4
of roof separation and movement between the varying
strata (see Figure 5). The typical multipoint roof extensom-
eter consists of four anchor points, although six-point and
eight-point versions have been implemented in the past.
Historically, anchor locations have been selected based on
anchorage horizons of the primary and secondary support
(Klemetti et al., 2017). The best practices and installation
procedures are as follows:
• Find a flat section of roof free of dips or protruding
rocks to ensure a secure attachment of the extensom-
eter enclosure.
• Using the roof bolting machine, drill a 1-3/8” hole to
the deepest anchor depth.
• Once the hole is drilled, install the corresponding
anchors at the predetermined depths with an inser-
tion rod, starting with the deepest anchor first.
• After all the anchors are installed, the anchor wires
must be fed through the 1-¼” mounting pipe.
• The mounting pipe will then be coated in PLEXUS
MA300 (ITW Performance Polymers, 2022) or sim-
ilar epoxy and pushed up into the hole, securing the
extensometer box to the roof. Wooden wedges can be
used to help secure the pipe inside the hole until the
epoxy is cured (see Figure 6).
• Attach the labeled anchor wire to its corresponding
eyelet on the roof extensometer box using a metal
wire crimp. Pull the eyelet about ¼” out and secure
the metal crimp, removing any slack in line and cre-
ating adequate line tension.
• Once all anchor points are connected, initial zero
readings should be recorded.
Multipoint Borehole Extensometers (MPBX)
The multipoint borehole extensometer (MPBX) is a geo-
technical instrument designed to monitor changes in the
distance between downhole anchors, each set at a speci-
fied depth in the borehole with a measurement head at the
mouth of the hole. Typically installed into the pillar or rib,
the MPBX applications in mines include but are not lim-
ited to being used:
• to study the deformation of the roof and rib of a
mine during an excavation (Rashed et al., 2021),
• to examine the effectiveness of roof and rib support
systems,
• to determine the potential for roof and rib
instabilities.
NIOSH researchers are currently using the MPBX pro-
duced by Mine Design Technologies, Inc. (MDT) (Mine
Design Technologies, 2018). Therefore, the following
installation procedures are applicable for the MDT, Inc.
brand of MPBX. Figure 7 shows the key components of the
MPBX produced by MDT. The installation procedure used
Figure 4. Rendering of the NIOSH custom multipoint roof
extensometer utilizing four anchor points
Figure 5. Cross-section view of an installed 4-point roof
extensometer depicting anchor horizons in the roof
Figure 6. Installation of a multipoint roof extensometer
depicting the insertion of mounting pipe into the borehole
and securing with wedges
of roof separation and movement between the varying
strata (see Figure 5). The typical multipoint roof extensom-
eter consists of four anchor points, although six-point and
eight-point versions have been implemented in the past.
Historically, anchor locations have been selected based on
anchorage horizons of the primary and secondary support
(Klemetti et al., 2017). The best practices and installation
procedures are as follows:
• Find a flat section of roof free of dips or protruding
rocks to ensure a secure attachment of the extensom-
eter enclosure.
• Using the roof bolting machine, drill a 1-3/8” hole to
the deepest anchor depth.
• Once the hole is drilled, install the corresponding
anchors at the predetermined depths with an inser-
tion rod, starting with the deepest anchor first.
• After all the anchors are installed, the anchor wires
must be fed through the 1-¼” mounting pipe.
• The mounting pipe will then be coated in PLEXUS
MA300 (ITW Performance Polymers, 2022) or sim-
ilar epoxy and pushed up into the hole, securing the
extensometer box to the roof. Wooden wedges can be
used to help secure the pipe inside the hole until the
epoxy is cured (see Figure 6).
• Attach the labeled anchor wire to its corresponding
eyelet on the roof extensometer box using a metal
wire crimp. Pull the eyelet about ¼” out and secure
the metal crimp, removing any slack in line and cre-
ating adequate line tension.
• Once all anchor points are connected, initial zero
readings should be recorded.
Multipoint Borehole Extensometers (MPBX)
The multipoint borehole extensometer (MPBX) is a geo-
technical instrument designed to monitor changes in the
distance between downhole anchors, each set at a speci-
fied depth in the borehole with a measurement head at the
mouth of the hole. Typically installed into the pillar or rib,
the MPBX applications in mines include but are not lim-
ited to being used:
• to study the deformation of the roof and rib of a
mine during an excavation (Rashed et al., 2021),
• to examine the effectiveness of roof and rib support
systems,
• to determine the potential for roof and rib
instabilities.
NIOSH researchers are currently using the MPBX pro-
duced by Mine Design Technologies, Inc. (MDT) (Mine
Design Technologies, 2018). Therefore, the following
installation procedures are applicable for the MDT, Inc.
brand of MPBX. Figure 7 shows the key components of the
MPBX produced by MDT. The installation procedure used
Figure 4. Rendering of the NIOSH custom multipoint roof
extensometer utilizing four anchor points
Figure 5. Cross-section view of an installed 4-point roof
extensometer depicting anchor horizons in the roof
Figure 6. Installation of a multipoint roof extensometer
depicting the insertion of mounting pipe into the borehole
and securing with wedges