1. Institute of Geotechnical Engineering, Xi'an University of Technology, Xi'an 710048, China; 2. Shaanxi Provincial Key Laboratory of Loess Mechanics and Engineering, Xi'an University of Technology, Xi'an 710048, China; 3. China Nuclear Power Engineering Co. Ltd., Shenzhen 518124, China
Abstract：The plane strain triaxial tests in which the minor active principal stress (also called σx) keeps invariable are performed on the compacted loess with different water contents. The influences of σx and water content (also called w) on characteristics of the principal stress in plane strain direction (also called σy) during loading are studied. Based on the test results, the expressions describing the bilinear relationships between the principal stress in the plane strain direction and that in other directions are proposed. It is verified whether or not σy can be predicted by the expressions for the intermediate principal stress based on different strength criteria for compacted loess. The test results show that σy is not the intermediate principal stress (also called σ2) but the minor principal stress (also called σ3) during the isotropic consolidation and the initial loading stage. The ratio of the principal stress in the plane strain direction to the minor active principal stress (also called σy/σx) fast increases after the gentle development stage with the increase of the ratio of the major active principal stress to the minor one (also called R), and the relationships between the principal stresses are respectively linear and nonlinear before and after the turning point. The ratio of the major active principal stress to the minor one at the turning point (also called Rz) is larger than that at the critical point where σy transforms σ2 to σ3 (also called Rc). w and σx have obvious influences on Rz but little ones on Rc. The effects of w and σx on σy/σx are little as R is small. The relationships between the principal stress parameter (=2σy/(σx+σz), also called K) and R can be describedas two-stage lines. The one is horizontal and K is constant Kc in the first stage. The other one is inclined upward in the second stage. The slope m and Kc are irrelevant to w and σx. The change of σy during the loading can be better predicted by the proposed bilinear function. The predicted results are approximately equal to the test ones only at the failure of soil samples, using the expressions for the intermediate
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