Effect Of Salt Content On Stress-Strain Relationship Of Unsaturated Ili Loess

The formation age and cause of loess in the Ili,Xinjiang and the Loess Plateau are the same as Aeolian loess during late Pleistocene.However,the formation of Ili loess was influenced by the Atlantic climate,which is different from the loess of the Loess Plateau affected by the East Asian Monsoon,mainly because of its extremely strong collapsibility and the content of soluble salt that exceeds the standard of salinized soil,Ili Loess is the only westerly region affected by Atlantic climate in China.In view of the particularity of Ili loess,it is necessary to study it specially,which is not only the need of engineering construction in Ili area,but also the supplement of loess theory.Based on the theory of unsaturated soil mechanics,the deformation and strength of unsaturated Ili loess under the strategic decision of "Belt and Road" are studied in this paper.It provides a reference for the engineering construction in Yili area.This study considers the characteristics of high soluble salt content in the Ili loess,using the characteristics of the original loess in the absence of overlying pressure,adding a small amount of water without collapsing and structural invariance,using the water film transfer method to divide the configured salt solution into multiple days and more.These were added dropwise to the prepared undisturbed Ili loess samples to make three kinds of samples with easily soluble salt contents of 5,14 and 26 g/kg,respectively,using an indoor unsaturated triaxial apparatus.Saturated Ili loess carried out an isometric compression-rebound test to control the matric suction(50,100,150 kPa)and the 27th(two-time rebound)net average stress under three easily soluble salt contents,and studied the soluble salt content,matric suction,and net average Influence of stress on compressive deformation and yield characteristics of Ili loess;triaxial consolidated drainage shear tests controlling matric suction and net confining pressure(100,200,300 kPa)for three kinds of easily soluble salts were studied.Various factors were studied for unsaturated Ili Loess strength characteristics.Finally,based on the Barcelona model,the influence of various factors on the model parameters was analyzed and the yield surface equation was derived.The following results have been obtained:(1)The results of isotropic compression-rebound test show that under the same conditions,the larger the net average stress,the greater the compressive deformation of the sample;when the soluble salt content and the net average stress are the same,the compressive deformation of the sample follows the matrix.The increase of suction is reduced,which reflects the effect of matrix suction on the structural enhancement of Ili loess.When the matrix suction is the same as the net average stress,the soluble salt content of 14 g/kg produces the largest compressive deformation and is easily soluble in salt.The content of 26 g/kg of the sample is the next,and the content of the easily soluble salt of 5 g/kg is the smallest.With the increase of matric suction,the yield stress of Ili loess increases.With the increase of the content of easily soluble salts,the yield stress first increases and then decreases.(2)Triaxial consolidation drainage shear test results show that the deviated stress-axial strain curves of all samples in the unsaturated Ili loess are hardened during the shearing process,and all are drum-shaped plastic failures during the shearing process.The sample volume decreases,showing shear characteristics.In the undisturbed Ili loess,under the same soluble salt content and the same matrix suction,the net confining pressure is higher and the strength is higher.Under the same net confining pressure,the matrix suction is higher and the strength is higher;the same net confining pressure,the same matrix Under the effect of suction,the content of easily soluble salts is 14 g/kg.The strength of unsaturated Ili loess is the highest.(3)Model parameters change rule: Based on the Barcelona model,the model parameters obtained by the experiment were arranged,and the following rules were obtained: When the other conditions are the same,with the increase of matric suction,the isotropic compressive elastic parameter κ and the consolidation parameter λ Both decrease,the effective cohesion increases,and the internal friction angle and the shear failure constant M almost do not change;with the increase of the content of soluble salt,both the isotropic compressive elastic parameter κ and the consolidation parameter λ increase,and the effective viscosity increases.The cohesion force,suction friction angle and the parameter k showed a tendency of increasing first and then decreasing.The effective internal friction angle and shear failure constant M first decreased and then increased.(4)Based on the Barcelona model,by analyzing the influence of the soluble salt content and the matrix suction on the parameters of the loading and humidifying yield line and the shear yield equation,a coupling change between the soluble salt content and the matrix suction can be considered.Yield surface equation.The research results of this article have deepened the theory of loess mechanics in the West Wind and deepened the understanding of the unsaturated loess constitutive relationship in the Yili area,which can provide a reference for the construction and disaster prevention of the Ili loess area.