Abstract：A lot of plane-strain problems have been witnessed in loess engineering. In this work, the loess was simulated in the in-situ deposit direction, and the plane-strain tests were carried out for intact loess in the isotropic consolidation condition with vertical loading and lateral unloading. Based on the tests, the shear deformation characteristics, the variation laws of yield strength and failure strength can be revealed. It is disclosed that the vertical columnar structure of loess may resist the compression action, the lateral swelling deformation is insignificant before yielding of the structure, but its development is obvious after yielding of the structure and the yielding characteristics are remarkable. During shearing, loess exhibits the shear shrinkage and hardening behavior, and the yield strength is different from the failure strength. In the lateral unloading condition, the lateral swelling deformation is obvious, and it is found that before yielding of the structure, the increase of vertical compression deformation is small, but after yielding of the structure the increase of vertical compression deformation is significant accompanied with obvious yielding characteristics. During shearing, loess exhibits shear dilatancy with perfect plasticity and the yield strength is consistent with the failure strength. Moreover, strength curves of loess with vertical loading follows the same variation law as that of loess with lateral unloading. Shear deformation characteristics and strength variation law of loess with different water contents under the vertical loading and lateral unloading conditions are basically similar. Plane-strain strength curves of loess with the same water content appear to follow the same linear variation law. With the increase of water content, the yield strength curve and failure strength curve drop accordingly.
