Summary

This review gives information about mine collapse and subsidence. Several publications on mine subsidence and a list of consultants specializing in subsidence are given. Information about mine subsidence in Canada is also given.

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INTRODUCTION

An inherent human assumption is that the ground beneath our feet will always be stable. Earthquakes and subsidence shake and undermine our faith in this common belief. The Loma Prieta, Northridge, and Hector Mine earthquakes woke me up to the excitement and damage caused by ground shaking. I was in California close enough to the epicenter of these three earthquakes to be affected; I still have not fully fixed the damage to my house wrought by the Hector Mine earthquake that shook us out of bed and into the open.

Ground subsidence impinged on my imagination a lot earlier. The final two miles of the ride home from high school took us past the old coal mine workings in Springs. The workings had collapsed long before, and now burnt out of control. There was always smoke rising gently from the area we were forbidden to approach. On a still, dark night there was a faint glow on the horizon that thrilled us as we peered from the back of my father's '49 Mercury traveling back from the town and the glittering shops along the road past the old mines.

Many years later as a consulting engineer I came up with a plan to protect the local rail line from these same fires which by then were threatening to undermine the main rail line. It took much head bashing to find a cost-effective solution, but in principle the proposed plan was simple enough: excavate a 30-ft deep trench along miles of line besides the coal workings, remove the coal that would soon enough catch alight, and backfill the excavation with inert soil and rock. I hope the rail line is still safe.

I earned enough to buy a brand-new red Volkswagen while working for Professor Jennings on mine-induced subsidence that had rendered brick kilns inoperable. The deep gold mine workings were not to blame. The cause was dewatering of the overlying strata to control inflow to the deep working. The area was windblown soil deposited over the fantastic peaks of a long-covered karst topography. Differential settlement of the wildly varying soil thicknesses caused erratic surface settlement. How I would love to find and bring to the light of modern curiosity the files that are now probably dusty in some legal office.

In New Mexico, I wrote a paper that was published in some forgotten proceedings about the work we did to prove to the U.S. Nuclear Regulatory Commission that even if all the underground workings were to collapse, there would be no detrimental impact on the uranium mill tailings pile we were remediating.

In Pennsylvania in a small town to the east of Pittsburg, I worried over the potential impact of collapse of the 100-ft deep underground mine workings from the early 1920's on ten surface trenches filled with waste from a plant that produced pellets for nuclear submarines. We decided that subsidence would not affect in situ closure of the trenches, and were grateful for the many coal seams between the waste and the mine workings, for they acted as the most effective natural geochemical (carbon) attenuator of seepage from the trenches we could get.

When I worked on the cases described above we had scarcely a written word to go by; we used gut-feel engineering and old-fashioned geotechnical logic. I am happy to report that if you now have to deal with mine workings collapse and surface subsidence, there are nearly 100 books on the topic listed by Amazon.com. I have bought none, and review none on these pages. In the State-of-the-Art Review I stick to writing about that which you too can easily access for nothing via your computer.