depllaring in coal mines

UMT ASSIGNMENT

ON DEPILLARING WITH

SAND STOWING

Name- Akhilesh Kumar Gupta Roll NO-114mn0275 Year-2015-2016

INTRODUCTION Bord and Pillar method of mining is one of the oldest

methods.Pillars are left as support and output is nearly 20%.after

development pillars are being extracted which follows different

procedure according to the geographical condition. And extraction of

pillars increases the output to 60%. So this project deals with extraction

of pillars to increase the efficiency of mining with safety

PRODUCTION RATE

1-Bord and Pillar method of mining is one of the oldestmethods . Pillars are left as support and output is nearly

20%.after development pillars are being extracted .2=. And extraction of pillars increases the output to

60%.

So this project deals with extraction of pillars to increase the efficiency of mining with safety.

DEPILLARING It is the process of extraction of coal from pillars . It is also calledpillar cutting or broken working.

Fig 1-sequence of pillar extraction with diagonal line of face

Types of depillaring

1-Depillaring with stowing

Depillaring with stowing is a method of pillar extraction in which the goaf is completely packed with incombustible material and generally plasticized where it is necessary to keep the surface and strata above the seam intact after extraction of coal. It is the safe method after the depillaring as it packs the goaf area so the chances of subsidence is decreased.

2-Depillaring with Caving-

In this method,the coal of pillars is extracted and the roof is allowed to break and collapse into the voids or the de coaled area, known as goaf. As the roof strata about the coal seam break, the ground surface develops cracks and subsides, the extent of damage depending upon depth, thickness of the seam extracted, the nature of strata, thickness of the subsoil and effect of drag by faults

Depillaring with StowingCircumstances for adoption of this methods-

1. Presence of water bearing strata above the coal seam being extracted.2. Railways, rivers, roads, etc. situated on the surface, which cannot be diverted.3.Surface buildings which cannot be evacuated.4. Restrictions imposed by local or Government authorities for the protection of the surface.

Problems in the extraction of pillars

1- The operations of pillar extraction are beset with the problems of strata control.

2-Usually, some coal is left in the goaf, which may be 15-20% of the panel reserve. Thisgets crushed, oxidation sets in and eventually fire may break out.

3-the production from district is not high andthe output per man-shift is low.

4-There may be a chance of subsidence.

Principles of Pillar Extraction 1. Roof exposure at one time should be minimal. For caving- 60-90 m^2For stowing- 90-100 m^2

2-The extraction line should be so arranged as to facilitate roof control. In practice diagonal line , or step diagonal line of face is common. In special cases a steep diagonalline of face or even straight line of face has been selected.

Fig 2- method of pillar extractionSource( R D Singh,2005)

3. The single lift extraction is limited to height of 4.8 m or less. If the thickness of the seam is more than 4.8 m, the extraction is done in multi-lifts .

4-Whatever the method of extraction, the working area is systematically supported by cogs and props.

Fig-3: Design of support system(source- Report of S. Jayanthu Sir from scientific study of roof and sides support in RK 6 incline))

Steps Of Depillaring1-Each pillar shall be split into two equal parts by driving a central level split gallery not exceeding width of original gallery.

2-Each half pillar so formed shall be extracted by driving slice not exceeding width of the original gallery.

3- a slice a rib of coal 2.00m to 2.50 m thickness shall be left against the goaf which act as a chowkidar.

4-Extraction of pillars shall commence from the dip and proceed systematically to rise side maintaining a diagonal line of faces .

5-Cog support and props support are placed in the appropriate places and then stowing pipes are placed in the goaf area to fill the area along with barricade placed to oppose the flow of sand particles.

Fig-4: Splitting and slicing of pillars of thick seam.(source-R.D. singh’s Coal Mining,1997)

Sand Stowing

It is the practice of backfilling of mined out area completely is called stowing.If the stowing materials used is sand then it is called Sand Stowing.

Advantages-1- No chances of gas accumulation .

2-Better roof control .

3-High extraction percentage.

4-Depillaring of contiguous seams in any order is rendered possible.

Fig-5:Mixing of sand and water arrangement(drawn by myself, source-From GDK 10 Incline)

Case StudyGEOMINING CONDITION

Panel- 1AS3 Seam-1A Seam Thicknesses -4.6 to 5.5 mInclination-1 in 7 gradient Width of gallery-4.3 mHeight of extraction- 3.0mSize of pillar-35 m * 32 mThe number of the pillars-40 Size of the panel -277 m * 135 m.

Fig-6:strata section of borehole. Source- Report of S. Jayanthu Sir from scientific study of roof and sides support in RK 6 incline

Fig-7:Working plan of 1AS3 panel of 1A Seam

Manner of extraction followed in the depillaring panel is shown in Fig-8

Fig-9: : Design of Support System in depillaring pillars

CONCLUSION

From the study , we concluded that depillaring should be done scientifically and with safety and more emphasis should be laid on roof and side support and rules of DGMS must be followed.Ribs should be extracted if possible judiciously.

REFERENCES

1- Scientific study of roof and sides support in RK 6 incline(Report of S. Jayanthu Sir)

2-Deshmukh D J(2014)”Elements of Mining Technology”, volume-3, Central Publication ,Nagpur,pp-295-309

3-Singh R D(1997)”Principles and Practices of Modern Coal Mining”New Age International Publishers, 1st Edition,pp-177-200.