Experiment study on strength and deformation characteristics of intact loess considering initial stress under plane strain loading and unloading conditions
Zhang Yu1,2 Shao Shengjun2,3 Liu Jin1 Ding Xiao1 She Fangtao2,3 Liang Xinyu1
1. Xi’an Technological University, Xi’an 710032, China;
2. Shanxi Key Laboratory of Loess Mechanics and Engineering, Xi’an University of Technology, Xi’an 710048, China;
3. Institute of Geotechnical Engineering, Xi’an University of Technology, Xi’an 710048, China
Abstract：Aiming at the loading and unloading plane strain problems in loess engineering, the loess was simulated in the in-situ deposit direction and initial stress state. The vertical loading and lateral unloading plain strain tests of intact loess with different initial stress state and different confining pressures were carried out by using the modified triaxial apparatus of Xi’an University of Technology. The strength and deformation characteristics of the intact loess under different stress path are revealed. The study results show that the stress-strain relationship curve is harden type under the two stress paths, the loading curves are higher than the unloaded ones and the loading strength is greater than the unloading strength, but the strength of the soil grows faster when unloading,. The result also reveals that the lateral deformation of loess has a non-linear relationship with the vertical one. The effect of the initial stress state on the soil strength and deformation is closely related to the confining pressure under vertical loading condition. The increase of the k value can limit the development of lateral deformation under lateral unloading condition. The volume deformation under vertical loading conditions is shear shrinkage, and the lateral unloading is dilatancy. Under the loading and unloading conditions, the failure strength lines in the p-q plane are basically the same with approximate linear relation. Under the condition of lateral unloading, the failure strain of the soil is much less than that of the vertical loading and the conventional triaxial test. With the increase of k value, the cohesive force decreases linearly and the internal friction angle increases linearly under the loading and unloading stress path.
