湖南宁乡大成桥地区岩溶地面塌陷分布特征及影响因素分析

湖南宁乡大成桥地区至2012年产生岩溶地面塌陷484处。文章通过对地质环境条件及岩溶地面塌陷时空分布特征的分析，总结出本区岩溶地面塌陷的分布特征和影响因素:（1）岩溶发育区发生塌陷428处，占总数的88.5%；冲沟地形中发生岩溶地面塌陷339处，占70%；覆盖层厚度小于10 m区发生塌陷335处，占总数的69.2%；双层结构区发生塌陷266处，占总数的55%，分布密度为7.82处/km2；冲洪积成因土体产生塌陷404处，残积土中产生塌陷80处；(2)岩溶地面塌陷在雨季的4-7月发生281处，占总数的58%；2001-2006年平均每年产生塌陷20处，2007-2012年平均每年产生塌陷54处，逐年增加趋势明显；（3）484处岩溶地面塌陷全部分布在煤炭坝疏干排水形成的降落漏斗范围之内；（4）本区地质环境极为脆弱:岩溶发育，覆盖层厚度较薄、力学性质差且双层结构土广泛分布于冲沟及冲积平原，是产生塌陷的内在因素；矿区疏干排水是主要诱发因素，降雨分布不均、地表水渗漏及河道整治对塌陷产生起促进作用。 

Distribution characteristics and factors influencing karst collapse in Dachengqiao, Ningxiang, Hunan

In the past few years,484 karst collapses with a total collapse area of over 300km2 have occurred in the Dachengqiao area of Ningxiang county.They caused direct economic losses of more than 1billion RMB and they have generally been increasing in number.Dachengqiao is located in the transition zone between the hills of Hunan and the Dongting lacustrine plain.The area＇s geomorphology is mainly hills,with a few gullies and the Weishui alluvial plains;the local strata are mainly Permian,Cretaceous and Quaternary with scattered Carboniferous outcrops.Basic data about the collapses and their current status was obtained through data collection,field investigation,geophysical prospecting,drilling,pumping tests,long time observation,and groundwater level measurement.The environmental and geological conditions of the karst collapses in study area were analyzed according to the correlation theory of karst collapse.The temporal and spatial distribution of the collapses was determined and the factors influencing collapse were ascertained.Main conclusions are as follows,（1）Most collapses occurred during the rainy season.For instance,282collapses（58% of total）took place between April and July.The number of collapses exhibited an increasing trend.（2）All of the karst collapses were located near cones of depression caused by drainage and dewatering.428collapses（88.43% of total）were in the intensely karstified zone.The collapse distribution density was greatest in gully areas,and higher in areas with non-karst overburden than in those without.404 collapses were caused by diluvial soil.（3）The main factors influencing karst collapse include the intensity of the karstification,the characteristics and thickness of the overburden,the double-layer soil structure widely found in gullies and on the alluvial plain.Drainage and dewatering in mining area were the main factors inducing collapse.The uneven distribution of rainfall,surface water leakage and river training also had important influence on the collapses.All of