Experimental Study On Non Coaxial Characteristics Of Sand Under Complex Stress Path

Under the action of traffic load and earthquake load,the change of the main stress direction and the rotation of the principal stress axis are universal.With the hollow cylinder apparatus has been widely used in geotechnical engineering test,the anisotropic soil has been studied deeply;the characteristic of deformation have been widely investigated on the rotation of principal stress axes path and other complex stress path.The anisotropy of soils were also included in the non coaxial behavior of soils;many scholars found that the non coaxial behavior has been very clear in the rotation of principal stress axes test through numerical analysis.But in the constitutive modeling and engineering,if we do not consider the non coaxial behavior of soil,which makes the engineering structure unsafe.However,various factors are not systematic considerated on the non coaxial study about sand,and the non coaxial behavior is less researched on the complex stress path.Therefore,this paper is researched on the influence of the uncoaxial characteristics of sand from two different stress paths for providing some reference on the establishment of non coaxial model.The main research contents and results are as follows:1.A series of directional shear tests were carried out on different medium principal stress coefficient,different main stress direction,different density and different materials.Comparative analysis of the influence of stress strain relationship and non coaxial relationship of the various factors of sand.The experimental results show that:(1)with the change of the main stress direction angle,the strength of sand is obviously different.When the direction of the principal stress direction is about 600,the shear strength of sand is the lowest,and the shear strength of sand is the strongest when the direction of the principal stress is 00.(2)the principal stress coefficient has obvious influence on the shear strength of sand.With the increase of the coefficient of the principal stress,the strength decreases gradually.When the principal stress direction is 300,the principal stress coefficient is smaller,and there is a peak value of shear stress.At the same time,the principal stress coefficient is very small,and the shear strength of sand is larger.(3)the non coaxial angle varies with the changes of principal stress direction angle;non coaxial angle is not only positive;when alpha > 600,non coaxial angle is negative.When the principal stress coefficient is low,non coaxiality of sand is relatively obvious,even can reach about 200.when the principal stress coefficient increases to more than 0.5,the non coaxial angle appears negative on the small direction of the major principal stress angle.(4)sand compaction has little effect on the non coaxiality,the non coaxial angle generally is about 100.The influence of particle shape on the strength is obvious,but has little effect on the non coaxial angle,the difference is generally about 20-30.So the particle shape on non coaxial behavior under certain conditions is negligible.2.The stress path of cyclic torsional shear is simulated according to the actual stress state of subgrade under the action of actual traffic load.The change of vertical stress accumulation and the relationship between volumetric strain change and non coaxial relation are investigated by changing the cyclic torsional shear ratio,density,confining pressure,cyclic vertical stress ratio and other variables.The results show that:(1)with the increase of the vertical stress ratio,the greater the vertical strain accumulation,the greater the rate of vertical strain accumulation in the early stage.In the early stage of cyclic loading,the deformation of the soil is gradually expanded.With the increase of the number of cycles,the cumulative deformation rate of the soil during the loading period is significantly higher than that in the later stage.In four different cyclic stress ratios,when the number of cycles is 1000 cycles,the vertical strain accumulation basically completed about60%.(2)the effect of density on the accumulation of vertical strain is not obvious.The increase of confining pressure changes the development of vertical strain,which is proportional to the confining pressure.The increase of torsion shear ratio increases the change of volume strain,and also increases the deformation of soil mass.(3)the the vertical stress ratio has little influence on the non coaxial angle,influence of density and confining pressure is also not obvious.Effect of different cyclic torsion shear ratio on the the non coaxial angle is obvious.