3
Typically, a mine will find the orientation of the prin-
cipal horizontal stress at or near to the regional horizontal
stress. At the Subtropolis Mine, the principal horizontal
stress differs from the regional horizontal stress and can
even differ across the mine itself. Evidence to support these
changes in the principal horizontal stress direction come in
the form of cutter roof failures and oval-shaped roof falls
oriented in different directions in specific areas of the mine.
The principal horizontal stress direction at this mine tends
to be generally N35W.
Roof falls at this mine fit the same characteristics of
examples of high horizontal stress found at other lime-
stone operations. Roof instabilities typically begin with the
development of compression zones consisting of low-angle
shears in a consistent orientation. When the roof falls occur,
many of them are oval in shape with the long axis oriented
in the same direction as the shears (Iannacchione et al.,
2001). Figure 4 details the mechanism of failure typically
seen at Subtropolis Mine. When layered strata are subjected
Figure 2. Subtropolis Mine Map with massive roof collapse
area circled in red
Figure 3. Subtropolis Mine Map with varying heading
orientations
Figure 4. Generalized sequence in which individual roof beams fail and develop into large roof
falls under elevated horizontal stress conditions (Iannacchione et al., 2005)
Typically, a mine will find the orientation of the prin-
cipal horizontal stress at or near to the regional horizontal
stress. At the Subtropolis Mine, the principal horizontal
stress differs from the regional horizontal stress and can
even differ across the mine itself. Evidence to support these
changes in the principal horizontal stress direction come in
the form of cutter roof failures and oval-shaped roof falls
oriented in different directions in specific areas of the mine.
The principal horizontal stress direction at this mine tends
to be generally N35W.
Roof falls at this mine fit the same characteristics of
examples of high horizontal stress found at other lime-
stone operations. Roof instabilities typically begin with the
development of compression zones consisting of low-angle
shears in a consistent orientation. When the roof falls occur,
many of them are oval in shape with the long axis oriented
in the same direction as the shears (Iannacchione et al.,
2001). Figure 4 details the mechanism of failure typically
seen at Subtropolis Mine. When layered strata are subjected
Figure 2. Subtropolis Mine Map with massive roof collapse
area circled in red
Figure 3. Subtropolis Mine Map with varying heading
orientations
Figure 4. Generalized sequence in which individual roof beams fail and develop into large roof
falls under elevated horizontal stress conditions (Iannacchione et al., 2005)