3.
DRILLING PATTERNS
1) Distance between Holes
The spacing between the holes depends on the
“breakability” of the rock or concrete. As a rule of thumb, in hard rock,
all perimeter holes (holes defining the rock/excavation contact) should be
at 6” centerline to centerline, to ensure clean shearing on the contact line.
The next line of holes can have a spacing of 12” centerline of hole to
centerline of hole. After that the pattern can be expanded to 18” center to
center. This pattern will produce chunks that weigh about 50-125 lbs. with
little or no secondary breaking required.
Preferable Hole Distance
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Fig 4-1>
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Free face
Rock splitting direction Rock splitting direction
( For very Hard Rock )
Caution
Generally you will drill the holes to a depth 5-6” longer than the Power
Cylinder length. When the Power Cylinders are inserted into the holes, they
must be suspended so that they do not drop too deeply into the hole. An 8”
rebar or drill steel would be appropriate.
Another consideration when orienting the pistons of the power cylinder is to look
for fractures, or small fault planes in the material to be split. These are indicators of
weakness in the “in situ” rock. The splitting force should be applied along the
fault or fracture, as this is the easiest and weakest plane.
If there is no definable plane of weakness, you may have to experiment with the
placement of the power cylinder and pistons to establish the best plane for breaking the
particular rock on your project.
18”
12 “
