50 • ROCK products • August 2016 www.rockproducts.com
– 3.33 ft.). This gives a total powder
column of 26.67 ft. which will be
loaded with detonating cord of
850 grains per ft. This is a total of
22,700 grains of detonating cord
per hole.
Once converting the detonating
cord from grains to lb. (3.24 lb.) and
adding a ½ lb. booster in the bottom
of the hole, the total explosive load
per hole is 3.74 lb. per delay. From
this the air overpressure and ground
vibration scaled distances can be cal-
culated. These are:
Using the environmental prediction
graphs (Figure 2 and 3) one can pre-
dict the maximum air overpressure
and ground vibration.
• Maximum Air Overpressure =
128 Db.
• Maximum Ground Vibration =
Less than 0.2 in. per second.
This also illustrates how in a pre-
cision presplit the concern, in
general, is not the ground vibration
but the air overpressure.
In this final article on precision
presplitting, graphs have been
given to estimate the explosive
load at any multiple spacing dis-
tances in different rock types.
The presplit constant (K) has also
been given for various rock types.
If a presplit is desired in differ-
ent rock types the coefficient
and explosive load curve can be
estimated based on the young's
modulus of the rock.
In addition to the explosive load
chart, predictions for air overpres-
sure and ground vibration from a
precision presplit have also been
discussed. In the example shown,
it is mentioned that the major envi-
ronmental concern from precision
presplitting is not the ground
vibration but the air overpressure.
Dr. Calvin Konya is the president
of Precision Blasting Services, and
Anthony Konya is a project engineer
for the company.
Precision Presplitting