Monitoring rock bolts

[barryn56]

Hi. I just joined the group as I don't have a background in hard rock mining directly, but have been in the upstream oil industry for many years.

I have a potential client looking for a method to monitor and identify when rock bolts fail and to send a radio frequency signal to a receiver identifying which bolt it is. This would be only for new bolts, not for monitoring already installed ones (although maybe that's another issue?).

One of the criteria is that the solution should not increase the cost of the rock bolt by more than 30%, so I'm interested to know the range of cost of rock bolts (I wouldn't like to pretend to be buying from a supplier to get the info).

I'd also like the group members' expert opinion on whether this sort of indicator would have a significant market, or if you think something else would be more useful to assist with cost, safety or any other aspect of the mining process.

Thanks in advance for any comments.

Regards,

Barry

 

[RedDirtDigger]

Hi Barry, i do not have a mining background and am probably way way off track. So disregard if i am.
I have worked in limestone caves for many years.
To measure any movement in rock piles/ cracks we glued tempered glass microscope slides across the crack, if they break, visual monitoring would tell us if the crack had moved slightly. I imagine a brittle ceramic/glass rod secured from the rock face to the bolt with a wire down the centre could be linked to a plc system so when the wire breaks, the circuit opens and an alarm can be triggered. or if the tolerances are ok a simple parting contact type switch attached between the bolt and rock surface could be used. I believe that a continuous "wire" system with dozens of sensors can be monitored and even tell you where the break is.
We monitored a dozen phones and many air and water quality sensors with monitoring data sent continuously via a comms cable to the main caves office.
RDD

 

[Guest]

My experience is with Coal mining but the issues would be similar with strata management.
If you (or your client) is having issues with rock bolts failing it would most likely be from poor installation or excess roof movement.
If it's an installation issue I would be addressing that prior to worrying about monitoring.
If it's from excessive roof movement there are monitoring systems for this already available such as Gel Multipoint Extensometer, Rock-it & Clock-it which are manually read during mine area inspection. These are used in underground coal mines but similar or the same would probably be used in hard rock mining?
There is also an automatic transmission system called Roofalert that utilises the Rock-it & Clock-it type monitors.
http://www.holville.com.au/Products/intrinsically-safe-roof-monitoring
The reason that roof monitoring rather than bolt monitoring is used is with roof monitoring you have an early warning system I.e. you can see areas of excess roof movement usually before issues such as failed bolts occur. If you monitored for failed bolts only then by the time bolts were failing it may be too late.
We also have the bolt manufacturer on site periodically to "pull test" random new bolt installations plus do QC checks on installation etc.
Edit: I should have mentioned that where excessive roof movement is detected a more dense pattern of bolting or utilising longer bolts like cable or strand bolts is undertaken to prevent bolt failure & ultimately roof failure.
Even with the roof monitoring in place we still do see the odd bolt "pop" when areas have a rapid acceleration of roof movement but even then it can usually be remedied before major issues occur.

 

[Guest]

Sigra Australia also have systems for monitoring rock bolt load. It's basically the same principle of early warning but can also alert you if bolts are failing (loss of load) due to poor installation/loss of bond, corrosion etc.
http://sigra.com.au/services/geomechanics/load-movement-monitoring/

 

[barryn56]

Thanks for the great input, guys. I agree that monitoring the rock is a good approach for general changes in movement - I'm wondering how many measure bolts you'd have per holding bolt (10%?).

I think the issues with bolts includes things like corrosion, shear failure, etc, as well as tensile load. The use of compression monitoring is pretty straightforward using strain gauge washers, etc. though power requirement, long lifetime (10+years without maintenance) and robustness of the solution might be issues(?). I've used the glass slide trick for monitoring foundation movement in a house wall which was cracked...

I've also been told that rock bolt monitoring that doesn't require pull testing is a useful requirement (there's one company using seismic equipment using a hammer as sound source), though I'd have thought that would be very costly and doesn't provide the early warning as well as a rock stress monitoring would?

If anyone could give a guide price on rock bolts (say per metre?) that would be useful.

Regards,

Barry