Rock-split granite with "cordless" SDS drill and "feathers"

An unexpected success! This is a new method. Though obvious - search of the Web ("YouTube" a good candidate) will surely find plenty of other instances of the same method.

The need - the challenge

Prior explanation : Condurrow mine is entirely in granite. Hard granite of the Carn Brea slope and plateau.

At Condurrow mine there are sub-levels up stopes where, when used as a training mine, there was blasting where not enough charge was used. So the rock was not shattered, being fractured into large-ish "boulders" part-obstructing those levels.

Which need disposing of.
The rocks are too large to move easily.
Hence must be broken-up.

The solution

• drill line of holes along intended split line of boulder
• insert "feathers" - rock-splitting wedges - and tap wedges until rock splits
• remove handleable split stones

In a mine this is a "new possibility", because of a mass-produced "new" tool, the "cordless" battery-powered "SDS" drill (rotary-plus-impact). The "SDS" drill-bit and chuck system delivers a useful impact force - and has been available for some time.
The "new" part is batteries - currently Li-ion batteries - now deliver enough to power a carryable "cordless" SDS-drill which will capably drill stone.

First boulder split

The drill - "SDS" rotary-plus-impact "cordless" drill

Split stone with the "feathers" used (large middle hole made by powerful compressed-air-powered mining rock-drill - but rock still wouldn't then split)

For what it's worth - I needed to drill with a 14mm masonry bit (tungsten-carbide tipped) to use "my" "10mm" "feathers" (the "feathers" are not accurately described (?)).

The "tool-store" drill, seen middle picture, took some careful choosing at some effort.
It is an unfashionable form but packs a lot more impact power for its size, weight and cost than the new favoured form.
In explanation - "my" drill is long-ish, which is no problem in the mine for this task. However in "domestic" building work the drill has to fit transverse between floor-joists, into tight corners, etc - so a shorter "block-shaped" form is needed. So "my" drill is optimum for a niche application.

On a pragmatic basis which really matters "in the real world" : this drill takes batteries I already have for impact drivers for wood-screws, pistol-grip drills for wood and metal, etc.
In-effect it's the biggest tool for the job which takes "small tool" batteries.
So I could buy the "bare" tool; a big cost saving. For the mine expeditions I can bring several batteries if the task is large - at no extra cost.

Coming down the mine - a rough environment - this must be an economical-cost piece of kit.

That no setup is involved, and the "kit" is readily carried in case the need to split rocks is encountered, is a "winning" aspect of this method.

Contrast to previous

There was no satisfactory solution for this task.

That said : here's a round-up of the topic...

Equipment down mines generally uses compressed air power.

• only a supply line - no return line - is needed - as the working fluid is air, which can exhaust into the mine
• compressed air tools are small, dense, robust, durable, reliable - and get cooler as they work, which is a bonus in an arduous task
• the air-compressor plant is at the surface - easy to site and maintain - and transmission underground is easy
• inherently quite safe - pressures are a few atmospheres, so while bursts not welcome, conseqences are typically vastly less than if alternative power sources fail

This compressed-air-powered rock-drill will drill a 32mm (typically comes out at 34mm) diameter hole 1.5m into hard granite in a few minutes.

It needs a diesel compressor at the surface because its compressed air use is far higher than an electric compressor on the mine's electricity supply would be capable of.

Jumping ahead - the holes this drill makes often do not weaken the stone enough it will split with sledgehammer blows.

Basically it's the size of the task of mobilising the compressed-air supply and getting the rock-drill into place.

• prepare the compressor for use
• bring an airline, water-hose and the rock-drill up the stope
• call the surface and ask for the compressor to be started (it's using diesel fuel while running)
• do the drilling - noting that the drill will push smaller boulders around the floor - so they have to be personhandled into a corner
• the drill-bit often breaks through the boulder then it has to be extracted
• "sledgehammer" the boulders apart
• the boulders often won't split anyway
• call the surface to say the compressor is no longer needed
• prepare the compressor for more storage

What was done was when the air-compressor was running for other reasons and everyone got a chance to try the rock-drill. But viable and an effective solution for this task it was not.

The "SDS masonry drill" and "feathers" works - why?

"puny" hardly starts to compare my "cordless" SDS drill to the compressed-air-powered rock-drill.

Stop rotation - impact only - and put in a chisel and it can make no more than a little chip in the granite before it can do no more.

It's the efficiency of what it makes possible - getting the "feathers" into those small (in diameter and depth) sockets in the boulders.

The 14mm hole diameter needed for the "feathers" is probably the upper limit of this "cordless" SDS-drill into granite.
It may be that "piloting" at about 6mm drill size then drilling to 14mm has advantages. To be measured if a lot of this task is encountered.

Closing comment

Very pleasing.
I was surprised this worked. Then not only worked but seemingly exactly meets the need.
I systematically worked at it, maximising the chance of it working. While mindful of the probability (low-ish?) of "something novel" working. "If it would work - why hadn't it been done before?", etc.
However; the logic aligned with realities and the solution did work.

Update 21Mar24 : works reliably and rapidly when applied as a "production" method

See next mine day where applied as "production" method - it works - well...

Update 26Apr24 : how portable this kit is

What's in the kit:

With more explanation ...

(R. Smith, 15Mar2024, 21Mar2024 (update), 26Apr2024 (pics-portable))