CIVIL ENGINEERING FORMULAS

SOIL AND EARTHWORK FORMULAS 201

determining the burden. The length of the burden relative to the depth of the cut
has a significant effect on fragmentation.

Langefors’ Formula Langefors suggested that the burden determination was
based on more factors, including diameter of hole, weight strength of explosives,
degree of packing, a rock constant, and the degree of fracture.
Langefors’ formula for burden determination is

(8.64)

where Vburden, m
dbdiameter of drill bit, mm
Pthe degree of packing 1.0 to 1.6 kg/dm^3
sweight strength of explosive (1.3 for gelatin)
rock constant, generally 0.45
f1 degree of fraction, for straight hole  1
Espacing
E/Vratio of spacing to burden

Konya Formula Currently the best formula for burden determination is one
developed by C. J. Konya. This formula uses the diameter of the explosives in
relation to the specific gravity of the explosive and of the rock.
The Konya formula is

(8.65)

where Bburden, ft
Dediameter of the explosive, in
SGespecific gravity of the explosive
SGrspecific gravity of the rock

The optimum length-to-burden ratio (L/B) is 3.

Spacing Determination

The spacing is calculated in relation to the burden length; that is, it is necessary
to complete the burden calculations before determining the spacing. Spacing is
the distance between blast holes fired, on the same delay or greater delay, in the
same row.
For a single-row instantaneous blast, the spacing is usually 1.8 times the bur-
den; that is, for a burden of 5 ft (1.5 m) the spacing would be 9 ft (2.7 m). For
multiple simultaneous (same-delay) blasting where the ratio of length of bore-
hole to burden (L/B) is less than 4, the spacing can be determined by the formula

SBL (8.66)

B3.15 De

B

3 SGe

SGr

c

V(db33)

B

Ps

cf(EV)