Environmental Engineering Reference
In-Depth Information
10.3.2
Longwall Panel Extraction
Extraction Procedures
Most of the coal currently produced in Pennsylvania uses the longwall mining method
(PaDEP, 2002). Mining begins with the excavation of hallways supported by pillars along
the sides of the panel to be mined, generally 600 to 7000 ft or more in width (Figure 10.7).
The hallways provide for access, ventilation, and the removal of the mined coal. Along the
face of the panel a cutting head moves back and forth, excavating the coal, which falls onto
a conveyor belt. A system of hydraulic roof supports prevents the mine from collapsing.
As the excavation proceeds, the supports move with it and the mine roof behind the sup-
ports is permitted to collapse.
NCB Studies
Based on surveys of 157 collieries, the National Coal Board of Great Britain (NCB, 1963,
1966) developed a number of empirical relationships for the prediction of the vertical
component of surface displacements
s
and the horizontal component of surface strain
e
,
associated with the trough-shaped excavation of the longwall panel method of coal extrac-
tion, illustrated in
Figure 10.8.
Surveys were made over coal seams that were inclined up to 25° from the horizontal,
were about 3 to 15 ft in thickness
m
, and ranged in depth
h
from 100 to 2600 ft. Face or
panel width
w
varied from 100 to 1500 ft, and the panel width to depth ratio
w
/
h
varied
from 0.05 to 4.0. Panel widths were averaged if the panel sides were nonparallel. The fore-
going conditions assume that there is no zone of special support within the panel areas.
The physical relationships are illustrated in Figure 10.8.
Subsidence Characteristics
Angle of the Draw
The area where the coal is mined is referred to as the “panel.” Extraction results in surface
subsidence termed “subsidence trough” or “basin.” The width by which the subsidence
trough exceeds the panel width is the “angle of the draw.”
Longwall mining
Longwall mining machine
cutting coal face
Coal
Conveyor
belt
Hydraulic
roof supports
Brattice
to control
ventilation
Gob area
collapsed roof material
Pillar
FIGURE 10.7
Longwall panel mining of coal beds. (From PaDEP, Commonwealth of PA, Department of Environmental
Protection, Bureau of Mining and Reclamation, Contract No. BMR-00-02, 2002. With permission.)
