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

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208.07
E. Maintain a stemming depth of at least 0.7 times the burden distance. If water
is present or when blasting within 200 feet (61 m) of a structure, use crushed No. 8
coarse aggregate for holes less than 4 inches (100 mm) in diameter and crushed
No. 57 coarse aggregate for holes 4 inches (100 mm) in diameter and larger for the
stemming material. Use the coarse aggregate gradations of Nos. 8 and 57
gradations on Table 703.01-1. If gravel is used, use crushed material with a
minimum of two mechanically fractured faces on 60 percent of the material. In
other locations, the Contractor may use drill cuttings for stemming, if it does not
compromise the shot integrity.
F. Take all necessary precautions in the production blasting to minimize blast
damage to the rock backslope.
G. Drill a line of buffer holes on a parallel plane adjacent to the presplit holes if
presplit results are not satisfactory and production holes are damaging the presplit
line. Drill the buffer hole 3 ± 1 inch (75 ± 25 mm) in diameter. Drill the line of
buffer holes approximately 3 feet (1 m) from the presplit line, and space 3 to 5 feet
(1 to 1.5 m) center-to-center. Do not load the buffer holes with more than 50
percent of the full explosive load that could be placed in a 3-inch (75 mm)
production hole. Delay the detonation sequence toward a free face.
208.07 Blasting Test Sections. Before commencing full-scale blasting
operations, demonstrate the adequacy of the proposed Blasting Plan. Drill, blast,
and excavate short test sections to determine which combination of methods, hole
spacing, and charge works best. Use a test section with lengths up to 150 feet (45
m) for presplitting and 120 feet (36 m) for production blasting when field
conditions warrant.
Do not exceed a production hole depth of 30 feet (9 m) for the first test section.
Begin the controlled blasting tests for presplitting with the controlled blast holes
spaced 36 inches (900 mm) apart, then adjust, if needed, until the spacing for fullscale
presplit blasting operations is approved. A new test section is required to
increase the spacing for the presplitting to a maximum of 48 inches (1200 mm).
Perform two test sections per project. Use explosive depths greater than 20 feet
(6.7 m) for these test sections. Use one test section for controlled blasting and one
test section for production blasting.
Apply the requirements specified for controlled and production blasting
operations to the test section blasting.
For controlled blasting and for production blasts within 10 feet (3 m) of the
finished slope, do not drill ahead of the test shot area until the test section has been
excavated and the results evaluated. If the test shots are unsatisfactory, revise
methods as necessary to achieve the required results. Unsatisfactory test shot
results include an excessive amount of fragmentation beyond the indicated lines
and grade, excessive flyrock, or violation of other requirements within Item 208.
If the drilling and blasting methods do not produce the desired result of a
uniform slope and shear face, within the tolerances specified, drill, blast, and
excavate short sections, not exceeding 150 feet (45 m) in length for a presplit line