等向应力下原状黄土的压缩及增湿变形特性研究

 用非饱和土三轴剪切渗透仪，在等向应力条件下对原状黄土进行增湿–加载，加载–增湿及加载–增湿–加载3个系列加载增湿路径试验，分析吸力对压缩变形和加载屈服特性的影响，探讨增湿时应力对变形及屈服特性的影响，通过对单线法及双线法的试验结果对比，确认原状黄土的增湿体积变形与加载增湿路径有关，加载及增湿屈服线不具有唯一性，进而提出等向应力条件下原状黄土的弹塑性体变模型。研究结果表明：吸力及应力分别对屈服前压缩及增湿变形特性指标几乎没有影响，而对屈服后的指标皆有明显的影响；单线法与双线法确定的增湿体积变形皆随应力的增大而先增大后减小，峰值点处应力与吸力丧失程度及加载增湿路径无关，且近似等于天然状态土样的初始屈服应力；增湿变形与加载增湿路径有关，单线法的值比双线法确定的值小，差值随增湿程度增大而减小，增湿至饱和时2种方法确定的湿陷变形近似相等。对于相同的塑性体应变，吸力减小屈服线位于加载屈服线之下方，二者随塑性体应变的增大而耦合联动扩大。提出的弹塑性体变模型可以较好地预测不同吸力下的压缩变形，比采用唯一加载湿陷屈服线的模型更好地预测不同应力下增湿变形。

Compression and wetting deformation behavior of intact loess under isotropic stresses

The wetting-loading，loading-wetting and loading-wetting-loading tests using the triaxial equipment for shearing and permeability measurement of unsaturated soil were performed to the intact loess under isotropic stresses. The influence of suction on the behaviors of deformation and yielding induced from loading and the influence of stress on deformation and yielding upon wetting were analyzed. The comparisons between the results of single and double triaxial equipment tests confirmed that the wetting induced volumetric deformation was dependent on the loading and wetting paths，and there was no unique yield curve identified from the loading and wetting paths. The elastoplastic volumetric model for the intact loess under isotropic stress was proposed. The results showed that the suction and stress had little effect on the compressibility and collapsibility parameters before yielding，but had remarkable impact after the yielding. The wetting induced volumetric deformations determined from the single and double triaxial equipment tests both increased first and then decreased with the increase in stress. The stresses at the peak points were independent of the suction loss，loading and wetting paths and were close to the initial yield stress of soil at the natural state. The wetting induced deformation was dependent on the loading and wetting paths. The wetting induced deformations from the single-triaxial equipment tests were smaller than the ones from the double-triaxial equipment tests. The difference decreased with the increasing of suction loss and approached to nearly zero until the saturation state was reached. The suction decrease(SD) induced yielding curve lay under the loading-collapse(LC) induced yielding curve for the same plastic volumetric strain. The LC yielding curve expanded with the increase in the loading-induced plastic volumetric strain，which produces the coupled outward movement of the SD curve，and vice versa. The proposed elastoplastic volumetric model predicted well the compression deformation at a given suction. The wetting-induced volumetric deformations before saturation at different stresses were better predicted with the model than with the unique loading-collapse yield curve.