平面应变加、卸荷条件下考虑初始应力的原状黄土#br# 强度与变形特性试验研究

针对黄土工程中的众多平面应变加、卸载问题，利用平面应变改造后的西安理工大学真三轴仪，模拟黄土原位沉积方向及不同初始应力状态，在不同围压下对不同初始应力状态原状黄土进行竖向加载和侧向卸载平面应变试验，揭示不同初始应力状态原状黄土在加、卸载不同应力路径条件下的强度和变形特性。研究结果表明：两种应力路径条件下的应力应变曲线均呈硬化型，加载曲线均高于卸载，加载强度大于卸载强度，但卸载时，土的强度发挥较快。剪切过程中，黄土的侧向变形与竖向变形均呈非线性关系。竖向加载时，土的初始应力状态k值对土强度和变形的影响与固结围压的大小关系紧密；侧向卸载时，k值的增大可以限制侧向变形的发展。竖向加载条件下的体积应变均为剪缩，侧向卸载时均为剪胀。加、卸载条件下p-q平面内的破坏强度线基本一致，近似呈线性关系。侧向卸载条件下土体破坏时的应变远小于竖向加载和常规三轴试验。随着k值的增大，加、卸载应力路径时，黏聚力均线性减小，内摩擦角均线性增大。

Experiment study on strength and deformation characteristics of intact loess considering initial stress under plane strain loading and unloading conditions

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.