Research On Constitutive Relation Of Intact Loess Considering Complex Stress Path

Different stress paths may be undergone by soil mass in different geo-technical engineering construction.Stress-strain relation of soil mass is influenced by stress path evidently.But at present,the parameters determined by conventional triaxial test are adopted in many engineering design,there is a few studies on constitutive relation of intact loess considering complex stress path.So,the research on constitutive relation of intact loess considering complex stress path is very important in theory and practice.Therefor,in this paper,based on different stress paths tests to Xi'an intact loess,the constitutive relation of intact loess considering complex stress path is istablished.Firstly,many triaxial drained shear tests(including unloading-loading tests)for intact and remolded loess were conducted under conventional triaxial stress path and equalη(5differentηvalue)as well as equal p stress path.The deformation and strength characteristics under different stress paths are stutied.The influence of stress path,structural characteristic and water content,spherical stress p,stress ratioηto the deformation and strength characteristics are analysied.The research result shows that the phenomina of unloading shrinkage doesn't exist under equalηstress path,but it exists under conventional triaxial stress path and equal p stress path.The phenomina of unloading shrinkage under equal p stress path is more evident than that under conventional triaxial stress path;The influence of stress path,structural characteristic,water content to deformation and strength characteristic is evident,but that to strength characteristic indexs is very little.Secondly,different patterns stress strain relationships are obtained by further analysis to the test data,which include volumetric strainε_vp～spherical stress p,deviator strainε_sp～spherical stress p under equalηstress path,volumetric strainε_vη～stress ratioη,deviator strainε_sη～stress ratioηunder equal p stress path,the relation between unloading shrinkage and stress ratioη.On the basis of volumetric strain relation of saturated remolded loess without structural characteristics,the difference of structural volumetric strain which reflects the influence of intact loess's structure is intrduced separately.The relationships of intact loess's volumetric strain-spherical stress p and the volumetric strain-stress ratiorηare presented.Lastly,considering the coupling of spherical stress and deviator stress to deformation, based on the result of equalηtest and equal p test,random stress path is decomposed into some different equal p unit and equalηunit,the relations which include dε_vp～dp,dε_vη～dη,dε_sp～dp,dε_sn～dηare established separately.The constitutive relation of intact loess is obtained which can be used to consider complex stress path,structural characteristic,unloading shrinkage etc.The rationality of this constitutive relationship is confirmed by the agreement of the stress-strain relation under conventional triaxial stress path caculated using this constitutive relationwith that tested.