6
has been extracted, the well is plugged up to the sensor
installation depth at roughly 1000ft. A fabricated lowering
assembly is recommended when installing the sensor as it
assists in vertical orientation within the casing and provides
an attachment point for a steel winch cable. This method
also allows for a safe and controlled decent, while provid-
ing support to the sensors data cable. Typical installation
procedures are as follows:
• Prepare/Fabricate a lowering assembly.
• Insert the sensor body into the assembly and tighten
the set screws to secure it.
• Attach 1/8” stainless steel cable to lowering assembly.
• Insure adequate winch cable for installation depth.
• If data cable needs extended, create watertight splice
as needed.
• Attach marking tags in 100ft increments to the data
cable.
• Install sensor into well casing and lower using a
power winch.
• Attached data cable to stainless steel cable with cable
ties at the 100ft marking tags.
• Lower until sensor reaches desired depth.
• Secure stainless-steel cable at the surface to support
the hanging assembly.
• Fill the well casing with grout to encapsulate the
sensor.
• Data cable is attached to a seismograph and continu-
ously monitored.
Historically, NIOSH researchers have used other geo-
phone and accelerometer offerings such as those from ESG
Solutions (ESG Solution, n.d.) and others. There are sev-
eral commercially available sensors on the market, some of
which may be better suited to other applications such as
microseismics, in mine installation, etc.
ROCK STRESS INSTRUMENTATION
Vibrating Wire Biaxial Stressmeters
Vibrating wire biaxial stressmeters measure the change
in strain in the surrounding rockmass. Due to its biaxial
orientation, this allows the change in principle stresses to
be calculated simultaneously. Currently, NIOSH uses the
GEOKON Model 4350 Biaxial Stressmeter (see Figure 11)
is designed to measure changes in stress in hard rocks, rock-
salt, potash, concrete, ice, and other elastic and viscoelastic
materials (GEOKON, 2023).
The sensor is commonly positioned in proximity to
active mining zones or regions anticipated to experience
stress fluctuations, aiming to quantify the stress changes
within the surrounding mine strata. This information can
be used on its own to infer the state of stress redistribution
or in conjunction with other methods, such as numerical
modeling, to validate or provide additional context (Slaker
et al., 2020 Zahl et al., 2002).
The sensor is designed as a thick-walled steel cylinder,
which is grouted in a borehole or embedded in the material
to be studied. Utilizing either three or six vibrating wire
strain gauges, radial deformations of the cylinder are cap-
tured. Through the application of derived theoretical equa-
tions, the corresponding stress variations are calculated. The
Figure 10. Photo depicting the initial installation of an IMS
Model 3G14 geophone into a gas well
Figure 11. GEOKON Model 4350 Biaxial Stressmeter (after
GEOKON, 2023)
has been extracted, the well is plugged up to the sensor
installation depth at roughly 1000ft. A fabricated lowering
assembly is recommended when installing the sensor as it
assists in vertical orientation within the casing and provides
an attachment point for a steel winch cable. This method
also allows for a safe and controlled decent, while provid-
ing support to the sensors data cable. Typical installation
procedures are as follows:
• Prepare/Fabricate a lowering assembly.
• Insert the sensor body into the assembly and tighten
the set screws to secure it.
• Attach 1/8” stainless steel cable to lowering assembly.
• Insure adequate winch cable for installation depth.
• If data cable needs extended, create watertight splice
as needed.
• Attach marking tags in 100ft increments to the data
cable.
• Install sensor into well casing and lower using a
power winch.
• Attached data cable to stainless steel cable with cable
ties at the 100ft marking tags.
• Lower until sensor reaches desired depth.
• Secure stainless-steel cable at the surface to support
the hanging assembly.
• Fill the well casing with grout to encapsulate the
sensor.
• Data cable is attached to a seismograph and continu-
ously monitored.
Historically, NIOSH researchers have used other geo-
phone and accelerometer offerings such as those from ESG
Solutions (ESG Solution, n.d.) and others. There are sev-
eral commercially available sensors on the market, some of
which may be better suited to other applications such as
microseismics, in mine installation, etc.
ROCK STRESS INSTRUMENTATION
Vibrating Wire Biaxial Stressmeters
Vibrating wire biaxial stressmeters measure the change
in strain in the surrounding rockmass. Due to its biaxial
orientation, this allows the change in principle stresses to
be calculated simultaneously. Currently, NIOSH uses the
GEOKON Model 4350 Biaxial Stressmeter (see Figure 11)
is designed to measure changes in stress in hard rocks, rock-
salt, potash, concrete, ice, and other elastic and viscoelastic
materials (GEOKON, 2023).
The sensor is commonly positioned in proximity to
active mining zones or regions anticipated to experience
stress fluctuations, aiming to quantify the stress changes
within the surrounding mine strata. This information can
be used on its own to infer the state of stress redistribution
or in conjunction with other methods, such as numerical
modeling, to validate or provide additional context (Slaker
et al., 2020 Zahl et al., 2002).
The sensor is designed as a thick-walled steel cylinder,
which is grouted in a borehole or embedded in the material
to be studied. Utilizing either three or six vibrating wire
strain gauges, radial deformations of the cylinder are cap-
tured. Through the application of derived theoretical equa-
tions, the corresponding stress variations are calculated. The
Figure 10. Photo depicting the initial installation of an IMS
Model 3G14 geophone into a gas well
Figure 11. GEOKON Model 4350 Biaxial Stressmeter (after
GEOKON, 2023)