continuous Miner-shuttle car combination and Mechanised roof Bolter. 

South Eastern Coalfields has already taken action for introduction of this technology in some of its U/G mines and expected to be operative in 2001.
A large quantum of coal is locked in developed pillars all over the country. If high production and productivity is to be achieved in extraction of these developed pillars, Short Longwall  needs to be tried at SECL  one such proposal is already on the anvil.
Earlier high technology area did not meet with desired level of success because of, as I earlier said, wrong selection of equipment, inadequate geo-technical information, lack of knowledge regarding strata control etc. and last but not the least the equipment supplier having no stake in success of technology.

Now SECL has entered into agreement with some of the equipment suppliers for supplying equipment on joint risk and gain sharing basis. In this agreement 50% of the equipment cost will be paid in installments and balance 50% will be paid on the basis of per tonne of production achieved. Maintenance cost   also will be paid on the basis of per tonne production. This will involve the equipment supplier in the entire production process, thereby eliminating the chance of wrong selection of equipment or wrong methodology of applying the technology. These suppliers of equipment will provide credit package from overseas bank for procurement of equipment.

Application of high technology like PSLW, Continuous  miner in large number of U/G mines will need huge capital investment and these may not be possible over night. In the meantime various operation like roof bolting, Coal getting etc. can befurther mechanised  as an intermediate step.

Roof bolting operation can be mechanised  by using portable hydraulic roof bolter mounted on or connected to side discharge loader. Or alternatively mobile hydraulic roof bolter can be developed making use of old SDL. Use of mobile drilling machine in place of hand held drill may also prove worthwhile.

Support of green zone area in Bord and Pillar development need to be re-looked. To prevent bed separation immediately after exposure, grouting with resin capsule instead of cement capsule should be thought of. It can be cost effective if small dia holes are drilled by using smaller dia drill bits and drill rods.

Lower capacity continuous miner with smaller capacity coal hauler can be tried. One road header has been converted to Continuous miner mode and is being used successfully in one of the SECL U/G mines. Seeing the success of this converted Continuous miner, 3 more Road headers are being converted for use in different mines. This technology needs quite modest investment almost equivalent to investment in SDL district, but district OMS achieved is much higher compared to SDL.

Wages cost constitutes nearly 50% or more of total cost of production. Rising trend of wages and salaries has got a substantial impact on the production cost. In order to minimise this impact, we do not have any alternative other than modernaisation our underground mines any longer.
To make the modern  technologies a success story in India, we must learn from our past mistakes so,

• We must select proper equipment. For this, we should try to involve the equipment suppliers in the production process.
• We must plan our mines very meticulously with proper provision of infrastructural  facilities like proper system of coal evacuation, ventilation, power supply etc. 
• We must develop and expand proper knowledge base regarding strata control etc. Our Research   Institute, Premier Educational Institutes should come forwards towards this direction and have more interactions with the field engineers to keep themselves abreast of the industry’s need.
• We must try to indegenise the manufacture of the equipment and spares.
• Develop human resource compatible with the technologies.

If we do all these, I firmly believe that the technologies, which have proved to be highly successful all over, the world, will succeed in India also.