Significant
achievements/contributions in the field of mining technology
1.
Development of Underpinning based Method of Mining for Depillaring of Thick Contiguous
Seams/Sections under Fragile Parting:
Extraction of clean coal from thick
and contiguous seams/sections is a major problem for mining engineers. Coal
mining industry of the country needs a suitable technology for extraction of
the same in the presence of weak and laminated parting in between. An idea of
underpinning was conceived to facilitate safe and optimal exploitation of coal
from contiguous seams/sections under thin, weak and laminated parting. The
underpinning provided solution for a three fold problem like (i) reinforcement
of the laminated parting to enhance the interface cohesion and thereby
enhancement in the effective strength of the roof rock mass, (ii) safely
leaving a thick and stable band of coal along the roof of the bottom section,
if required to enhance safety and (iii) systematic support of the roof rock
mass of the bottom section, consisting coal band and laminated parting, to
ensure coal cum parting as a single composite beam so that the roof coal band
of necessary thickness be maintained during depillaring. Underpinning
consolidated parting stability through reinforcement and provided additional
thickness to the critical parting as the roof coal band of the thick bottom
section is stitched together with the parting. The technology was first
experimented at Zero seam of Chirimiri colliery with lots of appreciation from
the industry. This method could find another quick successful application at
another mine (Nowrozabad East Colliery, SECL).
2.
Development of eco-friendly mining method (Wide Stall Method of Mining without
Stowing) for partial extraction of coal from locked-up pillars under various
surface and sub-surface features:
Mining of minerals, especially,
opencast mining is facing rough weather due to growing concern over its
environmental impact. Though underground mining is itself eco-friendly and
impact on overlying surface environment for deeper cover is comparatively less
but extraction of reserve lying in shallow depth and especially, in thick seams
experiences direct impact of mining on ecology by damaging surface and
sub-surface features due to large scale strata movement including
subsidence. The methods adopted in
India for winning of thick seams were invariably in conjunction with stowing in
ascending order even that also imposed serious constraints of sand and sand
stowing. But even with complete stowing some strata movement is likely to be
there for most of the mining methods in vogue. Moreover, due to
non-availability of stowing material the methods adopted for the exploitation
of thick seam under fragile ecology were invariably very partial in form of
pillar development as natural support with low recovery below 30-35 percent by
way of pillar mining in sections. In view of these problems and for the region
where stowing material is not available for packing of underground voids, an
eco-friendly mining method was developed to avoid surface subsidence with
optimal recovery of good quality coal, improvement in production, productivity
and safety of the workers and workings. The technique was first successfully
experimented in No. III seam underneath Bartunga hill at Chirimiri colliery
where mining posed serious problems due to protected forestland, the presence
of the seam No. II in the close vicinity and inaccessible terrain. Another
experimental trial was done for optimal extraction of coal locked in pillars
under aquifer and fragile ecology at Umaria colliery of Johilla Area of SECL.
This method of partial extraction had a great success at Umaria colliery near
Umaria district town also. This colliery still extracting coal by application
of this method. The competency of immediate roof and the size of pillars were
matched to optimise the width and height of the developed galleries for higher
production and adequate safety.
Investigations into stress and deformation during wide stall formation
in field and the study for stability of pillars and stalls helped in optimising
the recovery of coal from locked-up pillars under surface/subsurface features.
3. Development of cable bolting method
for depillaring of thick coal seams:
Based
on simple rock mechanics principles, the idea of using a grouted steel rope
under tension for supporting a high roof as well as overlying coal band, and to
improve safe span of overhanging strata near goaf edge for semi-mechanized
depillaring of a thick coal seam standing on pillars was first applied at NCPH
mine of the Chirimiri area of SECL. Taking advantage of the massiveness of the
coal seam and pattern of stress redistribution around a depillaring face, field
application of this technique made it possible to extract the full thickness
(6.0 to 8.0m) of the No. 3 seam of the colliery developed along the floor with
2.5m (avg.) gallery height in a single lift with improved the strata condition,
safety and achievement in respect of conservation, production and productivity.
The success of the field trial triggered a number of applications of the
technique in many other collieries in India due to its technical superiority
over the conventional method for underground extraction of thick and developed
coal seams. Feasibility study of the method for application in different
coalfields has been done.
4. Mining method for final extraction
of a critically thick coal seam standing on pillars and the development made
along the roof horizon
As per Coal Mines Regulations 1957,
superimposed development is a statutory requirement for contiguous sections.
While, on the other hand, minimum 3m thickness of the parting is must between the
workings of two close/contiguous sections/seams. Critically thick seams are
those, which do not provide the required minimum 3m thickness between the two
contiguous sections to be developed for optimal exploitation of the seam. A
complex situation arises if a critically thick coal seam is developed along the
roof horizon. One simple option is to depillar developed top section first and
then bottom section can be developed and depillared after settlement of the top
section goaf. Stress concentration over the stooks, left inside the goaf of the
top section, poses serious threat to the safety of the thin and incompetent
parting (less than 3m) during bottom section working besides problems of gas,
heating etc. Idea of cross development based controlled sub-level caving for
extraction of total thickness in one lift, has been developed by the nominee on
the basis of numerical modeling and the Singareni Collieries Company Limited
(SCCL) has requested us to conduct the field trial at their mine under the
formulated S&T project.
