Effect Of Structural Changes Caused By Sample Preparation Method On Mechanical Properties Of Unsaturated Loess

The undisturbed loess with macropores,undercompression and obvious vertical fissures is widely distributed in northwest China.Two methods of sample preparation are used to prepare anisotropy and isotropic remolded loess,which have remarkable structure.The difference of loess structure and its change are the important reasons for the failure and have a great influence on the engineering characteristics.Therefore,in order to better solve these engineering construction problems,it is of great significance to research the influence of structural changes caused by sampling methods on the mechanical properties of loess.In this paper,the following experimental studies have been carried out on anisotropic and isotropic remolded loess specimens:first,compression tests with different loading and unloading paths and stepped humidification tests under constant stress under lateral limit conditions;The other is the isotropic compression test of controlling suction and the consolidation and drainage triaxial shear test of controlling suction and net confining pressure.Based on the experimental results of undisturbed soils with the same physical properties as this test,the influence of structural changes on the mechanical properties of unsaturated loess caused by sampling method was discussed.Based on the compression tests of different loading and unloading paths and the graded humidification tests of constant stress with different vertical stresses,the effects of moisture content,structure and loading and unloading paths on the compression characteristics of loess are ana.yzed.it is revea.ed that the three have little effect on the elastic index and compression index,and have a great influence on the yield stress,The effects of vertical stress,force-water action path and structure on the humidification and collapsibility of loess are discussed.It is recealed that the static earth pressure coefficient ofloess is not constant,but is closely related to vertical stress,loading and unloading path,water content,hydraulic path and structure.The expression of the relationship between the static earth pressure coefficient and the vertical stress and water content under the condition of loading and unloading is put forward.Based on the equal-direction compression test of control suction,the influence of the suction force and the structure on the compression characteristics and yield characteristics of the loess and the like is analyzed,and the expression of the equal-direction compression index and the suction force is put forward.The effect of the structure on the initial and subsequent yield lines of the loading-wet-collapse(LC)of the loess is revealed.Based on the triaxial shear test,the effects of net confining pressure,yield characteristics,critical state and strength characteristics of loess are analyzed.It is revealed that both suction and structure have little effect on the slope of critical state line on the semi-logarithmic plane of pore ratio and net average stress,but have great influence on the slope and intercept of critical state line on the plane of partial stress and net average stress.The shear strength index of remolded loess shows a monotonous linear relationship between cohesion and suction.The fixed value of internal friction angle does not change with the change of suction.The stronger the structure of soil is,the greater the cohesion is,and the internal friction angle is basically unchanged.