depillaring in coal mines with sand stowing

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

2. 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

3. PRODUCTION RATE
1-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 .
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.

4. DEPILLARING
It is the process of extraction of coal from pillars . It is also called
pillar cutting or broken working.
Fig 1-sequence of pillar extraction with diagonal line
of face

5. 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.

6. 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

7. Depillaring with Stowing
Circumstances 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.

8. 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. This
gets crushed, oxidation sets in and eventually fire may break out.
3-the production from district is not high and
the output per man-shift is low.
4-There may be a chance of subsidence.

9. Principles of Pillar Extraction
1. Roof exposure at one time should be minimal.
For caving- 60-90 m^2
For 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 diagonal
line of face or even straight line of face has been selected.
Fig 2- method of pillar extraction
Source( R D Singh,2005)

10. 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))

11. Steps Of Depillaring
1-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.

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

13. 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.

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

15. Case Study
GEOMINING CONDITION
Panel- 1AS3
Seam-1A Seam
Thicknesses -4.6 to 5.5 m
Inclination-1 in 7 gradient
Width of gallery-4.3 m
Height of extraction- 3.0m
Size of pillar-35 m * 32 m
The 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

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

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

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

19. 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.

20. 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.