Plane Strain Test Of Jingyang Loess Under The Different Initial Stress State Conditions

Loess has a particular characteristic, is widely distributed in the western regions in our country. With the development of economy, more and more engineering constructions have been built on loess areas. Because of suffering different stress state in the different spatial position, the loess reflected a tremendous difference. Therefore, it is necessary to research loess’s properties by analysising reasonably stress state about it. At length, providing the basis for selecting soil’s index index to project planner, and it has a important practical significance to develop economy and to ensure the safety of people’s life and property.This paper will research deformation and strength characteristics of Jingyang loess under the different stress conditions, such as anisotropy (different initial principal stress angle), moisture content, dry density, consolidation confining pressure, by using plane strain apparatus (PY-10). More over, this paper will compare the results of plane strain with the results of conventional triaxial test. Finally, this paper will plans to deduce the shear strength of the expression of loess based on the loess shear strength of the expression on isotropic frictional materials under the plane strain condition and SMP, The main research conclusions are as follows:(1) Stress-strain relationships under the condition of plane strainThe stress-strain curves of samples affected by the confining pressure, dry density, moisture content, and even The initial angle of principal stress on plane strain test, are obvious. The higher moisture content, smaller the dry density and bigger initial principal stress angle the lower stress-strain curves, and undisturbed soil’s stress-strain curves is higher than disturbed soil’s stress-strain curves. The stress-strain curves are hardening type. Samples did not appear shear zone but be compacted into drum shape after shear failure.(2) Shearing strength under the condition of plane strainBy analyzing the external factors of influencing the strength of soil, we can get the cohesion and internal friction angle of soil will increase by decreasing moisture content and increasing dry density, shear strength index of undisturbed soil is higher than disturbed soil’s, and the bigger principal stress initial angle the lower cohesion and internal friction angle. A good exponential relationship between cohesion and principal stress initial angle as well as internal friction angle and principal stress initial angle. The effect of moisture content on cohesion is higher than the effect of moisture content on it.(3) The relationship between the principal stress under the condition of plane strainThe intermediate principal stress varies with time, basicly can be divided into two stages; first stage, intermediate principal stress can not change with time, tending to a line; second stage, intermediate principal stress increases with the increase of shearing time, until the destruction of soil.The major principal stress increases rapidly with the increase of axial deformation when shearing, and major principal stress value is much bigger than the other two main stress value. There is a intersection point between The intermediate principal stress curve and minor principal stress curve, Before the intersection point, intermediate principal stress curve is lower than minor principal stress curve, but after the intersection point, intermediate principal stress curve is higher than minor principal stress curve. The occurrence of intersection point means soil will failure.(4) Shear expression of loessThis paper establish the plane strain strength formula to suit for all kinds of stress states based on the extension of the SMP criterion and Satake’s plane strain conditions.