Experimental Study On Deformation Characteristics Of Remolded Loess Under Condition Of Principal Stress Axis Rotation

The problem of principal stress axis rotation is not uncommon in daily life.For example,the subgrade soil is often accompanied by cyclic rotation of principal stress axis under the action of dynamic loads,such as earthquake load,wave load and vehicle traffic load,and the deformation of soil is influenced by its stress history(the size and direction of the strain increment are not only related to the size and direction of the stress increment,but also influenced by the size and direction of the stress).Therefore,the strain increment of the subgrade soil has hysteresis phenomenon with the rotation of the stress increment,resulting in the stress and the strain are non-coaxial.The stress-strain non-coaxial phenomenon caused by principal stress axis rotation which not only causes the elastic deformation of the soil,but also causes the plastic deformation which has become the main reason for some geotechnical engineering accidents.In the past researches,the results show that principal stress axis rotation will leads to liquefaction of sand under the undrained condition[1,2],so the researchers pay more and more attention to geotechnical engineering problems of principal stress axis rotation.In order to study the deformation characteristics of loess under cyclic rotation of principal stress axis.In order to study deformation characteristics of loess under cyclic rotation of principal stress axes,carrying out two different torsional shear tests under different stress paths by using the hollow cylindrical torsional shear apparatus(HCA).The first stress path keeps the direction of principal stress axes unchanged and the size of deviator stress which was applied to the soil changed;The first stress path is to mainly study deformation characteristics of the soil under the condition of different principal stress direction angle ? and different intermediate principal stress parameter b,The second stress path keeps the direction of principal stress axes changed and the size of deviator stress which was applied to the soil unchanged.the second stress path is to mainly study effects of cyclic rotation of principal stress axes to characteristics of the soil.Experimental results show that(1)Deformation characteristics of loess have certain relationship with principal stress direction angle and intermediate principal stress parameter.While b is same,shear strength of the soil when ?=30°> shear strength of the soil when ?=60° > shear strength when ?=45°.While ? is same,shear strength of the soil when b=0 > shear strength of the soil when b=1 >shear strength of the soil when b=0.5.(2)Pure principal stress axes rotation will make the soil produce plastic strain,and plastic strain will be accumulated with the increasement of rotation cycles.When b=0,produced total axial strainz?,radial strainr? in same rotation cycles decrease with increasing of the rotation angle,while produced total shear strain?z? in same rotation cycles change from minus to positive with increasing of the rotation angle.(3)When b=0.5 and principal stress axis is rotated between-75° and 75°,the change of amplitude of each strain is obviously larger than that of the change of amplitude of each strain principal stress is rotated between-60° and 60°,-90°and 90°.(4)Principal stress axes rotation will make the soil produce the excess pore water pressure U,and U increases with the increase of the rotation periods N of principal stress axes rotation,and the rate of increase is different when ? rotates under different rotation angle and different intermediate principal stress coefficient b.When the principal stress axis rotates,the shear stress and shear strain form a hysteresis loop,and the hysteresis loop is slowly converted into a closed type from the non-closed type.