Abstract: To investigate the variation of matric suction of unsaturated soils under complex stress conditions, a series of isotropic consolidation and shear tests along the stress paths of different intermediate principal stress ratios b with constant water content is performed on intact loess with various initial suctions by using unsaturated soil true triaxial apparatus. The characteristics of suction of unsaturated intact loess under the condition of true triaxial stress are studied. The results show that suction decreases with the time in the process of isotropic consolidation. Suction decreases faster and the variation of suction is larger with the increase of initial suction and net mean stress. The suction after the completion of isotropic consolidation is smaller than the initial suction. The suction in the process of shear declines little or remains unchanged then rise rapidly with the time. The suction rising segment grows rapidly and the suction increment is larger with the increase of the net confining stress or ratio b. The suction after the completion of shear is greater than the suction after the completion of isotropic consolidation. The changes of the matric suction are closely related to the different combinations of the net confining pressure and the ratio b under the action of true tri-axial loading.

Key words: unsaturated intact loess, true triaxial test, matric suction, the intermediate principal stress ratio b