We would like to place stabilizing fill materials in the exposed workings so as to prevent subsidence of the workings which would then translate into progressive upslope failure. We are also interested in mine closure for public safety reasons. We are presently considering either pneumatic stowage of aggregate materials, or pumped placement of concrete,grout,or controlled density fill, to stabilize and close the mine workings exposed in the cutslopes. Our only experience with pneumatic stowage for this purpose in 1996 seemed to indicate that probably pumped placement of cementaceous materials ( concrete, grout, or controlled density fill) would be less expensive and more easily arranged.

The vertical mine shafts on our alignment range in depth from 50 to 100 feet. Their plan dimensions are unknown at this time. Shafts are expected to be currently filled with random backfill and/or collapsed cribbing and debris. We are somewhat undecided as to what the best, cost effective approach would be to backfill and stabilize the vertical mine shafts during new roadway construction. We are considering a number of options including clearing the shafts, backfilling them with dumped rock (start with large and progressively smaller toward the top) and then placing a vented concrete cap founded on stable top of bedrock. Our only previous project involving stabilization of mine shafts utilized initial angled drilling and grouting, followed by final vertical confirmation drilling and topping- off grouting. However those previously stabilized shafts were partially filled with a failing, random backfill material and were located beneath existing driving lanes of a 4-lane U.S. highway. Since our current project is a new build, we have considerablely more freedom to determine our form of vertical mine shaft stabilization.

Any suggestions or solutions to these two design challenges would be appreciated. Thanks!

Also, Missouri DOT used inverted cones to close some shafts.

The seven adjacent, extremely hazardous portals were probably exopsed during road construction some 40 years prior;{not too many placee to put roads in Floyd County, KY). Because of their premature exposure to the elements, the pillars between the exposed entries were weathering and spalling badly. By the time we evaluated them, no self-respecting Indiana brown-eared bat would even frequent the site.

To get to the point, we were able to clear out debris at the ravelled face in front of each portal, insert a protected drainage/venting system, cover the drainage system with essentially pea gravel and filter fabric, and pneumatically backstow DGA a distance of nearly 120 ft back into the compromised faceups with very good compaction results without puting a worker inside the actual portal. At the face, we pressure-injected polyurathane grout to a depth of about 40 feet into the compacted DGA. Since the polyurethane grout is extremely flamable, readilly vandalized and not all that aesthetically pleasing, we admixed some local soil debris for a colorant. We also backfilled the injected zone with local soils beginning at the edge of the roadway ditch on a slope of about 1.8(H):1.0(V) so that we could better protect our seal and provide an engineered, free-draining earth toe to help anchor large volumes of creeping colluvium "itching to come down" from the steep hillside above. We left the final foot of soi uncompacted and vegetated the soil backfill. It worked well, was cost effective and, if needed frequently, could be a common practice for use in your example conditions.

Shafts are another story.......for another time. I have located and designed temporary and permant closures for well over 100 shaft and slope entries and 500 drift mine portals in a dozen states over the years. Does Mineral Ridge ring a bell. Please feel free to contact me if you would like some additional follow-up, etc.. Good Luck!!!

John H. Gasper, MSEM, P.E., EnviRESTORE Engineering, LLP

Mineral Ridge does ring an old bell. I was a design and construction engineer with the OhioDNR AML program at the time of their 1985 Mineral Ridge Subsidence Study.

Thanks for your response. We may be contacting you directly in the future. Rick.

I believe that it took about two days per portal and that the contractor bid $11k (1985 dollars) per portal.

The subcontractor who performed the pneumatic backstowing portion of the project was out of Colorado and was trying to "sell" pneumatic backstowing as a viabil alternative to the KYDOAL at the time. As such, he may have reduced his costs (e.g., not charged for mobilization, etc.) in anticipation of additional applications of his process.

As I recall, his name was/is Russ Eby, a very flambouyant, bearded geologist type, and his company's name at the time was Eby Mining Services, or something to that effect.

Let me know via e-mail if you need additional input.

Regards, John Gasper

P.S., Re: Mineral Ridge: I did most of the grunt work (field effort, drill rig oversight, records search, graphics, etc. on the Mineral Ridge study. I was also the designated liason with Professor Harris from YSU. Dave Warder (ATEC) was my immediate supervisor. You and Dave Keefer reviewed our work. It was another lifetime ago.....