Highwall stability improvement through less blast vibration and displacement
Document type: Case Study

CASE STUDY

HIGHWALL STABILITY IMPROVEMENT THROUGH
LESS BLAST VIBRATION AND DISPLACEMENT
 After shooting a signature hole, delay times were chosen
 BACKGROUND to minimize vibration and particle displacement. A blast
 was divided into two sections. A seismograph was set
HIGHWALL DETERIORATION LEADS TO up 523 feet behind each shot. The first section was
POTENTIAL HAZARDS shot with delay times derived from DYNO 42 software
 analysis with a priority of reducing overall vibration and
At this Western U.S. surface coal mine, cast blasting is displacement while still maintaining nominal cast results.
done in all dragline pits. Bench heights are from 150 feet The other section was shot using progressive timing that
to 200 feet. The geology consists of clay, shale, sand, coal was chosen by a competitor for maximizing cast with no
rider seams, and occasional rock lenses. Water conditions regard to resultant vibration effects near field or far field.
vary from dry to severe.

Due to the above mentioned conditions coupled with
sleep time from start of loading to blast time, highwall
deterioration may occur. This poses a hazard to those
working under the wall during the coal drilling, blasting,
and removal. Damage to the highwall from blasting is
often cited as a contributing factor to highwall instability.

In an effort to minimize highwall damage associated with
blasting operations, vibration reduction has been sought
as a means to reduce damage to the new highwall created
by each cast blast.

TECHNOLOGY APPLIED
DYNO 42 SOFTWARE WAS USED TO PICK
THE BEST DELAY SEQUENCE THUS
REDUCING THE POTENTIAL DAMAGE TO THE
HIGHWALL
Current delay sequences have been chosen based on
giving good effective cast performance. The impact of
vibration was only addressed if there were engineered
structures such as power transformer stations or gas
wells in the area.

Usually peak particle velocity (PPV) was the only vibration
measurement that was considered. Now, particle
displacement is being reviewed with respect to influence
on final highwall conditions post blast.

CASE STUDY

RESULTS
DYNO 42 SOFTWARE ADDS VALUE BY
REDUCING PPV AND DISPLACEMENT
The first shot that used the DYNO 42 software had PPV
of 7.84 inches per second. Displacement was .40 inches.
The second shot that used progressive timing had a PPV
of 9.84 inches per second. Displacement was .52 inches.
There was no appreciable difference in effective cast
benefit. The results of this test indicated an approximate
reduction in peak particle velocity and associated particle
displacement of twenty percent (20%), again with no
discernable impact on effective cast.

NEXT STEPS
VIBRATION MEASUREMENTS WILL BE TAKEN
AT THE NEW HIGHWALL, APPROXIMATELY 40
FEET BEHIND THE BACK ROW OF THE CAST
An 80 inch per second geophone will be buried behind
the cast where the new highwall will be. The seismograph
reading will be a baseline. Future shots will use DYNO 42
software to choose delay sequences that should reduce
vibration. Wall stability will be watched for any changes.

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document or the information contained herein. User assumes sole responsibility for all results and consequences. © 2020 Dyno Nobel