Study On True Triaxial Test And Constitutive Model Of Saturated Silty Fine Sand In Chaobai River Area

The cause of soil formation,environment,previous force characteristics and force mode will all affect its mechanical characteristics.Saturated sand,as the research object of this paper,has important characteristics different from clay,that is,shear expansion.For example,under the action of shear stress,the volume of loose sand shrinks continuously,which is characterized by stress hardening;while dense sand will begin to shear shrink with the action of shear stress.Due to the roll and movement of sand particles to each other,the characteristics of shear expansion slowly appear.In order to explore the real force situation of sand more deeply,it is very necessary to use real three-axis instruments.Based on the true three-axis instrument,a number of groups of different confining pressures and different main stress coefficients of saturated silt sand are carried out,and the following research results are obtained:（1）A series of tests have been carried out on the influence of the main stress coefficient b on the stress and strain characteristics of saturated fine sand.The conclusion is drawn as follows:when the confining pressure remains unchanged,with the increase of the main stress coefficient b in the middle,the peak bias stress of saturated fine sand gradually increases.（2）Based on the results of the true triaxial test,the characteristics of the relationship between body strainε_v-large principal strainε₁,shear stress q-large main strainε₁and shear stress q-spherical stress p of saturated fine sand are systematically analyzed.（3）In order to analyze the influence of the confining pressure on saturated silt sand,a true triaxial test of 100k Pa,150k Pa and 200k Pa is carried out respectively.It can be seen that when b is unchanged,the larger the initial circumference,the larger the shear deformation of sand;conversely,the smaller the initial circumference,the larger the shear deformation.（4）The test results show that when the confining pressure is certain,the curve of the effective ball stress and bias stress of different main stress coefficients b is close to a straight line,and with the increase of the main stress coefficient b,the smaller the inclination of the curve,that is,the smaller the slope.（5）By introducing the main stress coefficient b to modify the shear expansion equation,and establishing an constitutive model based on the state parameters of the phase transition state,which better reflects the main mechanical characteristics of saturated silt sand and is in good agreement with the test results.