Forepoling With Tunneling

Atlas Copco Overburden Drilling

Forepoling with tunneling jumbo

Atlas Copco Overburden Drilling Tools

Forepoling is normally done with standard tunneling jumbos. The work anyhow requires certain changes to be done in the jumbo. Drill rig features Drill rods, casings and casing advancing

tools

The work procedure requires especially thoroughness in certain aspects like Spile parallelism (straightness) Grouting according to the prevailing

conditions



The drill rig

The drill rigs technical condition will affect the results. Loose joints and neglected maintenance will worsen the overall results.

Well maintained, good condition drilling jumbo will get the best results.



The drill rig

The drill rig feed needs to bespecially fitted for the job.

The front centralizer and the travelingcentralizer have to be made accordingto the casing outside diameter. Bothcentralizers must be of openabletype for easier operation.

Feed front support is needed for reliablewall support in order to keep feed alignment.



The drill rig

The front support and the travelling centralizer



The drill rig

Feeds have to be equipped withreasonable guiding system for reliable alignment

Laser assisted guiding and automaticelectronic controls are modern featuresin forepoling

Anyhow even water scale will do, if usedoften enough and keeping in mind the twodifferent axels out of which one changes from spile to spile



The drilling tools

The drill rods can be either speed rods or hexaconal rods. Easiest ones to use would be hexaconal speed rods when available

Centralizers (wing couplings) should be used for sizes (of casings) of 89 mm and up. One centralizer should be immediately behind drill bit and at least one at first drill rod joint. Centralizer will help reconnecting the drill bit if disconnected earlier.



The drilling tools

Please also note that the smaller the ring bit OD / Casing OD differenceis the straighter is the hole. The larger the void the more possibilitiesthere are for deviation.

Ring bit ODCasing OD



The drilling tools

T78 has integrated casing shoe, recommended T76 J has threaded casing shoe SX82 has wire retainer (casing shoe can be produced locally) T69 has small pilot OD (esp. for thick wall plastic casings)



The drilling tools



The Casings



The Casings / Thread



Feed alignment

Drilling starts with feed alignment. Right spotting and right start angle of drilling (in both planes) will very much decide the end result.

Alignment is done by using laser devices, electronic feed alignment controls or measuring direction planes and angles manually

Please note there are two different things: alignment, which is theoriginal intended direction from feed set up and deviation, which is caused by the ground (fissures, material changes etc), feed movementsand casing /drill rod bending during the drilling.



Feed alignment

Please note that while look out angle is one thing there is also another plane according which the feed needs to be set formed by the centerpoint of the tunnel. This is demonstrated in the photo of a long feed tunneling machine located at tunnel center point.



Casing and drill rod handling

Casing and rod handling requires normally manual work. There hasbeen attempts to develop a manipulator to ease the work but they are still too heavy to be attached to modern jumbo booms.

A separate scissor lift or other on ground moving basket is required. To do all work from loading basket alone is not recommended.




If a manipulator will be used, all cumulated weights have to be taken in consideration when checking the load carrying capacities of booms and loading basket.



Hole collaring

Collaring is done when drilling is started. Collaring means drilling with half feed and half drilling energy and with slowor with no rotation at all.

Collaring ensures that hole is started to aligned direction.Please note that when drilling from soft material to hard,sloping rock, collaring is done also when already inside theground



Drilling

Stiff rods, use of stabilizers and avoiding of the use of excess feed forces will give best results. When drilling to hard formations from soft material, use of collaring drilling features should be considered.



Adding of new rods and casings

Please note that feed is often moved to get threading of casings done.Feed should be set back to the direction of the already drilled casing, which should be the desired spile direction if collaring was done correctly.


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Forepoling With Tunneling