PERMEABILITY CHARACTERISTICS OF CLAY IN LAND SUBSIDENCE CENTER AT HENGSHUI,HEBEI,CHINA

The clay with low permeability in aquitard or/ and interbedded layer is the substance base of subsidence in the Huabei Plain,China.The seepage flow characteristics in clay can greatly impact the evaluation,simulation and prediction of the land subsidence.In this paper,soil samples are taken from the subsidence center at Hengshui and tested in laboratory.First,seepage tests are carried out by the high confining pressure triaxial seepage equipment.The test results indicate that the permeability of clay changes with the soil depth and the applied seepage pressure.The greater the soil depth and the seepage pressure are,the smaller the permeability is.Temporally,the permeability of the clay decreases rapidly at the beginning of the test.Then it stabilizes gradually.But due to the seasonally groundwater level fluctuations or excessive groundwater pumpage,the permeability values of some clay soil samples show different patterns.Finally,electron microscope scanning and fractal technology are used to analyze the control effect of microstructure of clay on the seepage flow characteristics.