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Shaft sinking is a very important part of mine development as it gives access to the resource that is
to be exploited.
A proper feasibility must be carried out and various considerations have to be made as to:
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The application/purpose of the shaft,
Its dimensions
Proximity to the ore body
Inclination
Method of shaft sinking.
Investment requirements
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The mine surveyor is very instrumental in:
• Locating of the shaft,
• Shaft plumbing
• General construction and the installation of infrastructure.
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Often a dedicated Project Surveyor is assigned to the shaft specifically for survey services as and
when required because:
• The whole procedure is meticulous and fairly tedious.
Fig 1.Kibble being lowered
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A shaft is an excavation from the surface into the earth. It can either be vertical or inclined,
rectangular or circular. Often there is initially no access to the bottom of the shaft.
Shaft sinking is the general activity associated with the task of excavating a shaft.
Initial considerations include:
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Analysis of local geology
Topography
Possible depth
Ore body proximity
Project and operational risks
Operational costs
System maintenance.
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Transportation of men and materials
Ventilation
Utility conduits
Dewatering systems
Emergency escape route.
General uses of shafts are:
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Shaft sinking is one of the most notorious undertakings in development due to:
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Given the risks involved in the task, the business is often left in the competent hands of
shaft sinking contractors who employ specialized methods and equipment.
• Working in restricted space
• Interaction with high volumes of ground water
• Difficult geological conditions which often worsen with depth.
• There are three shaft sinking methods discussed in this
presentation:
• Raise bore
• Horidiam
• Blind Sinking
• The raise bore method employs a raise borer to create a shaft and is a very
capital intensive piece of equipment and requires competent workmen to
operate.
• The method is applicable in areas where there is access at the target point
of the shaft that will allow access for the reamer to be attached to it once
the directional hole has been drilled. In the case of very deep shafts a mid
access point may be required to facilitate the aforesaid procedure.
• Location of shaft is done through survey work.
• Utilities are brought to the site (Power and water that meets the
requirements of the size of the equipment. )
• A foundation is dug for a concrete pad which is constructed over the area
where the machine will be mounted.
• Raise borer is mounted in the desired location and an accurate pilot hole is
drilled using directional drilling techniques. This hole has to be large
enough to accommodate the drill string. For deep shafts this is done in two
phases. The depth of the pilot hole is determined and limited by the
capacity of the equipment to lift the drill rods. Should a high level of
accuracy be required the cost of drilling also shoots up.
• When the pilot hole has reached its target point a shaft collar is constructed
to sustain loads that will be generated by the raise borer once reaming
commences. The reamer head is then attached to the drill string to increase
the diameter of the pilot hole from about 400mm to anything up to 2.7 m
depending on the size of shaft required and machinery used. Muck
generated is collected at the bottom of the shaft by either air loader or LHD
to a waste disposal point.
Raisebore Reaming
Raisebore attachments
Reamer Attachment
Raise bore machine and Control Panel
• This method is initially similar to that of the raise borer but only up
to the end of the reaming phase of the job.
• It is mainly applicable to very competent ground and is used in
shafts in excess of 1000m and those of large diameters, in particular,
ventilation shafts.
• The reamed out hole is then used to drill and charge holes from the
Horidiam stage that is lowered to the bottom of the shaft.
• Holes are drilled into the shaft barrel at 1.2m intervals from the
bottom – up the length of the shaft.
• A man cage is used as a conveyance to and through the Horidiam
stage. After drilling is completed the holes are charged from bottom
going up and blasts are carried out for two rounds at a time.
• Blast rock is then collected at the bottom of the shaft in the same
way as that for the raise bore method.
• This method results in a rough wall finish thus making equipping
difficult.
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Blind sinking refers to the fact that there is no access to the bottom of the shaft by
some other means. The technique is often employed using conventional drilling and
also by raise bore reverse circulation technology.
In the former case it is necessary that a shaft collar be established and the following
shaft sinking infrastructure be in place. This includes the headgear, stage winders,
kibble, compressed air, mucking and drilling equipment. A concrete batching plant
may be used for the liner.
A presink is often required so as to get clear of the weathered ground up to about
50m below surface. A cycle is practiced for the establishment of safety standards as
well as efficiency. The Galloway stage is lowered into the shaft at this point. Once the
presink is complete sinking equipment is then commissioned. The size of the
equipment differs with the size of the shaft being sunk. For large shafts the stage may
be too high to be installed once the headgear is installed in place. The kibble and
stage winders are commissioned with the load testing and mucking system.
Generally the shaft sinking cycle is:
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Drill charge-holes
Charge the holes
Move the stage up
Fire the round
Activate force ventilation and allow for re-entry period, make safe and clear the round.
Depending on competency, the shaft barrel is lined for every 6.0m of progress so as to
provide protection and support to the country rock. Ground conditions dictate the
type of support necessary in the shaft, it can be in various forms e.g. bolting and
meshing.
Shaft Steel Reinforcement
Galloway Stage
Cactus grab lashing
Finally the shaft sinking
comes to an end once the
desired bottom is
reached. Permanent
structures are installed as
sinking equipment is
removed. Commissioning
is carried out thereafter.
New Headgear Installation
Shaft Winder
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The precise location of a shaft wholly lies in the hands of a competent surveyor. It is often
necessary to have gyro bases installed close to the desired location of the shaft so that errors from
previous surveys are minimized and not transferred down to the new levels. This process requires
the use of a gyro theodolite which may be hired for the task or otherwise a competent team be
contracted for the purpose.
Shaft plumbing involves the transfer of survey from one level to another. At set up point pegs are
established preferably from the gyro bases afore mentioned at a location that will not be affected
by shaft sinking despite their proximity.
The centre of the shaft is then located and the corners marked off. Preferably pegs can be installed
that allow the centre to be located by means of strings crossing over it. Mining can then
commence to about 15-20m when it’s safe to establish the collar set.
The shaft collar is then constructed and the collar set is set in the concrete therein. For the purpose
of control of the shaft barrel during sinking, plumb bobs are used to mark out the shaft outline.
These are hung at pre- prescribed points along the perimeter of the shaft.
Shaft brackets are welded on the collar set frame and very small holes drilled to allow the
plumbing wires to pass through. The wire used for plumbing is known as piano wire.
The holes on the brackets are often about 200mm from the side wall. Wires used for plumbing are
lowered by means of winches secured close to the shaft.
During sinking, the exercise has to be planned very carefully so as to avoid unnecessary delays and
errors. This requires communication with mining and those that are involved in the shaft
construction that shaft sinking activities will be suspended until the exercise is complete.
• It is important to have:
• Equipment for two survey crews, one at the top level and the other
at the bottom level.
• Necessary attachments
• Plumb bob winches
• Piano wire to reach the desired level from the top,
• Half drums
• Used oil in sufficient quantity to immerse plumb bobs and the
bobs themselves.
• At best this should be checked off before taking off to underground.
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The following steps are then taken once in position,
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I . Two or more wire are secured at the top level and suspended in the shaft from top to bottom at least a meter
apart.
ii. Heavy bobs are then attached to the wires
Iii .Bobs are then immersed in drums of oil to minimize wire oscillations as much as possible
Iv . Care should be taken that the wires do not foul the sidewall.
v. One crew is stationed at the top level and the other at the bottom level. The instrument at the bottom level
should be stationed at the new peg. At best 2 to 3 pegs should be located at the new station.
Vi . Once the wires are steady observations are then made to both wires for angles and distances. Offsets are also
taken at this point
vii. As a check it is important that the distance between the wires is measured at the top and at the bottom.
viii. When all observations have been completed it is important that both teams communicate and agree to remove
their equipment from the shaft.
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Calculations are best carried out at the survey surveyors use the Weisbach triangle to calculate the new set of coordinates. Surveys on the shaft should be fairly regular so as to control the barrel profile and minimize over and
under sly ping of the walls. This also assists in the design of shaft steel and other related furniture.
Of late 3d technology is being applied to shaft surveying. This often involves the scanning of the walls of the shaft
after mucking has been completed by means of a scanner. Scanners define the shaft profile very rapidly and
accurately thus allowing for timely adjustments and quick decision making.
• The procedure of shaft sinking require a lot of forethought and
preliminary analysis. Given the three methods discussed above it is
the up to management to take up the decision on the best route to
follow for the task at hand. Where possible it is best to have the
process highly mechanized.
• Mechanization generally offers much more rapid rates and generous
savings on time and resources.
• The advent of technology also allows all shaft work to be monitored
and managed by means of shaft dedicated software like Sight Power
Mine Shaft Construction software. This application also reduces costs
by avoiding unnecessary delays in information relay to the
stakeholders in the project.