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NIOSH Highwall Safety Project
In October of 2021, the Geomechanics Team at the
National Institute for Occupational Safety and Health
(NIOSH) Spokane Mining Research Division (SMRD)
started the Highwall Safety project, which will run for 5
years. This project is a continuation of a pilot project con-
ducted by Warren et al. [10] where one of the main goals is
to quantify the performance of available criterion for rock-
fall catchment bench design in a variety of bench configura-
tions and optimize said criterion based on field calibration.
As shown in Equation 1, the MRC only considers bench
height in determining catch bench width however, field
testing and statistical analysis programs show that addi-
tional variables related to geology and operational practices
play a role in rockfall runout distance and necessary catch
bench width.
In 2022, researchers within the NIOSH Highwall
Safety project team conducted a numerical sensitivity
analysis using RocFall 2D looking into the various factors
that influence how far rocks roll on a single bench to gain
insight into required catch bench width to achieve safe
mining conditions [11]. The conclusions gathered from the
RocFall sensitivity analysis study included the following:
• Bench height and bench face angle are the dominant
factors in forecasting runout distance compared to
slope material type and rock size/shape with some
cases showing bench face angle having more influ-
ence in forecasting rockfall runout distance than
bench height
• Modeling does not effectively capture the effect of
rock size on runout distance
• The coefficient of restitution plays a minor role in
predicting rockfall runout distance when compared
to bench configuration (height/angle) however, it
does influence runout distance and
• The MRC rockfall catchment performance can vary
widely over different bench configurations, from
very good (100%) to poor (1%–2%) rockfall catch-
ment depending on the model used (lump mass ver-
sus rigid body).
The next step in the NIOSH Highwall Safety project’s
research agenda was to confirm the statistical modeling
data with real-world rockfall studies, requiring the develop-
ment of a rockfall testing program, which is the focus of
this paper.
NIOSH ROCKFALL TESTING PROGRAM
There are several components to the NIOSH rockfall
testing program including mine scouting and safety plan
development, equipment requirements, synthetic rock
development for uniform testing across varying bench
configurations, local rock collection for testing of mine-
specific geology, data acquisition during testing, and data
processing.
Mine Scouting and Safety Plan Development
The most crucial element to successful empirical rockfall
testing at a mine site is detailed scouting and safety plan-
ning. This allows for the gathering of runout data that is
most useful to each individual mine site and allows the
opportunity for proper identification of associated hazards
with each rockfall test. To start, a trip is planned by the
researchers on the Highwall Safety project team to visit the
collaborating mine site and work with the mine staff to
review what site safety requirements are needed to conduct
rockfall testing while staying in compliance with MSHA
standards and additional safety standards specific to the
individual site. The NIOSH researchers visiting the site will
undergo sites training if necessary for that trip, while the
rest of the team will undergo sites training when they arrive
for the testing dates. From there, the collaborating team will
review maps of the open pits in question for rockfall testing
and drive to the pits to further analyze the potential for suc-
cessful testing. Bench configurations to be tested are subject
to the desire of the mine staff which usually includes a mix
of single bench testing for runout analysis and full highwall
testing for bench catchment analysis.
If allowed, NIOSH researchers will send 6-inch syn-
thetic rocks down the slope of the chosen test locations to
establish rockfall trajectory and an approximate landing
area. This helps in developing a site safety plan, identify-
ing the ideal rock drop location, the rock trajectory, and a
safe location of an observation area for camera recording of
the rockfall tests. A drone flight of each testing location is
acquired by NIOSH researchers using their own equipment
to develop a photogrammetry model for planning purposes.
An example of a rockfall test safety planning schematic with
chosen zoning locations is shown in Figure 1.
After the site visit, a rockfall testing proposal plan is
developed by the NIOSH Highwall Safety project team
outlining the following:
NIOSH Highwall Safety Project
In October of 2021, the Geomechanics Team at the
National Institute for Occupational Safety and Health
(NIOSH) Spokane Mining Research Division (SMRD)
started the Highwall Safety project, which will run for 5
years. This project is a continuation of a pilot project con-
ducted by Warren et al. [10] where one of the main goals is
to quantify the performance of available criterion for rock-
fall catchment bench design in a variety of bench configura-
tions and optimize said criterion based on field calibration.
As shown in Equation 1, the MRC only considers bench
height in determining catch bench width however, field
testing and statistical analysis programs show that addi-
tional variables related to geology and operational practices
play a role in rockfall runout distance and necessary catch
bench width.
In 2022, researchers within the NIOSH Highwall
Safety project team conducted a numerical sensitivity
analysis using RocFall 2D looking into the various factors
that influence how far rocks roll on a single bench to gain
insight into required catch bench width to achieve safe
mining conditions [11]. The conclusions gathered from the
RocFall sensitivity analysis study included the following:
• Bench height and bench face angle are the dominant
factors in forecasting runout distance compared to
slope material type and rock size/shape with some
cases showing bench face angle having more influ-
ence in forecasting rockfall runout distance than
bench height
• Modeling does not effectively capture the effect of
rock size on runout distance
• The coefficient of restitution plays a minor role in
predicting rockfall runout distance when compared
to bench configuration (height/angle) however, it
does influence runout distance and
• The MRC rockfall catchment performance can vary
widely over different bench configurations, from
very good (100%) to poor (1%–2%) rockfall catch-
ment depending on the model used (lump mass ver-
sus rigid body).
The next step in the NIOSH Highwall Safety project’s
research agenda was to confirm the statistical modeling
data with real-world rockfall studies, requiring the develop-
ment of a rockfall testing program, which is the focus of
this paper.
NIOSH ROCKFALL TESTING PROGRAM
There are several components to the NIOSH rockfall
testing program including mine scouting and safety plan
development, equipment requirements, synthetic rock
development for uniform testing across varying bench
configurations, local rock collection for testing of mine-
specific geology, data acquisition during testing, and data
processing.
Mine Scouting and Safety Plan Development
The most crucial element to successful empirical rockfall
testing at a mine site is detailed scouting and safety plan-
ning. This allows for the gathering of runout data that is
most useful to each individual mine site and allows the
opportunity for proper identification of associated hazards
with each rockfall test. To start, a trip is planned by the
researchers on the Highwall Safety project team to visit the
collaborating mine site and work with the mine staff to
review what site safety requirements are needed to conduct
rockfall testing while staying in compliance with MSHA
standards and additional safety standards specific to the
individual site. The NIOSH researchers visiting the site will
undergo sites training if necessary for that trip, while the
rest of the team will undergo sites training when they arrive
for the testing dates. From there, the collaborating team will
review maps of the open pits in question for rockfall testing
and drive to the pits to further analyze the potential for suc-
cessful testing. Bench configurations to be tested are subject
to the desire of the mine staff which usually includes a mix
of single bench testing for runout analysis and full highwall
testing for bench catchment analysis.
If allowed, NIOSH researchers will send 6-inch syn-
thetic rocks down the slope of the chosen test locations to
establish rockfall trajectory and an approximate landing
area. This helps in developing a site safety plan, identify-
ing the ideal rock drop location, the rock trajectory, and a
safe location of an observation area for camera recording of
the rockfall tests. A drone flight of each testing location is
acquired by NIOSH researchers using their own equipment
to develop a photogrammetry model for planning purposes.
An example of a rockfall test safety planning schematic with
chosen zoning locations is shown in Figure 1.
After the site visit, a rockfall testing proposal plan is
developed by the NIOSH Highwall Safety project team
outlining the following: