1
25-082
Slope Failures Involving Draglines: Lessons Learned from
Operational Experiences
Russell Sheets
Barr Engineering Co., Bismarck, ND
Lyall Workman
Barr Engineering Co., Bismarck, ND
Michael Haggerty
Barr Engineering Co., Minneapolis, MN
Jed Greenwood
Barr Engineering Co. Minneapolis, MN
INTRODUCTION
Draglines often work from a position on the active highwall
or spoil side bench to remove undisturbed waste material
and spoil in the previously mined pit. To protect the drag-
line crew members and the machine, it is necessary that the
highwall remain stable while the dragline is present on the
bench.
In the past several years, we have been involved in
determining the causes for highwall failures that included
the dragline. While there have been no injuries and limited
dragline damage with these incidents, the potential cer-
tainly exists for a more serious outcome.
In all cases, the operation had completed a geotech-
nical study to support the ground control plan and pit
designs. However, all these incidents included aspects that
would not likely have been identified in studies to deter-
mine highwall and spoil designs to support ground control
procedures. In general, these events included aspects that
were localized and would have been difficult to identify in
initial slope stability studies either observationally or dur-
ing the soil testing and modelling efforts.
Although the authors do not have quantitative evi-
dence of this, it does seem there has been an increased
number of events in recent years. This may be due to loss of
institutional knowledge, mining in more challenging areas,
or simply an increase in localized variation.
This paper will describe some of the issues we have seen
and what the causes of failure were. It becomes clear that
avoiding similar incidents in the future requires on-going
observation and inspection of active highwalls and spoil
benches to try and identify local variability and impact on
mining. The information can proactively be used to update
stability modeling of any concerning issues to determine
likelihood of problems and to develop solutions.
Recent Dragline Bench Failures
Several incidents of highwall instability that incorporated
a large, walking dragline are described in this section.
These examples are not intended to be detailed case studies
which would more appropriately require standalone papers.
Rather the examples demonstrate the range of variable
geologic conditions that locally impacted dragline bench
stability.
Example #1. Adverse Geologic Structure Intersects Dig
Sequence
For this situation, the highwall failure immediately beneath
the dragline resulted in the large walking dragline rest-
ing on the failed material and tilting downward about
21 degrees toward the open pit. The operator attempted to
walk the machine away from the unstable area. When the
dragline was on the shoes, significant ground movement
toward the pit occurred and the dragline tilted downward.
Subsequently, earthwork was completed to level the drag-
line and successfully walk it onto solid ground.
The failure occurred where the strike of the pit high-
wall changed from a near east-west alignment to a north-
west-southeast alignment. West of the inflection, the strike
appears to be about 110 degrees. A crack was observed,
after the failure occurred, running across the active mining
cut and under the dragline tub. The crack had a strike of
about 122 degrees. This crack was approximately linear and
intersected both the previous highwall and the edge of the
cut next to the new highwall (see Figure 1). The observed
25-082
Slope Failures Involving Draglines: Lessons Learned from
Operational Experiences
Russell Sheets
Barr Engineering Co., Bismarck, ND
Lyall Workman
Barr Engineering Co., Bismarck, ND
Michael Haggerty
Barr Engineering Co., Minneapolis, MN
Jed Greenwood
Barr Engineering Co. Minneapolis, MN
INTRODUCTION
Draglines often work from a position on the active highwall
or spoil side bench to remove undisturbed waste material
and spoil in the previously mined pit. To protect the drag-
line crew members and the machine, it is necessary that the
highwall remain stable while the dragline is present on the
bench.
In the past several years, we have been involved in
determining the causes for highwall failures that included
the dragline. While there have been no injuries and limited
dragline damage with these incidents, the potential cer-
tainly exists for a more serious outcome.
In all cases, the operation had completed a geotech-
nical study to support the ground control plan and pit
designs. However, all these incidents included aspects that
would not likely have been identified in studies to deter-
mine highwall and spoil designs to support ground control
procedures. In general, these events included aspects that
were localized and would have been difficult to identify in
initial slope stability studies either observationally or dur-
ing the soil testing and modelling efforts.
Although the authors do not have quantitative evi-
dence of this, it does seem there has been an increased
number of events in recent years. This may be due to loss of
institutional knowledge, mining in more challenging areas,
or simply an increase in localized variation.
This paper will describe some of the issues we have seen
and what the causes of failure were. It becomes clear that
avoiding similar incidents in the future requires on-going
observation and inspection of active highwalls and spoil
benches to try and identify local variability and impact on
mining. The information can proactively be used to update
stability modeling of any concerning issues to determine
likelihood of problems and to develop solutions.
Recent Dragline Bench Failures
Several incidents of highwall instability that incorporated
a large, walking dragline are described in this section.
These examples are not intended to be detailed case studies
which would more appropriately require standalone papers.
Rather the examples demonstrate the range of variable
geologic conditions that locally impacted dragline bench
stability.
Example #1. Adverse Geologic Structure Intersects Dig
Sequence
For this situation, the highwall failure immediately beneath
the dragline resulted in the large walking dragline rest-
ing on the failed material and tilting downward about
21 degrees toward the open pit. The operator attempted to
walk the machine away from the unstable area. When the
dragline was on the shoes, significant ground movement
toward the pit occurred and the dragline tilted downward.
Subsequently, earthwork was completed to level the drag-
line and successfully walk it onto solid ground.
The failure occurred where the strike of the pit high-
wall changed from a near east-west alignment to a north-
west-southeast alignment. West of the inflection, the strike
appears to be about 110 degrees. A crack was observed,
after the failure occurred, running across the active mining
cut and under the dragline tub. The crack had a strike of
about 122 degrees. This crack was approximately linear and
intersected both the previous highwall and the edge of the
cut next to the new highwall (see Figure 1). The observed