The effects of the principal stress direction on the deformation behavior of frozen silt clay under the cyclic loading

When considering the dynamic loading processes in the real engineering, such as seismic loading and traffic loading processes, the principal stress direction (PSD) of the of subgrade soil is not always consistent with the vertical direction. As a key factor that determines the deformation behavior of frozen soil, the inclination of PSD is happened quit often in the engineering practice. Meanwhile, the PSD can partially reflect the complexity of the actual cyclic stress fields. Due to the limitation in the test instruments and related technology, few studies had been carried out so far in this field. In order to investigate the impact of the PSD on the deformation characteristics of frozen soil under cyclic loading conditions, a series of hollow cylinder experiments were performed by taking the frozen silt clay as the object and by setting up different PSDs as the main experimental conditions. The test results indicated that when the inclination angle of PSD was less than 15 degrees, it was mainly the axial strain that generated on the samples, but when the angle varied between 15 degrees to 45 degrees, there was a higher increasing rate in the circumferential torsional strain than axial strain. When alpha exceeded 45 degrees, axial strain manifests as tensile deformation. Therefore, the angle of PSD equal 45 degrees could be regarded as a threshold of axial strain behavior, at the same time, the circumferential torsional strain increased fastest under the degree. When the angle of PSD less 45 degrees, the axial strain was decreasing while the circumferential torsional strain was increasing as the angle of PSD. When the angle of PSD>45 degrees, the circumferential torsional strain started decreasing as the alpha increased, and the axial strain manifested as negative tensile strain, and it oppositely increased with the angle of PSD increased. Finally, an empirical model that can calculate the accumulated principal strain direction and quantity under different angle of PSD was determined.