The consolidated undrained triaxial shear test is carried out on unsaturated undisturbed loess (Q3) in the case of moistening. According to the test results

the relation curves of ultimate strength of collapsible loess and initial moisture content and confining pressure are obtained; and the shear strength characteristics of loess during moistening process are analysed. It is concluded that the strength envelope of unsaturated undisturbed loess under original moisture content is composed of two beelines. However

the strength envelope under high moisture content still follows Mohr-Coulomb criterion. The cohesive force of unsaturated loess is decreased significantly with increasing initial moisture content

but its internal friction angle is affected slightly by the change of initial moisture content. With the increase of initial moisture content

total stress indices are always smaller than corresponding effective stress indices. It is found that the relation between effective cohesive force of unsaturated loess and initial moisture content can be exactly fitted with exponential function. Finally

the influence of initial moisture content and confining pressure on shear strength indices of loess is analyzed briefly