Simulating cave material in block caving and sublevel caving mines

[Adrian Halim]

Hi all,

Has anyone ever simulated cave material (cave column) in a block caving or sublevel caving mine models? If yes, what is the resistance of the muckpile inside the cave column that you use? It is extremely difficult to find "accurate" resistance value of the cave material because it depends on the porosity inside the cave column, which can vary significantly across the column itself depending on the fragmentation. You can have some parts inside the cave column that have fine fragmentation (hence low porosity and high resistance) and other parts that have coarse fragmentation (hence high porosity and low resistance). There are very few studies about this topic and all of them are based on CFD simulations and lab experiments using marbles and balls, which have many limitations.

I understand that determining the resistance with PQ survey using barometer is extremely difficult but perhaps anyone has tried to do this? In this survey, one person (with a barometer) stands on the surface next to the subsidence and another (with a barometer) stands at the drawpoint. Based on measured pressure differential and air leakage into the drawpoint, the resistance of the cave path between these two people can therefore be calculated.

Thanks for your help!

 

 

[Claudia Vejrazka]

Hi Adrian,

For years we used 0.0018Ns2m-8, which was back calculated from the Lift 1 airblast. Later on, when one of our neighbours did actual measurements across two accesses into the cave their measured values were out by a magnitude.  We figured out that the muckpile resistance has to be further normalised for the cross-sectional area of the undercut following the square law of mine ventilation based on the Chezy-Darcy relationship.The value we came up with was 0.0203 Ns2/m8 per m at 10,000 m2 undercut area, which is what the Ventsim simulations use. The measurement was probably at a similar general porosity as Lift 1, which was 25% at the time.

I agree the actual resistance is locally dependent on varying porosity, so this is more of a global constant. But I always found with my simulations that your worst affected areas are not your footprints themselves, but the main accesses where the air from the whole footprint flows together. So while the model might not be very accurate on a drive by drive basis the error should be a lot smaller in your high velocity areas, same as the normal ventilation modelling really. You never get fantastic correlation in individual drives, but the in and out of the footprint usually work really well. You could also argue that the risk of airblast is the highest in the first years of caving operation, which would mean you would expect similar porosities (at least for porphyry type deposits).

I did write a paper for Massmin 2016 about this as well. I can't remember if you did come to that. It's been a while. If you want to have more of a detailed chat, feel free to send me an email: claudia@resolvemining.com.au

We really don't know enough about the fundamentals of airblast and have been trying for years to convince people to give me an ore pass that we can fill with different fragmentation rock and do PQ surveys on to get some better ideas, but it would involve significant costs.

Hope that helps a bit.

[Felipe Montalvo]

Hi All,

I think that this topic is controversial, because in the Mine that i Worked, i use topografical information(sectios each 100 meters of ramp, to comparate with a ideal section) with this información we have a average roughness, with this factor you can find your real Friction in each air branch.

 

Best regards

 

Felipe Montalvo

Lima, Perú