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Drilling with the Xs GT drill
casing systems
Preparing the equipment
Place the casing
crown over the end of the casing taking care to align the crown to the square
edge of the casing. Tack weld in three places to hold the crown in position then
weld around the upper edge of the crown using an electrode approx 3/32
diameter. Grind the weld after welding to minimise interference between crown
and the drilled hole. In cold weather it is recommended that the components to
be welded should be preheated.
Insert the Driver/Bit into the DTH Hammer in the conventional manner, and if a
short starter tube is to be used, attach it to the DTH hammer at this time.
Starter Casing
The crown and first casing assembly
should be cut to match the length of the DTH Hammer (or DTH Hammer and starter
tube) minus 8 this should put the top of the casing to approximately 2- 3
below the top wrench flats. This will allow access to the wrench flats and
enable the adding and removal of drill tubes as drilling progresses.
Casing length
Ideally subsequent casing should
match the length of each drill pipe. However many casings are of random length,
and care should be taken when adding random casings, not to cover the top wrench
flat of the drill pipe, or be too low for the reach of the diverter. It is
desirable to measure each casing and record the length on it so that it is known
before adding to the column. Occasionally a casing can be cut to offset these
discrepancies.
Assembling the Driver and Crown
Locate the Diverter into the raised
position by raising the control handle.
With the winch raise the driver/bit, DTH hammer and starter tube assembly and
attach it to the thread of the saver sub on the rotation head. Raise the
assembly and rotation head high into the drill mast to allow the casing to be
positioned. With the winch, lift the starter casing with the crown onto the
drill table, and secure. Slowly guide the driver bit into the starter casing and
feed it all the way to the crown. By lifting the driver up and down and turning
the driver a few degrees each time, locate the driver through the crown. The
driver is in position when the driver protrudes through the crown approximately
2. Turn the driver slowly in the normal drilling direction and the crown will
lock onto the driver. Lower the diverter by operating the up/down lever until
the diverter locates on top of the casing.
Starting to Drill
Drilling is started by lowering the
starter casing with the driver to the ground whilst slowly rotating with the
hammer air supply partially on. As the driver bit closes into the DTH hammer, it
will start to drill.
(Note, it is easier to start a casing hole with an air pressure of less than
200psi) It is imperative that the operator monitors the discharge pipe to verify
a good flow of debris, once the casing is penetrating the ground, it is
advisable to commence water or foam injection. When the casing is level with the
drill table, drilling is stopped and the hammer air turned off. The diverter is
raised (if using Xs air diverter) to expose the flat on the top of the starter
tube, which can then be secured in the table with the drill tube wrench. The
rotation head can then be unscrewed and travelled to the top of the mast.
Adding Casing
The length of casing should match
the length of the drill pipe. Many casings are of random length, and care should
be taken when adding casings not to cover the top wrench flat of the drill pipe.
It is advantageous to measure each casing and record the length so that
occasionally a casing can be cut to offset these discrepancies.
Drill tubes need to be inserted into the casings whilst in the horizontal
position, preferably on the ground; this can be done manually or with a draw
cable. To lift the assembly into the drill mast, it is recommended that a proper
double hook and chain be attached to the winch. The drill tube/casing assembly
is then raised into the mast, the upper drill tube thread aligned into the saver
sub and the two screwed together.
The winch with the casing still engaged then can be lowered until the hook sits
on the drill table leaving the drill tube hanging from the rotation head.
The winch rope can now be slackened allowing the top loop to run down the
casing.
A sling can now be attached to the casing then the casing lifted enough to allow
the hook to be disengaged. At this point the drill tube is to be engaged and
tightened on to the tube held by the wrench below. The casing is then lowered
onto the previously drilled casing, clamped into position and tack weld in three
places. The casing joint should then be welded all around using an electrode
approx 3/32 diameter. In cold weather it is recommended that the components to
be welded should be preheated.
The sling can now be removed from the casing.
Continuing to Drill
Locate the Diverter into the lower
position by raising the control handle, if using Xs air diverter) and ensure the
diverter is located on the top of the casing.
Drilling can now recommence by slowly rotating with the hammer air supply on,
and water or foam injection engaged As the driver bit closes into the DTH hammer
it will start to drill. With the addition of each casing only enough down thrust
should be applied to make the DTH hammer run smoothly. Again it is important
that the operator monitors the discharge pipe to verify a good flow of debris.
Drilling can continue in this manner until the top of casing is level with the
drill table, when the whole process starts over again.
Change drivers position for sub-drilling
When the
casing is drilled to the desired depth, the driver bit can be disengaged from
the crown bit by reverse rotation. It helps the disengagement process if the
driver bit is thoroughly flushed with air water, and foam if available. This can
be done with the DTH hammer in the lifted position to allow the hammer to go
into the by-pass mode which allows more flushing air and fluids to pass. The
driver should then be rotated in reverse approximately 1/8 of a turn and then
lifted. If the driver is disengaged, the drill tubes will rise leaving the
casing in the hole. If the driver bit does not disengage on the first attempt,
rotate it back and for into and out of the locked position with the rotation
motor. After the driver/bit is disengaged pull back 12 and then turn exactly 90
degrees. You are now in the correct pass through position. Always with the air
turned off, lower the drill string until you reach the bottom of the drilled
hole. Once you are sure of your position, the rotation and the air can be turned
on again so you can drill the socket.
Retrieving the driver bit
When the
socket is drilled to the desired depth, the driver bit can be retrieved from the
hole. Pull back the driver bit against the bottom of the crown bit. Then turn
slowly and apply a light pressure on the drill string so you can feel when it is
in lifting position. Once you pass back through the crown, pull straight back.
Relocating the Driver Bit
Should it
be found necessary to advance the casing further after the driver bit is
disengaged, it can be re-engaged by lowering into the casing whilst inducing the
flushing fluids and rotating the driver/bit slowly in the direction of drilling.
When the driver contacts the crown, continue to turn slowly with the hammer air
off, until the drill tube is seen to drop. The operator can ascertain if the
driver/bit is engaged in the crown by lifting the drill string, if the drill
string lifts without the casing then the driver/bit is not engaged. If
resistance to lifting is felt then the driver and crown are engaged.
© Georocfor,
2009
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