(1. Institute of Geotechnical Engineering，Xi?an University of Technology，Xi?an，Shaanxi 710048，China；
2. Shaanxi Provincial Key Laboratory of Loess Mechanics and Engineering，Xi?an University of Technology，Xi?an，
Shaanxi 710048，China；3. Beijing Leading Software Co.，Ltd.，Beijing 100044，China)
Abstract：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.
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2017, Vol. 36 
