Abstract Longwall mining is a common mining method in Iran that is often affected by out-of-seam dilution (OSD). The field investigations performed in Tabas coal mine show that OSD often occurs due to roof falls in front of the face area before support setting and also removing some floor material. The increase in unsupported roof span above the shearer may cause difficulty in controlling the roof and consequently increases dilution of the run of mine (ROM) coal. The paper presents the results of a study on some dominant factors causing OSD in prop-free front of the face in longwall retreat mining method. A series of two-dimensional numerical models are developed and analyzed to examine the effects of mining depth, in-situ stress, unsupported roof geometry above the shearer as well as roof and floor strata quality and dip of coal seam on OSD. Two criteria were established, one considers the roof falls, defined as low stress level or plasticity zones under yield tension which roof material unravels and other is about removing floor, defined as depth of support and shearer sinking into the floor. The equivalent linear relaxation depth (ELRD) and depth of removing floor (DRF) concepts were used to quantify OSD. The methodology presented in this study is useful since it can be applied to develop mine-specific design tools for the prediction of OSD.
[1]
Howard L. Hartman,et al.
Introductory Mining Engineering
,
1987
.
[2]
Christopher Mark,et al.
Behavior of simulated longwall gob material
,
1993
.
[3]
Jucheng Wang,et al.
Influence of stress, undercutting, blasting and time on open stope stability and dilution
,
2004
.
[4]
Alwyn E. Annels.
Mineral Deposit Evaluation: A practical approach
,
2005
.
[5]
G. Revey.
EFFECTS AND CONTROL OF OVERBREAK IN UNDERGROUND MINING
,
1998
.
[6]
G. Popov.
The Working of Mineral Deposits
,
1971
.
[7]
B. N. Whittaker,et al.
An appraisal of strata control practice : 4F, 4T, 30R. TRANS. INSTN. MIN. METALL. V83, JULY, 1974, P.A85–A95
,
1974
.
[8]
Bahtiyar Ünver,et al.
3D numerical modeling of longwall mining with top-coal caving
,
2005
.
[9]
S. Yazici,et al.
Mining-induced stress change and consequences of stress path on excavation stability — a case study
,
2001
.
[10]
K. Shahriar,et al.
Prediction of Surface Subsidence Due to Inclined Very Shallow Coal Seam Mining Using FDM
,
2009
.
[11]
Hani S. Mitri,et al.
Numerical modelling of ore dilution in blasthole stoping
,
2007
.
[12]
An introduction to mining
,
1979
.