Study on Mechanical Properties of Q₃ Undisturbed Loess Under Different Suctions and Stress Paths

In order to study the influence of suction and stress path on the mechanical properties of Q₃ intact loess in Lanzhou, such as stress-strain, critical state and strength, stress path compression tests (IC, CTC, TC, RTC) were carried out on unsaturated loess samples with different suctions using a GDS unsaturated triaxial instrument. The test results show that: (1) with the increase of suction, the elastic index of the specimen does not change much, while the structural yield stress and plastic index increase; (2) the initial modulus, hardening degree, resistance of undisturbed loess to the stress path and suction shear strength, shrinkage and dilatancy have obvious effects, with the increase of suction, the stress-strain curves under RTC path appear softening and dilatancy, and the order of sample failure deviatoric stress under different shear paths is CTC>TC>RTC; (3) The critical state points of q-p and v-lgp of different stress paths converge on a straight line, the critical state lines under different suctions are approximately parallel. The q-p and v-lgp critical state lines for different suctions and stress paths can be normalized, and unified critical state equations were proposed. (4) As the suction increases, the cohesion increases, while the internal friction angle is almost unchanged; stress paths have no effect on shear strength parameters.