12
The FLAC3D models suggest that cutter failure primar-
ily impacts the roof at the face when using the flat-front
cutting method. However, with the arrowhead cutting
method, high horizontal stress affects both the face and the
sides of the unmined side, as illustrated in Figure 16. Based
on field observations and model results, it is recommended
to advance the face using the flat-front method when the
roof is subjected to high horizontal stress.
When the maximum horizontal stress is perpendicu-
lar to the headings, outer headings experience more yield
than inner ones, as illustrated in Figure 17. This figure
depicts the yield pattern from the FLAC3D model. In the
flat-front method, cutter failure occurs in the roof at the
sidewall locations while the face remains unaffected. In
contrast, the arrowhead method results in failure at both
the front face and the unmined sidewall, with significantly
higher failure magnitudes.
EFFECT OF CROSSCUT DEVELOPMENT
METHODS ON ROOF STABILITY
At Subtropolis Mine, two methods are used for crosscut
development:
1. Method 1: A crosscut is developed from an exist-
ing entry, then the newly developed crosscut is
used to create another entry. In this case, the cross-
cut becomes longer as it includes both the length
of the crosscut and the width of the newly devel-
oped entry. The rock in the extended crosscuts
requires four cuts for excavation. The encircled
numbers indicate the cutting sequence, as illus-
trated in Figure 18: Entry 1 was excavated in cut
1, the crosscut was excavated in cuts 2, 3, 4, and 5,
and Entry 2 was excavated in cut 6.
2. Method 2: A crosscut is developed by connect-
ing two existing entries. the rock in the crosscut is
excavated in two cuts. Entry 1 was excavated in cut
1, Entry 2 was excavated in cut 2, and the crosscut
was excavated in cuts 3 and 4.
The stability of a newly developed crosscut (Method 1
versus Method 2) was analyzed using a numerical model,
with results validated against field observations. The thick-
ness of the caprock used in these models is 4 ft (1.2 m).
There was strong agreement between the field observa-
tions and the FLAC3D model results. It was found that
Figure 16. Yield patterns from the strain-softening FLAC3D
model for (a) flat-front mining and (b) arrowhead mining in
advancing headings. Red areas indicate zones of yielding
Figure 17. Yield patterns for flat-front and arrowhead
advance based on the FLAC3D model, with yielded regions
highlighted in red when the maximum horizontal stress is
perpendicular to the headings
The FLAC3D models suggest that cutter failure primar-
ily impacts the roof at the face when using the flat-front
cutting method. However, with the arrowhead cutting
method, high horizontal stress affects both the face and the
sides of the unmined side, as illustrated in Figure 16. Based
on field observations and model results, it is recommended
to advance the face using the flat-front method when the
roof is subjected to high horizontal stress.
When the maximum horizontal stress is perpendicu-
lar to the headings, outer headings experience more yield
than inner ones, as illustrated in Figure 17. This figure
depicts the yield pattern from the FLAC3D model. In the
flat-front method, cutter failure occurs in the roof at the
sidewall locations while the face remains unaffected. In
contrast, the arrowhead method results in failure at both
the front face and the unmined sidewall, with significantly
higher failure magnitudes.
EFFECT OF CROSSCUT DEVELOPMENT
METHODS ON ROOF STABILITY
At Subtropolis Mine, two methods are used for crosscut
development:
1. Method 1: A crosscut is developed from an exist-
ing entry, then the newly developed crosscut is
used to create another entry. In this case, the cross-
cut becomes longer as it includes both the length
of the crosscut and the width of the newly devel-
oped entry. The rock in the extended crosscuts
requires four cuts for excavation. The encircled
numbers indicate the cutting sequence, as illus-
trated in Figure 18: Entry 1 was excavated in cut
1, the crosscut was excavated in cuts 2, 3, 4, and 5,
and Entry 2 was excavated in cut 6.
2. Method 2: A crosscut is developed by connect-
ing two existing entries. the rock in the crosscut is
excavated in two cuts. Entry 1 was excavated in cut
1, Entry 2 was excavated in cut 2, and the crosscut
was excavated in cuts 3 and 4.
The stability of a newly developed crosscut (Method 1
versus Method 2) was analyzed using a numerical model,
with results validated against field observations. The thick-
ness of the caprock used in these models is 4 ft (1.2 m).
There was strong agreement between the field observa-
tions and the FLAC3D model results. It was found that
Figure 16. Yield patterns from the strain-softening FLAC3D
model for (a) flat-front mining and (b) arrowhead mining in
advancing headings. Red areas indicate zones of yielding
Figure 17. Yield patterns for flat-front and arrowhead
advance based on the FLAC3D model, with yielded regions
highlighted in red when the maximum horizontal stress is
perpendicular to the headings