Direct Shear Tests Study On Static Characteristics Of Interface Between Filling Soil Of Chongqing Airport And Structures

In order to develop the economy of mid-west mountainous area,it's necessary to improve the transportation condition.The complex topographic and geological condition in those mountainous regions determines that air transport is one of the most convenient transportation mode and airport construction in mountainous regions is always high fill project with many stability problems,and it is found that the static characteristics of filling soil-bedrock interface have important influence on the stability of high fill body.In this paper,the static characteristics of filling soil-structure interface are studied by physical test and discrete element simulation.Firstly,the physical properties of testing soil,which comes from the high filled ground of Chongqing airport fourth stage expansion project,and the direct shear test of testing soil were carried out.The particle size gradation,water content,density and specific gravity of soil grain were determined by laboratory tests.By direct shear test,the shear stress-shear displacement curve and normal displacement-shear displacement curve were analyzed,shear strength and internal friction angle were determined.The test results show that the shear strength of wet soil is greater than that of natural soil because of matrix suction.Filling soil-bedrock interface and filling soil-steel interface were studied by direct shear test.The influence of surface roughness,material types of structure and soil water content were analyzed.The test results show that the friction angle and frictional resistance of interface increase as surface roughness increases.The interface frictional resistance is lower than the shear strength of soil,which means the interface is weaker than soil.The relationship between interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion.The interface friction and shear displacement curve close to the Clough-Duncan hyperbola.The relationship between normal displacement and shear displacement is mainly shear contraction.The material types of structure and soil water content have significant influence on friction angle and frictional resistance of interface.The interface is weakened by water under specific conditions.Finally,DEM models of soil direct shear test and soil-structure direct shear test are established using PFC.The results show that the shear stress-shear displacement curve and the normal displacement-shear displacement curve of soil are in good agreement with the physical test results,which proves the validity of the discrete-element model.The influence of normal stress and surface roughness were analyzed.The results show that the interface frictional resistance increases firstly and then decreases as surface roughness increases.The relationship between interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion.The interface friction and shear displacement curve and normal displacement and shear displacement curve are affected by normal stress and surface roughness.