武汉地区浅层岩溶发育特征与岩溶塌陷灾害防治

运用综合分析和数学统计的方法,较为深入地研究了武汉地区浅层岩溶的发育特征。武汉地区存在6个走向 NWW-SEE、各自相对独立的碳酸盐岩条带。根据上覆盖层工程地质性能的差异,划分出5种岩溶地质结构类型。武汉地区浅层岩溶主要类型有溶隙、落水洞及小型溶洞等,钻孔遇洞率46.0%~50.1%,线岩溶率5.93%~6.00%。浅层岩溶带中,1/3的溶洞洞高小于0.6 m,50%小于1.0 m,90%小于3.0 m。1/3的溶洞顶板在基岩面以下2.5 m 以内,50%在4.5 m 以内,90%在12.5 m 以内。溶洞充填物主要是黏土,含有灰岩碎块石。全充填溶洞占70.8%,未充填溶洞约占1/5,半充填溶洞不到8%。全充填溶洞顶板在基岩面以下平均埋深5.13 m,半充填5.71 m,无充填7.69 m,且具有全充填和半充填溶洞埋深较小、无充填溶洞埋深较大的特点,反映出溶洞充填方式是自上而下充填,充填物主要来源于上部覆盖层。武汉地区浅层岩溶为上部“垂直渗流岩溶带”地下水垂直渗流作用下的产物。根据岩溶发育程度的差异,基岩面以下浅部碳酸盐岩在垂直方向上可分为上部强岩溶和下部弱岩溶两个带;岩溶塌陷灾害平面上可划分出高、中、低3个危险性区,各区防治原则不同。高危险区是岩溶塌陷灾害防治的重点,防治的基本原则是阻止上覆粉细砂的流失;中等危险区的防治原则是保护中部老黏土层或红层的完整性;低危险区应注意远城区土洞存在的可能性。各危险区治理应以岩溶地质结构为基础,在防治原则指导下制定相应的防治措施。此外,工程建设中应合理选择和利用弱岩溶带。

Features of the shallow karst development and control of karst collapse in Wuhan

In order to reveal the shallow karst development laws and provide the basis for prevention and con-trol measures of karst collapse disaster,the development characteristics of covered karst in Wuhan are stud-ied by the means of comprehensive analysis and mathematical statistics method.There are 6 independent car-bonate rock belts with the trend of NWW to SEE.According to the characteristics of the overlying carbonate rock covers,5 karst geologic structure types are divided.The shallow karst types in Wuhan are mainly solu-tion fissure,grike,grooves and sink as well as small caves.The cave encountering rate of borehole （ECR）is 46.0 %-50.1 %;the linear karst rate of borehole （LKR）is 5.93 %-6.00 %.In shallow karst belt,the height in 1/3 karst caves is less than 0.6 m,a half less than 1.0 m,90 percent less than 3.0 m.The depth from bed rock surface to cave roof in 1/3 karst caves is less than 2.5 m,a half less than 4.5 m,90 percent less than 12.5 m.The fillings of karst cave are mainly clay with limestone detritus and block.And 70.8 %of karst caves is fully filled,about 20 % is unfilled,less than 8 % is half filled.The average depth below bedrock surface of fully filled caves is 5.13 m,half filled cave 5.71 m,and unfilled 7.69 m.From the fully filled to half filled or unfilled caves,the depth below bedrock surface of karst cave roof gradually increases, reflecting the caves are filled downward from the top and the fillings are from overlying cover layers.The shallow kart in Wuhan belongs to the “vertical seepage karst zone”and is the result of vertical seepage ac-tion.On vertical section,the shallow carbonate rock can be divided into strongly developed karst upper zone and weakly developed lower karst zone.In plane view,3 risky areas of collapse can be divided,namely the high,the middle and the low risk area.The prevention and control principles of karst collapse disaster are different in different risk areas.High risk area is the focus of karst collapse disaster prevention,and the basic principle is to prevent the overlying sand erosion.The prevention and control principle of the middle risk are-as is to protect the integrity of the old clay or red layer.In low risk area,we should pay attention to the soil caves located in the interface of old clay and carbonate rock far from the city.The governing works should be based on the karst geologic structure and it should be guided by the principles in make relevant governing measures.Moreover,weak karst zone should be reasonably selected and utilized in engineering construction.