我国近日多地出现“巨坑”,请各位从技术角度分析一下原因 [复制链接]

How do sinkholes form? \6o%gpUkD  
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Rainfall percolating, or seeping, through the soil absorbs "SC}C  
carbon dioxide and reacts with decaying vegetation, creating x"xl3dRu  
a slightly acidic water. That water moves through spaces ~+w'b7T,=  
and cracks underground, slowly dissolving limestone and xUl=N   
creating a network of cavities and voids. As the limestone 4po zTe  
dissolves, pores and cracks are enlarged and carry even SQ%B"1&$D  
more acidic water. Sinkholes are formed when the land FG/".dU  
surface above collapses or sinks into the cavities or when ..BIoSrj  
surface material is carried downward into the voids. }jHS  
Drought, along with resulting high groundwater withdrawals, "ee:Z_Sz  
can make conditions favorable for sinkholes to form. Also, A|>~/OW=@  
heavy rains after droughts often cause enough pressure qv\n]M_&  
on the ground to create sinkholes. q6DuLFatc*  
Sinkholes can be triggered by human activities such as: R-8>,  
• Overwithdrawal of groundwater &Omo\Oq&W>  
• Diverting surface water from a large area and \]R
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concentrating it in a single point 7\x7ySM  
• Artificially creating ponds of surface water iAD'MB  
• Drilling new water wells ZlQ@k{Es~  
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In urban or suburban areas, sinkholes are hazardous ~ 8L]!OQ9=  
because they can destroy highways and buildings. K8[vJ7(!|  
Sinkholes also can cause water quality problems. During T DOOq;+  
a collapse, surface waters may leak into the aquifer, our Y,BzBUWK  
underground source of drinking water.

Can sinkholes be prevented? 32h}+fd  
Many natural sinkholes cannot be prevented. However, J>_|hg=  
those caused by human activity may be avoided, especially *IBT!@*Q&  
those caused by over-pumping groundwater. During dry {wsO8LX  
conditions, water tables drop in the limestone and cavities SSG57N-T  
under Florida’s sand and clay soil. The combination of gravity, )CgKZ"  
loss of buoyancy and water pressure can activate a collapse. sa8JN.B  
By keeping water tables high, water conservation rules *_feD+rq  
and drought restrictions are tools to help prevent sinkholes }AfX
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from occurring. The St. Johns River Water Management o/0cd  
District promotes year-round water conservation and qw^kA?  
issues water restrictions to prevent water shortages and 2ZTz{|y  
over-pumping during Florida’s inevitable times of drought. WUOoK$I~K  
The District is responsible for providing long-term protection Bgb~Tz'  
of the water supply. While water restrictions can cause A^lJlr:_`  
some inconvenience to residents and businesses, limiting .
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outdoor watering is critical throughout the year, and c;siMWw;  
especially during a drought. Public cooperation is vital to g7\MFertR^  
ensuring long-term water resource protection.

Drought, along with resulting high groundwater withdrawals, 
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can make conditions favorable for sinkholes to form. Also, RcJ.=?I!  
heavy rains after droughts often cause enough pressure *}fs@"S   
on the ground to create sinkholes.

Warning signs GD(gm,,)  
A rapid sinkhole caused by well drilling or other sudden gbvM2  
alterations to the terrain may not give any warning signs. q!UN<+k\h  
Otherwise, the collapse process usually occurs gradually _:dt8+T#  
enough that a person may leave the affected area safely. =NJ:%kvF  
The final breakthrough can develop over a period of a few \Af25Mcf:  
minutes to a few hours. z!`aJE/  
Some warning signs of a naturally occurring sinkhole include: Qm9r>m6p@N  
• Gradual localized ground settlement

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• Doors and windows fail to close properly ?\Fo|__  
• Cracks in a foundation %[3?vX  
• A circular pattern of ground cracks outlining the sinking area yFt$L'#  
• Vegetation stress due to a lowered water table #6
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• Turbidity in local well water due to sediment washing )?_x$GKY  
into the limestone’s pores 117`=9F  
There are many other causes of localized ground settlement N RB>X  
and vegetation stress, and depressed areas are not DX3xWdnr  
necessarily indications of an imminent sinkhole.

岩溶。。。

我认为是大范围持久降雨造成的

长沙也出现了该情况，地下水的解释似乎讲得通！ d}d1]@Y\  
1

为什么这些“天坑”都是圆的，四周皆被刀削似的悬崖绝壁?

2012  2012

主要内因还是岩溶塌陷,不排除部分是地下采空或地下工程活动造成的地下空隙/松散区;;集中出现可能有干旱后长时间暴雨因素,地下水作用有潜蚀/虹吸说等等. W#|30RU.G  
另外要说明的是:土洞也是岩溶的一种形态,实际上岩溶塌陷,有人统计96.7%都是岩溶地区上覆土层塌陷. /R/\>'{E&c  
我一直觉得工程界有一个误区,就是对岩溶过分的关心基岩溶洞顶板垮塌的问题,实际上我认为更应该关注的是,岩溶土层塌陷问题.,而引发岩溶塌陷的最大和最可能因素,不是荷载,而是地下水活动.

同意7楼弟兄的分析，总体上还是应该与岩溶地区的背景、地下水因强降雨活动加强导致上部土层掏蚀，形成的土洞有关，当然，具体个例须结合当地情况具体分析

我觉得一直都是这样，这样的现象很正常，只是现在媒体关注了，所以就觉得突然增多了。以前应该也很多，只是没有报道而已。