5
turn our attention to the next crucial step in our study: cali-
brating the LaModel program to accurately represent and
further analyze the collected data.
BUILDING THE MODEL
The LaModel 3.0 program was selected to model the mea-
sured pillar behavior because its calibration procedures
are considered to be directly comparable to the widely
used ARMPS 2010 (Mark, 2010) and ACPS (Mark and
Agioutantis, 2018) programs.
Utilizing LAMPRE 4.0, the preprocessor software for
LaModel, the coal seam was discretized using 5-ft. elements
(See Figure 10). A grid size of 1,200 x 800 elements or
6,000 x 4,000 ft. was selected to provide an ample buf-
fer against any potential edge effects. Boundary conditions
were modeled as symmetric on all sides.
The overlying overburden was discretized using 50-ft.
elements. A grid size of 160 x 120 elements or 8,000 x
6,000 ft. was selected resulting in a 1,000-ft. buffer around
the underlying seam grid. An overburden grid that is larger
than the seam grid is required in LaModel, and one that is
more than the overburden thickness away from the edge of
the seam grid reduces edge effects from the projection of
the overburden grid to the seam level.
CALIBRATION OF THE MODEL
It is well established that the calibration of input param-
eters for numerical models is of vital importance. In the
context of conducting a LaModel analysis, it is imperative
to note that the precision of the output is directly related
to the accuracy of the input parameters. These parameters
should be calibrated utilizing the most reliable data sources,
which could be measurements, observations, or empirically
derived. The critical parameters for accurate stress and load
calculations, and consequently pillar stability and safety
factors, are the rock mass stiffness, the gob stiffness, and
the coal strength. The parameters must be calibrated in the
order listed, with each subsequent parameter’s calibrated
value determined by the preceding ones (Heasley, 2008).
In the LaModel framework, the stiffness of the rock
mass is characterized by two key parameters: the rock mass
modulus and the lamination thickness (see Figure 11). By
adjusting these parameters, one can effectively alter the
stiffness of the overburden, which in turn affects the abut-
ment extent. In the context of this study, the rock mass
modulus was held constant at a value of 3,000,000 psi. The
lamination thickness, on the other hand, was adjusted to
align with the measured abutment extent. To match the
measured 200-ft. abutment extent at the edge of the panel,
a lamination thickness of 90 ft. was found to be necessary.
The calibrated lamination thickness is approximately 25%
Figure 9. Average BPC pressure for Sites 2 and 3 versus the
distance from the pillar line depicting the arrival of the front
abutment load, the peak pressure measured in the pillar, and
pillar yield.
Figure 10. Portion of the seam grid generated in LaModel
including pillars, openings, and gob areas.
Figure 11. Overburden layers indicating thickness, modulus,
and Poisson’s ratio.
turn our attention to the next crucial step in our study: cali-
brating the LaModel program to accurately represent and
further analyze the collected data.
BUILDING THE MODEL
The LaModel 3.0 program was selected to model the mea-
sured pillar behavior because its calibration procedures
are considered to be directly comparable to the widely
used ARMPS 2010 (Mark, 2010) and ACPS (Mark and
Agioutantis, 2018) programs.
Utilizing LAMPRE 4.0, the preprocessor software for
LaModel, the coal seam was discretized using 5-ft. elements
(See Figure 10). A grid size of 1,200 x 800 elements or
6,000 x 4,000 ft. was selected to provide an ample buf-
fer against any potential edge effects. Boundary conditions
were modeled as symmetric on all sides.
The overlying overburden was discretized using 50-ft.
elements. A grid size of 160 x 120 elements or 8,000 x
6,000 ft. was selected resulting in a 1,000-ft. buffer around
the underlying seam grid. An overburden grid that is larger
than the seam grid is required in LaModel, and one that is
more than the overburden thickness away from the edge of
the seam grid reduces edge effects from the projection of
the overburden grid to the seam level.
CALIBRATION OF THE MODEL
It is well established that the calibration of input param-
eters for numerical models is of vital importance. In the
context of conducting a LaModel analysis, it is imperative
to note that the precision of the output is directly related
to the accuracy of the input parameters. These parameters
should be calibrated utilizing the most reliable data sources,
which could be measurements, observations, or empirically
derived. The critical parameters for accurate stress and load
calculations, and consequently pillar stability and safety
factors, are the rock mass stiffness, the gob stiffness, and
the coal strength. The parameters must be calibrated in the
order listed, with each subsequent parameter’s calibrated
value determined by the preceding ones (Heasley, 2008).
In the LaModel framework, the stiffness of the rock
mass is characterized by two key parameters: the rock mass
modulus and the lamination thickness (see Figure 11). By
adjusting these parameters, one can effectively alter the
stiffness of the overburden, which in turn affects the abut-
ment extent. In the context of this study, the rock mass
modulus was held constant at a value of 3,000,000 psi. The
lamination thickness, on the other hand, was adjusted to
align with the measured abutment extent. To match the
measured 200-ft. abutment extent at the edge of the panel,
a lamination thickness of 90 ft. was found to be necessary.
The calibrated lamination thickness is approximately 25%
Figure 9. Average BPC pressure for Sites 2 and 3 versus the
distance from the pillar line depicting the arrival of the front
abutment load, the peak pressure measured in the pillar, and
pillar yield.
Figure 10. Portion of the seam grid generated in LaModel
including pillars, openings, and gob areas.
Figure 11. Overburden layers indicating thickness, modulus,
and Poisson’s ratio.