武汉市岩溶塌陷的演化机理研究

摘要

This paper is based on the analysis of 29 karst sinkholes in Wuhan.Their system structure is determined from three elements,i.e.karst,cover and groundwater.The sinkhole mechanism of rainfall,drilling and pile constructing importing karst system is discussed via field monitoring and numerical simulating.The results are as follows.(1) The geological conditions developing sinkhole include the following three aspects.The cover structure is upper clay and lower sand.The shallow karst is developed.The hydraulic connection between pore water-karst water is good.(2)In natural environment,the cave in cover soil has two developing stage that is from hydraulic corrosion to stress failure.(3) Drilling and pile constructing often trigger sinkhole that is from two aspects of structure changing.The covering soil has high hydraulic gradient at the moment of drill connecting pore water and karst water.The head difference of two groundwater is more than 15m during pile constructing.%基于武汉市易发生的29处岩溶塌陷,从岩溶、覆盖层和地下水3方面分析了岩溶塌陷的内部结构;通过现场监测和数值模拟,分析了降雨、钻探和桩基施工的输入作用,并探讨了武汉市岩溶塌陷的演化机理.结果表明:(1)“上黏下砂”的盖层结构、浅部岩溶发育、孔隙水与岩溶水具良好水力联系是塌陷形成的基础条件;(2)自然环境下开口岩溶上方土洞扩展存在水力潜蚀和应力集中破坏两个演化阶段;(3)钻探和桩基施工联通孔隙水和岩溶水的瞬间,孔壁周边松散砂土快速进入临界水力梯度而破坏.桩基施工在覆盖层内的振动荷载和超孔隙水压力,易造成覆盖层整体破坏.在岩溶区施工产生的冲击作用可使岩溶水和孔隙水形成不同步波动,两者存在高水头差,致使覆盖层内砂层在压力差作用下破坏.