1
25-015
Assessment of Impact of Dirt Bands on Coal Pillar Strength at
Different Depths of Cover—A Numerical Simulation Study
Abhishek Kumar Singh
Department of Mining Engineering,
National Institute of Technology Rourkela, India
Sahendra Ram
Department of Mining Engineering,
National Institute of Technology Rourkela, India
Priyadarshi Onam
Department of Mining Engineering,
National Institute of Technology Rourkela, India
ABSTRACT
A numerical simulation study is carried out for assess-
ment of stability of coal pillars having dirt bands by vary-
ing its size and depths. Physico-mechanical properties of
dirt bands including thickness and its position in pillar
system are varied in the simulation study. Results of the
simulation study are correlated with the available empirical
approaches of pillar strength are validated with field obser-
vations. It is observed that the presence of weak dirt bands
significantly influences the strength of pillar. An attempt is
made to develop correction factor for the available empiri-
cal approaches, which are developed without considering
the weak dirt bands in pillar system. The findings of the
study will be helpful for suitable design of different size
of coal pillars at different depths and stages of depillaring
operations.
Keyword: Coal pillar. Dirt bands. Depth of cover. Pillar
strength. Numerical modelling
1. INTRODUCTION
The stability of coal pillars within underground extrac-
tion processes represents a crucial safety issue, significantly
shaped by geological discontinuities including dirt bands,
weak bedding planes, and various other discontinuities. In
methodologies such as room and pillar mining, wherein pil-
lars are retained to uphold the overlying strata, the design
of these pillars becomes vital. Researcher [1] emphasizes the
criticality of meticulously engineered pillars to avert pro-
gressive collapses in underground operations. Numerous
investigations have illustrated that the integrity of coal pil-
lars may be profoundly endangered by elements such as dirt
bands [2, 3], alongside stress redistributions resultant from
mining-related activities [4].
Empirical models like the Salamon and Munro for-
mula [5], though widely applied, often assume homogene-
ity in coal seam conditions and may overestimate strength
in pillars affected by weak planes [6]. Sheorey [7] discusses
the need to account for the specific triaxial strength of coal
and the effect of environmental conditions like water and
weathering on pillar design, which are often simplified in
traditional models. New insights are increasingly sought to
account for the specific characteristics of coal seams and
geological discontinuities, as advocated by recent stud-
ies [8, 9], which underscore the limitations of traditional
design approaches.
Pillar strength prediction also benefits from under-
standing the impact of bedding planes and dirt bands across
varied depth conditions. As noted by [10], empirical mod-
els tend to be conservative, sometimes leading to uneco-
nomic designs. Numerical approaches [11, 12] emphasize
the influence of in-situ stresses, particularly at depth, show-
ing that traditional empirical models may overlook critical
factors related to discontinuities. Studies by [13, 14] have
similarly demonstrated that discontinuities like cleats and
joints affect stress concentrations, requiring adjustments
in design approaches to improve both safety and extrac-
tion efficiency. Researcher [2, 7] point to the limitations of
empirical models in capturing stress variations and propose
the use of small-scale coal strength in equations to improve
accuracy.
25-015
Assessment of Impact of Dirt Bands on Coal Pillar Strength at
Different Depths of Cover—A Numerical Simulation Study
Abhishek Kumar Singh
Department of Mining Engineering,
National Institute of Technology Rourkela, India
Sahendra Ram
Department of Mining Engineering,
National Institute of Technology Rourkela, India
Priyadarshi Onam
Department of Mining Engineering,
National Institute of Technology Rourkela, India
ABSTRACT
A numerical simulation study is carried out for assess-
ment of stability of coal pillars having dirt bands by vary-
ing its size and depths. Physico-mechanical properties of
dirt bands including thickness and its position in pillar
system are varied in the simulation study. Results of the
simulation study are correlated with the available empirical
approaches of pillar strength are validated with field obser-
vations. It is observed that the presence of weak dirt bands
significantly influences the strength of pillar. An attempt is
made to develop correction factor for the available empiri-
cal approaches, which are developed without considering
the weak dirt bands in pillar system. The findings of the
study will be helpful for suitable design of different size
of coal pillars at different depths and stages of depillaring
operations.
Keyword: Coal pillar. Dirt bands. Depth of cover. Pillar
strength. Numerical modelling
1. INTRODUCTION
The stability of coal pillars within underground extrac-
tion processes represents a crucial safety issue, significantly
shaped by geological discontinuities including dirt bands,
weak bedding planes, and various other discontinuities. In
methodologies such as room and pillar mining, wherein pil-
lars are retained to uphold the overlying strata, the design
of these pillars becomes vital. Researcher [1] emphasizes the
criticality of meticulously engineered pillars to avert pro-
gressive collapses in underground operations. Numerous
investigations have illustrated that the integrity of coal pil-
lars may be profoundly endangered by elements such as dirt
bands [2, 3], alongside stress redistributions resultant from
mining-related activities [4].
Empirical models like the Salamon and Munro for-
mula [5], though widely applied, often assume homogene-
ity in coal seam conditions and may overestimate strength
in pillars affected by weak planes [6]. Sheorey [7] discusses
the need to account for the specific triaxial strength of coal
and the effect of environmental conditions like water and
weathering on pillar design, which are often simplified in
traditional models. New insights are increasingly sought to
account for the specific characteristics of coal seams and
geological discontinuities, as advocated by recent stud-
ies [8, 9], which underscore the limitations of traditional
design approaches.
Pillar strength prediction also benefits from under-
standing the impact of bedding planes and dirt bands across
varied depth conditions. As noted by [10], empirical mod-
els tend to be conservative, sometimes leading to uneco-
nomic designs. Numerical approaches [11, 12] emphasize
the influence of in-situ stresses, particularly at depth, show-
ing that traditional empirical models may overlook critical
factors related to discontinuities. Studies by [13, 14] have
similarly demonstrated that discontinuities like cleats and
joints affect stress concentrations, requiring adjustments
in design approaches to improve both safety and extrac-
tion efficiency. Researcher [2, 7] point to the limitations of
empirical models in capturing stress variations and propose
the use of small-scale coal strength in equations to improve
accuracy.