Mining_Methods_UnderGround_Mining - Mining and Blasting

Boxhole boring.
raiSe BOring
production. Standard RBMs are capable
of boring at angles between 45 degrees
and 90 degrees from horizontal, and with
minor adjustment can actually bore at
angles between 45 degrees and horizontal.
A whole host of methods of mechanical
raise and shaft excavation have been
developed around the use of the RBM.
These include boxhole boring, blind
shaft boring, rotary drilling, down rea-
ming, pilot up/ream down, pilot down/
ream down, hole opening, and BorPak.
alternative boring
methods
Boxhole boring is used to excavate raises
where there is limited access, or no access
at all, to the upper level. The machine is
Clearance for derrick
erection from the
transporter system
Typical raise boring underground site showing overhead clearance.
set up at the lower level, and a full diameter
raise is bored upward. Stabilizers
are periodically added to the drill string
to reduce oscillation and bending stresses.
Cuttings gravitate down the hole and
are deflected away from the RBM at the
lower level.
Blind shaft boring is used where access
to the lower level is limited, or impossible.
A down reaming system is used,
in which weights are attached to the
reamer mandrel. Stabilizers are located
above and below the weight stack to
ensure verticality of the hole. Cuttings
are removed using a vacuum or reverse
circulation system.
Rotary drilling is used for holes up
to 250 mm-diameter, and is similar in
concept to pilot hole drilling in that a bit
is attached to the drill string to excavate
the required hole size.
Down reaming involves drilling a
conventional pilot hole and enlarging it
to the final raise diameter by reaming
from the upper level. Larger diameter
raises are achieved by reaming the pilot
hole conventionally, and then enlarging
it by down reaming. The down reamer
is fitted with a non-rotating gripper and
thrust system, and a torque-multiplying
gearbox driven by the drill string.
Upper and lower stabilizers are installed
to ensure correct kerf cutting and to reduce
oscillation.
Pilot up/ream down was a predecessor
of modern raise boring techniques
using standard drilling rigs. Pilot down/
ream down, or hole opening, employs
a small diameter reamer to follow the
Overhead
clearance
for complete
derrick
extension
pilot hole. Stabilizers in the drill string
prevent bending.
The BorPak is a relatively new ma-
chine for blind hole boring which climbs
up the raise as it bores. It comprises a
guided boring machine, power unit,
launch tube and transporter assembly,
conveyor and operator console. Cuttings
pass through the centre of the machine,
down the raise and launch tube, and onto
the conveyor. The BorPak has the potential
to bore holes from 1.2 m to 2.0 mdiameter
at angles as low as 30 degrees
from horizontal. It eliminates the need
for a drill string and provides the steering
flexibility of a raise climber.
raise boring machine
The raise boring machine (RBM) provides
the thrust and rotational forces ne-
cessary for boring, as well as the equipment
and instruments needed to control
and monitor the process. It is composed
of five major assemblies: the derrick;
the hydraulic, lubrication, and electrical
systems; and the control console.
The derrick assembly supplies the ro-
tational and thrust forces necessary to
turn the pilot bit and reamer, as well as
to raise and lower the drill string. Base-
plates, mainframe, columns and headframe
provide the mounting structure
for the boring assembly. Hydraulic cy-
linders provide the thrust required for
lowering and lifting the drillstring, and
for drilling and reaming. The drive train
assembly, comprising crosshead, main
drive motor, and gearbox, supplies the
26 underground mining methods