2010 Construction and Material Specifications - Ohio Department of ...

208.09
tolerances and produce a uniform slope. If more than 5 percent of the presplit
holes are misaligned in any one lift, reduce the depth of the lifts until the 12-inch
(300 mm) alignment tolerance is met.
G. If a cut height requires more than one lift or if there is a slope change (for
example, when changing from a 1:1 slope to a 0.75:1 slope), use a maximum 2foot
(0.6 m) offset between lifts for drill equipment clearances. Begin the presplit
blast hole drilling at a point that allows for the necessary offsets and adjust to
compensate for any drift that may occur in the upper lifts. Move the controlled
blast line back if required to accommodate for these conditions.
H. The Contractor may drill 2 feet (0.6 m) below ditch bottom to remove the toe
berm.
I. Before placing charges, determine if the hole is free of obstructions for its
entire depth. Exercise all necessary precautions so that the placing of the charges
will not cause caving of material from the walls of the holes.
J. Drill hole conditions may vary from dry to filled with water. Use whatever
types of explosives and/or blasting accessories necessary to accomplish the
specified results.
K. Use a maximum diameter of explosives that is not greater than one-half the
diameter of the presplit hole.
L. Do not use bulk ammonium nitrate and fuel oil (ANFO) in the presplit holes.
M. Use only standard explosives manufactured especially for presplitting in the
presplit holes.
N. If using a continuous column cartridge type of explosives with detonating
cord, assemble and affix the detonating cord according to the explosive
manufacturer’s instructions. Furnish a copy of the instructions to the Engineer.
O. The Contractor may make the bottom charge of a presplit hole larger than the
line charges but not large enough to cause overbreak. Place the top charge of the
presplitting far enough below the collar, and reduce the change sufficiently, to
avoid overbreaking and heaving.
P. Stem the upper portion of all presplit holes, from the top most charge to the
hole collar. Use stemming material conforming to the stemming specified for the
production holes in 208.06.
Q. As long as equally satisfactory presplit slopes are obtained, either presplit the
slope face before drilling for production blasting or presplit the slope face and
production blast at the same time, provided the presplitting drill holes are fired
first. If required to reduce ground vibrations or noise, delay the presplit holes,
except that the hole-to-hole delay must be less than 25 milliseconds.
R. Do not deviate the presplit slope face more than 1 foot (0.3 m) from a plane
passing through adjacent drill holes, except where the character of the rock is such
that irregularities are unavoidable. Measure the 1-foot (0.3 m) tolerance
perpendicular to the plane of the slope. Do not encroach on the roadbed with any
portion of the slope.
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