Experimental Study On Drying Shrinkage Of Kaolin

Due to evaporation and transpiration of plants,the water content of surface soil will decrease continuously,and the soil will always be in unsaturated state.The soil will produce a certain amount of shrinkage deformation during the process of water loss,which will cause ground subsidence and cracking,even lead to engineering problems,and the effective stress in the soil is controlled by the deformation.Through a large number of experiments and theoretical derivation,a number of researchers have proposed different types of formulas for calculating the effective stress of unsaturated soils,including the unified effective stress equation proposed by Professor Shao Longtan.The equation,based on continuous medium mechanics,unify saturated soil and unsaturated soil,not only has a certain theoretical basis,but also clearly points out the physical significance of effective stress in the soil.In this paper,the drying shrinkage test is used to verify the equation from the perspective of deformation.On the basis of the unified effective stress equation,the dry shrinkage test of soil,the triaxial consolidation test of saturated soil and the test of soil water characteristic curve are carried out in this paper,and the following conclusions are obtained.(1)In the treatment of dry shrinkage test data of soil,the CAD software and digital image correlation method(DIC method)are used for the first time to calculate the radial deformation of the specimen,and the similar results are obtained,which shows the applicability of the radial deformation in the process of drying shrinkage of the specimen.(2)The specimen is dominated by radial deformation during the drying shrinkage process.With the increase of initial saturation,the specimen tends to isotropic contraction.The axial deformation or radial deformation can be measured only during the drying shrinkage.This simplification measure does not reduce the accuracy of the test.Under the premise,the workload of the test is reduced.(3)When measuring the characteristic curve of soil water,combining the pressure plate method with the filter paper method can greatly increase the measurement range of the matrix suction,and use the VG model of the four parameters to fit the test points,and a smooth and complete soil water characteristic curve can be obtained.(4)A uniform effective stress equation is used to calculate the relationship between the effective stress and the deformation of the unsaturated soil during the drying shrinkage process.The curve is basically coincided with the test curve of saturated soil,and the unified effective stress equation is verified from the angle of deformation.(5)On the basis of the triaxial consolidation test of saturated soil,the dry shrinkage test of soil and the filter paper method,two simple methods for inversion of soil water characteristic curves are put forward: the two points method is determined by the drying shrinkage test,the consolidation test method and the drying shrinkage test.These two methods overcome the disadvantages of time-consuming and high cost of conventional soil water characteristic curve test technology.The soil water characteristic curve of the reverse performance is in good agreement with the measured curve.