Study On The Shear Failure And Yield Characteristics Of Loess Under Plane Strain Condition

Loess has special characteristics of the structure and water sensitivity and widely distributed in China,the strain state of most practical engineering belongs to the problem of plane strain,and failure characteristics of loess under the condition of isobaric consolidation are emphasized in the previous study of plane strain test,the actual confining pressure and the difference between shear failure and yield are not fully considered.The paper aims at usual problems of plane strain engineering in loess areas with the influence of initial consolidation stress conditionsthe,the vertical loading plane strain tests of unsaturated intact loess with different moisture content,confining pressure and initial consolidation stress ratio are conducted under isotropic and anisotropic consolidation by utilized plane strain altered true triaxial apparatus,to study the shearing deformation and shear failure and yield characteristics of intact loess under different consolidation conditions,and investigated the similarities and differences of the stress conditions of failure and yield through compared and analyzed.In order to provide theoretical and experimental basis for the research on loess mechanics under plane strain condition and construction of plane strain engineering in loess area.The main research results are as follows:(1)The strength of the intact loess under anisotropic consolidation is obviously higher than that of the isobaric consolidation during plane strain state,and got higher with the lower water moisture or the higher consolidation pressure;The intermediate principal stress and the coefficient of intermediate principal stress increase nonlinear with the increase of vertical strain during shearing process.With the increase of water moisture or confining pressure,the curvilinear forms changed from weak hardening to strong hardening or approximately linear gradually;The higher of initial consolidation stress ratio makes the intermediate principal stress increase,but makses the coefficient of intermediate principal stress decreases.(2)The lateral deformation of intact loess is mainly lateral expansion under low confinement conditions,and more obvious during lower moisture content or higher initial consolidation stress ratio.The lateral contraction embodied under high confinement conditions mainly,and divided into two types:lateral expansion after the peak point of lateral contraction or lateral contraction constantly,the latter appears under anisotropic consolidation,and lateral deformation is greater under anisotropic consolidation.The lateral contraction is more obviously with increasing of initial consolidation stress ratio;The intact loess mainly shows shear contraction,and shear contraction first and then shear dilatation under low confining pressure and moisture content conditions merely,shear contraction is more obvious with the increase of water moisture or confining pressure,also obvious with the smaller consolidation stress ratio,but on the contrary under higher confining pressure.(3)The shear yield point is determined by the intersection point of the head and tail tangent line of ?-?s relation curve,the yield shear stress ratio ranged from 0.02 to 0.19,and decreases with the increase of water moisture or confining pressure,and increases with the increase of initial consolidation stress ratio.The yield characteristic of the intact loess is not only related to the water content,the confining pressure and the initial consolidation stress ratio,but also related to the strength of primary structure and the characteristics of vertical fissure.(4)The stress conditions and strength of failure are higher.The intermediate principal stress and intermediate principal stress coefficient of failure and yield decreases with moisture content increases,but increases with higher confining pressure or initial consolidation stress ratio,the intermediate principal stress at failure is more regular;The intermediate principal stress coefficient at failure and yield got higher with larger initial consolidation stress ratio,confining pressure and the relationship between water moisture and plastic limit influence the regularity of intermediate principal stress and intermediate principal stress coefficient at failure or yield,and intermediate principal stress ratio at failure time is more regular;The intermediate principal stress coefficient ranged from 0.15 to 0.45 at the failure time,and from 0.03 to 0.25 at the yield time.(5)According to the Mohr circle strength envelope,the cohesion decreases rapidly if water moisture exceeds plastic limit,and decreases linearly with the increase of initial consolidation stress ratio;The internal friction angle attenuates linearly with the increase of water moisture,and increases linearly with the increase of the initial consolidation stress ratio.