sink holes
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.
the title of this thread made my hair stand up on the back of my neck. i have a whacky sink-hole phobia. some people are deathly afraid of spiders crawling into their mouths at night when they are sleeping. some people fear germs. some people fear blood so much they picture their internal organs and circulatory system as if it was giant roll of bologna just to make it through each day (trust me, i know a guy). i, on the other hand, have a fear of 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.
here in the highveld areas of south africa, around johannesburg, there have been a number of mining-induced sinkholes. they occur in areas where near-surface dolomitic (limestone) rock strata are overlain by other (sometimes shallow gravel) deposits. the limestone gets dissolved by rain-water passing through the ground, and occasionally the surface falls in.
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.
sinkholes are tricky business in florida, which is where i live and practice structural engineering. there are areas that are more prone to sinkholes than others. i always work closely with my geotechnical engineers to assess the sinkholes possibilities in my projects area. for example here on the east coast of florida, i hardly loose any sleep fearing sinkholes. however, in areas near orlando and winter park and even parts of altamonte springs, i would be more concern.
i recommend that you visit the sinkhole web site for more details and information about them. here is there webs site link
talk about facing your fears.
llg...lutfi is right on target. rare occurrences east of the st. john's river, but west of the river from its source in brevard/indian river counties northward to the gainesville/lake city area sinkholes do occur. many active areas occur west of i-4 in the orlando area, particularly as lutfi mentioned in the altamonte springs area. though the polk county area is probably a bit more potentially active, there have been some significant sinkholes in the the winter park, maitland, and altamonte springs area in the last 20 years.
llg
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 陆 years to complete
10,000 m3 cave detected during exploration resulted in the relocation of the bathtub grout curtain
south africa train 1975 鈥?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 鈥?2 left hanging over the sinkhole.
hope these have been retrieved since.
west driefontein mine 鈥?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 鈥?with 29 people 鈥?never found
the hole was 55 m in diameter and more than 30 m deep
2009-09-15, 10:59 PM
sink holes
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