Study On Structural Mechanical Properties And Evolution Laws Of Loess Under Plane Strain Conditions

Loess is mainly distributed in northwestern China.It is a typical structural soil with strong water sensitivity and collapsibility.A large number of projects such as embankments,retaining walls,and foundation pits can be similarly attributed to plane strain problems.The existing researches on the strength and structure of loess are mostly based on conventional triaxial,which fails to fully reflect the stress and deformation state of the soil in a plane strain state.There are few studies on the structural properties and quantitative parameters of loess under plane strain conditions.The paper uses a true triaxial apparatus after plane strain transformation to conduct plane strain consolidation drainage shear tests on loess under different water content,consolidated confining pressure and initial structural state.Based on the idea of comprehensive structural potential,combined with the normalized stress ratio structural parameters and structural degree,the structural strength,deformation and yield characteristics of loess under plane strain conditions and the attenuation evolution law of the structural whole process are revealed.Research to further improve the construction and development of loess areas,provided the experimental basis and theoretical analysis.The main research results of this paper are:(1)Under low confining pressure and low water content,loess appears to be weakly strain-softened,and under other conditions,loess appears to be weakly hardened or strongly hardened.The strength of plane strain loess is the highest in intact soil,followed by remolded soil,and saturated soil is the smallest.The stress-strain curve of loess under plane strain conditions increases with the increase of the consolidated confining pressure or the initial structural strength or the decrease of the moisture content.(2)The lateral deformation of the undisturbed loess is always lateral swelling,and the degree of lateral swelling decreases with the increase of the consolidated confining pressure,and the change of water content has little effect on the lateral swelling of the undisturbed soil.Remolded and saturated loess has two types of lateral deformation,namely lateral expansion and lateral compression.The lateral pressure deformation of remolded and saturated loess increases with the increase of consolidation confining pressure and water content.The lateral deformation of loess under low consolidated confining pressure is more affected by external force disturbance than water immersion;with the increase of consolidated confining pressure,the influence of water immersion on the lateral compression of loess gradually increases.The volume deformation of intact loess only increases first and then attenuates when the confining pressure and water content are low;in other initial states,the volume strain of loess increases with the increase of confining pressure and water content.The volume deformation of remolded loess under low confining pressure is higher than that of intact and saturated loess.(3)At low confining pressure and water content,the q-εs curve of the intact loess shows a softening type;the q-εs curve of the loess under other conditions shows a strain hardening type.According to the "two-line method",the structural stress yield point of loess was determined.It was found that the lower the water content and the greater the confining pressure,the greater the structural yield stress of the loess,and the stronger the initial structural property,the greater the structural yield stress of the loess.(4)There is a nonlinear attenuation relationship between the stress ratio structural parameters of loess and the shear strain.Before the shear strain reaches 2%,the structural parameters quickly decay,and when the shear strain exceeds 2%,the structural parameters slowly decay to a certain value.The attenuation law of normalized structural parameters is consistent with the stress ratio structural parameters.There is a strong cubic attenuation relationship between the initial structural parameters of loess and the moisture content.The structural parameters of loess after the combined structure degree are nonlinearly attenuated from the initial structural parameters to 0.The larger the consolidation confining pressure,the larger the structural parameters and the smaller the attenuation rate.The structural parameters of loess under plane strain conditions increase with the decrease of water content,the structural properties of loess increase with the increase of consolidated confining pressure,and the increase of water content weakens the structural strength of loess.(5)According to the Mohr-Coulomb strength criterion,it can be obtained that the stronger the initial structure of the soil,the greater the shear strength parameter.The shear strength parameters decrease with the increase of water content,the attenuation of cohesion is obvious,and the decrease of friction is relatively small.