基于平面应变改造后的西安理工大学真三轴仪，在不同围压条件下对不同含水率黄土进行了侧向卸载平面应变试验，研究了平面应变条件下原状黄土的卸载强度、变形特性以及原状黄土的破坏方式。研究结果表明：不同固结围压条件下，各含水率原状黄土的侧向卸载应力-应变曲线均为硬化型，近似呈理想塑性曲线。剪切过程中，黄土的侧向与竖向变形呈非线性变化，侧向应变的发展要快于竖向应变，体积变形均为体胀。侧向卸载条件下土的破坏应变要比平面应变竖向加载和常规三轴试验小得多。黄土的卸载破坏强度与含水率、围压和球应力状态密切相关；随着含水率的增大，黏聚力衰减明显，内摩擦角略有减小。侧向卸载条件下，原状黄土呈剪胀滑移破坏形式。

Using of the modified true triaxial apparatus in Xi’an University of Technology, the intact loess strength, deformation characteristics and failure modes of intact loess are investigated through lateral unloading plain stress tests of loess under different moisture contents and different confining pressures. The stress-strain relationship curve under different confining pressures shows hardening behavior at the different moisture contents, similar as ideal plasticity curves. The lateral deformation of loess has a non-linear relationship with its vertical deformation. Lateral strain increment is larger than the vertical strain increment, indicating dilatant volume deformation. The failure strain is smaller in the lateral unloading plain strain test than vertical loading plain strain and conventional triaxial test. In brief, the failure strength of loess is closely related to moisture content, confining stress and spheric stress state. With the moisture content increasing, cohesion reduces and internal friction angle decreases slightly. The intact loess is develops dilatant slip failure modes under lateral unloading conditions.