Sink Holes
Sink Holes
(OP)
I live in Florida and I hear horror stories all the time about sink holes developing in people's houses. I thought it would be an informative thread to discuss people's interesting experiences with sink holes in terms of what kind of damage there was, how long the house was there before the sink hole developed, how it was fixed and how much it cost. I had a friend of a friend that recently had a sink hole develop and it cost $80,000 to fix it! I'm not sure of the details, but if it cost that amount, there must be an interesting story to tell. I have nothing to gain in this discussion, except to hear people's fascinating stories. Us engineers get a kick out of things like this. :)






RE: Sink Holes
Now for some therapy. It all started in engineering school. I thought, heck, engineering seems like it can sort through and solve just about anything. There's an engineered solution to everything, right? Then I get to grad school, and all of a sudden there's a fluids professor trying to convince me of the merits of identifying the flow characteristics of lava flowing down a volcano using the complete 3-D equations of motion (80 some odd characters across, in each plane) as a starting point, to see if a train can get out of the way in time. I snapped. I figured, what's the point? How futile an exercise is this? Ever since, I've had a fear of most natural disasters - and sink holes are number one. I also had trouble sitting through Armagedon and Deep Impact.
I have four short stories. The first had to do with Route 78 in western NJ. Every few years or so a sink hole opens up along the highway. Seems nobody bothered checking for mine shafts back when they built the road.
The second has to do with unscrupulous builders. There was a cluster of small sinkholes that cropped up in the Franklin/New Brunswick area a few years ago. Back when the home developements were being built, builders would sometimes just push whatever brush that didn't burn (stumps, roots, etc) into a hole and bury it. Twenty five years later the wood rotted away, and these small sink holes would crop up out of nowhere right in the middle of a yard or common area. A child was killed when he fell into one head first and suffocated.
The third also has to do with mine shafts. In western NJ, there apparently were a slew of copper and iron mines operating back in the 18th and 19th centuries. The popular method of closing a mine shaft was to back a few wagons or rail cars into the vertical shaft and backfill with whatever material was available. Fast forward to 1990, and suddenly people's yards where collapsing as the rail cars finally disintegrated. There's a family nearby with a honker of a hole in his yard (is it too corny to say you can drive a rail car through it?). It's been fenced off for almost a decade now because no one knows how to fix the problem.
The fourth also has to do with mines. Apparently farmers in Normandy have been mining subteranean chalk since the last ice age to fertilize their fields. The layer is about 20 feet below ground, and they were able to carve out rooms that you could stand up in that went pretty far in all directions. The farmers were able to eeke out small family-run chalk mines for centuries. They would leave these columns of chalk every so many meters to support the roof of the mine. Fast forward to 2000. Upscale homes are being built all over Normandy, there's a few years of heavy rain, and whamo, the chalk columns soften up and start giving way under people's homes, and these massive sink holes started developing. The story that caught my eye was of a retiree who stepped off his back patio one morning and was never seen again. They never even recovered his body.
That's hardcore, man.
RE: Sink Holes
Some houses and parts of houses have been swallowed, but the problem is now fairly well understood and suspect areas are monitored. Over several decades a small number of people have died in these sinkholes, but I do not know of any deaths in the last 10 years.
The problem of dissolving limestone is speeded up by the deep mines pumping water out of the ground. However the problem goes back a long time, and the prehistoric human skeletons found in the Sterkfontein caves may have resulted from humans falling into sinkholes.
RE: Sink Holes
I recommend that you visit the sinkhole web site for more details and information about them. Here is there webs site link http://www.sinkhole.org/
They are a fact of life. I put them there with Hurricanes and earthquakes.
Now the mines pose different challenge. I lived in West Virginia as well and worked with coalmines. The main concern is subsidence. It occurs if the mining is not done in accordance with well-engineered plan. Mining engineering requires a particular pattern of mining so that when they are done and complete, pillars are left behind to support the earth above. Geology of the area above and surrounding the mine has big influence on this. I have heard stories where farmers lost their water wells because of mining changes the flow of underwater and minimum operations caused cracks the diverted water away from its path. If you live in areas near coal mining, you would hear the word subsidence frequently.
Good luck
RE: Sink Holes
http://www.sinkhole.org/facts12.htm
RE: Sink Holes
RE: Sink Holes
Google for geology of plutonic rocks and note the case studies.
Here are a few samplers:
Grout Curtain at El Cajon Dam
thin arch dam 238 m high to be built in karstic area
overlain with volcanics and 4 major faults in the area
drillings revealed caves 200 m lateral extent
grout curtain made in form of a bathtub
514 km of drillings
14 km galleries
grout curtain area 530 000 m2
2 ½ years to complete
10,000 m3 cave detected during exploration resulted in the relocation of the bathtub grout curtain
South Africa train 1975 – near the Driefontein mine
ground water lowered in the Dolomite
railroad was closed for passenger trains for over a year during which remedial measurements were taken
8 days after the route was re opened a sinkhole formed
the train driver could not stop the train in time
3 coached derailed – 2 left hanging over the sinkhole.
Hope these have been retrieved since.
West Driefontein mine – South African mine
increased rate of ground-water withdrawal caused the main surface stream to go dry
cavern had developed
117m deep boring in residual soils
grouted in 171 holes, 9-15 m deep
surface paved to prevent infiltration around the plant 60 m in all directions
the entire crushing plant disappeared into a sinkhole – with 29 people – never found
the hole was 55 m in diameter and more than 30 m deep