Analysis of Hangups and Structural Failure
in Underground Mine Ore Passes

Objective

Develop field measurement and computer modeling methods to
predict the potential for hang-ups and structural failures in un-
derground mine ore passes.

Background

Analysis of Mine Safety and Health Administration (MSHA) ac-
cident statistics has identified ore pass hazards as a significant
safety problem in underground metal mines in the United States,
Recent ore pass failures have underlined the lack of ore pass design
methods and standards available to both MSHA and mine en-
gineers. Injury and fatality data for the 20-year period between
1975 and 1995 show that nearly 75% of the injuries were directly
or indirectly related to pulling or freeing ore pass chutes, the use of
hand tools, falls of broken rock, and structural failures of chutes or
gates and ore pass walls,

Risk assessment methods, such as fault tree analysis (FTA), re-
vealed the most probable causes of ore pass failures, assisted in
defining research priorities, and allowed analyses of the causes of
malfunctioning ore passes. Important structural design factors are
the static and dynamic loads that ore pass chutes and gates must
withstand, Functional design factors may involvé considerations
of malfunctions in material flow, such as hang-ups, piping, and
water inundations.

Approach

Static and dynamic loads were measured on an underground ore
pass and truck chute (figure 1). The weight of material dumped in

the ore pass was in excess of 27,300 kg (60,000 Ib); however, a
maximum static load of only 6,800 kg (15,000 Ib) was measured,
which was approximately the weight of the waste material needed
to fill the chute itself. The rest of the static load was carried by the
ore pass walls and the timbers adjacent to the chute.

A three-dimensional particle flow code was used to predict the
static and dynamic loads resulting from the flow and impact of
material on the control gate in an ore pass chute. Figure 2 shows
total static and dynamic loads normal to the chute gate after a
typical dump from a load-haul-dump (LHD) unit. The load re-
sponse from 14 dumps is shown in figure 3. Analysis of the initial
time steps indicated that dynamic loads were a factor on the control
gate only during the first few dumps. Dynamic load factors ranged
from 1.06 to 1.33 on the chute and gate assembly and were reduced
significantly because the chute was offset from the ore pass. The
accumulated calculated loads on the control gate after the first 14
loads were compared to results from the actual field test. Total
calculated static load exceeded actual load for a full muck chute by
about four times, considering just the cross-sectional area exposed
to the muck carried by the support bolts.

‘The combination of numerical modeling, scaled experiments, and
full-scale testing have provided a methodology to determine static
and dynamic loads involved in ore pass failures. Research is
continuing to evaluate methods that will increase awareness of the
proper functioning of mine ore passes, warn of potentially dan-
gerous situations, and improve hang-up removal techniques.

Patent Status

An invention report has been filed for a device to determine hang-
up location in ore passes.

2 % U.S. Department of Health and Human Services

i Public Health Service

% Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health

CDC

(CENTERS FOR DISEASE CONTROL


For More Information

NIOSH is seeking cooperators to assist in further study of mine
ore pass safety issues. Additional information can be obtained by
contacting Bill Stewart at (509) 354-8064, Steve Iverson at (509)
354-8089, or Elaine Cullen, technology transfer officer, at 354-
8057, Spokane Research Laboratory, Spokane, WA, 99207

Mention of any company name or product does not constitute
endorsement by the National Institute for Occupational Safety and
Health.

To receive additional information about mining issues or
other occupational safety and health problems, call 1-800-
35-NIOSH (1-800-356-4674), or visit the NIOSH
Home Page on the World Wide Web at hitp:/Awww.cde.
gov/niosh/homepage.html

As of October 1996 the safety and health research functions
of the former U.S. Bureau of Mines are now located in the
National Institute for Occupational Safety and Health
(NIOSH).

‘Muck in ore pass

Ore chute

To
at control gate

for transport
to surface

Figure 1.—An ore pass system used for fiold tests and PFCTM
modeling.

ind
ec

LOAD, 10° kg
&

Initial impact from
leading edge of
muck column
: 1

@

=

CBee eG S40 aA
IMPACT TIME, sec

Figure 2.—Plot of normal loads on chute gate from one LHD dump.

=
Pr
&

2 D>
x
Pa 30
25 2 2
Qs 2 2
°
3}| 15 C|
2.|I KEY ral
S2 10 W
> — Actual load a
Q1 Model load (3
<=

0 0

0 20 40 60 80 100 120 140

IMPACT TIME, sec
Figure 3.—Plot of calculated and actual loads on chute gate

following 14 LHD dumps.