2
overhead, are designed using the supported case history
design curve. The ability to support the back allows for
larger hydraulic radii.
The limitation to this method and associated cable bolt
design charts, is that they do not specify how much of the
back must be supported using long support (typically cable
bolts). Figures 1 and 2 present a typical cable bolting layout
and stope layout respectively. If the back is not effectively
supported considering the site-specific conditions, then
raveling type failures along the stope shoulders can result
in total collapse of the stope back. Contributing factors in
stope shoulder stability include the following:
• Stope Dimensions (stope width, top cut width and
height, and stope orientation)
• Rock Quality
• Rock Density
• Joint Fabric (joint set orientations, lengths, spacing,
and joint in-fill)
• Installed Ground Support (type, amount, and orien-
tation of installed bolts)
• Induced Stresses
• Adjacent Mining (primary vs. secondary stopes)
CASE STUDY
An underground mine in the western United States experi-
enced recurring falls of ground where destabilization initi-
ated along the stope shoulders resulting in back collapse.
The following were the conditions unique to the site:
• Stopes designed at 35ft wide serviced by 16ft × 16ft
TC
• Stopes oriented East-West (90 Deg. Azimuth)
• Steeply dipping joint structures with lengths between
5 to 10ft, 1ft nominal spacing between joints
• Densities: skarn rock (240pcf) breccia (210pcf)
marble (181pcf)
• 8ft Swellex (12T) bolts installed in TC ribs (4ft s
4ft spacing) and back’ 20ft Cable Bolts (0.6in, twin
strand) installed in TC back (6ft × 6ft spacing)
The FOG mechanism was identified as a progressive
raveling failure where raveling initiated within the undercut
stope shoulder and advanced upwards above the installed
support until the back collapsed (Figure 3).
Forensic study of the multiple failures concluded that
stope shoulders in tension will fall under gravitational
Figure 1. Common Top Cut and Cable Bolting
Configuration Figure 2. Typical LHOS Layout
overhead, are designed using the supported case history
design curve. The ability to support the back allows for
larger hydraulic radii.
The limitation to this method and associated cable bolt
design charts, is that they do not specify how much of the
back must be supported using long support (typically cable
bolts). Figures 1 and 2 present a typical cable bolting layout
and stope layout respectively. If the back is not effectively
supported considering the site-specific conditions, then
raveling type failures along the stope shoulders can result
in total collapse of the stope back. Contributing factors in
stope shoulder stability include the following:
• Stope Dimensions (stope width, top cut width and
height, and stope orientation)
• Rock Quality
• Rock Density
• Joint Fabric (joint set orientations, lengths, spacing,
and joint in-fill)
• Installed Ground Support (type, amount, and orien-
tation of installed bolts)
• Induced Stresses
• Adjacent Mining (primary vs. secondary stopes)
CASE STUDY
An underground mine in the western United States experi-
enced recurring falls of ground where destabilization initi-
ated along the stope shoulders resulting in back collapse.
The following were the conditions unique to the site:
• Stopes designed at 35ft wide serviced by 16ft × 16ft
TC
• Stopes oriented East-West (90 Deg. Azimuth)
• Steeply dipping joint structures with lengths between
5 to 10ft, 1ft nominal spacing between joints
• Densities: skarn rock (240pcf) breccia (210pcf)
marble (181pcf)
• 8ft Swellex (12T) bolts installed in TC ribs (4ft s
4ft spacing) and back’ 20ft Cable Bolts (0.6in, twin
strand) installed in TC back (6ft × 6ft spacing)
The FOG mechanism was identified as a progressive
raveling failure where raveling initiated within the undercut
stope shoulder and advanced upwards above the installed
support until the back collapsed (Figure 3).
Forensic study of the multiple failures concluded that
stope shoulders in tension will fall under gravitational
Figure 1. Common Top Cut and Cable Bolting
Configuration Figure 2. Typical LHOS Layout