Deformation properties of remolded loess under cyclic loading

To study the effect of coupling changes in principal stress direction and magnitude on the stress-strain state and non-coaxiality of soil, a series of cyclic torsional shear tests were carried out on the saturated remolded loess by using a hollow cylindrical torsional shear apparatus, and the variation rules and influencing factors of stress-strain state and non-coaxial angle were analyzed. Experimental result shows that the axial strain is always in a compression state, the hoop strain accumulates negatively first and then positively, the radial strain is basically in a tension state, the tension and compression states of shear strain alternate, the fluctuation characteristics of axial, hoop and shear strain curves are obvious, while the fluctuation characteristic of radial strain curve is weak, indicating that each strain component shows different development laws under the cyclic loading. The axial and radial strains and the variation amplitudes of hoop and shear strains increase first and then decrease as the intermediate principal stress coefficient increases, indicating that the intermediate principal stress coefficient affects the cumulation of each strain component. With the increase of rotation range of principal stress direction angle, the axial and radial strains decrease gradually, the trend of hoop strain changing from negative to positive advances, and the variation amplitude of shear strain decreases gradually, indicating that the rotation range of principal stress direction angle affects the development trend of each strain component. The hysteresis phenomena of shear and normal differential stress-strain curves are obvious, and the stiffness consolidates cyclically, but the cyclic strengthening of shear stiffness is more obvious than that of normal differential stiffness, indicating that the secondary anisotropy occurs in the soil. This is an intrinsic cause of the non-coaxial phenomenon. The non-coaxial angle curve moves down first and then moves up as the intermediate principal stress coefficient increases, and moves up gradually as the cycle number increases. The variation range of non-coaxial angle curve increases as the deviating stress amplitude increases. Thus, the intermediate principal stress coefficient, cycle number and deviating stress amplitude can obviously affect the stress-strain state and non-coaxiality of saturated remolded loess, which should be considered in loess engineering design and constitutive relationship research.