Bolt failures (multiple): Aberllyn Zinc & Lead Mine

[GT]

I had a look at the big pitch in Aberllyn today, having had some reports of some bolt failures on that pitch (floor 1 to 4).

The bolts holding the fixed rope that access the somewhat airy take off all failed, 4 of them. I was able to pull them out of their holes by hand with very little effort, in fact it looked like somebody had already pulled the bolts out and slid them back in given the illusion that the rigging was fine; clearly not the smartest of ideas!!

The method of failure appears to be significant corrosion of the bolt expansion sleeve itself, I suspect related to the minerals within the rock. This is not the first time we've had bolts fail in this mine. 

I'd suggest keeping clear of that pitch until some better/other bolts are placed and the ones in the roof looked at a little more carefully!

 

[SamT]

So you'll be replacing them with stainless glue ins then..

Good lad. 

 

[Dave Tyson]

Miles Moulding has a couple of glue-in batinox bolts fail for the level 4 -> 5 pitch. It was not clear what happened, they were fine when we used them, but were loose a few weeks later. I think your right that there is something in the rock causing the problem, but glue-in bolts may also be unreliable 

Dave

 

[TheBitterEnd]

So you'll be replacing them with stainless glue ins then..

Just because stainless doesn't "rust" does not mean it is immune to corrosion - see recent work done on stainless bolts wrt chlorides (IIRC they turned out to be OK in a caving context). You would need to know the chemistry in the mine to be certain.

 

[droid]

Anyone got a reactivity series?

Re. Fe/Zn.....

 

[GT]

I placed those Battinox bolts with Miles, and after about an hour or so tested them, found them solid, and used them. Several months later on a return trip, found the bolts loos and with the help of a short bar, unscrewed the 50kn rated resin bolts out of the rock. Needless to say this was a little worrying!!

I'm hoping to get some time to updates some of the bolts in there in the near future, but will be very selective with they're placement!

 

[bograt]

Anyone got a reactivity series?

Re. Fe/Zn.....

Only relevant for elements, not alloys.

 

[droid]

Even for displacement reactions in an acidic environment?

 

[bograt]

Even for displacement reactions in an acidic environment?

Yes, or even alkali (Basic) environments.
Alloying changes the state of elemental metals.

 

[droid]

That's THAT hypothesis junked then....

 

[bograt]

 

[AR]

Just to throw a random thought in, if the mine water's acidic, has it mobilised something which could react with the chromium oxide layer of the stainless, or degraded the resin?

 

[Antwan]

Sounds like all the pitches should be drilled for abalakov threads if the bolts are not holding

 

[Simon Wilson]

I placed those Battinox bolts with Miles, and after about an hour or so tested them, found them solid, and used them. Several months later on a return trip, found the bolts loos and with the help of a short bar, unscrewed the 50kn rated resin bolts out of the rock. Needless to say this was a little worrying!!

I'm hoping to get some time to updates some of the bolts in there in the near future, but will be very selective with they're placement!

Where are those Battinox anchors and resin plugs now? What was the mode of failure? Did the resin to anchor bond fail or the resin to rock bond? I find it hard to believe that there would be significant corrosion of the anchor so what was the condition of the resin?

 

[GT]

Hi Simon,

The Battinox placed/failed around 2008, and was found suspect around 2 weeks after placing it. It was placed in a really difficult spot to reach so difficult to inspect thoroughly, however the anchor itself unscrewed from what was left of the resin bond. The anchor appeared fine and was replaced in another hole not far away from the original (failed) placement. If I get the chance I'll go back and check it's condition as it's not a pitch I've used for a while.

 

[Simon Wilson]

I have no experience of these highly corrosive mine environments so I'm not going to speculate. However, even with my very limited knowledge of chemistry,  if the resin was mixed correctly I find it hard to believe that the rock chemistry could so adversely affect the resin to make the anchor so loose due to failure of the resin. Was the failure due to the rock deteriorating?

We could do with more information about this. We could do with information about any anchor failures.