安庆市怀宁县马山口地区岩溶塌陷的分布特征及形成条件分析

安庆市怀宁县马山口地区岩溶塌陷灾害是安徽省大型地质灾害点。在对该区地质环境条件及岩溶塌陷时空分布等分析的基础上，系统总结出了马山口地区岩溶塌陷的形成与分布特征:（1）马山口岩溶塌陷形成始于1987年，盛发于1988-1992年，该高发时段共产生塌陷坑39个，占全区塌陷总数的 43.8 %，特别是1992年，形成的塌陷坑达 24 个，而1993 年以后年均塌陷仅为2.6 个。（2）地貌上塌陷坑主要分布在地势低洼的河漫滩，其次为低丘山坡地貌；在地层岩性上，塌陷坑主要分布在三叠系下统南陵湖组、中统月山组灰岩、大理岩地层中；在水文地质上，塌陷坑主要分布于地下水的降落漏斗范围内，特别集中于地下水主要径流方向和水交替强烈的河谷及地表水与地下水联系密切地段。可溶岩地层的存在、松散覆盖层厚度小（一般在10 m以内）和地下水位频繁波动变化是马山口地区岩溶塌陷产生的必要条件，其中由于矿区疏干排水引起的地下水动力场急剧变化对岩溶塌陷的形成至关重要，是岩溶塌陷发生的主要因素。 

Distribution features and forming conditions of the Mashankou karst collapse in Huaining County, Anqing City

The Mashankou karst collapse in Huaining County is a large-scale geological hazards site in Anhui Province. On the basis of systematic analysis on geological environment and space-time distribution in this area, the formation mechanism and distribution characteristics of the Mashankou karst collapse are summarized as follows,(1) The Mashankou karst collapse is formed in 1987 and enters the outbreak period during 1988-1992 when 39 collapse pits, account for 43.8 % of the total collapse. Especially in 1992, the collapse pits are up to 24, but after 1993 the average annual collapse is only 2.6, (2) Geomorphologically speaking, the collapse pits are mainly distribute in the low-lying floodplain, then in the low hill slope; lithologically, collapse pits are mainly distributed in T1n, T2y1 and T2y3; hydro-geologically, collapse pits are mainly distribute in the groundwater depression cone range with special focus on groundwater run off direction, and in valleys where water alternates strongly and in area where surface water and groundwater contact closely with each other. The necessary conditions which cause the Mashankou karst collapse include soluble stratum, thin debris cover (generally within 10 m) and frequent fluctuation of the groundwater table. And among them, dramatic change in groundwater dynamic field caused by mine dewatering is the most important factors, which is considered the major cause of the karst collapse.