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Blasting of pillars to cause ground subsidence and stabilization

Blasting of pillars to cause ground subsidence and stabilization

Blasting of pillars to cause ground subsidence and stabilization

(OP)
I am working on a project site that is underlain by an abandoned limestone mine. We are looking at blasting out the pillars to subside and stabilize the ground surface to allow for future development. This is instead of grouting the mine as that would likely be way more costly to do so given the void height is up to 20ft. I am wondering if anyone has done this before and has any tips or read about it and has articles related to the subject.

Thanks

RE: Blasting of pillars to cause ground subsidence and stabilization

We considered it on a similar project over prior mine voids, where the owner also considered grouting as cost-prohibitive. Our voids were only about 6' high and less than 50' below ground surface. Unfortunately there is a lot of surrounding area that was already developed with high-end residential, so blasting was quickly eliminated from consideration due to the potential (or perception thereof) to break glass or trigger unintended ground movement in adjacent areas that might damage existing buildings. In the end we shifted the plan for development to avoid the areas over the voids, and provided a geogrid reinforcement and flexible joints to mitigate utilities that crossed perpendicularly over them. Our voids were relatively low-height by comparison, so future failures should only result in minor surface depressions.

So my only advice is to make sure you understand what else is nearby and that you don't trigger collapse of voids or ground movement beyond your intended area.

#

RE: Blasting of pillars to cause ground subsidence and stabilization

Any experienced underground mining contractor can do this for you , but before getting too far ahead, do you propose using underground miners to do the drilling and blasting, or using surface drills?? Do you have accurate plans of where the pillars are located?? Without stating the obvious, if using surface drills this is critical, less so for regular miners. Do you have access to the underground workings for a physical inspection for overall safety concerns?. Does the local regulatory authority have mining experience?? How many years since the mine was shut down??? Are the workings dry or flooded. All points need answers before any contractor could even begin to put budgets together for you.

RE: Blasting of pillars to cause ground subsidence and stabilization

I don't have experience in this but I'm intrigued. How much overburden material is there above the mine ceiling? If you were to proceed, I'm not sure that the overburden material would collapse into a dense or stiff state leaving you with a potential issue after the forced collapse.

RE: Blasting of pillars to cause ground subsidence and stabilization

Well certainly the elevation difference between the " mine ceiling " and surface is a very important number used in predicting the amount of surface subsidence, but I can almost guarantee that the entire mined area will collapse given adequate time, provided the pillars are adequately destroyed. Similarily, the expected areal extent of the subsidence is partially related to the ratio of extraction heights to the depth below surface of the mine workings.

RE: Blasting of pillars to cause ground subsidence and stabilization

Hi Hammer,

We are a active mine operation with a surface subsidence problem. The operation is under national highway infrastructure, gas line, railway, etc.

For the past 8 years, we have had to intervene at regular intervals with filling and pressure grouting. We know we haven't solved the situation. It's probably going to happen again.

My advice is this. Do not think that surface subsidience is a process that happens suddenly. If you cause it, it will happen. It's very difficult to put a time frame on it. It will be very difficult to declare that all subsidience has happenned and that civil construction can then begin, unless the overburden (rock and soil) is thin.

I wonder wether the regulator in your jurisdiction would allow mining subsidience to be caused intentionnaly.

In the jurisdiction I work in, it is prohibited unless you plan to mine your stope to daylight and then backfill it with a cemented rockfill.

Ingenieur Minier. QuTbec, Canada.

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